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In this article, a dual-band dual-circularly polarized (CP) narrow slot antenna with stable in-band gain and reduced frequency ratio (FR) is proposed by resonating the $0.5\lambda $ -, ${\it \lambda }$ -, and $2{\it \lambda }$ -modes. For this purpose, two critical issues are significantly investigated and explored. The first effort is attempted to construct two pairs of orthogonal polarization with opposite rotation, i.e., (${\it \lambda }$ - and $0.5{\it \lambda }$ -modes) and ($0.5{\it \lambda }$ - and $2{\it \lambda }$ -modes), by properly reshaping the equivalent magnetic currents of the slot radiator. Another attempt is to reallocate these modes in proximity to each other in virtue of stub-loaded technique and ensure them to resonate in the designated sequence of ${\it \lambda }$ -, $0.5{\it {\lambda }}$ -, and $2{\it \lambda }$ -modes instead of the inherent sequence. With these improvements, the dual-CP performance can be successfully realized for our designed antenna. Finally, for experimental verification, a dual-band dual-CP slot antenna in virtue of the proposed design approach is implemented and tested. It proves that the left- and right-hand CP radiation patterns toward the ${z}$ -axis are satisfactorily obtained around 1.88 and 2.39 GHz by simultaneously employing the triple resonance, thus revealing a small FR of 1.27. Moreover, the dual operation bands hold stable in-band gains of about 2.8 and 3.5 dBic. In addition, the CP antenna still maintains the single-layer, single-fed, and single-radiator properties, which evidently confirms the validity and effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

This article tries to address the unstable radiation pattern issue of the planar‐coupled patch antennas with two different methods. First, characteristic mode analysis (CMA) reveals that the coupled patch antennas generate three characteristic modes with distinctive radiation patterns. A slot‐loading scheme is proposed to reshape the current distribution of the higher mode and reduce its sidelobe level significantly. Then a 13.4% bandwidth with consistent radiation patterns and high gain is achieved by exciting modes 1 and 3 while suppressing unwanted modes with an aperture‐coupled feeding. Second, the radiation pattern stability of the coupled patch antennas is further improved by employing shorted parasitic patches. The presented antenna can be equivalent as the same magnetic current array model under the in‐phase and out‐of‐phase modes, and thus the radiation patterns hardly get changed. Moreover, the non‐radioative nature and high radiation quality factor of the higher mode improve the radiation performance in a new principle. It not only enhances the bandwidth up to 18.5% but also results in a sharp filtering edge of gain response. [ABSTRACT FROM AUTHOR]

Aiming to realize series-fed antenna array with good return loss, low sidelobe level (SLL), and small gain variation over a wide bandwidth, this article presents a unified synthesis method of designing series-fed networks (SFNs) under the equal/unequal distributions with the bandwidth enhancement. We find that the return loss and current distribution bandwidths of SFN are dominated by its input reactance slope. The ratio of SFN main line impedance Z0 and antenna impedance ZL plays an important role in it. When the optimal Z0/ZL makes the input reactance slope equal to zero at the center frequency, the bandwidth of SFN can be highly extended by 2–4 times compared with nonoptimal solutions. In this context, four classical types of SFNs are investigated and synthesized. The closed-form optimal formulas for these SFNs are further deduced under the specified element number N and current distributions I1, $\text{I}_{2}, \ldots $ , and IN. For experimental verification, an eight-element series-fed antenna array driven by the SFN with Dolph–Chebyshev current distribution is designed and fabricated based on the proposed design method. By virtue of the improved SFN, the designed series-fed array exhibits enhanced impedance and radiation bandwidths as predicted. The measured results show designed array achieves an impedance bandwidth of 52.2% (3.34–5.70 GHz) with S11 ≤ −10 dB and the radiation bandwidth with SLL ≤ −20 dB is 20.9% (3.85–4.75 GHz). The measured antenna gain is 11.3 dBi with a small variation of 1.3 dB and the efficiency of array is better than 82% over the operational bandwidth of 18.7% (3.88–4.68 GHz). [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) antenna with enhanced axial-ratio and half-power beamwidths (HPBWs) using nonuniformly compressed high-order mode dipoles is proposed in this article. First, wide HPBW at E-plane is obtained by a third-mode dipole with proper nonuniform compressed parameters. Then, a crossed nonuniformly compressed high-order mode dipole is proposed, and wide axial-ratio beamwidths (ARBW) and HPBWs are both achieved in two orthogonal planes. Next, a S-shaped CP antenna based on nonuniformly compressed high-order mode dipoles is presented with wide beamwidths in all cut-planes in the upper hemisphere. Finally, the antenna is fabricated and measured to verify the design. The measured results show that the HPBWs are larger than 109° and ARBWs are larger than 118° in eight cut-planes. [ABSTRACT FROM AUTHOR]

The fundamental working principle of front-to-back ratio (FTBR) enhancement of the quadruple inverted-F antenna (QIFA) is clearly revealed for the first time, and a unified design method is then proposed in this article. The characteristic mode analysis (CMA) demonstrates that the QIFA actually operates in two orthogonal modes, and analytical derivation validates that each mode acts as a pair of parallel magnetoelectric (ME) short dipoles for radiation. More specifically, the FTBR of the antenna is determined by the amplitude ratio and phase difference of the two pairs of equivalent ME dipoles. The equivalent model and analytical method can greatly facilitate the design. First, by leading or lagging phase of either characteristic mode through excitation, the beam direction can be flexibly prescribed as forward and backward. Second, the bending direction and bending degree of radiators, respectively, determine the phase and amplitude of its equivalent magnetic dipole, by which the FTBR can be improved. A practical design is carried out with the proposed method, and the antenna achieves an electrically small size of $0.068\lambda _{0} \times 0.068\lambda _{0} \times 0.052\lambda _{0}$ and an FTBR of 12.3 dB. [ABSTRACT FROM AUTHOR]

A design approach to a planar dual-sense bidirectional circularly polarized (CP) antenna is advanced. The resultant antenna can exhibit orthogonal CP radiations in arbitrary directions between 90° and 180°, i.e., the flared angle formed by pure left-handed CP (LHCP) and right-handed CP (RHCP) directions could be set in a wide range from 90° to 180°. The operational principle is revealed by an equivalent source model at first. Then, prototype antennas are advanced by incorporating a high-order mode resonant, V-shape dipole to a planar magnetic dipole, and a parasitic electric dipole. As numerically simulated and experimentally validated, the flared angle formed by LHCP and RHCP directions can be adjusted as 90° and 135°. In the 90° case, the presented bidirectional CP antennas can exhibit impedance bandwidth of 6.6%, 3 dB axial ratio (AR) bandwidth of 13.0% in the $+ x$ -axis, and 8.9% in the +z-axis. The advanced low-profile (height < 0.05 wavelength) antenna can simultaneously provide spatial and polarization diversity abilities in one principal-cut elevation plane. Therefore, it would be a promising colocated, spatial/polarization diversity antenna in future wireless systems. [ABSTRACT FROM AUTHOR]

