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A magnetic Yagi-Uda antenna applying higher order mode in millimeter-wave (mm-Wave) band with vertically polarized endfire radiation is proposed in this article. Surface wave mode analysis is applied to spot TE mode for magnetic Yagi-Uda antenna in contrast to TM mode for electric Yagi-Uda antenna. A modified structure evolved from conventional U-shaped cavity is used to address the reversed current issue for higher order mode, which exhibits a more uniform phase distribution at the Yagi-Uda array end. Then, a composite end-feeding structure with reflector integrated is further introduced to minimize its parasitic effects for practical antenna design in mm-Wave band. To validate the design, a prototype with a size of 2.7 $\lambda _{\mathbf {0}}\times1.25\lambda _{\mathbf {0}}\times0.088\lambda _{\mathbf {0}}$ is fabricated and tested. It can achieve anendfiregain of 8–11 dBi within 24–26 GHz with –10 dB impedance band covering an even wider frequency range. The measured front-to-back ratio (FBR) is larger than 16.1 dB. Vertically polarized radiation is realized with cross-polarization level lower than –20 dB atendfiredirection. [ABSTRACT FROM AUTHOR]

A design approach of triband conformal monopolar antenna combining cavity mode and equivalent circuit (Ec) is proposed. First, based on mode analysis, two lower and closer resonant frequencies in the VHF-band are generated by introducing two slot rings and two circles of short vias to a circular parallel-plate structure. Second, its Ec is extracted and modified. Then, the geometry structure is improved accordingly. An inverted truncate cone is introduced to modify the characteristic impedance of the monolithic radial transmission line to obtain an available band in the middle frequency (UHF). Finally, a high-frequency (L) antenna is embedded into the truncate cone and excited by a novel composite feeding structure. Furthermore, the conformal performance of the triband antenna is investigated. The conformal antenna prototype is fabricated and achieves a triband within 69.3–72.5 MHz, 317–348 MHz, and 1.38–1.71 GHz with a size of $0.42\lambda _{0}\times 0.42\lambda _{0}\times 0.014\lambda _{0}$ (maximum wavelength). The realized gain in triband is −7.6 to −5.9, 4.7–5.4, and 4.7–5.9 dBi, respectively. For a 6 cm-thick FR-4 substrate combined with shorted metal columns, the triband conformal antenna has the potential on serving as a vehicle roof to bear the load, and it is attractive in vehicle communication too. [ABSTRACT FROM AUTHOR]

A Ku-band electronic 2-dimensional (2-D) beam-scanning transmitarray employing a new reconfigurable dual-layer Huygens element is developed in this article. The Huygens element consists of two metallic crosses printed on two layers of a dielectric substrate, which enables a near nonreflection Huygens resonance. A 1 bit phase compensation with low transmission loss is realized by controlling two p-i-n diodes on the element. Compared with many other reconfigurable transmitarray elements using multilayer structures with metallic vias, the proposed reconfigurable Huygens element has a much simpler configuration with a simpler biasing network, and it is not affected by multilayer alignment errors. This particularly facilitates large aperture array development at higher frequencies. To validate the design concept, an electronically reconfigurable transmitarray with the proposed element is fabricated at 13 GHz. Good agreement between the measured and simulated results is found, showing 2-D scanning beams within ±50° in the E-plane and ±40° in the H-plane with a maximum realized gain of 18.4 dBi. [ABSTRACT FROM AUTHOR]

Frequency-multiplexing metasurfaces are typically attributed to the integration of multiple resonators, where mode coupling may significantly affect their performances. In this communication, we develop a dispersion-assisted dual-phase hybrid strategy for dual-frequency independent control of amplitude and phase with a single resonance. Therein, the frequency and phase decoupling can be achieved by precise dispersion control between two frequency states, while the amplitude distribution of each meta-atom can be controlled by properly allocating the energy of copolarized and cross-polarized waves. As a proof of concept, a bi-functional meta-mirror shaping multifocal points at two different frequencies have been experimentally demonstrated. The measured results are in good agreement with simulated results, showing the diffraction efficiencies (DEs) of 38% and 45%, and a signal-to-noise ratio (SNR) of 8.36 and 10.35 at $f_{1}$ and $f_{2}$ , respectively. In addition, another three meta-mirrors with tailorable amplitudes at dual frequencies are designed to further verify our strategy. This method offers an alternative platform for designing high-performance devices with dual-frequency wavefront manipulations, which may find potential applications in microwave integrated systems and wireless communication systems. [ABSTRACT FROM AUTHOR]

