Cavity Antenna Research Articles

Simulation of classical axion electrodynamics using COMSOL multiphysics

The axion is a hypothetical particle motivated to address the strong CP problem, and is one of the appealing dark matter candidates. Numerous experimental searches for dark matter axions have been proposed relying on their coupling with photons. The classical equations of motion for the axion-photon coupling are well known but need to be fully computed for complex experimental setups. The partial differential equations of axion electrodynamics can be numerically solved using finite element methods. In this work, we simulate axion electrodynamics using COMSOL Multiphyics, a commercially available simulation software, for various experimental schemes, including the dish antenna haloscope, cavity haloscope, dielectric haloscope, and axion-photon regeneration. We show that the numerical results are in good agreement with the analytical solutions.

All-metal cavity antenna with light weight, high efficiency and circular polarization for satellite platform applications

In this paper, a lightweight high-efficiency circularly polarized (CP) all-metal antenna design method is presented for satellite industry applications. The proposed antenna is composed of a rectangular waveguide feeder, a high-order mode cavity and a metasurface circular polarizer (MCP). The cavity high-order mode TE440 is directly excited by four coupling slots in the waveguide. The MCP is placed on the cavity to generate the CP radiation. Due to the introduction of high-order mode technology and MCP, all metal walls inside the antenna can be removed, which are necessary in conventional waveguide structures, and weight is thereby significantly reduced. To reflect the weight advantage, a conventional metal wall-loaded waveguide antenna of the same size is designed. The measured results show that the proposed antenna has wider impedance and axial ratio bandwidths, and higher radiation efficiency. In particular, the proposed antenna is 40% lighter than the comparative one, indicating that it is more applicable to satellite platforms with limited loading capacities.

A continuous frequency tuning Fabry–Perot Cavity antenna with stable radiation performance

AbstractThis paper presents a continuous frequency tuning Fabry–Perot Cavity (FPC) antenna of which the operating frequency can be varied from 4.87 to 5.84 GHz (18.1%). The cavity of the proposed antenna is excited by a double-layer antenna structure, which is made up of a main square patch and a parasitic one. The superstrate is a frequency-selective surface, consisting of 6 × 6 square-patch-type unit cells. The frequency tuning property is realized by employing 48 phase-changing elements placed around the main patch, which forms a reconfigurable high impedance surface (HIS). By controlling the biasing voltages of the varactors inserted in the HIS element, its capacitances and reflection phases can be varied continuously, which leads to a variation of the operating frequency. An antenna prototype has been fabricated and measured for validation. The measured results are in good agreement with the simulated ones. In the frequency tuning range, the measured realized gains have a smaller variation from 10.2 to 14.1 dBi compared with other reported frequency tuning FPC antennas.

Circularly Polarized Fabry–Pérot Cavity Sensing Antenna Design Using Generative Model

We consider the problem of designing a circularly polarized Fabry-P'erot cavity (FPC) antenna for S-band sensing applications such as satellite navigation and communication. The spatial distribution of peripheral roughness of the unit cell of FPC's partially reflecting surface (PRS) serves as an important design optimization criterion. However, the evaluation of each candidate design using a full-wave solver is computationally expensive. To this end, we propose a deep generative adversarial network (GAN) for realizing a surrogate model that is trained with input-output pairs of antenna designs and their corresponding patterns. Using the GAN framework, we quickly evaluate the characteristics of a large volume of candidate designs and choose the antenna design with an axial ratio of 0.4 dB, a gain of 7.5 dB, and a bandwidth of 269 MHz.

A Wideband Fabry–Perot Cavity Antenna With Single-Layer Partially Reflective Surface

A gain-stabilized broadband Fabry–Perot cavity antenna (FPCA) is presented, based on a single-layer partially reflective surface (PRS). The proposed PRS employs compact double-sided structure in a regular hexagonal arrangement to achieve a wide range of positive phase gradient from 7.9 to 10.9 GHz. The PRS unit is composed of a circular patch and a fan-shaped tripod within a circular aperture, which printed on both sides of the thin dielectric substrate. A slot antenna with nonuniform parasitic patches is applied as the source antenna of the FPCA, which provides a smooth gain while offering a wide impedance bandwidth. Simulation and measurement results verify that the PRS can effectively improve the performance of the FPCA in terms of widening the bandwidth, reducing the size, and improving the gain stability. The proposed antenna has a measured 3 dB gain bandwidth of 7.9–11 GHz (32.8%) with a peak gain of 13.67 dBi, and an overall size of 2.1 × 2.1 × 0.57 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> being wavelength at the center frequency of 9.5 GHz).