A single-layer, dual-band, shared-aperture array with a broad fan beam in the lower band centered at 5 GHz and a narrow pencil beam in the adjacent upper band centered at 5.8 GHz is presented in this article. First, the schematic of a dual-band array with its beamwidth regulation capability is presented. Then, two key components, i.e., a novel dual-band patch antenna element and a compact filtering phase shifter (FPS) are developed. The antenna element has counterintuitive beam patterns with broad azimuthal half-power beamwidth (HPBW) of 183.3° in the lower band but much narrower azimuthal HPBW of 68.5° in the upper band, indicating its excellent ability in beamwidth regulation with a figure of merit (FoM) of 2.31. Meanwhile, the FPS serves as a band-stop filter in the lower band and a phase shifter in the upper band. Furthermore, a two-element series-fed subarray is designed by cascading two properly designed antenna elements through the FPS. Finally, a parallel-series-fed array consisting of four rows of the series-fed subarrays is implemented, and a prototype is fabricated and tested. The measured results, in good agreement with the simulated ones, have demonstrated that the array satisfactorily attains a broad fan beam with azimuthal HPBW of 156° and gain of 11.05 dBi at 5 GHz and a narrow pencil beam with azimuthal HPBW of 30° and gain of 16.23 dBi at 5.8 GHz under a shared aperture of $1.37\lambda _{0} \times 3.53\lambda _{0} \times 0.05\lambda _{0}$ , indicating an enhanced FoM up to 4.48. The FoM and gain could be further improved by simply expanding the array’s dimension based on the developed array topology. [ABSTRACT FROM AUTHOR]

In this letter, a novel slot-loaded high-gain circular patch antenna is proposed to realize reconfigurable ±45° polarizations. Initially, a pair of y-oriented open slots 1 is loaded to the edges of a TM31-mode circular patch to manipulate its current distribution, which contributes to desired broadside radiation and high directivity. Second, two x-oriented slots 2 and four fan-shaped slots 3, which are mostly parallel to current vectors, are introduced to reconstruct the patch with the least perturbation. By controlling the on/off states of the PIN diodes planted at two ends of each of slots 3, reconfigurable orthogonal ±45° polarizations are achieved. Moreover, enhanced polarization discrimination is realized by optimizing the connection strategy between the patch's segments. The simulated and measured results demonstrate that the proposed antenna can achieve reconfigurable ±45° polarizations with 5.7% impedance bandwidth, 10.3 dBi realized gain, more than 25 dB polarization discrimination, and 23 dB backside radiation suppression. [ABSTRACT FROM AUTHOR]

This article designs a class of low-profile compact multiple-input–multiple-output (MIMO) antennas on a single radiating patch using simple and systematic characteristic modes (CMs) method. Rather than using conventional method of radiation pattern and polarization diversities, this work demonstrates that by taking advantage of a proper superposition of some even/odd modes, it is able to generate similar radiation pattern and polarization no matter which port is excited. It is also found that port isolation and impedance matching are dependent on not only operating modes but also input couplings. The proposed CMs method consists of three main steps. First, adjust desired even and odd modes to be equal in resonant frequency (ResF). Second, suppress unwanted modes without affecting desired ones. Lastly, determine feeding positions to obtain proper input couplings. In this way, satisfactory port isolation and impedance matching could be achieved simultaneously and quickly, getting rid of complicated decoupling structures and time-consuming optimization. To exemplify how the proposed CMs method works, two MIMO antennas are successfully designed by just using simple slots and shorting pins. A prototype for the proposed four-port MIMO antenna is fabricated and measured for validation. [ABSTRACT FROM AUTHOR]

In this paper, a novel decoupling scheme is proposed to suppress the mutual coupling between the two ports of a single patch antenna (SPA), while maintaining the radiation properties of each port with co‐linear polarization, co‐radiating aperture, and broadside radiation patterns without deterioration in gain. For this purpose, a pair of λ/4 nonradiative stubs are introduced and loaded symmetrically in the SPA. Thanks to the good feature that the nulls of the composite fields of TM20 and TM30 modes are present only near the coupled port, both radiating apertures of the SPA can operate simultaneously. Moreover, the decoupling principle, equivalent transmission‐line models, and design guidelines are extensively illustrated. The measured results show that each port of the SPA has a broadside radiation pattern with co‐linear polarization and about 7‐dBi gain under isolation improvement. As such, this two‐port SPA, with the size of 0.41*0.37*0.04*λ03, can be equivalent to a two‐patch antenna array with 0 edge‐to‐edge distance. Most importantly, the proposed decoupling method is achieved without compromise in the three degrees of freedom (i.e., co‐polarization, similar radiation pattern, and co‐radiating aperture), which is a tough challenge nowadays. This decoupling approach allows the two‐port SPA could be an alternative solution in MIMO systems or in‐band full‐duplex systems [ABSTRACT FROM AUTHOR]

A novel low-profile circularly polarized (CP) diversity patch antenna with extremely small edge-to-edge distance, reduced size, and low mutual coupling is proposed under dual modes. Initially, the single microstrip patch antenna (MPA) is theoretically investigated by using characteristic mode analysis. It demonstrates that a large number of radiative modes, i.e., CM1 to CM7, are excited for the traditional MPA. By selecting its quarter patch configuration with shorting pins, only a few modes, i.e., CM2 and CM7, could be resonated for the quarter patch antenna (QPA). Meanwhile, their nonbroadside radiated fields could be transformed into the broadside radiation. Particularly, the polarizations of CM2 and CM7 are maintained orthogonally with each other. Next, a linear slot is etched on the patch to reduce the magnitude ratio between $\vert E_{\mathrm {\theta }}\vert $ and $\vert E_{\varphi }\vert $ components. After that, the resonant frequency of CM7 is moved closely to that of CM2 for nearby 90° phase difference. With these arrangements, the compact CP performance is acquired by combining its CM2 and CM7. Furthermore, a pair of QPAs with CP diversity is deeply studied. The results prove that the antenna has successfully acquired both of left-handed CP (LHCP) and right-handed CP (RHCP) performances at dual ports. Moreover, the low mutual coupling between them is generated under extremely small spacing. In final, the proposed antenna is fabricated and tested. Both of LHCP and RHCP patterns are formed of around 4.785 GHz. Besides, the proposed antenna occupies the small overall volume $0.023\lambda _{\mathrm {g}}^{3}$ ($\lambda _{\mathrm {g}}$ is the guided wavelength), that is only half of the traditional patch ($0.045\lambda _{\mathrm {g}}^{3}$), and maintains the isolation as high as about 24 dB under extremely small distance (0.3 mm). [ABSTRACT FROM AUTHOR]

A novel design concept to reshape radiated fields of a slot antenna for improved bandwidth and stable radiation pattern is proposed. Initially, the radiated fields of the traditional slot antenna are theoretically studied using characteristic modes (CMs). The results demonstrate that its CM1, CM2, and CM3 are resonated around 2.39, 4.78, and 7.17 GHz, respectively. Both CM1 and CM3 maintain the bidirectional radiation patterns, whereas CM2 generates a radiation null in the broadside direction. Then, in order to utilize the nearby CM1 and CM2 for wide bandwidth, the linear slot is properly folded so as to transform the nonbidirectional pattern of CM2 into the bidirectional one. After that, the narrow slot is reformed as the stepped scheme, thus reallocating these dual modes in proximity to each other. With these arrangements, the impedance bandwidth of the antenna is dramatically widened with two attenuation poles, while keeping a compact size and stable radiation pattern. Finally, the proposed antenna is fabricated and tested. Measured results show that the antenna without any extra feeding network has gained a wide bandwidth ($\vert S_{11}\vert < -10$ dB) of around 31.4% ranging from 3.22 to 4.42 GHz, which is about 2.24 times wider than its traditional counterpart (14%). Besides, the overall size of the slot radiator is kept as small as about $0.42\lambda _{0} \times 0.06\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength). Particularly, the bidirectional radiation pattern, stable gain of around 5 dBi, and low cross-polarization of below −12.3 dB are all satisfactorily generated during the operating band. [ABSTRACT FROM AUTHOR]