A novel low-profile phased antenna with dual-port and its two types of 1-D linear array to 2-D space wide-angle beam scanning are proposed. The antenna unit is composed of fishbone structure and rhombus parasitic patch, which is folded into n-shaped to low profile $0.08\lambda $. By adjusting the phase difference ($\Delta \varphi$) from 0° to 180°, the antenna working mode is changed from even mode to hybrid mode and to odd mode eventually. Therefore, the proposed antenna unit realizes wide-angle scanning characteristics and continuous switching state from broadside lobe to endfire lobe. Furthermore, the proposed phased antenna element is extended to two kinds of 1-D linear phased array (Array#1 and Array#2) based on the generalized principle of the pattern multiplication. The fabricated Array#1 can realize beam scanning range $- 116^{\circ }< \theta _{\mathrm {m}} < 0^{\circ }$ (xo z plane), $0^{\circ }< \theta _{\mathrm {m}} < 63^{\circ }$ (yo z plane), and $90^{\circ }< \Phi _{\mathrm {m}} < 169^{\circ }$ (xoy plane) and the fabricated Array#2 can achieve $0^{\circ }< \theta _{\mathrm {m}} < 60^{\circ }$ (xo z plane), $0^{\circ }< \theta _{\mathrm {m}} < 65^{\circ }$ ($\text{y}{o}\text{z}$ plane), and $90^{\circ }< \Phi _{\mathrm {m}} < 152^{\circ }$ (xoy plane). The proposed phased antenna unit and its 1-D array can realize 2-D space wide-angle scanning, improving scanning performance and expanding scanning dimensional space in phased array. [ABSTRACT FROM AUTHOR]

A 2-D scanning phased array with large element spacing using pattern reconfigurable stacked patch antenna at Ka-band is presented. The pattern reconfigurable stacked patch antenna is composed of four patches on the top integrated with four p-i-n diodes and a driven patch on the lower layer, where the top patches are located along the diagonals of the proposed antenna. By switching the reverse/forward bias states of p-i-n diodes, the phase gradients in different directions are generated and beam steering on the E-, D-(diagonal), and H-planes can be delivered. Subsequently, a 2-D scanning $4\times 4$ phased array with large element spacing is proposed by applying the pattern reconfigurable stacked patch antenna. The 2-D space is divided into nine subsets and covered by nine states of the proposed antenna. The measured results show that a scanning range of ±55° on the E-, D-, and H-planes can be provided. The maximum realized gain is 20.9 dBi at 26.5 GHz with an aperture efficiency of 62.0%. Compared with conventional half-wavelength phased array, the complexity and cost can be reduced for 2-D scanning phased array by introducing the proposed pattern reconfigurable stacked patch antenna. [ABSTRACT FROM AUTHOR]

An elevation and azimuth direction-finding (DF) method is presented by introducing the pattern reconfigurable antenna (PRA) into a two-element array. An equivalent multidimensional array is built by the two-element PRA array with switchable beams of same or opposite directions. With the introduction of same- and opposite-direction modes of PRAs, the elevation and azimuth angles are estimated by the methods of time-modulated array (TMA) and amplitude comparison, respectively. Meanwhile, a 2-D lookup table is built to correct the coning-error effect of the amplitude comparison. Compared with the conventional 2-D DF method with two orthogonal linear arrays, only a single linear array with not less than two elements is needed in the proposed method. Hence, it has the advantages of simple structure, compact size, and low cost. Simulated results are provided to verify the proposed 2-D DF method, and an S-band two-element PRA array is constructed to demonstrate its experimental feasibility. [ABSTRACT FROM AUTHOR]

