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This letter introduces a novel wideband, low profile, tightly coupled dipole subarray for wireless communication systems. The proposed subarray, composed of 3 × 3 unit elements, offers a planar structure with high aperture efficiency. The unit element is a bow-tie-shaped tightly coupled dipole antenna covered by a frequency-selective surface for wideband operation. Using power dividers with quarter-wave transformers, the proposed subarray achieved an impressive impedance-matching bandwidth of 28.6–41.6 GHz (37.8%). This wideband performance was maintained in a 4 × 4 array configuration as well. The antenna’s low-profile design (0.08λc) and high aperture efficiency (77.2%) set it apart from existing wideband patch array antennas, making it a promising candidate for future wireless communication applications.

An efficient gain-enhancement technique for millimeter wave (mmWave) planar patch antennas (PPAs) using a novel slot-loaded and segmented-cavity backed structure is newly proposed in this study. By incorporating a main radiator with a rectangular slot and employing a muli-layered segemented-cavity, the proposed antenna design significantly increases antenna gain beyond conventional approaches. Unlike traditional patch antennas or those with shorting pin structures, our gain-enhanced PPA utilizes the rectangular slot to electrically expand the radiation aperture, while the addition of substrate integrated pillars acorss multiple segmented ground layers markedly improves antenna directivity. The strategric use of a segmented cavity not only facilitates flexible impedance matching but also ensures consistent performance within the n257 band, accompanied by minimal gain variation. To verify the gain enhancement from the conventional patch, the proposed antenna was fabricated with a size of 1.03 λ0 × 1.03 λ0 × 0.1 λ0 at 28 GHz. The measured 10-dB impedance bandwidth was 12.14 % with a maximum measured gain of the 11.28 dBi at 28 GHz. Compared to the measured gain of the conventional PPA with the same size, the gain was 39.6 % higher, which represents the highest gain per total antenna volume observed for a single PPA in the mmWave spectrum for high-gain applications, to the best of our knowledge.

A wideband wide-scan array based on dual-polarized elements is presented in this paper. The proposed element consists of two flared metallic wings and two shorting posts over a ground plane which is excited by a RF connector vertically. Without complex feeding network, the antenna element features wideband, low-profile, and high power handling capability. Besides, elements do not require electrical connection and can be arranged with gaps between neighbors, allowing for modular construction. The dual-polarized array in a square lattice can achieve wideband wide-scan performance. To verify the design, an $11\times 11$ prototype has been fabricated and measured. The measurements of this prototype are presented and are in good agreement with the simulations. The results reveal that the array element can achieve a relative bandwidth of 100% for VSWR $\le 3$ at scans out to $\theta \,\, = \,\, 45^{\circ }$ and an enhanced gain of 1 dB in lower frequency band. The array can obtain better than 20 dB polarization purity at 4 GHz and scan loss of lower than 3 dB over the band, respectively.

An arrayable dual‐polarized antenna is proposed in this paper, which exhibits a low profile and broad bandwidth. A metasurface and a square ring are introduced to realize the broadband operation of the low‐profile dual‐polarized antenna. The total size of the broadband antenna is 0.39λL×0.39λL×0.105λL $0.39{\lambda }_{{\rm{L}}}\times 0.39{\lambda }_{{\rm{L}}}\times 0.105{\lambda }_{{\rm{L}}}$ (where λL ${\lambda }_{{\rm{L}}}$ is the wavelength at the lowest frequency of the operation band [1.31 GHz] in free space), suitable for use as an element of an antenna array. Four elements of the proposed antenna are arrayed to develop an array to demonstrate its application for the base station. The measured impedance bandwidth (return loss >10 dB) of the array is about 70% (1.31–2.74 GHz). Stable radiation patterns are obtained with an average gain of 14 dBi. [ABSTRACT FROM AUTHOR]

A dielectric‐loaded slot antenna with the characteristic of broadband, low profile, and low cross‐polarization is presented. The antenna incorporating a low permittivity (εl=4.1 ${\varepsilon }_{l}=4.1$) and multiple high permittivity (εh=22 ${\varepsilon }_{h}=22$) rectangle dielectric is fed by two rectangle slot, which generates three slot modes and achieves measured 10 dB impedance bandwidth of 88% $ \% $ from 1.57 to 4.04 GHz covering the long term evolution (1.71–2.69 GHz) and sub‐6G (3.3–3.6 GHz). Furthermore, the presented slot antenna with a footprint of 0.81 × 0.56λ02 ${\lambda }_{0}^{2}$ and a low profile of 0.09λ0 ${\lambda }_{0}$ (λ0 ${\lambda }_{0}$ is the wavelength in the air region at the center frequency) appears the performance of measured peak gain of 9 dB without using any dielectric resonator mode. On the basis of the single‐polarized design, the dual‐polarized design with a profile of 0.09λ0 ${\lambda }_{0}$ is investigated and fabricated. According to the measured results, the dual‐polarized prototype achieves a 10‐dB impedance of 60% $ \% $ from 1.6 to 3 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a capacitively-fed, ultra-wideband (UWB), and low-profile monocone antenna is proposed for vehicle-to-everything (V2X) applications. The proposed antenna consists of a monocone design with an inner set of vias. Additionally, an outer ring is added with a small gap from the monocone and shorted with six folded wires of different lengths to extend the operating band. The proposed antenna covers the frequency range from 0.75 GHz to 7.6 GHz and has a 164% fractional bandwidth, with a gain value varying between 2 and 10 dBi. The dimensions of the antenna are 0.37 λ L   × 0.37 λ L   × 0.067 λ L . The antenna was fabricated using a 3D printer with low-cost polylactic acid plastic (PLA) material and then sprayed with aerosol copper nanoparticles. The efficiency was approximately 90% throughout the frequency bands of interest. Finally, the proposed antenna was installed on a vehicle and tested with an OBU (onboard unit) and a RSU (roadside unit) in the field. The results show a longer wireless communication range for V2X applications. [ABSTRACT FROM AUTHOR]