In this article, two coupled patch radiators are intensively investigated to characterize two pairs of even/odd modes by virtue of characteristic modes analysis (CMA). It is discussed that both radiation patterns and characteristic angles (CAs) of the two orthogonal odd modes are critical factors in the design of dual-beam circularly polarized (CP) antennas. However, neither of them could be correctly derived from a two-element-array model. By adjusting resonant frequencies (ResFs) in different ways, the two odd modes could achieve a 90° difference in CA. Moreover, the two odd modes have similar dual-beam radiation patterns with peak values in the same vertical plane. By further effectively exciting the two odd modes and fully suppressing the two even ones, four CP dual-beam patch antennas are successfully designed. Both simulated and measured results validate the effectiveness of the proposed technique in the design of low-profile high-directivity dual-beam CP patch antennas. It is also discussed that the pointing angle of dual-beam could be reduced by enlarging patch distance or utilizing higher-order odd modes, while the axial-ratio (AR) bandwidth could be improved by increasing substrate height or introducing a broadband feeding network. [ABSTRACT FROM AUTHOR]

A low‐profile wideband patch antenna with pattern diversity is proposed in this paper. In our design, custom‐designed feeding schemes are utilized to substitute for conventional power dividers beneath the ground plane, thus selectively generating the broadside or conical beam and introducing additional resonant modes. Then, by placing two novel feeding schemes orthogonally to realize pattern diversity, a new resonant mode is successfully excited, which fully makes use of the configuration of the two‐port antenna. Moreover, for reallocating radiating modes, an array of four shorting pins is introduced to push up the resonant frequency of each first desired resonant mode, which enhances the overlapped impedance bandwidth. Finally, the proposed antenna is designed, fabricated, and measured. The measured results show that the antenna achieves a broad overlapped impedance bandwidth of around 28.5% ranging from 2.11 to 2.81 GHz. Meanwhile, the peak‐measured gain is 7.0 dBi for the conical beam and 9.9 dBi for the broadside beam, while an isolation of 23 dB is also realized. Most importantly, novel feeding schemes still maintain the low‐profile property of around 0.066 λ0 (λ0 is the free‐space wavelength at 2.46 GHz). [ABSTRACT FROM AUTHOR]

This communication presents a method to make the EH0-mode microstrip leaky wave antenna (MLWA) radiate single beam in its transversal plane based on the differentially excited coupled microstrip line structure with low cross-polarization. The conventional EH0-mode MLWA is constructed by periodically loading a series of shorting pins along the center line of the uniform line, but it mainly radiates dual beams in its transversal plane. If a ground plane approaches to one of its edges with rotation of the whole structure, only one radiation aperture will be left to radiate single beam in the broadside direction. Herein, a planar differentially excited coupled line configuration is implemented to validate the proposed method and simultaneously inherits the original outstanding characteristic of freely designed narrow strip width. In design, a unified equivalent model is first established to provide insight into its radiation principle through propagation characteristics. Then, the dispersion and radiation properties are further investigated under mixed geometrical parameters. Finally, a prototype MLWA with transversal single-beam radiation is designed and fabricated with good agreement between the simulated and measured results, which validates the proposed method for designing a single-beam EH0 mode MLWA. [ABSTRACT FROM AUTHOR]

Novel design concept of reconfigurable full-metal cavity-backed slot antennas (CBSAs) using movable metal posts is proposed in this article. It is found that the cavity mode with purely directional electric field is only affected by the metal post to be placed in parallel to its electric field. Thus, two orthogonal cavity modes TE101 and TE011 can be perturbed by two respective metal posts so as to independently tune the resonant frequencies of these two modes. Electromagnetic energy of the cavity modes can be radiated out through the slots on the top wall of the cavity. In this context, reconfigurable slot antennas with different functionalities, such as single-band, dual-band, dual-mode wideband, the tunable frequency with constant bandwidth, and tunable bandwidth with constant frequency, are thus constituted to demonstrate its attractive design feasibility. The frequency-reconfigurable cavity-back slot antenna with movable metal posts is proposed for the first time. The utilization of the metal posts allows us to achieve a continuous frequency tuning property, while the full-metal structure of the proposed antenna holds a high power-handling capacity and a high radiation efficiency. In final, a prototype of the dual-mode wideband slot antenna is designed, fabricated, and tested to reveal its total efficiency higher than 88% and stable radiation pattern over the tuning band. Good agreement between the measured and the simulated results well validates the presented design concept. [ABSTRACT FROM AUTHOR]

In this communication, an $S$ -band wide-bandwidth and wide-beamwidth full-metal circularly polarized (CP) cavity-backed slot antenna is proposed. A pair of triangular prisms placed at the corners of the cavity is introduced to produce TE101 and TE011 modes with orthogonal electric fields. These two modes are used to achieve the CP radiation and radiate the energy through a single-circular slot. By simultaneously varying the prisms’ size and slot radius, the axial ratio (AR) bandwidth (ARBW) improves. The ARBW is further improved by replacing the circular slot with an elliptical slot. As a result, the ARBW increases from 1.0% to 10.3% without complicating the antenna structure and without enlarging the antenna size. Besides, the antenna still operates at two degenerate modes to introduce stable radiation gain and pattern. In addition, the proposed CP slot antenna features a wide ARBW. The final measurement shows that the proposed CP antenna can achieve a 9.5% bandwidth, a stable gain of 7.65 dBic ± 0.15 dBic, and higher than 140° ARBWs in a wide frequency range. The peak total radiation efficiency and aperture efficiency are about 97% and 91%, respectively. [ABSTRACT FROM AUTHOR]

This letter presents a method to convert the split dual-beam into a single one in the quasi-E-plane with low cross-polarization level for the pin-loaded fundamental EH0-mode microstrip leaky-wave antennas (MLWAs). By exciting a pair of them under differential operation with proper configuration, the ϕ-polarized dual beams can be reshaped to achieve a single-beam radiation, so as to widen its potential application. The proposed method for transversal single beam still preserves the merits of the original pin-loaded EH0-mode MLWA with simple structure and freely designed narrow width. A prototype MLWA with single-beam radiation in the quasi-E-plane is designed, fabricated, and measured. Good agreement is attained between simulated and measured results, and thus validates the unique feature of the proposed method in design of single-beam pin-loaded EH0-mode MLWAs. [ABSTRACT FROM AUTHOR]