This communication presents a gain-equalized $K_{a}$ -band Rotman lens-fed antenna by using phase gradient transmission lines (PGTLs). With PGTLs, the variation trend of the output progressive phase differences among the feeding ports is inverted. The aperture loss of the planar antenna array is then partially compensated by the efficiency of the lens when performing a wide-angle beam scanning. Hence, gain equalization is achieved among multiple beams with an acceptable gain degradation. To reduce the total size, the Rotman lens with PGTLs, the feeding networks, and the antenna array are stacked vertically. Meanwhile, the feeding network is implemented with substrate integrated coaxial lines, suppressing the parallel-plate mode inside the multilayer structure. In order to validate the proposed design, a compact Rotman lens-fed antenna operating at 24.75–27.5 GHz (FBW = 10.5%) is designed and fabricated. The results show that the gain drop of the Rotman lens-fed multibeam antenna is reduced from 4.4 to 1.5 dB at the design frequency of 26 GHz, covering a wide angular range between ±56°. [ABSTRACT FROM AUTHOR]

While electromagnetic (EM) metasurfaces have been extensively studied for wavefront manipulations, the real 3-D manipulation of wavefront remains challenging. In this article, an advanced strategy of noninterleaved multitasked metaplexer for 3-D manipulation of dual-helical EM wavefronts is reported. We first develop a general method to derive the metasurface phase distribution required to form the desired 3-D electric field patterns. Then, the spin-decoupled meta-atoms are designed to achieve this goal and further increase the degrees of freedom in EM manipulation. As a proof of concept, cascaded multiplane digital images in the propagation direction are employed as the 3-D wavefronts, which are encoded into the spin-decoupled meta-atoms array, making the outputting circularly polarized waves carrying different image information at different planes. Both the simulations and experiments verify the desirable 3-D wavefront manipulation capacities of our strategy for dual-helical states. Besides, this scheme can be further extended to achieve arbitrary energy allocation in 3-D space for dual-helical EM waves. Our strategy paves an alternative route for applications such as multiple-input multiple-output (MIMO) communications, multitarget radar detection, information storage, as well as 3-D microwave imaging. [ABSTRACT FROM AUTHOR]

A grating lobe suppression approach based on the null scanning antenna (NSA) for a sparse phased array is proposed. The NSA provides continuous null scanning and beam steering on two orthogonal planes, by connecting four varactor loaded impedance reconfigurable circuits to the four edges of a square patch antenna, respectively. The NSA is introduced into a sparse phased array and the grating lobe is suppressed by keeping the radiation pattern null of NSA pointing at the angle of the grating lobe during beam scanning. Meanwhile, the beam direction of NSA is steered to a wider angle with the variation of null angle. The main lobes during beam scanning are located within the 3 dB beamwidth of NSA. Thus, the sidelobe level (SLL) and scan loss over the wide scanning region are improved considerably. A $2\,\,\times \,\,4$ sparse phased array with NSA is designed and measured for verification. Both simulated and measured results indicate that the SLL of the sparse phased array with NSA can be suppressed below −9.3 dB within the scan range from −76° to 75°. The maximum realized gain during beam scanning is 17 dBi, with an aperture efficiency of 69.86% and a maximum gain fluctuation of 4.4 dB. [ABSTRACT FROM AUTHOR]