Background and Objectives: Microstrip patch antennas are widely used due to their advantages of compact size and easy fabrication compared to other types. However, they have low-performance parameters. As a result, several techniques are used to improve performance parameters in newly designed microstrip antennas. In this study, a novel miniaturized microstrip antenna with circular polarization (CP) is proposed for GNSS applications. Methods: In the design process, the semi-fractal structure is used to reduce the antenna size. Circular polarization is generated using a three-feed configuration with 120? phase shift. The CP value is increased by use of perturbing slots and also removing the corners. The novel design of the feeding network and also considering the ground size same as the patch layer, keep the antenna size small. The co-axial probe is used in the feeding network and it is printed on Taconic RF-43 substrate with a low loss tangent of 0.0033. Numerical simulation is applied via CST commercial software to evaluate the antenna performance. The simulations are repeated in two other software, HFSS and FEKO, to validate the study. Results: The proposed antenna has a compact size of 17.56 cm2. The single-layer structure of the designed antenna leads to easy fabrication feature. The proposed antenna has a bandwidth of 55 MHz (1.558-1.614 GHz). It can operate at GPS L1 (1575 MHz), GLONASS G1 (1602 MHz), Galileo E1 (1589 MHz), and E2 (1561 MHz) bands. Results show a high front-to-back ratio (FBR) of 40 dB, RHCP gain of 3.45 dB, and pure CP with axial ratio (AR) beamwidth of 108?. Furthermore, the phase center variation (PCV) is less than 0.16 mm. Conclusion: Key features of the proposed antenna are its novel fractal structure that leads to compact size, high front-to-back ratio, wide RHCP beamwidth with desirable bandwidth, and axial ratio beamwidth. [ABSTRACT FROM AUTHOR]

This paper presents a low-profile wideband, dual-polarized patch antenna using differential-paired, multi-mode arms. By employing the arrow-shaped, differential-paired arms, three modes of them are excited simultaneously, leading to a broad bandwidth. The shorting pins are uniquely inserted at the wings of the arms to obtain stable radiation patterns. Then, two pairs of arms are structured like the dipoles and a dual-polarized antenna is designed. In addition, by employing coplanar coupling feeding structures, a good wideband impedance matching is also achieved without increasing the height. For demonstration, a wideband dual-polarized patch antenna is designed and measured. Benefitting from the advantages of the multi-mode patch and symmetrical structure as a dipole antenna, the proposed dual-polarized antenna operates between 2.10–3.95 GHz, possessing a 10-dB impedance bandwidth of 61%, a profile of 0.1λ0, an average gain of 7.31 dBi, and stable radiation patterns. [ABSTRACT FROM AUTHOR]

Abstract A low‐profile dual‐mode antenna is proposed in this paper. The antenna is composed of a semi‐rectangular‐annular (SRA) coaxial line with sleeve loading structures vertically mounted on the ground plane. The proposed antenna has two radiation modes, mode 1 of the vertically polarised (VP) radiation characteristics at 500 MHz and mode 2 of the horizontally polarised (HP) radiation characteristics at 588 MHz. The two vertical components of the SRA coaxial line contribute to the VP radiation, which is achieved with the in‐phase electric currents on the two vertical components by adjusting the length of the in‐body inductive loading structures. The horizontal component of the SRA coaxial line is mainly contributed to HP radiation when the electric currents on two vertical components are reversed. And the antenna is well matched with the additional impedance matching network, which consists of two inductors and a capacitor. The height of the fabricated prototype is only 25.9 mm (about 0.04λ) at 500 MHz. The fabricated prototype possesses monopole‐like radiation pattern at 500 MHz and loop‐antenna‐like radiation pattern at 588 MHz. The measured maximum gain of the proposed antenna at 500 MHz is −6.8 dBi, and the measured maximum gain of the proposed antenna at 588 MHz is 2.5 dBi. The antenna is suitable for unmanned aerial vehicles communication systems due to its advantages of low‐profile and dual‐mode radiation.

Featured Application: Low-profile antenna for terrestrial wireless communication. A traditional whip antenna is suitable for terrestrial wireless communication due to its omnidirectional radiation pattern which is capable of transmitting and receiving signals from all directions. However, the length of a whip antenna is long for the very high frequency (VHF) band applications; for example, the ideal length is 80 cm at 90 MHz, which restrains the mobility when mounted on a vehicle. Many studies have been conducted to develop a low-profile antenna that can substitute a whip antenna but most of them are for relatively high frequency (GHz) applications. In this paper, a planar low-profile antenna operating in the VHF band is proposed. The height of the antenna is only 9 cm by utilizing a quarter-mode substrate-integrated waveguide (QMSIW) structure with shorting pins at the edges. The latter promotes omnidirectional radiations despite its short height. The antenna design was optimized by 3D full-wave simulation software. Subsequently, an antenna prototype was fabricated and tested. The results demonstrated that the antenna resonated at 86 MHz with a maximum gain of 1.7 dB along the azimuth direction. [ABSTRACT FROM AUTHOR]

We investigate and present a very low-profile, high-efficiency, and high-gain 2-D leaky-wave antenna (2DLWA) implemented on a high permittivity substrate operating in the millimeter-wave range, paving the way for the seamless integration of a high-gain and high-efficiency antenna with a frontend. In contrast to the typical air-filled 2DLWA, where a perturbation of the first higher-order mode (TE1/TM1) results in highly directed broadside radiation, in the proposed antenna, the propagation and leakage of a quasi-TEM (Q-TEM) mode results in an extremely low-profile ($0.065\lambda _{0}$), high-gain (~15 dBi) antenna. In this scenario, the transverse resonance condition for a Q-TEM mode is established by employing a capacitive partially reflective surface (PRS) in a thin ($0.065\lambda _{0}$) substrate with a relative permittivity of 10.2. The proposed periodic 2DLWA, unlike the conventional uniform/quasi-uniform air-filled counterparts, radiates based on the $\mathbf {n}=-\mathbf {1}$ space harmonic operation. Due to a strong mutual interaction between the PRS and ground plane, conventional design and analysis approaches are no longer relevant in this low-profile architecture. Instead, we employ the Floquet modal expansion theory to create an equivalent circuit model (ECM) for the PRS that takes into account the contributions and mutual interactions of the Floquet harmonics as well as the ground plane effect. By employing reflecting boundaries realized with edge truncation (air trenches) in a high permittivity substrate, we show that the aperture efficiency is enhanced by 15% compared to conventional counterpart. [ABSTRACT FROM AUTHOR]