A low-profile high-directivity circularly polarized patch antenna is proposed in this article. Two orthogonal slots are etched out in the middle of a square patch. As a result, radiation patterns of original TM12/21 modes are reshaped to the desired ones that are similar to those of TM10/01 modes, leading to significant enhancement of broadside radiation. To accommodate the modified current distributions of the two operating modes, a pair of perturbed stubs is proposed and then loaded on the slot-loaded patch, which leads to the quadrature-phase difference. In order to suppress unwanted modes that tilt the radiation pattern away from broadside direction, differential-fed configuration instead of single-fed one is adopted to excite modified TM12/21 modes. Characteristic modes theory (CMT) is used to analyze the input impedance of differential-fed patch antenna and determine the two feeding positions. Next, the proposed antenna is compared with three conventional ones, which reveals its superiority in the highest directivity. Besides, it is also discussed how to determine the size of the finite ground plane. We find that the size of $1.5\lambda _{0} \times 1.5\lambda _{0} $ can increase directivity slightly and effectively prevent radiation pattern from tilting tendency. Finally, a prototype antenna is fabricated and measured for validation. [ABSTRACT FROM AUTHOR]

A novel design of bandpass frequency selective surface (FSS) with high selectivity is proposed based on the antenna-filter-antenna (AFA) concept. Traditional AFA-based FSSs improve filtering performance by adding the order of resonator or the coupling paths. On account of the reciprocity theorem, transmission zeros are here introduced by the antenna's radiation null. The proposed FSS consists of two patch antennas connected with one pin and a C-type slot on the ground. The aforementioned structure generates two controllable radiation nulls related to the lengths of slots without any extra circuits. Therefore, two transmission zeros at both edges of the passband can be controlled by adjusting the dimension of slots. A prototype is fabricated and measured. Numerical simulation and measured results are in good agreement, which demonstrates that the proposed AFA-based FSS exhibits a quasi-elliptic bandpass response and a low profile. [ABSTRACT FROM AUTHOR]

Wideband differentially fed patch antennas under dual high-order modes for stable high gain are proposed in this communication. The working principle is verified on a differentially fed circular patch antenna operating in TM31 and TM12 modes at first. Two open slots are loaded to the patch’s edge to reconstruct the current distribution of TM31 mode, thus substantially increasing the broadside radiation. An additional slot is introduced at the patch center to perturb the TM12 mode and reshape its current to be more in-phase, by which sidelobe radiation is dramatically reduced. With use of loading of slots and shorting pins, the two modes are allocated in resonant frequencies to make up an enhanced bandwidth of 13.4% and produce high gain up to 13.7 dBi, with the beamwidth and gain level nearly unchanged in band. Then, the proposed method is further developed on a rectangular patch antenna, where three cascaded slots and four shorting pins are loaded to perturb TM21 and TM03 modes, and reshape their current distributions. In a similar way, the broadside radiation of TM21 mode is enhanced and the sidelobe of TM03 mode is suppressed. At last, the antenna obtains a bandwidth of 12.4% and stable realized gain as high as 14.0 dBi. [ABSTRACT FROM AUTHOR]

A novel design concept to reduce the frequency ratio of a dual-band dual-circularly polarized (CP) microstrip patch antenna (MPA) is presented by using its reshaped TM10, TM01, and TM20 modes. First, the far-zone radiated fields of the traditional MPA are theoretically investigated. It demonstrates that the normal |Eθ| and |Eϕ| fields at xoz plane are orthogonally generated under its TM10 and TM01 modes, respectively. Unfortunately, its TM20 mode radiates the nonbroadside |Eθ| fields at xoz plane. Then, an open-ended stub is loaded around the edge of the radiator, aiming to reshape the TM20 mode as the broadside radiation. After that, the patch width is decreased with the loading of two shorting pins. The main target is to move the TM01 mode resonating between TM10 and TM20 modes. Finally, the proposed antenna is fabricated and tested. The results illustrate that its left-hand CP and right-hand CP radiation patterns are satisfactorily acquired at around 2.134 and 2.223 GHz, respectively, thus gaining a small frequency ratio of around 1.04. Meanwhile, the antenna holds the low-profile (0.02 free-space wavelength), small-backlobe, single-layer, single-fed, and single-radiator properties. [ABSTRACT FROM AUTHOR]

Ground-based multichannel microwave radiometers (MWRs) can provide continuous temperature and humidity profiles of the troposphere. MWR antenna pattern measurements are important for reliable and accurate antenna temperature measurement and are usually carried out in a microwave anechoic chamber. Measurement using an anechoic chamber is complex and expensive because the conventional measurement procedure requires a special situation and professional instruments. More importantly, the construction of the anechoic chamber and the installation method of the absorbing material can directly influence the performance of the anechoic chamber and the result of the antenna measurement. This paper proposes a new method of MWR antenna measurement by observing the sun, and this method can be used to measure other radar antenna patterns. During the measurement, the MWR observes the microwave radiation brightness temperature (TB) to measure the antenna pattern by high-resolution raster scanning of the azimuth and elevation of the sun under a clear sky in Xi'an, China. Analysis of the TB scanning data of the sun at four frequencies, 22.235, 26.235, 30.000 and 51.250 GHz, showed that the microwave radiation TB of the sun is strong enough to be observed by the MWR. Furthermore, the antenna pattern was illustrated and analyzed based on these data, which fully proves that the sun can be used to measure the antenna pattern. Finally, the antenna pattern derived from the solar observation was compared with the result of the far-field measurement with a point source in the microwave anechoic chamber at 30 GHz, the maximum error of the beamwidth is less than 0.1°, which showed that this pattern matched well to the pattern measurement using a point source in the microwave anechoic chamber. Therefore, the antenna pattern of the MWR can be measured by scanning the sun without a point source in the microwave anechoic chamber, and this method can be used for convenient MWR antenna measurements and can reduce the measurement complexity and cost. [ABSTRACT FROM AUTHOR]

A novel design concept to widen axial-ratio (AR)-bandwidth of a single circularly polarized (CP) patch antenna is presented by resonating its TM $_{1/2,0}$ , TM $_{1/2,1}$ , and TM $_{3/2,0}$ modes. First, a set of shorting pins is loaded around the edge of the patch with decreased width, aiming to suppress undesired nonbroadside modes. Second, the far-zone radiated fields of the antenna are theoretically studied by using equivalent magnetic currents (EMCs). The results demonstrate that its broadside $\vert {E}_{\theta }\vert $ , $\vert {E}_{\varphi }\vert $ , and $-\vert {E} _{\theta }\vert $ components of xo z plane radiation patterns could be orthogonally generated under TM $_{1/2,0}$ , TM $_{1/2,1}$ , and TM $_{3/2,0}$ modes, respectively. Most importantly, these three broadside EMCs must be sequentially rotated. Third, the resonant frequencies of these triple radiative modes (${f}_{1/2,0}$ , ${f}_{1/2,1}$ , and ${f}_{3/2,0}$) are extensively analyzed and reallocated by loading the shorting pins. It proves that the ${f}_{1/2,0}$ and ${f}_{1/2,1}$ could be progressively pushed up to around the ${f}_{3/2,0}$ , resulting in generating the CP radiation as expected. With these arrangements, the AR-bandwidth of the proposed CP antenna is significantly widened under triple-mode resonance. In final, the proposed antenna is fabricated and measured. Simulated and measured results are in good agreement with each other. The measured results depict that the CP antenna has acquired an enhanced AR-bandwidth with two minima poles, covering a fractional bandwidth of about 5% from 3.25 to 3.41 GHz, which is about 3.3 times wider than the traditional counterpart (1.5%). Besides, its profile is kept only about 0.03 free-space wavelength. Particularly, the single-layer, single-fed, single-radiator, and high-efficiency properties are simultaneously maintained for the CP antenna without needing to rely on any extra feeding networks, patches, or resisters. [ABSTRACT FROM AUTHOR]