A novel dual-port phase antenna is proposed to realize 2-D scanning. The antenna consists of two monopoles on both sides and a fishbone structure in the middle. By changing the phase difference ${\Delta \varphi }$ between two monopoles, energy is coupled to the proposed structure, exciting different degrees of superposition of even and odd modes. The continuous switching from the broadside lobe to the end-fire lobe is realized, and it has the characteristic of 2-D scanning. Furthermore, to provide an in-depth insight into the 2-D scanning mechanism, two linear arrays (Array 2 and Array 3) based on the proposed antenna element and a generalized principle of pattern multiplication (GPPM) are developed. The fabricated Array 2 can offer scanning angles of 0°–73° along the $\theta $ -direction with the gain of 6.5–10.4 dBi and 90°–140° along the $\Phi $ -direction with the gain of 6.1–11.7 dBi. Its scanning coverage of 3 dB beamwidth is $0^{\circ } < \Phi < 140^{\circ }$ , $0^{\circ } < \theta < 90^{\circ }$. The manufactured Array 3 can scan 0°–90° along $\theta $ -direction with the gain of 8.2–11.1 dBi and 50°–90° along the $\Phi $ -direction with the gain of 6–9.36 dBi, and its 3 dB coverage of the main beam scanning is $0^{\circ } < \Phi < 180^{\circ }$ , $0^{\circ } < \theta < 90^{\circ }$. Consequently, the proposed antenna and GPPM can be readily extended to wide-angle scanning phased arrays. [ABSTRACT FROM AUTHOR]

A novel single-channel direction finding (DF) method with spatial spectrum estimation is proposed based on 1 bit time-modulated array (TMA). Its performance is analyzed from theoretical derivation to numerical simulations and compared with other existing DF methods. The proposed DF method is implemented as follows. First, the received sideband signals from the 1 bit modulated single-channel signal are deduced, followed by the detailed analysis of the received noise distribution. Second, the harmonic recovery (HR) method with the $l_{2} $ -norm approximation is utilized to recover the original array signals. Finally, conventional spatial spectrum estimation methods are easily applied for high-accuracy DF. Meanwhile, The DF accuracy of the proposed 1 bit method is analyzed under the Gaussian noise model, and its Cramér–Rao lower bounds (CRLBs) are deduced for the first time and compared with conventional arrays and other DF TMA systems. Numerical simulations are provided to show that the proposed 1 bit TMA system and HR method can achieve better accuracy performance over the existing TMA systems when the circuit noise is predominant in the received noises. An $S$ -band 1 bit TMA system is fabricated and implemented to experimentally verify the feasibility of the proposed method under circumstances of a single incident source and two coherent sources. [ABSTRACT FROM AUTHOR]

An extremely low-frequency (ELF) magnetomechanical antenna with the size of one-millionth wavelength based on a three-phase induction motor is reported, whose working frequency is no longer limited by the resonant wavelength. The rotating three-phase induction motor with nonmagnetic material shell is just equivalent to a rotating magnetic dipole with 1.5 times magnetic dipole moment. It can transmit the modulated electromagnetic (EM) signal by modulating the rotating speed of the motor. A near-field ELF EM signal transmission experiment system is constructed based on the magnetomechanical antenna with $\Phi 10$ cm $\times50$ cm size, and the transmitted EM signals were received by a 200-turn coil, which is 10–200 m far away from the transmitter. The EM signal frequency is almost the same as the rotating speed of the motor, and it varies with the rotating speed too. With arbitrary waveform generator and variable-frequency drive (VFD) modulating the rotating speed of the motor, a near-field ELF transmitter with modulating EM signal is built, and the sawtooth wave (STW)-modulated EM signal was transmitted and received clearly during 10–200 m. The square wave (SW)-modulated EM signal was communicated too. The proposed magnetomechanical antenna has a compact size and is very suitable for ELF remote wireless communication. [ABSTRACT FROM AUTHOR]