We report here that spiral and curl antennas are essentially the same when using the moment method. This aids in the understanding and design of the two antennas, and serves as the groundwork for new ideas regarding antennas. First, the spiral antenna height above the ground plane was gradually reduced, and at each height, the spiral configuration parameters were optimized for an axial ratio of less than 0.1 dB. It was found that the spiral antenna had configuration parameters almost the same as those for a curl antenna at a height of 0.15 wavelengths. Next, the curl antenna was analyzed with a reduced height. The antenna, at a height of 0.10 wavelengths, showed a 3 dB axial ratio bandwidth of 3%, with a VSWR of less than two. The analysis results are verified with experimental results. [ABSTRACT FROM AUTHOR]

A low‐profile dual‐mode antenna is proposed in this paper. The antenna is composed of a semi‐rectangular‐annular (SRA) coaxial line with sleeve loading structures vertically mounted on the ground plane. The proposed antenna has two radiation modes, mode 1 of the vertically polarised (VP) radiation characteristics at 500 MHz and mode 2 of the horizontally polarised (HP) radiation characteristics at 588 MHz. The two vertical components of the SRA coaxial line contribute to the VP radiation, which is achieved with the in‐phase electric currents on the two vertical components by adjusting the length of the in‐body inductive loading structures. The horizontal component of the SRA coaxial line is mainly contributed to HP radiation when the electric currents on two vertical components are reversed. And the antenna is well matched with the additional impedance matching network, which consists of two inductors and a capacitor. The height of the fabricated prototype is only 25.9 mm (about 0.04λ) at 500 MHz. The fabricated prototype possesses monopole‐like radiation pattern at 500 MHz and loop‐antenna‐like radiation pattern at 588 MHz. The measured maximum gain of the proposed antenna at 500 MHz is −6.8 dBi, and the measured maximum gain of the proposed antenna at 588 MHz is 2.5 dBi. The antenna is suitable for unmanned aerial vehicles communication systems due to its advantages of low‐profile and dual‐mode radiation. [ABSTRACT FROM AUTHOR]

A design of a low-profile circular cavity-backed slot antenna with conical radiation patterns is presented for X-band application. A low-profile cavity is realized with the help of substrate integrated waveguide (SIW) technique. The top metal cladding of the cavity is engraved with a circular ring slot for conical radiation and coax-probe is used to excite the antenna element at the center of the cavity. To improve the radiation performance, three radial-spoke-like slots cum three vias combination is employed which comes in handy for enhancing bandwidth matching better than − 15 dB over the operating frequency range. Finally, the proposed concept is validated with experimental results in terms of bandwidth, gain performance, and radiation patterns. The experimental result displays an impedance bandwidth of measured, which displays a bandwidth of 15.92% (9.71–11.41 GHz) with an average gain of 5.71 dBi in the operating frequency band. The antenna shows stable, uniform, and similar radiation profiles at different frequencies with good out-of-band selectivity. The advantages of simple configuration and compact size empower its suitably for light-weighted wireless transceivers to be used. [ABSTRACT FROM AUTHOR]

This article presents a low‐profile disk‐loaded monopole antenna specifically designed to be embedded into a manhole cover and a method to improve the bandwidth of the antenna. The antenna is placed deep inside a circular cavity formed on a manhole cover and is covered with a thick radome to protect the antenna from strong external impacts. The effect of the cavity size on the bandwidth of the antenna was studied, and as a result, it was found that the bandwidth of a low‐profile monopole antenna is greatly enhanced when the cavity diameter is about one wavelength. The bandwidth enhancement mechanism due to the cavity size is analyzed in terms of the quality factor (Q) of the antenna. A prototype was fabricated and measured; the disk‐loaded monopole antenna with a diameter of 0.2λ0 and a height of 0.04λ0 (λ0 is the free‐space wavelength at the center frequency) provides a wide impedance bandwidth of 14.3% (10‐dB return loss) when placed inside a cavity with a diameter of 0.82λ0 and a depth of 0.1λ0. The antenna radiates vertically polarized omnidirectional fields in the horizontal direction and has a stable measured peak gain that varies from 4.5 to 5.5 dBi across the measured impedance bandwidth. [ABSTRACT FROM AUTHOR]

In this article, a low‐profile dual‐band patch antenna for vehicle communication is proposed. With two sets of shorting vias on the hexagonal‐shaped patch at different positions and single feed at the center, three different resonant modes are excited, forming two operating bands with omnidirectional and conical beam radiation respectively. The omnidirectional radiation at 2.45 GHz is used for wireless local area network (WLAN) communication while the conical beam radiation is used for cellular vehicle‐to‐everything (C‐V2X) communication. The proposed antenna is fabricated using the printed circuit technique. Both the measured reflection coefficient and radiation pattern match well with the simulations. With the advantage of low profile, dual‐band, and dual radiation characteristics, the antenna owns a good potential to be used in vehicle communications. [ABSTRACT FROM AUTHOR]

In this article, a balanced low‐profile, unidirectional circularly polarized (CP) stacked loop antenna with wide beamwidth is proposed. The antenna is composed of a pair of stacked nonuniform loops with different radii. The larger loop serves as a principal radiator, and the smaller one acts as an auxiliary one. The feed structure consists of a pair of dipole launchers with vertical transmission line. A bonded coaxial cable is used to simultaneously excite the loops at the center. As experimentally validated, the predicted results are in good agreement with the measured results. Compared to its unbalanced counterparts, the proposed antenna can exhibit impedance bandwidth of 40% (20 log |S11| < −10 dB), 3‐dB axial ratio (AR) bandwidth of 4%, front‐to‐back ratio (FBR) up to 18.5 dB and beamwidths in E‐plane and H‐plane of 118°/90° with low profile of 0.09‐wavelength. [ABSTRACT FROM AUTHOR]