A Novel Reflection-Mode Fabry–Perot Cavity Antenna With Broadband High Gain and Large Beam-Scanning Angle by Janus Partially Reflective Surface

Operational mechanism and design methodology of a novel reflection-mode (R-mode) Fabry–Perot cavity antenna (FPCA) are proposed in this article. Unlike common transmissive-mode (T-mode) FPCAs, the R-mode one places the feed antenna outside the cavity and introduces a Janus partially reflective surface (PRS), reducing the coupling between the feed and the FP cavity, while obtaining flexible displacement freedom of the feed to achieve a large beam scanning angle. The proposed R-mode FPCA employs a compact triple-layered Janus PRS, a simple ground plane, and a linearly polarized microstrip feed. The Janus PRS is applied to achieve bidirectional asymmetric transmission from the outside to the inside of the cavity to ensure the excitation efficiency and gain enhancement. In addition, a beam scanning model is proposed to obtain the spatial position of the feed and the maximum beam scanning angle under the specific antenna size. Finally, a proof-of-concept prototype is designed, fabricated, and measured at X-band. The measurement results agree well with the simulation, the 3 dB gain bandwidth of 19.7% is achieved. The peak gain in this range is 17.35 dBi and a large 3-D beam scanning range of [−35°, 35°] is also obtained.

Textile Bandwidth-Enhanced Half-Mode Substrate-Integrated Cavity Antenna With V-Slot for WLAN Communications

In this letter, a textile bandwidth-enhanced half-mode substrate-integrated cavity (HMSIC) antenna is designed for the wireless local area network (WLAN) communications. Through simulations over the vector surface current on the top layer of a basic HMSIC antenna, a simple strategy of adding a slot on the top layer to shift the resonance frequency of the rotated TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ {_{2,2,0}^{\rm {HM}}}$</tex-math></inline-formula> mode towards the counterpart of the fundamental TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${_{1,1,0}^{\rm {HM}}}$</tex-math></inline-formula> mode is presented. Based on this, the parameters of the slot are optimized to merge the two corresponding bands into one with an enhanced bandwidth. A prototype with a 0.35 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ {\times }$</tex-math></inline-formula> 0.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ {\lambda _{\varepsilon }^{2}}$</tex-math></inline-formula> cavity is fabricated and measured to verify the design. The measured −10 dB impedance band is 5.04–5.90 GHz with a 15.7% factional bandwidth covering the 5 GHz WLAN band, and the radiation efficiency is above 94% in free space and 80% on the human body. Besides, the proposed antenna shows high robustness against the human body and cylindrical bending conditions, and the simulated specific absorption rate proves its safety on the human body.

Development of a Wideband Slotted Antenna Array with Low Profile and Low Sidelobe

In this paper, a novel multi-layered waveguide-fed slotted cavity antenna array operating in the K-band (i.e., 18–27 GHz) is presented. The antenna is composed of 64 (8 × 8) groups of 2 × 2 subarrays with low profile, and fed by a 1–64 ways waveguide corporate-feed-network. In order to obtain a low sidelobe level (SLL), the Chebyshev power distribution is introduced into the feeding network to accurately taper the power distribution among the subarrays. To realize the amplitude-tapering network, a simple T-junction, which can provide equal phase but unequal power, is used. The antenna array is analyzed and validated by using the finite element method (FEM). Simulation results demonstrate that the proposed antenna array can achieve a broad bandwidth of 21.9%, and a good gain as 29.1 dBi. Additionally, the first SLL can be as small as −28.3 dB and −20 dB in the E-plane and the H-plane, respectively. The overall size of the slotted cavity antenna array is 169.6 × 169.6 × 7.23 mm3.