A novel periodically rotated spoof surface plasmon polaritons (R-SSPPs) structure of s-shaped arms distributed along z-axis is proposed. The R-SSPPs structure can generate an endfire radiation lobe with rotating E-field in odd mode, and omnidirectional radiation pattern with higher gain in quasi-even mode under different polarization plane waves, respectively. The endfire antenna based on the R-SSPPs structure fed by a vertical monopole was designed and fabricated. It works in odd mode and achieves 20.35% impendence bandwidth from 2.185 to 2.68 GHz. It provides a circularly-polarized endfire radiation pattern with gain 6–7.43 dBi in the range of 2.41–2.52 GHz in experiment. Based on the same R-SSPPs structure, a broadside antenna fed by SMA connector through coplanar waveguide (CPW) connecting to the R-SSPPs axis was designed and fabricated. It works in quasi-even mode and provides a quasi-omnidirectional radiation pattern. Its available impedance bandwidth is about 24.3% ranging from 2.35 to 3 GHz with gain of 2–6 dBi. By using different feeding means, the proposed R-SSPPs structure can radiate different patterns with different polarizations, which can be quite promising for different applications coping with the dynamic environment. [ABSTRACT FROM AUTHOR]

The time-modulated array (TMA)-based space-division multiple access (SDMA) approach is studied and verified, including the performance analysis and experimental verification. It utilizes the multibeam characteristic of TMA to implement the SDMA. For the uplink, the main power of signals with different incident angles would be redistributed to different harmonic components after time modulation. In this case, it plays a key role in this system to determine the harmonic order, which is selected to detect the received signal. A novel harmonic selection method for the uplink TMA-based SDMA systems is proposed by maximizing the received signal power. Furthermore, a closed-form expression of the spectral efficiency is deduced to verify the advantage of the simple harmonic selection scheme. Numerical results show that the TMA-based SDMA system can significantly improve the spectral efficiency compared with traditional single radio frequency (RF) chain systems. Meanwhile, it does not increase the number of RF chains. An L-band eight-element TMA is fabricated and tested to validate the feasibility of the TMA-based SDMA method. [ABSTRACT FROM AUTHOR]

A low radar cross section (RCS) transmitarray is presented in this communication using phase controllable absorptive frequency-selective transmission (AFST) elements. The element consists of asymmetrical resonators with resistors to obtain an absorption–transmission–absorption response. The transmission phase within the transmission band can be controlled by rotating the AFST elements, achieving a 1 bit phase change. A low-RCS transmitarray using the developed elements is designed, fabricated, and measured. Compared with a reference transmitarray, the radiation performance of the low-RCS one is almost unchanged with a realized gain of 24.4 dBi. Significant RCS reductions have been realized for dual polarizations of the impinging electromagnetic (EM) waves. The 10 dB RCS reduction bandwidths are 18% and 14% for the lower and upper absorption bands, respectively. [ABSTRACT FROM AUTHOR]

A novel periodic phase modulation method is proposed and verified for the fast diagnosis of phased array. Taking the diagnosis of receiving paths as an example, its principle is as follows. Periodic phase modulations with different frequencies are added to each phase shifter of the phased array. Because of the periodic modulation, harmonic components are generated in all the elements. As modulation frequencies added to all the elements are different from each other, the generated harmonic components have different frequencies correspondingly. If some elements suffer failure, the corresponding harmonic components will vanish from the output of the power combiner. Therefore, the faulty elements can be located by analyzing the spectrum of the received signal after the power combiner. The proposed method needs no the auxiliary hardware and its signal processing is concise. An eight-element $S$ -band phased array is fabricated to examine its effectiveness. [ABSTRACT FROM AUTHOR]

Direction finding with time-modulated array (TMA) has attracted considerable attention recently. In this communication, a multiharmonic analysis for direction finding based on TMA is proposed. The linear regression model of the two-element direction-finding system is established, and its noise covariance matrix is also analyzed. With the best linear unbiased estimator (BLUE), the high-order harmonic components which were previously ignored in the estimation can be effectively utilized to improve the direction-finding accuracy. Compared with conventional single harmonic analysis, simulation results are provided to demonstrate validation of the proposed method for improving the direction-finding accuracy. An experimental system based on two-element TMA is constructed and implemented to verify the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