A printed circuit board (PCB) implementable multi-slot loaded antenna with a low-profile air-gapped structure for both gain and efficiency enhancement is proposed. The proposed planar antenna is configured by the upper substrate with a radiation patch separated from the lower substrate consisting of a pair of matching pads and a ground plane by the air-gap. The radiation patch on the upper substrate is loaded by two rectangular slots and a single narrow slot with a symmetrically placed feed point and a shorting pin. The narrow slot on the center of the radiation patch with the shorting pin improves both gain and radiation efficiency. The pair of two additional rectangular slots increase the gain while maintaining the required air-gap very low. Further, the symmetric matching pads are integrated along the feed and shorting vias to improve the realized antenna gain for the whole operation band. As a result, the proposed structure obtains a high gain-to-volume ratio as well as the enhanced efficiency. The proposed structure was fabricated at 5.9 GHz with the overall volume of 1.08 λ0 × 1.08 λ0 × 0.05 λ0 (55 mm × 55 mm × 2.7 mm) including the whole ground plane. The measured antenna gain was 9.4 dBi at 5.9 GHz verifying the high realized gain-to-volume ratio. Also, the measured half power beamwidths in E and H planes were about 72° and 74°, respectively. Lastly, the measured 10-dB impedance bandwidth of the proposed structure showed approximately 5.5 %.

This paper presents the modeling and design of a frequency agile antenna using an anisotropic artificial dielectric layer (AADL) for multi-band phased array radar applications. The proposed AADL material is placed underneath the patch radiator and is designed using periodically arranged metallic cylinders in which varying height, diameter, and the distance used between them allows the control of the effective permittivity of the patch antenna. Closed form design expressions are formulated to synthesize the dielectric properties of the AADL as a function of the cylindrical unit cell dimensions. Design trade-offs based on the proposed formulation and numerical simulations show the overall performance of the AADL on microstrip patch (MS) antennas. To validate the proposed concept, five individual AADL MS patch antennas in C-band were designed, fabricated, and tested. Simulated and measured results (s-parameters and radiation patterns) are in good agreement with the results obtained from the theoretical model. The proposed AADL concept has the potential to be used in the development of future reconfigurable tunable multiband antennas that use liquid metal to dynamically change the heights of the cylinders.

Millimeter wave antennas have applications in several sensing and communication systems. Such antennas, designed for modern miniaturized devices and systems, must be low profile, flexible, and low cost. Some applications also require beam steering for detection purposes. Combining all these features into an antenna system and delivering decent antenna performance is challenging. In this study, we combined a partially reflective surface with a parasitic patch array to create a simple beam-switching, low-profile, and flexible wearable detection system. To ensure lower costs as well as compatibility with wearable systems, screen printing was utilized on a flexible substrate. The antenna array was optimized for the 77 GHz band and had a high gain of 11.2 dBi. The designed system has three independent beams, which can be oriented from bore-sight to ±32° through a simple switching mechanism. The antenna array maintains its performance in both flat and flexed conditions. Finally, the antenna array was tested in the field to successfully detect objects moving in three different directions.

A short-range terahertz (THz) wireless transmission in the 300 GHz band is demonstrated using low-profile wavelength-scaled dielectric transmitting and receiving cuboid antennas (DCAs). These dielectric cuboid antennas are made of polytetrafluoroethylene with dimensions of approximately 1.2 mm × 1.2 mm × 1.3 mm. The near-field pattern of a DCA at 300 GHz was measured using an electro-optic sensing technique, and its far-field pattern characterization was based on the near-field to far-field transformation. The measured antenna gain was 15.06 ± 0.06 dBi. By employing DCAs as transmitting and receiving antennas, a 17.5 Gbps data transmission rate at distances of approximately 200 and 50 mm with bit error rates of 3.31 × 10–3 and 7.51 × 10–7 respectively, is demonstrated. The proposed mesoscopic scale DCA is a promising antenna type in intra-device communications and Kiosk download applications for future mobile devices operating in the 300 GHz band.

A low-profile wideband microstrip antenna is proposed based on the structure of composite right/left-handed transmission lines (CRLH TLs). The dimensions of the proposed antenna are 64 × 64 × 4 mm. The impedance matching bandwidth is 5.05–5.92 GHz (16.5%). The unit cell of the CRLH TLs is a mushroom structure. Several different resonant modes with different radiation patterns are excited to obtain the pattern diversity. Particularly, TM10 and TM20 modes are merged to realize a wideband performance with broadside radiation pattern, whereas the TM20 mode is used to realize a conical radiation pattern. The simulations and measurements are in good agreement, and the envelope correlation coefficient shows that the proposed antenna owns an excellent diversity performance. [ABSTRACT FROM AUTHOR]

A traditional whip antenna is suitable for terrestrial wireless communication due to its omnidirectional radiation pattern which is capable of transmitting and receiving signals from all directions. However, the length of a whip antenna is long for the very high frequency (VHF) band applications; for example, the ideal length is 80 cm at 90 MHz, which restrains the mobility when mounted on a vehicle. Many studies have been conducted to develop a low-profile antenna that can substitute a whip antenna but most of them are for relatively high frequency (GHz) applications. In this paper, a planar low-profile antenna operating in the VHF band is proposed. The height of the antenna is only 9 cm by utilizing a quarter-mode substrate-integrated waveguide (QMSIW) structure with shorting pins at the edges. The latter promotes omnidirectional radiations despite its short height. The antenna design was optimized by 3D full-wave simulation software. Subsequently, an antenna prototype was fabricated and tested. The results demonstrated that the antenna resonated at 86 MHz with a maximum gain of 1.7 dB along the azimuth direction.