This communication presents an effective approach to design the dual-band dual-mode (DBDM) patch antenna with flexible frequency ratio, wide achievable range, and compact configuration. Initially, the TM00 and TM10 modes of such an antenna are theoretically studied based on the transmission-line model. It is revealed that the lower resonant frequency of the TM00 mode could be effectively reallocated by properly introducing the inductance at its center. Meanwhile, the upper resonant frequency of TM10 mode remains unaffected during this process. This theoretical analysis provides a physical insight into its working mechanism. Then, a set of shorting pins is symmetrically loaded in the center of the patch radiator to make use of their equivalent inductance for flexible control of its operating frequency. After parametric analysis is extensively executed, a unified design procedure is summarized. With these arrangements, a wide frequency ratio of two operating bands could be flexibly realized in a range from 1.38 to 3.36. Finally, two DBDM antennas with the same patch contour but distinct frequency ratio, i.e., 1.38 and 3.36, are designed, fabricated, and tested. The simulated and measured results are found in good agreement with each other, thereby certifying the validity of the proposed method. All these results indicate that the proposed design approach with flexible frequency ratio, wide achievable range, concise procedure, and compact configuration could be widely applied to the modern communication systems. [ABSTRACT FROM AUTHOR]

A novel design concept to excite and produce the broadside circularly polarized (CP) radiation is presented in a shorted-patch antenna (SPA). First, the far-zone radiated fields of the SPA under radiation of TM0,1/2 and TM1,1/2 modes are theoretically studied. It demonstrates that the broadside |Eθ| component of its TM0,1/2 mode is generated in yoz plane. In contrast, the orthogonal |Eϕ| component of its TM1,1/2 mode is produced in this plane. Then, the resonant frequency of the TM0,1/2 mode is gradually pushed up to around that of TM1,1/2 mode, aiming to generate the normal CP radiation between these dual modes. After that, a linear slot is etched out on the core radiator so as to counteract the equivalent inductance caused by the loaded pins and feeding probe. Finally, the proposed antenna is fabricated and tested. The measured results reveal that it's operating bandwidth (|S11|<–10 dB and AR<3 dB) is kept at about 1.2% or at a range of 2.720–2.752 GHz. Most importantly, the CP radiation (AR<3 dB) of the antenna at the broadside direction is indeed resonated at around 2.738 GHz, while keeping the reduced length, single-layer, and single-fed properties. [ABSTRACT FROM AUTHOR]

A dual‐band dual‐mode microstrip Yagi antenna with quasi‐end‐fire radiation patterns is proposed in this paper. It consists of five radiating patches driven by a single slot‐loaded patch placed in the middle. Meanwhile, two slot‐loaded parasitic patches are symmetrically located on two sides of the driven patch, respectively. In the lower band, the five patches involved resonate at TM01 mode. While in the upper band, all the patches resonate at TM02 mode. In order to ensure quasi‐end‐fire radiations in the both bands, four slots are symmetrically etched around the strongest surface currents of each patch resonating at TM02 mode. As a result, the resonant frequency of TM02 mode is decreased dramatically, while the resonant frequency of TM01 mode almost remains unchanged. With these arrangements, the separations between any two of the adjacent patches at their centers satisfy the requirements in design of the microstrip Yagi antenna in both bands, so as to realize the dual‐band dual‐mode microstrip Yagi antenna on a single‐layer substrate. Finally, an antenna prototype is fabricated and tested. The measured results reveal that the dual operating bands of 2.76~2.88 and 4.88~5.03 GHz for |S11| < −10 dB are satisfactorily achieved. Most importantly, the proposed antenna can indeed realize the quasi‐end‐fire radiation patterns in dual operating bands. [ABSTRACT FROM AUTHOR]

A novel design concept to reduce high H-plane cross-polarization of a shorted patch antenna (SPA) with broadside radiated patterns is presented by loading a pair of open-ended stubs. Initially, the nonbroadside $\vert E_{\mathrm {\theta }}\vert $ component of the traditional SPA at TM $_{\mathrm {1/2,2}}$ mode is demonstrated to be much larger than its broadside $\vert E_{\varphi }\vert $ component in H-plane or yoz plane radiation patterns. In order to maintain its peak radiation in the normal direction, the far-zone radiated fields of the antenna are theoretically studied and analyzed. The results demonstrate that the dual nodal lines of the TM $_{\mathrm {1/2,2}}$ modal fields could be gradually moved far away from each other by increasing the stub length. As such, its $\vert E_{\varphi }\vert $ and $\vert E_{\theta }\vert $ components in H-plane or yoz plane radiation patterns could be progressively strengthened and weakened, respectively. After that, by reallocating these dual nodal lines around the corners of the radiating patch, the nonbroadside radiated fields of TM1/2,2 mode are successfully transformed into the broadside radiation, while keeping a low H-plane cross-polarization level. Additionally, the symmetric open-ended stubs are folded so as to reduce the dimensions of the core radiator. In final, the proposed SPA is fabricated and measured. Simulated and measured results are found in good agreement with each other, and both of them illustrate that the antenna has satisfactorily acquired a normal radiation pattern at reshaped TM1/2,2 mode. Most importantly, its high H-plane cross-polarization is dramatically reduced from −4.3 to −21.4 dB as compared to the traditional SPA at TM1/2,0 mode. [ABSTRACT FROM AUTHOR]

A dual-band single-layer microstrip patch antenna (MPA) with simultaneous improvement in impedance bandwidth and radiation beamwidth is proposed in this communication. The performances of the MPA are implemented by resonating its radiative TM10 and TM12 modes at the lower and upper bands, respectively. Initially, the far-zone radiated fields of the MPA working in the TM10 mode are theoretically investigated. It demonstrates that its E-plane half-power beamwidth (HPBW) in the lower band is significantly widened by removing the array factor between dual equivalent slots. After that, the MPA working in TM12 mode is deeply studied and analyzed. The results depict that its wide E-plane HPBW and low H-plane sidelobe level (SLL) in the upper band could be obtained by reshaping radiation patterns of its improved TM12 mode via the shorting pins. Additionally, a linear slot is cut on the core radiator so as to achieve a good impedance matching. With these arrangements, the E-plane HPBW, H-plane SLL, and impedance bandwidth of this designed MPA can be simultaneously enhanced in the dual bands. Finally, the proposed antenna is fabricated and measured. The experimental results show that the antenna has gained an improved bandwidth ($\vert S_{11}\vert < $ –10 dB) ranging from 3.45 to 3.77 GHz and 5.75 to 6.04 GHz with two attenuation poles. Most importantly, the HPBW of its E-plane radiation pattern is successfully widened to around 135° over these dual operating bands. Moreover, the high H-plane SLL of the antenna is decreased to about −10 dB in the upper band. [ABSTRACT FROM AUTHOR]