A novel beam scanning method utilizing the carrier frequency component for time-modulated array (TMA) is proposed and a significant algorithm based on the non-uniform period modulation is implemented to suppress the maximum sideband radiation (SR) level. The signal in each channel is modulated by a pair of high-speed radio-frequency (RF) switches and totally three or four delay lines with different phases. In each modulation period, three selected delay lines are connected successively with proper pulse durations to keep the switches in ON states constantly and ensure the maximum efficiency in the feeding network. Additionally, in order to suppress the relatively higher SR generated by both switches and delay lines, each channel of the TMA system has a different modulation period, which will separate the harmonic components of different elements on the frequency axis. A desired relatively low maximum SR level without complicated optimization is obtained compared with uniform period modulation and optimization algorithms. Several numeric simulations are brought out to examine the performance of the proposed methods, and the results for comparison to existing methods are also provided. A group of experiments have been done to verify its effectiveness. [ABSTRACT FROM AUTHOR]

A novel direction-finding method with time-modulated array (TMA) is proposed for modulating the echo linear frequency modulation (LFM) signal and analyzing its harmonic characteristics. Unlike conventional analysis method where each coefficient of harmonic components is analyzed by discrete Fourier transform, in the proposed method, the harmonic coefficients of modulated signals are calculated by using the pulse compression technology. After the modulated LFM signal is compressed by the matched filter, a closed-form expression of the corresponding output signal is derived and the harmonic coefficients of the input modulated signals can also be obtained. Meanwhile, in order to avoid being affected by other harmonic components in the process of analyzing each harmonic coefficient, the constraints to acquire independent harmonic coefficients are highlighted. Numerical simulations are provided to verify the performance of the proposed method, and a simple S-band eight-element TMA is constructed to experimentally verify its feasibility. [ABSTRACT FROM AUTHOR]

A varactor loaded pattern reconfigurable patch antenna with shorting pins is presented. Continuous beam reconfigurability and null scanning are realized by introducing two sets of shorting pins and only four varactors into a square patch antenna. For this antenna, the edge-shorting pins are placed along with the parallel edges of the square patch for different $E$ -fields. Another set of shorting pins are fixed symmetrically along the diagonal of the square patch for directivity and null depth enhancement. To achieve continuous pattern reconfiguration, varactors are connected with the edge-shorting pins to provide continuously tunable phase difference. The mechanism of the pattern reconfiguration and effects of the shorting pins are discussed based on a transmission-line model. The proposed antenna has a compact size of $0.4\,\,\lambda _{0} \times 0.4\,\,\lambda _{0} \times 0.06\,\,\lambda _{0}$. Both the simulated and measured results confirm that the proposed antenna has the capabilities of beam steering and null scanning. The measured main beam scans from −55°to −15.5°and 19° to 54°, with a gain reduction of 3.22 dB relative to maximum (7.55 dBi). Meanwhile, the coverage of radiation pattern null is from −74° to 62°. [ABSTRACT FROM AUTHOR]

Metasurfaces deployed for generating electromagnetic waves that carry orbital angular momentum (OAM) in the transmission mode are generally inefficient in operation. In this paper, we present a method for the design, fabrication, and characterization of an ultra-thin metasurface which could be used for generating OAM waves at microwave frequencies with high efficiency. We achieve this objective by proposing a novel bilayer subwavelength scatterer having $\pi $ retardation phase between two orthogonal polarizations of an incident circularly polarized (CP) wave that also have high amplitudes. When analyzed our setup using Jones matrices, we find that the scatterer inverts the spin direction of the incident CP wave with high efficiency. Furthermore, the setup provides full phase control with the spatial rotation of the scatterer as per Pancharatnam-Berry Phase Mechanism. To further illustrate the utility of the proposal, a metasurface was designed based on the proposed scatterer and the generation of OAM waves is validated through both simulations and experimental measurements. To further clarify the points, a rigorous analysis for the transmission and conversion efficiencies is presented. [ABSTRACT FROM AUTHOR]