A low-profile ultrawideband antenna of circular polarization (CP) is proposed in this communication. This antenna consists of two layers of Rogers RT/Duroid 5880 PCB board of 0.79 mm thickness. The size of the top PCB is 54.6 mm × 54.6 mm, and four pairs of semicircular patches are printed on both its top and bottom sides. This top PCB is placed 10.5 mm above the bottom PCB, which is 95 mm × 95 mm in size. On the top side of the bottom PCB is a 1-to-4 microstrip feeding network with 90° phase difference between the adjacent ports, while the ground plane is on its bottom side. The top PCB is supported by four small trapezoid-shaped PCB boards at the center of its four edges, respectively. A slot line is printed on each trapezoidal PCB to feed the patches. Both the simulation and measurement results show that this low-profile antenna has a very wide 10 dB return loss bandwidth from 2.9 to 9 GHz. Meanwhile, lower than 3 dB axial ratio can be achieved from 3 to 7.8 GHz and its right-hand circular polarized (RHCP) gain is higher than 8 dBic. The good performance of this antenna can justify that it is a promising candidate for indoor positioning applications that require CP. [ABSTRACT FROM AUTHOR]

In this article, a novel low‐profile asymmetric dipole antenna with artificial magnetic conductor (AMC) is presented for wideband circularly polarized operation. First, the asymmetric dipole is adopted to realize a wide impedance bandwidth. By modifying the shape of dipole arms and combing a rhombus‐shaped arm with a quasi‐triangle‐shaped arm, three resonances are achieved by the asymmetric dipole, leading to a wide impedance bandwidth. Second, an AMC surface with square patch units is introduced to reduce the antenna profile to 0.11λ0, where λ0 denotes the lowest operation wavelength in free space. Finally, the presented wideband circularly polarized (CP) antenna design was fabricated and tested. Reasonable agreement between the measurements and simulations is obtained, demonstrating that this CP antenna achieves a 115% impedance bandwidth (1.45‐5.4GHz) and a 97% axial ratio bandwidth (1.69‐4.88GHz). Within the CP operation band, the presented antenna yields symmetrical and unidirectional radiation patterns with a 6.7‐dBic average gain. Such a broadband and low‐profile CP asymmetric dipole antenna can be a promising candidate for a wide variety of CP wireless applications. [ABSTRACT FROM AUTHOR]

A single-layer low-profile circularly polarized (CP) filtering patch antenna is investigated for wireless local area network (WLAN) applications. The CP antenna mainly consists of a feeding loop, four L-shaped radiating patches, and a square ground plane. To integrate the filtering function, four thin microstrip stubs and four shorting pins are introduced to the patches, and two U-shaped slots are etched in the feeding loop. These parasitic elements can realize the bandpass filtering function without requiring an external filter. In addition, these elements are skillfully added into the CP antenna, without increasing either the antenna footprint or profile. To verify the design, a prototype operating at 2.4 GHz WLAN band is fabricated and tested. The measured results show that the prototype has a low profile of 0.02λ0, a passband bandwidth (|S11| < –10 dB and axial ratio (AR) < 3 dB) of 4.1%, and a peak gain of 8.3 dBic. Moreover, the prototype also shows a sharp roll-off rate near the passband edge and a good out-of-band suppression level of more than 20 dB in the stopbands. [ABSTRACT FROM AUTHOR]

The previously proposed resonance-based reflector (RBR) antennas have the merits of wide impedance bandwidth, low-profile, and unidirectional pattern; however, their front-to-back ratio (FBR) bandwidths are narrow. In this paper, a wideband RBR is proposed for FBR bandwidth enhancing antenna with a low profile. The proposed RBR consists of a metallic ring with three stubs printed on a substrate. It has a ±90° in-phase bandwidth of 63.57% (3.23-6.24 GHz) and its reflection magnitude values range from -0.02 to -11.5 dB within the in-phase band (-90° L at the lowest operating frequency, and the RBR has the same size as the bowtie antenna. Compared to the previous RBR antennas, the proposed RBR antenna has wider FBR bandwidth. The operating band of the antenna is suitable for 5G system applications.

In this paper, the design of a wideband high-gain low-profile linearly polarized antenna is presented. The design objectives were achieved by encircling a folded strip around a planar radiating element on the top substrate with corner-cut parasitic patches on the bottom substrate placed above the ground plane. A half-wavelength printed dipole utilized as a radiating element was employed to generate linearly polarized radiation. The contributions of the folded strips and parasitic patches are significant factors in enhancing the bandwidth by producing extra resonance and phase compensation. The experiments and full-wave electromagnetic simulations have provided a platform for the analysis, validation, and verification of the antenna design. The antenna structure has the overall dimensions of 120 mm × 120 mm × 16.3 mm (0.69λo × 0.69λo × 0.094λo at 1.74 GHz), and it demonstrated satisfactory measured performance characteristics with a -10-dB impedance bandwidth of 1.39-2.09 GHz (40.22%), a broadside gain of 6.1-8.2 dBi, and a radiation efficiency >88% within the impedance bandwidth.

We report here that spiral and curl antennas are essentially the same when using the moment method. This aids in the understanding and design of the two antennas, and serves as the groundwork for new ideas regarding antennas. First, the spiral antenna height above the ground plane was gradually reduced, and at each height, the spiral configuration parameters were optimized for an axial ratio of less than 0.1 dB. It was found that the spiral antenna had configuration parameters almost the same as those for a curl antenna at a height of 0.15 wavelengths. Next, the curl antenna was analyzed with a reduced height. The antenna, at a height of 0.10 wavelengths, showed a 3 dB axial ratio bandwidth of 3%, with a VSWR of less than two. The analysis results are verified with experimental results.