Optically Transparent Metasurface Radome for RCS Reduction and Gain Enhancement of Multifunctional Antennas

In this article, we theoretically propose and experimentally demonstrate a compact, optically transparent metasurface radome with asymmetric electromagnetic absorption for making low-radar cross section (RCS) and gain-enhanced multifunctional antennas. The proposed unseeable metasurface has a bilayer structure consisting of periodically patterned and unpatterned transparent conductive films separated by a thin acrylic layer. Such a bilayer metasurface is highly reflective when illuminated by microwave from one side, while exhibit a high absorption when illuminated from the other side. Moreover, when the optically transparent, weather-proofing bilayer metasurface acts as a radome, it can greatly enhance the gain and reduce RCS of the solar panel-integrated microstrip antenna without affecting the performance of optical devices (e.g., photovoltaic panels, flat panel displays, or light emitting devices). We provide the analytical formulation and design guidelines for the bilayer metasurface and the integrated cavity antenna. Our experimental results show that the realized gain of the microstrip antenna can be increased by 6.1 dBi and its RCS can be reduced by more than 20 dB around the operating frequency of 8.1 GHz. The proposed low-profile, flexible, hydrophobic, and optically transparent bilayer metasurface may be beneficial for many applications, including the next-generation radomes, self-powered 5G/6G base stations, satellite communication (CubSat), and other compact, multifunctional RF and microwave modulus integrated with optical sensors, lidar, displays, and solar panels.

Wideband High-Gain Circularly Polarized Substrate Integrated Cavity Antenna Array for Millimeter-Wave Applications

A wideband high-gain circularly polarized (CP) substrate integrated cavity (SIC) antenna array is presented for millimeter-wave applications. The proposed antenna element is simply composed of a slot-coupled high-order-mode resonant square SIC and a pair of obliquely placed strip-shaped parasitic patches on the top surface of the SIC. The parasitic patches are used to adjust the aperture electromagnetic field distribution and phase of the two orthogonal resonant modes of TM211 and TM121 in the SIC to achieve a high-gain CP radiation and meanwhile introduce an additional cavity-backed slot-dipole CP radiation to extend axial ratio (AR) bandwidth of the proposed antenna element. By combining the above two high-gain CP radiation mechanisms, a wideband high-gain CP SIC antenna element is achieved. The simulated results of the proposed antenna element show an overlaid bandwidth of 20.36% from 26.20 to 32.14 GHz, while considering the −10 dB reflection coefficient, 3 dB AR, 3 dB gain bandwidths properties, and a maximum right-hand CP gain of 10.53 dBi at 29.40 GHz. On this basis, a wideband high-gain 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 CP array fed by a full-corporate substrate integrated waveguide (SIW) network is designed and fabricated. The measured results show that the proposed array has an overlaid bandwidth of 21.72% from 25.85 to 32.15 GHz and a measured gain of up to 26.10 dBic at 29.00 GHz.

Photoresponse enhancement in a cavity-antenna-coupled graphene terahertz detector.

The unique and excellent optoelectronic properties of graphene make it a promising material for THz detection. However, the huge gap between the atomic thickness of graphene and the long wavelength of THz radiation severely limits the efficiency of light absorption and the photoresponse. Although optical antennas are commonly used to concentrate THz waves into deep subwavelength regions, a large amount of power is re-radiated out as waste rather than being absorbed by the active material. Here, we propose a cavity-antenna hybrid structure to enhance the THz absorption in a graphene flake through interference manipulation and impedance matching. The photoresponse of the device under an impedance-matched condition is 15 times higher than that under an impedance-mismatched condition. The cavity-antenna-coupled graphene THz detector exhibits a responsivity of 10.2 mA W-1 and a noise-equivalent power of 0.92 nW Hz-0.5. The excellent performance of our device makes it one of the best room temperature sub-THz graphene detectors that we investigated. A theoretical model was established to analyze the interaction between the antenna-coupled graphene and the cavity structure. With a combination of both electrostatic doping and interference manipulation, the light coupling management by impedance matching can enhance the absorptance of graphene by more than two orders of magnitude. This work experimentally and theoretically revealed that the cavity-antenna hybrid structure can prominently enhance the responsivity of a tiny piece of graphene in the sub-THz regime. Meanwhile, this strategy can also be applied to enhance the absorptance of other low-dimensional or bulk materials.

Wideband Polarization Independent Resonant Cavity Antenna for 6G Applications

In this paper, a planar polarization independent resonant cavity antenna (RCA) is proposed to achieve higher gain with a single patch connection instead of using antenna arrays with additional feeding losses. The planar metasurface is based on sub-wavelength complementary circular metallic patches, which provide the same magnitude and phase response for both TE and TM polarized waves. In order to excite the metasurface, an aperture coupled antenna with a circular patch is used to make its integration easier with the metasurface. The proposed antenna design works from 8.97 GHz to 13.1 GHz with a measured 3dB gain bandwidth of 24.2 % and it is used to increase the antenna’s gain from 8 dBi up to 14.67 dBi. The RCA achieves the measured bandwidths (input matching <-10 dB) above 4 GHz or 37.4 %, among the highest reported in the literature with 2 layers.