We present a broadband metasurface Luneburg lens for full-angle operation. The design of the Luneburg lens is based on an inverted substrate parallel-plate-waveguide structure with nonuniform circular holes etched on the upper metallic plate. We show that this structure is superior to existing designs as it allows significant simplification of the fabrication process. To achieve a smooth variation of the effective refractive index profile as well as circular symmetry for the Luneburg lens, size-variable meta-atoms are used for synthesizing the metasurface. The effective refractive index profile can be tuned by varying just the hole diameters. By introducing tapered microstrip ports that are evenly distributed on the circumference of the Luneburg lens, full-angle operation of the lens can be achieved. A prototype with a diameter of 400 mm is fabricated and experimentally evaluated at operating frequencies ranging from 6 to 9 GHz. We show good conceptual agreement between the simulated and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical analysis of orbital angular momentum (OAM) wave propagation properties in terms of reflection and refraction is introduced by decomposing OAM waves into infinite plane waves in the spectral domain with different elevation and azimuth angles. Transformations of phases and amplitudes at the interface of two media for different incident angles and elevation angles are numerically analyzed. Similarly, based on the idea of decomposing OAM waves, reflection and refraction properties of OAMwave propagating through slabs are also analyzed and simulated. Finally, experiments on OAM waves with both mode numbers 1 and 2 are conducted to demonstrate the reflection and refraction properties of OAM waves. [ABSTRACT FROM AUTHOR]

This communication proposes a novel method for finding the direction of the linear frequency modulation (LFM) signal, which has a bandwidth that is much larger than that of the modulated frequency, based on the time-modulated array (TMA). The relationship between the LFM signal and the modulated frequency is discussed and the constraint to avoid aliasing is also derived. To verify the proposed constraint, simulation signals are separately analyzed in the time domain, time–frequency domain, and frequency domain. Meanwhile, simulation results are provided to examine the validation of the proposed method with different factors such as incident angles and signal noise ratios. An S-band two-element TMA is constructed and implemented to experimentally verify the feasibility of the method. [ABSTRACT FROM AUTHOR]

In this communication, rigorous analysis of dual-port excitation in beam-forming network (such as Butler matrix and Rotman lens) is presented. The strategies for selecting two input ports of beam-forming network in dual-port excitation and choosing the phase differences between two input ports are both given. A simple reconfigurable network is presented for realization of the single-/dual-port excitation, which can be easily extended for more input ports in beam-forming network. For verification, a $4 \times 4$ Butler matrix with the reconfigurable network and four-element array is designed and fabricated. The measured results show a good agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

The direction finding method by the time-modulated linear array (TMLA) is analyzed and verified. The direction of arrival (DOA) can be calculated out by analyzing the spectrum characteristic of the received signal after the time modulation. Its principle is as follows. Because of the periodic modulation, the fundamental and harmonic components are generated in each element simultaneously. After the combiner, the harmonic components’ characteristic of the combined signal is influenced by the DOA. Through analyzing their mathematical relationship, the DOA can be calculated out directly. Compared with the existing direction finding methods, the proposed method has two main advantages. One is that only a single RF channel is used, and the other is that its precision can be improved by the time accumulation. The main calculation amount of the proposed method locates in the spectrum estimation for the received signal and the matrix inversion for the harmonic characteristic matrix. Numerical simulations are provided to verify the proposed method, and the related factors influencing on the direction finding precision are analyzed. A simple $S$ -band eight-element TMLA is constructed and tested to verify its effectiveness. Finally, some conclusions are drawn, and the further research is sketched out. [ABSTRACT FROM AUTHOR]

Time modulated array (TMA) suffers from relatively low efficiencies due to the power absorption in switches during off state. In this paper, we present the design of a novel TMA by using a reconfigurable power divider/combiner (RPDC) for improving the array’s efficiency, where the power absorbed during off state can evenly be transferred to other array elements during on state. An improved pulse sequence strategy is developed to control the radiation pattern of the TMA with RPDC. The impact of the RPDC on radiation features of the TMA is further discussed. To experimentally verify the feasibility of the proposed design, a six-element TMA with RPDC is constructed and characterized. Compared with a six-element conventional TMA with single-pole single-throw switches, the TMA with RPDC shows a significant enhancement of gain by 0.98, 1.27, and 1.65 dB when the sidelobe levels are −20, −25, and −30 dB, respectively. [ABSTRACT FROM PUBLISHER]