Design approach to a planar bisensing circularly polarized (CP) antenna is presented. The antenna is composed of a circular sector magnetic dipole and two concentric annular electric dipoles. At first, the flared angle, radius of the circular sector magnetic dipole, and the feed positions of electric dipole are determined by the phase difference condition for bisensing CP radiations. Then, the arc length of concentric annular electric dipoles is determined. Finally, a concentric annular parasitic element is properly employed to compensate the phase and amplitude difference. In these ways, bisensing CP antenna with the main beam in parallel to its plane can be realized by using a simple planar configuration with only a few design parameters. As experimentally validated, the proposed antenna exhibits a nearly perfect bisensing CP characteristic at 2.50 GHz band. [ABSTRACT FROM AUTHOR]

In this communication, a differentially fed wideband slot antenna on a single layer with endfire radiation and filtering response under multi-resonant modes is proposed. By using the $\lambda $ /4 slot radiator with its opened terminal at one side, the endfire-radiated fields of the slot antenna is initially formed with compact dimension and endfire radiation. After that, the $\lambda $ /4 slot radiator with two distinctive portions of different slot widths is presented and investigated. The results demonstrate that the resonant frequencies of the first two odd-order modes could be progressively reallocated in proximity to each other as the length and width ratios of these two portions are properly selected. Thus, the bandwidth in input impedance of the entire differentially fed slot antenna could be significantly improved under operation of dual-resonant modes. Next, an extra microstrip-line resonator is introduced in the feeding part so as to produce a third resonant mode and improve its frequency selectivity in the wide operating band. To validate these predicted performances, a filtering slot antenna operating from 3.33 to 4.50 GHz is in final fabricated and tested. The measured results exhibit good impedance matching property, flat radiation gain of about 5 dBi, and improved endfire radiation characteristic with the front-to-back ratio (FBR) better than 9.0 dB in the operating band. Both the simulated and measured results are provided with good agreement. [ABSTRACT FROM AUTHOR]

This paper presents a second higher-order-mode microstrip leaky-wave antenna (LWA) for single main beam radiation. Different from its conventional second higher-order leaky-mode counterpart with two symmetric radiation beams, the proposed antenna with an array of I-shaped slots radiates only one main radiation beam at the cross-sectional center plane. By introducing a transversally loaded slot array along the microstrip line, the cross-polarization of the antenna can be largely enhanced, while a longitudinally loaded slot array interrupts the current flow and thus effectively reduces the original two radiation beams. Subsequently, an array of I-shaped slots, including transversal- and longitudinal-slot portions, is etched on the strip conductor and its unique characteristics are then analyzed to obtain a single main radiation beam in the center plane. To validate this proposal, a prototype of single main beam LWA with second higher-order mode is designed, implemented, and fabricated. Owing to larger leakage constant, the LWA presented in this paper radiates higher power within a shorter length in terms of guided wavelength, resulting in a higher gain. The measured results show a beam-scanning capability from 20° to 55° as the frequency varies from 5.1 to 4.6 GHz, while the maximum gain of 14.6 dBi is achieved at 4.9 GHz. [ABSTRACT FROM AUTHOR]

A low-profile printed cavity antenna (PCA) under triple-mode resonance is proposed towards a simultaneous impedance bandwidth and a radiation pattern improvement. Based on the cavity model, the far-zone radiated fields of the PCA are theoretically investigated. The results demonstrate that its E-plane half-power beamwidth (HPBW) could be significantly improved by using two half-mode cavities instead of a single-patch resonator. After that, the width of the radiating patch is progressively enlarged and separated in order to excite three resonant modes for bandwidth-enhancement. Moreover, two additional conductive vias are loaded below the radiating patch in order to reduce its increased E-plane cross polarization. In final, the proposed antenna is fabricated and tested. Experimental results show that its impedance bandwidth is obviously extended to about 14.3% with appearance of three in-band attenuation poles. Meanwhile, a low-profile property with the height of 0.027 free-space wavelength is achieved. In particular, the PCA has acquired a wide E-plane HPBW of around 135°, while keeping a low cross polarization of below –20 dB in both E- and H-planes. [ABSTRACT FROM AUTHOR]

A novel planar endfire circularly polarized antenna with simple configuration and enhanced directivity is proposed. Two V-shaped dipoles operating at resonant 1.5-wavelength dipole mode are arranged to form a planar Yagi structure. In this way, both the azimuthal and elevational principal-cut planes could be effectively narrowed down. This leads to a directivity enhancement up to 4 dB in the endfire direction. As experimentally validated, the proposed antenna with a very low profile of 0.034 wavelength can exhibit measured gain of 6.1 dBic in the endfire direction. [ABSTRACT FROM AUTHOR]

A design approach to a novel planar self-balanced magnetic dipole antenna with wide beamwidth is proposed. By incorporating a parasitic rectangular strip to a circular sector magnetic dipole at its angular bisector on the bottom layer, a virtual magnetic wall boundary condition is partly introduced within the horizontal plane. In this way, the unbalanced current can be utilized to generate unidirectional radiation behavior, leading to the formulation of a self-balanced antenna with widened beamwidth. As numerically demonstrated and experimentally validated at the 2.45 GHz band, the half-power beamwidth (HPBW) of a planar, air-substrate magnetic dipole antenna can be effectively broadened up to 100° without increasing antenna profile, inquiring symmetrically rotational configurations, utilizing multilayered substrates or periodic loadings. The proposed approach not only provides a clear physical insight but also works out a set of closed-form formulas. As exhibited, the planar wide beamwidth antennas have a simple configuration and wide impedance bandwidth up to 20%. [ABSTRACT FROM AUTHOR]

In this letter, a microstrip Yagi antenna with a resonating patch driver, one slot-loaded patch reflector, and two pin-loaded patch directors is proposed. Different from all the reported counterpart antennas, the lengths and widths of all the patch elements involved herein are set to be the same, and a parasitic patch reflector and patch directors are realized by loading the slot and shorting pins on the patches, respectively. For a square patch, its resonance frequency can be reduced by etching out a slot, acquiring a reflective function. However, its resonance frequency can be increased by adding a pair of shorting pins underneath the patch, thus acquiring a directive function. By placing these two types of parasitic patches in the two sides of the driving patch radiator, an alternative microstrip Yagi antenna can be constructed to achieve a quasi-endfire radiation pattern with an enlarged beam tilt angle. A prototype operating at 5 GHz is finally fabricated and tested. The measured results achieve an impedance bandwidth of 8%. In addition, the maximum deviation angle reaches approximately 56° from the broad side, and its 3 dB beamwidth in the xoy plane exceeds 62°. [ABSTRACT FROM AUTHOR]

A low-profile wideband aperture-fed microstrip patch antenna (MPA) under radiation of TM12 and TM30 modes is proposed with improved radiation patterns. Initially, the radiation characteristic of a rectangular MPA operating in TM30 mode is theoretically investigated. The results demonstrate that its E-plane sidelobe could be gradually reduced by decreasing the resonant frequency of TM30 mode (${f} _{30}$). As such, a pair of parallel slots is etched out on the radiating patch so as to significantly decrease the ${f} _{30}$. After that, the MPA under an operation of TM12 mode is further studied. It illustrates that its radiation pattern has the maximum off broadside direction and can be transformed into the broadside radiation by enlarging the length of the parallel slots. In addition, the width of the radiating patch is progressively enlarged in order to reallocate the dual modes in proximity to each other. With these arrangements, a wide bandwidth with improved radiation characteristics is obtained for the antenna under dual resonance. Finally, a prototype aperture-coupled MPA is fabricated and measured. The simulated and measured results agree well with each other, thus demonstrating that its impedance bandwidth is dramatically extended to about 14.8% with a low-profile property of about 0.048 free-space wavelength in thickness. Besides, the antenna has achieved a stable gain varied from 7.0 to 9.9 dBi over the operating band. In particular, the E-plane sidelobe level of the proposed antenna has been successfully suppressed. [ABSTRACT FROM AUTHOR]