2-Dimensional (2D) Beam Steering-Antenna Using Active PRS for 5G Applications.

This paper presents a compact coaxial-fed square microstrip patch antenna integrated with a beam-steering Partially Reflective Surface (PRS). The proposed design has a two-dimensional (2-D) Fabry-Perot Cavity (FPC) antenna acting as a radiator and the PRS as a beam-steering superstrate operating at 5.5 GHz. The PRS consists of 6 × 6 reconfigurable unit cells etched on Rogers 5880 with a thickness of 1.57 mm. By controlling the switching of PIN diodes in different sections of PRS, beam steering can be achieved up to ±47° in the azimuth plane with a gain of 9.1 dB and 10.2 dB and ± 15° steering in an elevation plane with a measured gain of 9.3 dB and 8.9 dB, respectively. The antenna prototype is 2.56 λ × 2.56 λ at 5.5 GHz, and the measured gain values are around 10 dBi for all the states. The beam is able to radiate at boresight or tilted to 42° in two azimuthal directions and 45° in elevation direction by adjusting the PIN diodes ON/OFF states. The 10 dB impedance bandwidth of 5.4-5.52 GHz is achieved.

Non-intrusive microwave technique for direct detection of concrete compressive strength monitoring by multivariate modeling

This paper investigates using microwaves from 1.5 to 14 GHz for monitoring concrete compressive strength in real-time to implement a non-intrusive sensor. The approach is based on acquiring reflected microwave spectra by the concrete irradiated through a rectangular cavity antenna connected to a Vector Network Analyzer (VNA) and investigating their relationship with strength. Since the information is hidden in the spectrum, we used the multivariate statistical analysis technique to create both classification and regression models. The acquired Voltage Standing Wave Ratio (VSWR) spectra were statistically inferred with compressive strength from destructive tests. The experimentation was performed on 16 concrete samples, lasted 28 days, and the acquired data consisted in 409 spectra where the reflected spectra are correlated with the compressive strength during curing time. The inference processes show high predictability, with an F1 score from 0.91 to 0.99 for classification and a cross-validation value of the parameter R2 of 0.997.

A Dual Wideband Compact Shared-Aperture Microstrip Patch/Fabry–Perot Resonator Cavity Antenna

In this article, a dual wideband compact shared-aperture microstrip patch/Fabry–Perot resonator cavity antenna is proposed. A reflective meshed patch is designed to conduct as the shared surface, which works as the radiator at the lower band but the partial reflective sheet (PRS) at the upper band. A transmissive meshed patch is designed as the parasitic element to broaden the lower bandwidth without influence on the upper band radiation. The shaped ground is used to improve the front-to-back ratio at the lower band while maintaining a compact size. Moreover, the reflective meshed patch, which is built by two complementary frequency selective structures (FSSs), shows a positive reflection phase gradient to broaden the bandwidth of the antenna at the upper band without influence on the lower band radiation. The measurements reveal that a common bandwidth of ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11(22)}\vert &lt; -10$ </tex-math></inline-formula> dB, gain reduction < 3 dB) 25.4% and 21.3%, an isolation higher than 40 and 22 dB, a peak gain of 9.01 and 16.6 dBi at UHF band and C-band are achieved, respectively. The above properties make the proposed antenna suitable for dual-band point-to-point line-of-sight (LOS)/non-LOS (NLOS) communication systems.

A Compact-Size and High-Efficiency Cage Antenna for 2.4-GHz WLAN Access Points

In this communication, a compact-size and high-efficiency air cavity antenna with a cage-like structure is proposed for 2.4 GHz wireless local area networks (WLAN). The air cavity antenna is constructed with four sides of hybrid metallized vias, including sparsely arranged blind vias and tightly arranged shorting vias. First, the antenna size is significantly reduced by utilizing the shorting vias, which makes the antenna operate at the high-order TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1/2,1/2}}$ </tex-math></inline-formula> mode. Then, by loading the capacitive blind vias at the radiating apertures, the antenna size is further miniaturized. Notably, high radiation efficiency is obtained attributed to the lower dielectric loss of the air-medium structure. Finally, a prototype of the proposed cage antenna has been fabricated and tested with good agreement between simulated and measured results. In such a compact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.128\lambda _{0} \times 0.128 \lambda _{0} \times 0.10 \lambda _{0}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength at the center frequency), the measured total efficiency over 90% is achieved in the WLAN band by the cage structure. Compared with the existing 2.4 GHz antennas, the proposed one is with the ascendency of compact size and high radiating efficiency for WLAN applications.