A novel design of a coplanar waveguide (CPW) feed antenna array with circular polarization (CP) and a high front-to-back ratio is described. The proposed CP array is achieved by using a compact CPW–slotline transition network etched in the ground plane. The measured results show that this kind of feeding method can improve the impedance bandwidth, as well as the axial ratio bandwidth of the CP antenna array and provide adequate gain. The proposed array can achieve a 6.08% impedance bandwidth and a 4.10% CP bandwidth. Details of the antenna design and experimental results are presented and discussed.

In this paper, a wearable ultra‐wideband (UWB) monopole antenna with a compact structure and low profile is presented for wireless body area networks, wireless local area networks, and UWB applications. The antenna is composed of three triangular radiators on the basis of the mono‐cone antenna. By the methods of reactive and slot loading, the dimension of the antenna can be greatly reduced. The overall height of the antenna is 0.06 λ0 at its lowest operating frequency. The radiated structure of the proposed antenna with the dimension of 31 × 31 × 9 mm3, which operates in 2.3 to 12.6 GHz, is fabricated and the measurement results are in good agreement with the simulated ones. Moreover, the influence of the human tissue on the antenna was evaluated, and stable performance can be obtained on the human tissue under different bending conditions. The specific absorption rate values are lower than the limitation set by the European Telecommunications Standards Institute, which indicates that the antenna is suitable for wearable applications. [ABSTRACT FROM AUTHOR]

A dual-band planar dipole antenna, incorporated with a zigzag-shaped dual-band artificial magnetic conductor with gain enhancement, is proposed here. By using 5×9 AMC surface as substrate to the dipole antenna, the bidirectional radiation pattern of the dipole antenna is transformed to unidirectional radiation pattern. The separation distance between the dipole antenna and the AMC surface is λ/6 at 5.5 GHz. The proposed antenna has been fabricated and measured to verify the simulation results. The experimental results ensure good impedance matching (S11 < −10 dB) over two frequency bands (i.e. 5.1–6.2 GHz and 6.75–7.24 GHz). The composite antenna also provides a maximum gain of 8.94 dB at 5.5 GHz with a gain variation of only 0.5 dB over the two operating frequency bands. In addition, the cross-polarization level is less than −15 dB for both E and H planes. [ABSTRACT FROM AUTHOR]

This paper proposes a high-frequency (HF) band on an extremely low-profile antenna that can be mounted on the roof of a car. This antenna generates a monopole-like omnidirectional radiation pattern despite the low height of the patch shape (5 cm, 0.0034λ @ 20 MHz). A coil was installed at the edge of the antenna feeding part and the patch to increase the quality factor (Q-factor) and a shorting pin was connected next to the coil to ensure that in-phase current flows through the feeding part and shorting pin. The coil is designed such that the quality coefficient reaches 1,000 considering the mutual inductance and internal resistance. The Q-factor of the antenna is increased by changing the shorting pin to a shorting plate. A quarter-wavelength monopole antenna with a target frequency of 20 MHz is 6 m in length, whereas the proposed antenna height is only 5 cm (0.0034λ @ 20 MHz) and the patch size is 70 cm × 70 cm (0.047 λ×0.047 λ @ 20 MHz), making it easy to install the antenna on the vehicle roof. The gain in the Q-factor of the antenna, calculated using a 3D radio wave simulation software, was −9 dBi, and the gain when it was mounted on the vehicle roof was −2.7 dBi. The power value measured by introducing the antenna showed a star similar to the gain value calculated via simulations. [ABSTRACT FROM AUTHOR]

In this letter, a low-profile wideband pattern diversity antenna based on metasurface (MTS) is proposed. Initially, based on the theory of characteristic mode (TCM), the two adjacent intrinsic modes, which correspond to the broadside and conical radiation pattern, respectively, are exploited to realize a wideband pattern diversity characteristic under a low profile. Then, by analyzing the modal current distribution on the MTS, the optimal locations, orientations and relative phases of the four L-shaped feeding probes are determined to excite the above two modes. However, the in-band high-order modes (HOMs) introduced by the feeding structure will deteriorate the radiation pattern. Therefore, chamfering corners on the MTS is used to suppress the HOMs for radiation pattern improvement. Finally, by combining TCM and MTS, the modes are manipulated to achieve a pattern diversity antenna with an extremely low profile of 0.06 λ0 (the free-space wavelength at the center frequency) and an isolation of better than 38 dB, which also maintains an operating bandwidth of 20.24%. Based on these excellent performances, the proposed antenna is an attractive solution for pattern diversity applications requiring low profile, especially in unmanned aerial vehicle communications. [ABSTRACT FROM AUTHOR]

Low‐profile and wideband gain enhancement Fabry–Perot cavity antennas (FPCA) is proposed using gradient Partially Reflective Surface (PRS) and gradient Artificial Magnetic Conductor (AMC). A wideband source antenna is designed with a −10 dB impedance bandwidth of 58.1% (6.1–11.1 GHz). The PRS is constructed by a complementary frequency‐Selective Surfaces (FSS) with a square hole and four small patches in a unit, which realizes phase increasing with frequency. The PRS and the AMC are gradient alone x‐direction to achieve wideband phase compensation. While they are uniform in y‐direction to realize better gain enhancement. Compared with the source antenna, the gain enhancement of the proposed FPCA is about 4–7 dBi. Moreover, the simulated and measured 3‐dB gain bandwidths are 7.26–10.33 GHz (34.8%) and 6.8–10.8 GHz (46%), respectively. The gain enhanced bandwidth is about 52.3% (6.5–11.1 GHz). The impedance bandwidth is 6–11.1 GHz (59.65%). By using the gradient size AMC, the profile of the FPCA is reduced from 0.5λ0 to 0.2λ0, where λ0 is the wavelength of 8.5 GHz. The proposed FPCA has the characteristics of wide impedance bandwidth, wide 3‐dB gain bandwidth, wide gain enhanced bandwidth and low‐profile. [ABSTRACT FROM AUTHOR]