A low profile shorted-patch antenna (SPA) with enhanced bandwidth and reduced the H-plane cross-polarization (cross-pol) is proposed in this communication. Initially, the radiated field of a conventional SPA is theoretically investigated. It is demonstrated that its high cross-pol of the H-plane radiation patterns can be reduced by introducing a pair of shorting walls underneath the nonradiating edges of the SPA. Then, the width of the radiating patch is progressively enlarged so as to decrease the resonant frequency of TM1/2,2 mode. After that, an array of six shorting pins is loaded underneath the patch radiator toward pushing up the resonant frequency of TM1/2,0 mode. In addition, the linear Slots 1 and 2 are cut on the rectangular patch to reduce the resonant frequency of TM3/2,0 mode and achieve a good impedance matching, respectively. With these arrangements, all of these three radiative modes are reallocated in proximity to each other, leading to the formulation of the improved SPA with low profile, wide-bandwidth, and low cross-pol performances. Finally, the proposed antenna is fabricated and measured. The measured results show that its impedance bandwidth is extended up to about 26.2% under triple-mode resonance. In addition, its thickness is maintained as small as about 0.059 free-space wavelength. In particular, the H-plane cross-pol of the SPA is successfully decreased to below −12.3 dB over the operating band. [ABSTRACT FROM AUTHOR]

A co-design of a wideband circularly polarized (CP) patch antenna is proposed in this paper. The patch antenna is seamlessly integrated with two bandpass filter networks consisting of one and two $\lambda $ /2 resonators, respectively, which are designed to excite two orthogonal modes with equal magnitude and quadrature phase over a widened bandwidth. In co-design of this filtering antenna, the patch antenna is equivalently treated as the last-stage resonator and the output port of the filter network. In analysis of its far field, axial ratio (AR) of CP wave is mapped to its magnitude and phase responses. By simultaneously synthesizing the magnitude ratio and phase difference of the two filter networks’ transmission coefficients to vary around 1° and 90°, respectively, wideband AR response with three minima is realized. Based on this design method and the theoretically derived results, a CP patch antenna prototype with a height of $0.028\lambda _{0}$ is fabricated and measured. It is experimentally demonstrated that around 8.8%, bandwidth can be achieved with VSWR < 2, AR < 3 dB, and 3 dB gain variation. [ABSTRACT FROM AUTHOR]

A wideband circularly polarized (CP) patch antenna with enhanced axial ratio (AR) bandwidth via co-design of feeding network is proposed in this paper. One $\pmb \lambda/4 $ resonator and one $\pmb \lambda/2 $ resonator are introduced and coupled in proximity to two orthogonal points of a square patch radiator to excite two orthogonal modes. These two resonators not only function as impedance matching elements to achieve equal magnitude of two orthogonal modes in a wide frequency band but also provide the required 90° phase difference. In this way, two minima in the AR response appear, resulting in extended AR bandwidth. The wideband design of the antenna is carried out based on the equivalent circuit model, where the patch radiator is treated as a conductance, inductance, and capacitance parallel resonator. In particular, the feeding network and the patch are jointly considered as a three-port network for synthesis design. By mapping the radiated far field to the magnitude and phase on the radiation conductance in the circuit model, the AR response of the antenna becomes predictable in a straightforward manner. Measured results experimentally demonstrate that the 3-dB AR bandwidth of our proposed CP patch antenna is 2.7 times that of the traditional one fed with two 90° offset lines. [ABSTRACT FROM AUTHOR]

A low-profile differential-fed microstrip patch antenna (MPA) using TM10 and TM12 modes is proposed in this communication toward simultaneously achieving the impedance-bandwidth enhancement and sidelobe reduction. Based on the transmission-line model, the radiation patterns of TM10 mode of the MPA loaded with shorting pins and slots are at first deeply investigated. The results demonstrate that the E-plane sidelobe could be gradually reduced by lowering the resonant frequency of TM10 mode (f10) less than two times of the fundamental frequency (f0). After that, the two adjacent TM10 and TM12 modes of the MPA are relocated to resonate in proximity to each other for bandwidth improvement and sidelobe reduction. By inserting the shorting pins underneath the radiating patch, f10 is progressively pushed up with a slight effect on that of TM12 mode (f12). Then, the patch width is enlarged with the parallel slots etched out on it to move f12 closely to f10. Moreover, a narrow slot is etched at the center of the patch for good impedance matching. With these arrangements, f10/f0 can be decreased dramatically to about 1.27. Finally, the antenna prototype is fabricated and measured. Experimental results show that the impedance bandwidth of the MPA is tremendously extended to about 10%, while keeping a low profile of 0.039 free-space wavelength. In particular, the sidelobe level of the antenna is dramatically reduced to about −12 dB. [ABSTRACT FROM AUTHOR]

An integrated method of broadband duplex–filtenna based on a 3-D metallic cavity structure is proposed in this paper. In our design, two broadband filtennas with different operation frequency bands share the same metallic cavity-backed resonator. The two operation bands are realized with fractional bandwidths (FBWs) of 24% and 18%. The whole total FBW of two bands achieves 57%, and there are radiated nulls at the transition band showing a good filtering property. By integrating these two filtennas, a duplex–filtenna is formed with unidirectional radiation property. The radiation gain of these two filtennas exhibits good filtering property. The filtenna gain frequency responses have two transmission zeros near the lower and upper cutoff frequencies of both lower and upper operation bands. To validate the proposed concept, one cavity-backed duplex–filtenna with low-profile metallic cavity is designed and fabricated. The measured results have verified the simulation results well, and the isolation between the two wideband channels exceeds 30 dB as predicted in theory. [ABSTRACT FROM AUTHOR]

We present a design approach to a novel nonturnstile planar endfire circularly polarized (CP) antenna with a widened beamwidth and an enhanced front-to-back ratio. This approach combines a semicircular magnetic dipole and a V-shaped open loop to widen the azimuthal beamwidth at first. Then, to further enhance the front-to-back ratio, the V-shaped loop is appropriately rotated with respect to its feed apex. The tradeoff between the azimuthal beamwidth and the front-to-back ratio is theoretically revealed based on the approximate closed-form radiation pattern functions. Antenna prototypes are simulated accordingly, and they are then designed and measured to validate the design approach. The measured impedance bandwidth for |S11| &lt;-10 dB covers a frequency range of 2.25-2.5 GHz (10.5% in fraction), and the axial ratio (AR) bandwidth of &lt;3 dB is 2.3-2.57 GHz (11.1% in fraction). The measured 3-dB AR beamwidths of the proposed antenna are equal to 180&deg; and 115&deg; in the elevational and azimuthal plane, respectively, at 2.35 GHz. In addition, the measured in-band average frontto- back ratio reaches up to 13.7 dB. [ABSTRACT FROM AUTHOR]