In this communication, switched multibeam circular array with a reconfigurable network is presented. By using the reconfigurable network instead of the switch in the conventional switched multibeam array, an additional beam can be provided with each two adjacent elements, and the gains at the depressed areas between each two adjacent original beams are improved. Good matching and isolation performances are realized in single-path mode (single element selected) and two-path mode (two adjacent elements selected). In addition, better mitigation of the fading from multipath propagation can be obtained, since more diversity patterns with low correlations are provided. For verification, a 5-GHz array with a reconfigurable network and six square patch antennas is designed and measured. [ABSTRACT FROM AUTHOR]

A dual-band orthogonally and circularly polarized antenna array with disparate elements is presented. By using corner-truncated stacked patches as elements, both left hand circular polarization (LHCP) in 12 GHz band and right hand circular polarization (RHCP) in 14 GHz band are realized in a shared antenna aperture. Furthermore, by employing disparate elements, the coupling between the two bands is suppressed effectively inside the feed network, hence improving isolation. The measured results of a four-element array agreed well with the simulated ones, achieving isolation better than 20 dB in the dual bands, and a maximum gain of 13.2 dBic for the LHCP and 13.9 dBic for the RHCP. The proposed array can find applications in satellite communications. [ABSTRACT FROM PUBLISHER]

A novel parallel calibration method for the phased array is proposed and verified. By modulating the phase shifts of the RF channels periodically, their mismatches can be calculated out in parallel by analyzing the harmonic characteristic of the combined calibration signal. There are two main advantages for the proposed method. First, it can be a fast far-field calibration method, which needs no measurement between the calibration source and sink. Second, no auxiliary calibration elements are needed. The calculation amount of the proposed method is mainly the discrete Fourier transform (DFT) at the fundamental and harmonic frequency points. The theory of the proposed calibration method is mathematically deduced. Two numerical simulations are provided to examine its performance. A simple four-channel \rm S-band circuit is constructed and tested to verify its effectiveness. [ABSTRACT FROM PUBLISHER]

An investigation of the performance of printed dipole antenna with finite periodically corrugated-reflectors for low-profile ultrawideband (UWB) applications is presented. According to the relative orientations of the linear-polarized source antenna and the corrugated-reflectors, the problem could be divided into H and E cases. Their fundamental differences and design guidelines are discussed in detail. A novel composite corrugated-reflector based on the combinations of H-type and E-type ones is proposed for the first time, and fully characterized with a UWB source dipole which was optimized in the free space for better comparisons. An example antenna with only 21 mm core profile, composed of a printed UWB dipole, a microstrip balun and a composite corrugated-reflector, has an impedance bandwidth (VSWR<2.0) of 2.75 GHz to 8.35 GHz. Both numerical and experimental results show that the example antenna also has stable uni-directional radiation patterns and a realized gain of over 6 dB within the frequency band from 2.3 to 6.0 GHz, which could be a decent alternative to the EBG antennas due to significant improvements on pattern and gain bandwidth. [ABSTRACT FROM AUTHOR]

A single-layer microstrip antenna for ultrawideband (UWB) applications, in which an array of rectangular microstrip patches was arranged in the log-periodic way and proximity-coupled to the microstrip feeding line, is presented. In order to reduce the number of microstrip patches in the UWB log-periodic arrays, a large scale factor k = 1.1 was firstly reported and proved to be highly effective. Furthermore, instead of using an absorbing terminal loading, a novel loss-free compensating stub was proposed. Detailed parameters study was also presented for better understanding of the proposed antennas. The impedance bandwidth (measured VSWR < 2.5) of an example antenna with only 11 elements is from 2.26-6.85 GHz with a ratio of about 3.03:1. Both numerical and experimental results show that the proposed antenna has stable directional radiation patterns, very low-profile and low fabrication cost, which are suitable for various broadband applications. [ABSTRACT FROM AUTHOR]