A compact ultrawideband antenna on folded ground plane is proposed, which is a compact and low-profile structure. The proposed antenna mimics the operation of a unit element of the tightly coupled dipole array (TCDA) with modified boundary condition. The antenna does not have the PMC boundary required by the original TCDA, which makes the implementation and the impedance matching of the proposed antenna easy. All the design procedures are explained and confirmed by the EM simulation. The measured results show that the impedance bandwidth (IBW) is 0.72–3.43 GHz (130.6%) for the VSWR < 2 and that the radiation efficiency is over 89% in the operating band. The average peak gain is 2.33 dBi. These results are in good agreement with those of the simulation. The proposed antenna is compact, with an electrical size ($\kappa \alpha $) of 0.82 at the lowest operating frequency and an overall dimension of $0.17\lambda _{\mathrm {low}} \times 0.17\lambda _{\mathrm {low}} \times 0.11\lambda _{\mathrm {low}}$ in terms of the wavelength at the lowest operating wavelength. [ABSTRACT FROM AUTHOR]

A low-profile spiral antenna backed by a circular high-impedance surface (HIS) reflector composed of homogeneous (CirHISRhomo) fan-shaped patch elements is investigated. The total antenna height from the bottom of the CirHISRhomo to the spiral antenna is very small: 0.09 wavelength at a lowest design frequency of 3 GHz. It is revealed that the CirHISRhomo contributes to a constant input impedance and a small axial ratio (AR) across the design frequency range of 3–10 GHz (the fractional bandwidth is approximately 108%). For comparison, the AR for the spiral antenna backed by a conventional perfect electric conducting reflector is also presented. The analysis results are verified by the measured results of the fabricated antenna. [ABSTRACT FROM AUTHOR]

A low-profile microstrip antenna with pattern diversity is proposed in this letter. By setting the inner boundary of an annular microstrip patch as short-circuit, a half-mode annular ring antenna is obtained, whose two resonant modes, i.e., TM11 and TM01 modes, with different radiation patterns can degenerate. Besides, the shorting boundary also contributes a low coupling between the antenna and the other circuits in the center of the annular ring. The antenna is designed based on characteristic equations of the cavity model and also verified by characteristic mode analysis. The final prototype has three ports, representing two orthogonal broadside patterns and a conical pattern. All the ports can cover the 5.8 GHz Industrial, Scientific, and Medical (ISM) band. Isolations between all the ports are higher than 15 dB, and the envelope correlation coefficients are lower than 0.08, which ensure an excellent diversity performance. Numerical and experimental results agree well and prove the function of the proposed design. Due to the simple topology and the competitive performance, the proposed antenna will be a suitable candidate for ISM applications in a wireless local area network. [ABSTRACT FROM AUTHOR]

A novel ultrawideband directive antenna for ground-penetrating radar (GPR) applications is presented in this letter. The antenna is designed for operation at frequencies below 500 MHz to allow for high-depth-resolution imaging of the deeply buried targets such as buried pipes and other deep underground man-made structures such as tunnels. The antenna is formed by a pair of coupled antennas inspired by an electrically narrow very low profile (ENVELOP) antenna with differential feeding to provide a directive pattern normal to the antenna ground over a wide bandwidth. An antenna operating in the range of 140–510 MHz is designed and fabricated using the printed circuit board (PCB) substrates. The antenna is designed and optimized for operation in the proximity of a half-space soil medium to achieve efficient coupling of power from the air to the ground. The measured reflection coefficient of the antenna near concrete and wet soil covered by sand and grass is shown to be better than −9.5 dB within the specified band. The simulated realized gain of the antenna in the presence of dry soil is better than 4.9 dBi within the range of 140–510 MHz. The antenna is low-profile with a total height of 153 mm and a lateral dimension of 600 $\text {mm} \times 600$ mm. The performance of the antenna for GPR applications is evaluated through a field measurement of a buried object in wet soil with high losses. [ABSTRACT FROM AUTHOR]

A pattern diversity antenna with low profile and wideband operation is proposed in this letter. The topology combines a 3-D folded monopole antenna together with a differential L-plate fed patch antenna. The monopole antenna is realized by a pair of bent hexagon-shaped plates, which can provide a conical pattern in the horizontal plane. A common top hat is capacitively loaded to reduce the overall height of the monopole antenna. This hat is excited as a microstrip antenna by differential feeding plates, which achieves a broadside radiation pattern. The operating band of the proposed antenna is in the range of 1.65–2.7 GHz (48%), covering the GSM1800/1900, UMTS, and LTE2300/2500 bands. By the method of differential feeding, the coupling between the two radiation modes can be greatly reduced, which can provide a low envelope correlation coefficient (≤30 dB) and a high isolation (>30 dB) between different ports. A prototype of the antenna with dimensions 60 × 60 × 20 mm3 is fabricated, and the measured results are in great agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

A novel wideband (11.1% −10 dB bandwidth) and low-profile (0.03 λ0 height) metamaterial transmission line (TL)-inspired circularly polarized (CP) antenna for radio-frequency identification (RFID) application is proposed. A capacitor-loaded TL (CL-TL) is realized by inserting multiple series metal–insulator–metal (MIM) capacitors into the TL. The MIM capacitor works as a series left-handed (LH) capacitor as well as a radiator. First, the CL-TL is studied and analyzed through circuit model and dispersion curves. Then, a linearly polarized (LP) antenna and a CP antenna based on the CL-TLs are implemented. Compared with the conventional right-handed (RH) TL-based antennas, here the size reduction is achieved by pushing down the dispersion curve to lower frequency using multistage structures and larger LH capacitance. The measured −10 dB impedance bandwidth, 3 dB axial-ratio (AR) bandwidth, and radiation efficiency for this CP antenna is 859–959 MHz (11.1%), 902–923 MHz (2.3%) and 83.9%, respectively. It features a compact size, low cost, wide bandwidth, and good radiation performance, which could be conveniently used for RFID reader. [ABSTRACT FROM AUTHOR]