A differentially fed circular patch antenna working in TM11 and TM12 modes is proposed for dual-band high-gain and stable radiation patterns. A set of shorting pins are loaded in circular contours underneath the circular patch to substantially increase the resonant frequency of TM11 mode, and the radiation gain in lower band can be hence effectively enhanced due to the enlarged patch size at resonance. Meanwhile, a narrow slot is introduced to the center of patch, in order to interrupt the out-of-phase current of TM12 mode on patch for sidelobe reduction. As the electric current distribution on patch is significantly reshaped by the slot, the antennas act like a full-wave dipole in this case, so both high gain and low sidelobe level are realized in upper band. Besides, by properly adjusting the shorting positions of pins and length of slot, the antenna can be well matched in the desired 3.6 and 5.9 GHz wireless local area network bands. Simulated and measured results show that at least 10 dBi realized gain can be obtained in both the lower and upper bands, and the patterns in the two bands show agreeable beamwidths. [ABSTRACT FROM AUTHOR]

A patch antenna with loading of slot and shorting pins is proposed in this paper to enhance the radiation gain without increasing the patch size. At first, a straight slot is transversely introduced in the central line of a patch. For the dominant TM01 mode, this central line behaves as a virtual electric wall with zero electric field and maximum surface current underneath and on the patch, respectively. By doing so, the central slot serves as an extra radiator so that this slot-loaded patch produces radiation as an equivalent three-slot array. Meanwhile, a pair of shorting pins is longitudinally placed at the two symmetrical sides of this central slot to maintain the resonant frequency. Due to the out of phase between the electric fields in the central slot and two sided slots, the far-field radiated by the three slots can be canceled with each other in specific directions away from broadside. Thus, this cancellation results in sidelobe of low level in the E-plane due to emergence of radiation nulls, and further makes the main radiation beam more directionally selective. Accordingly, the directivity and gain of this proposed patch antenna are enhanced with no need of enlarging the overall size of patch. Finally, the simulated and measured results are provided to validate the operating principle and show that the directivity is increased by about 1.7 dB increment. [ABSTRACT FROM AUTHOR]

A low-profile planar inverted-F antenna (PIFA) under the operation of TM0,1/2 and TM2,1/2 modes in a single patch resonator for bandwidth enhancement is proposed. Initially, our study demonstrates that all of the even-order modes can effectively be suppressed by employing a rectangular PIFA instead of the conventional microstrip patch antenna. Then, a pair of shorting pins is appropriately loaded underneath the side-shorted radiating patch to investigate the variation of their odd-mode resonant frequencies. The results indicate that the resonant frequency of TM0,1/2 mode ( f0,1/2 ) is dramatically increased up while almost maintaining that of TM2,1/2 mode ( f2,1/2 ). After that, the width of the radiating patch is progressively enlarged in order to move the f2,1/2 more closely to the f0,1/2 . By using this approach, the dual radiative resonant modes can be reallocated in proximity to each other. Additionally, a narrow slot is etched out on the radiating patch so as to counteract the equivalent inductance caused by the shorting pins and probe. As such, a wide-bandwidth with stable radiation pattern is achieved for the PIFA under the operation of these dual-resonant modes. After the extensive analysis is executed, the proposed antenna is fabricated and tested. Simulated and measured results are found in good agreement with each other, demonstrating that its impedance bandwidth is tremendously widened to about 15.3% with appearance of two in-band attenuation poles. In particular, a low-profile property with the height of 0.036 free-space wavelength is achieved. [ABSTRACT FROM PUBLISHER]

A comprehensive study on the mechanism of bandwidth enhancement for an equilateral triangular microstrip patch antenna (MPA) under differential excitation is presented in this paper. Attributing to the way of differential excitation, the radiation directivity of TM11 mode in such a patch has been improved a lot, and field distributions for both TM10 and TM11 modes are found to be simultaneously excited for radiation. Next, two shorting posts are introduced to thisMPA so as to generate an additional mode, i.e., zero mode, which resonates in a frequency between TM10 and TM11 modes. With the proper arrangement of these three modes in proximity to each other, a wide bandwidth for radiation can be satisfactorily achieved. To demonstrate the validity of the proposed concept, a prototype antenna is finally designed and fabricated. As theoretically expected, the impedance bandwidth of the final designed patch antenna has been increased to 50.46% and the gain is around 6.5 dBi. Both simulated and measured results exhibit wide bandwidth and good performance of radiation. [ABSTRACT FROM AUTHOR]

A novel design concept to enhance the bandwidth of a differential-fed patch antenna using the dual-resonant radiation of a stepped-impedance resonator (SIR) is proposed. The SIR is composed of two distinctive portions: the radiating patch and a pair of open stubs. Initially, based on the transmission line model, the first and second odd-order radiative resonant modes, i.e., TM10 and TM30, of this SIR-typed patch antenna are extensively investigated. It is demonstrated that the frequency ratio between the dual-resonant modes can be fully controlled by the electrical length and the impedance ratios between the open stub and radiating patch. After that, the SIR-typed patch antenna is reshaped with stepped ground plane in order to increase the impedance ratio as highly required for wideband radiation. With this arrangement, these two radiative modes are merged with each other, resulting in a wide impedance bandwidth with a stable radiation pattern under dual-resonant radiation. Finally, the proposed antenna is designed, fabricated, and measured. It is verified in experiment that the impedance bandwidth ( \vert S\mathrm{ dd11}\vert < -10 dB) of the proposed antenna has gained tremendous increment up to 10% (0.85–0.94 GHz) with two attenuation poles. Most importantly, the antenna has achieved a stable gain varying from 7.4 to 8.5 dB within the whole operating band, while keeping low-cross polarization. [ABSTRACT FROM PUBLISHER]

A novel wideband planar endfire circularly polarized (CP) antenna with wide 3 dB axial ratio (AR) beamwidth is presented. The operation principle of the proposed CP antenna is described at first through the combination of a planar magnetic dipole and a V-shape open loop. Then, it is demonstrated how its AR beamwidth can be precisely controlled with resorting to the shape and thickness of the open loop element. Finally, the theoretical design approach is numerically verified, and the results are then experimentally validated. It is observed that a 3 dB AR beamwidth is achieved in an extremely wide angular region up to 250° within the principal elevation plane over a frequency range of 2.41–2.51 GHz. The proposed antenna has exhibited a wide impedance bandwidth of 22.23% in fraction, a 3 dB AR bandwidth of no less than 8.00% in fraction, and a simple planar profile in geometry. In addition, its endfire beam is in parallel with its plane. [ABSTRACT FROM PUBLISHER]

A novel broadband dual-polarized slot antenna with stable radiation pattern is presented. Two U-shape microstrip lines are introduced at two feeding ports to excite a cross-shape slot for realizing dual-polarized antenna. The simulated results are given to explain how the ground plane, short metallic pillars, and reflector affect the reflection coefficient, \vert S11\vert . The beamwidth of the proposed antenna is stable within the operating band, whereas a broad fractional bandwidth ( \vert S11 \vert < - 10 dB) up to 68% is achieved, covering a frequency range of 1.3–2.65 GHz. The measured half-power beamwidth of H -plane is 66.8° ± 3.4°. [ABSTRACT FROM PUBLISHER]