Extremely Compact Interconnected Half-Mode Cavity Antennas With Enhanced Isolation for MIMO System

We propose the interconnected half-mode cavity antennas (HMCAs) with enhanced isolation that have a very close center-to-center distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.13 \lambda _{0} $ </tex-math></inline-formula> . First, by both tuning the differential mode (DM)-first impedance through a pair of inductors and creating an extra coupling path through the feeding branches, the half-mode of the cavity could be formed, and the isolation between the dual feeding ports in a single cavity could be greatly enhanced from 2 to 25–50 dB over the working band from 4.9 to 5.1 GHz. Then, we extend the dual-port to four-port HMCAs with a total length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.54 \lambda _{0} $ </tex-math></inline-formula> through the connection of dual cavities, and the isolation between the adjacent cavities could be enhanced from 7 to better than 23 dB by employing the tuning lines to tune the common mode (CM)-second impedance. Furthermore, the extremely compact interconnected eight-port HMCAs are presented with a total length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.08 \lambda _{0} $ </tex-math></inline-formula> . Finally, the experimental results also validate the effectiveness of our proposed HMCAs with excellent decoupling performance. Our proposed design should provide promising application values for the extremely compact multiple-input multiple-output (MIMO) systems.

A Novel Dual-Band Shared-Aperture Antenna Based on Folded Reflectarray and Fabry–Perot Cavity

This communication proposes a novel dual-band shared-aperture antenna hybridizing Fabry–Perot cavity antenna (FPCA) and folded reflectarray (FRA), which operates at both sub-6 GHz and millimeter-wave bands with a large frequency ratio of 1:4.6. This antenna is composed of two substrates, with metasurface printed on the upper substrate and reflector layer printed on the lower one. The metasurface works as partially reflective surface (PRS) of FPCA at the sub-6 GHz band while acts as polarization grid of FRA at the millimeter-waveband. Thus, the FPCA and the FRA are able to share the same aperture with high aperture reuse efficiency. A composite feed structure combining waveguide with microstrip patch antenna is used to feed at two bands, implementing shared-aperture feed. This antenna achieves high gains at two bands without complicated feeding networks. A prototype operating at 5.4 and 25 GHz bands is designed, fabricated, and measured to verify the idea.

초소형‧고효율 Fabry-Perot Cavity(FPC) 안테나의 설계 방법

We propose a novel design method for an ultrasmall high-efficiency Fabry-Perot cavity (FPC) antenna using an artificial magnetic conductor (AMC). Unlike conventional FPC antennas, which are approximately 2 λ, 3 λ in size, the proposed antenna has an ultrasmall size of 0.37 λ×0.37 λ, and it is enclosed by metallic walls blocking leaky waves. By installing an AMC on the metal walls, we significantly improve the radiation efficiency by up to 91 %. When the proposed antenna is utilized as an element of array antennas, it is expected to demonstrate a wide beam-steering range without grating lobes, owing to the narrow interval of the elements and the high steering accuracy resulting from the inhibition of undesirable couplings between the elements by the side walls.

A Millimeter-Wave Resonant Cavity Antenna With Multibeam and High-Gain Capabilities for 5G Applications

In this article, a technique to obtain a high-gain multibeam antenna for millimeter-wave (mmW) fifth-generation (5G) base stations (BSs) is proposed using the Fabry–Pérot Cavity (FPC) structures. A thin single metallodielectric layer is used as the partially reflective surface (PRS) layer to enhance the radiation performance of the FPC antenna (FPCA) and provide an off-axis pencil beam. As the feeding structure illuminating the PRS layer, a cylindrical cavity is designed using a right-angle-type semi-waveguide (RATSW) structure. An array of coaxial probes is used to obtain beam switching at the azimuth plane by exciting different probes. To confirm the functionality of the proposed FPCA, a prototype is fabricated with five coaxial probes to generate five radiation beams; however, the structure can be extended to provide more antenna beams using higher number of probes. The cavity structure of the proposed antenna is fabricated by the 3-D printing technology as an easy manufacturing process. The measurement results show that multiple switchable beams with high antenna gain are obtained over the desired frequency bandwidth of 27–30 GHz. The maximum measured gain is 19 dBi at 27.5 GHz when a single probe is excited. A conceptional scenario for the potential applications of the proposed antenna in the 5G BSs is presented.