A planar low-profile log-periodic antenna based on cavity-backed slot is proposed in this letter. The slot element is made of a microstrip patch on a large ground plane with three edges shorted and one edge open. It is excited by a probe protruding into the cavity from the back of the ground. Through choosing different length and width, each slot element of the array can resonate at different frequency with a same height. A meandered microstrip line on the bottom is used to feed the array, achieving endfire radiation with wide bandwidth. The proposed antenna has been fabricated using printing technology. Measured results show that an operating frequency band from 6.9 to 17.4 GHz (2.52:1) for VSWR < 2.2 and a low profile of 0.047 λL at the lowest operating frequency are obtained. The proposed array has a good overall performance of wide bandwidth, low profile, and planar structure with easy printing fabrication process, which may be useful for the demand of endfire radiation with low profile. [ABSTRACT FROM AUTHOR]

A low-profile MIMO antenna is proposed for applications in mobile devices. The antenna is designed by placing multiple inverted-F antennas (IFAs) on an artificial magnetic conductor (AMC) ground. The IFAs excite two distinct modes on the AMC, i.e., the local resonant mode and the TM0 surface-wave mode. By combining the two modes, a fractional bandwidth of 12% is realized with a profile of $0.01\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the center frequency. Within the working band, the radiation efficiencies are higher than 50%, the mutual couplings among antennas lower than −10 dB, and envelope correlation coefficients (ECCs) lower than 0.2. To validate the antenna design, a MIMO antenna with eight elements is fabricated and measured. The antenna can work from 3.4 to 3.8 GHz. The total thickness of the antenna is only 0.97 mm, which can be integrated into smartphones as their back-covers without occupying the inner space of the device. The throughput achieved by the antenna in an outdoor environment is also tested using a fifth-generation (5G) MIMO system. The MIMO performance will be discussed and compared with traditional antennas. [ABSTRACT FROM AUTHOR]

A mesoscopic dielectric cuboid antenna (DCA), which can be connected to a standard waveguide, is proposed to achieve high directivity with a simple-structure and low-profile antenna compared with that of a horn antenna of same dimensions. We optimized the antenna dimensions based on simulation to maximize the antenna gain of 14.22 dBi, which is 1.9 dB higher than that of the horn antenna with the same dimensions. Simulation was performed both at 300 and 24 GHz. As a proof of concept, we designed and fabricated a scaled DCA with dimensions of 1.2 $\lambda \,\times \,1.2\lambda \,\times \,1.36\lambda$ and experimentally evaluated the radiation pattern at 24 GHz band. The full-width at half-maximum (FWHM) values were approximately 21% and 34% narrower than those of the horn antenna in the E-plane and H-plane, respectively. The frequency characteristic of sensitivity enhancement using the DCA as the reception antenna shows that the DCA is a nonresonant antenna with a wide bandwidth. Narrower FWHMs of the DCA have been discussed with respect to a two-dimensional near-field phase distribution measured using the electrooptic sensing technique. [ABSTRACT FROM AUTHOR]

In this paper, a wideband, low-profile, 1-D tightly coupled dipole array (1-D TCDA) antenna with vertical metal strips (VMSs) is proposed. The 1-D TCDA has a limited scanangle due to variations in vertical wave numbers according to the scanangle. Floquet theory and the electric field profile can be used to analyze the theory of a TCDA, obtaining scan-independent characteristic. Removing some metal strips from the side walls also improved the radiation efficiency. The overlapped impedance bandwidth (IBW) for dual polarization was 0.8–2.5 GHz (3.1:1) for VSWR < 3, and the maximum scanangle was ±50°. The radiation efficiency was over 70% within the IBW and maximum scanangle. The measurement results show that the gain was 7.0–12.4 dB for vertical polarization and 7.3–15.4 dB for horizontal polarization within the IBW and maximum scanangle. Furthermore, the height of the antenna was $0.13\lambda _{\mathrm {low}}$ at the lowest operating frequency, and the overall dimension of the full array structure was $1.69\lambda _{\mathrm {low}}\times 0.59\lambda _{\mathrm {low}}\times 0.13\lambda _{\mathrm {low}}$. [ABSTRACT FROM AUTHOR]

In this letter, a low-profile pattern-reconfigurable antenna has been designed. The antenna is modified from a conventional windmill loop antenna, with the radial arms disconnected at the center and a shorting via added between the top and bottom layers. Three different patterns are controlled by three p-i-n diodes, which are located at the center of the bottom layer and operate as switches. A half-wavelength bent dipole with a reflector provides a boresight radiation with directional pattern on the azimuth plane. The second boresight pattern is obtained by a coupled fed half-wavelength dipole together with another one-wavelength dipole. The radiation nulls of the two boresight patterns are complementary to each other on the azimuth plane. A third pattern with omnidirectional radiation on the azimuth plane is obtained when the current is uniformly distributed along the arcs, forming a typical magnetic dipole. The antenna operates at 2.4 GHz wireless local area network (WLAN) band (2.40–2.485 GHz), with the measured average efficiencies of 82%, 82%, and 80% for the three modes, respectively. [ABSTRACT FROM AUTHOR]

A symmetrical E-shaped patch antenna with multimode resonance is proposed for 5G broadband millimeter-wave (mmWave) applications. A longitudinal slot is etched on the patch surface to change the original E-field distribution of the TM20 mode without affecting that of the TM10 mode. This etching also tunes the resonance frequencies of these two modes to be sufficiently close to each other. Therefore, the antenna is able to realize good impedance performance within the wide designated bandwidth. Moreover, two transverse slots are etched to suppress undesirable modes, but the slots have a small effect on the current distribution of the two designed modes. Thus, the antenna is able to realize a stable radiation pattern and low cross-polarization within the whole operating band. The proposed patch antenna is designed, fabricated, and measured around the $Ka$ -band. The fabricated prototype achieves a wide impedance bandwidth of 45.4%. The simulated total efficiency of the proposed antenna is more than 85.0%. The proposed broadband symmetrical E-shaped patch antenna has a very simple structure and great electrical performance and is a very attractive candidate for 5G mmWave applications. [ABSTRACT FROM AUTHOR]