Partially Reflective Surface Research Articles

A Millimeter-Wave Fabry–Perot Cavity Antenna With Unidirectional Beam Scanning Capability for 5G Applications

In this article, a millimeter-wave (mmW) leaky-wave antenna (LWA) with unidirectional beam scanning (UBS) capability based on the Fabry–Perot cavity (FPC) structure is proposed for fifth-generation (5G) applications. The proposed antenna consists of a main radiating element, a metallic wall, a ground plane, and a single-layer partially reflective surface (PRS). To improve the UBS performance, a single radiating element is designed such that it provides a tilted beam with good radiation performance over the scanning angles. The metallic wall is used close to the radiating element as a reflector to suppress the propagation in undesired directions. A general design guide is given by a theoretical analysis of the FPC structures using the ray-tracing method to formulate the beam-steering functionality versus frequency over desired predetermined angles. The PRS layer is designed without any tuning elements to provide the beam scanning over the angles of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^\circ &lt; \theta &lt; 45 ^\circ $ </tex-math></inline-formula> and the frequency range of 24–30 GHz. The proposed Fabry–Perot cavity antenna (FPCA) structure is fabricated and the measurement results show a beam steering from 19° to 54° over the frequency band from 24 to 30 GHz, which is in good agreement with the calculated results from the theoretical analysis. A maximum measured gain of 14.5 dBi at 24 GHz is achieved. The proposed antenna can be used in the 5G mobile communication systems and 5G base station antennas (BSAs), where beam steering with high-gain and low fabrication cost features over the mmW spectrum is required.

High-Gain Fabry–Pérot Antenna With Reconfigurable Scattering Patterns Based on Varactor Diodes

In this article, a low radar cross section (RCS) and high-gain Fabry–Pérot (F-P) antenna with reconfigurable scattering beams based on varactor diodes is proposed. The partially reflecting surface (PRS) of the proposed F-P antenna is composed of an anisotropic frequency-selective absorber (AFSA) and an active phase gradient metasurface (PGM) loaded with varactor diodes. The proposed AFSA can absorb the cross-polarized wave and make the co-polarized wave pass through. The in-band co-polarized scattering beams can be tuned continuously with stable radiation beams by changing the capacitance of the varactor diodes. Therefore, the proposed device can reduce the RCS for in-band co- and cross-polarized incident waves. Moreover, taking advantage of the path difference between the radiating and scattering waves, the gain enhancement and RCS reduction (RCSR) are realized simultaneously. Simulated results show that the scattering beam can be tuned dynamically from –40° to 40° with a maximum gain enhancement of 7.2 dB. The co-polarized in-band reconfigurable scattering beam and the stable gain enhancement are first implemented in a single antenna. A significant monostatic RCSR is obtained for the co- and cross-polarized wave in the frequency band of 5.5–7 GHz with a maximum reduction value of 20 dB. The experimental and simulated results are in good agreement.

Broadband high gain cavity resonator antenna using planar electromagnetic bandgap (EBG) superstrate

AbstractThis paper presents a broadband miniaturized Fabry–Perot cavity resonator antenna (CRA) made of novel electromagnetic bandgap (EBG) superstrate as partially reflecting surface (PRS) and reactive impedance surface (RIS) backed rectangular patch antenna. To the best of the authors' knowledge, the proposed EBG exhibits the highest stopband bandwidth (BW) with a bandgap existing between 7.37 and 12.4 GHz (50.9%). Frequency-selective property of the EBG is utilized under plane wave incidence to demonstrate it as PRS superstrate in CRA antenna. The cavity is excited with a rectangular microstrip antenna which is made of two dielectric substrates with an additional RIS layer sandwiched between them. The RIS provides wideband impedance matching of the primary feed antenna. A 7 × 7 array of the EBG superstrate is loaded over the patch antenna having an overall lateral dimension of only 45 × 45 mm2 or 1.62 λ0 × 1.62 λ0 where λ0 is the free space wavelength at the center frequency of 10.8 GHz. The proposed Fabry–Perot CRA (FP-CRA) achieves gain enhancement of 6.59 dB as compared with the reference antenna and has a 10 dB return loss BW of 23.79% from 10.07 to 12.79 GHz. A prototype of the FP-CRA is fabricated and experimentally tested with single and dual layers of EBG superstrate. Measured results show BWs of 21.5 and 24.8% for the two cases with peak realized gain of 12.05 and 14.3 dBi, respectively. Later a four-element antenna array with corporate feeding is designed as the primary feed of the CRA. The simulation result shows a flat gain of &gt;13 dBi with gain variation &lt;1.2 dB over the impedance BW of 13.2%.

High Gain and Wideband Fabry-Perot Resonator Antenna Based on a Compact Single PRS Layer

In this paper, a wideband and high gain Fabry Perot Resonator Antenna (FPRA) is proposed. It is based on a synthesized compact single partially reflective surface (PRS) layer acting as a superstrate to a slot-coupled feed antenna, which acts as a radiating source element for the proposed design. The PRS is based on a 2-D printed unit cell, where the lower part is a simple circular ring Frequency Selective Surface (FSS), incorporated with a synthesized FSS unit cell, using an automated system through a VBA based interface established between CST Microwave studio and Matlab, and optimized using a binary genetic algorithm. This new FSS layer acts as the upper part of the proposed PRS layer and provided a positive phase gradient. It almost perfectly resembles that of the optimum PRS over the desired frequency range, with a relatively high reflection magnitude, which makes it a promising superstrate candidate for wideband and high gain FP resonator antennas. The fabricated prototype achieved an important performance in terms of impedance bandwidth with 42%, ranging from 11.32 to 17.35 GHz. In addition, the 3-dB gain bandwidth is 36 % from 11.68 to 16.78 GHz, with a maximum peak gain of 14.72 dB achieved at 16 GHz. Consistent and almost invariant radiation patterns are achieved over the Ku-band frequency band of interest. The experimental and simulated results are in good agreement, justifying the feasibility of the proposed design as a high gain and wideband FP resonator antenna.

Differential-Fed Dual-Polarized Filtering Fabry-Perot Antenna With High Isolation

In this paper, a dual-polarized filtering Fabry-Perot antenna (FPA) with high-isolation is proposed. It consists of a feed element of differential-fed dual-polarized square patch and a partially reflecting surface (PRS). The patch is capacitively coupled with T-shaped resonators and shorting-vias to obtain broadband characteristic and radiation nulls. The PRS structure is composed of two complementary metasurface layers are selected for achieving a positive reflection phase gradient within the broad frequency range. More interestingly, thanks to the frequency selectivity feature, the PRS significantly enhances the filtering characteristic of the FPA. For verification, a prototype of the proposed antenna operating at the 5.5-GHz center frequency has been fabricated and measured. The prototype with an overall size of ~2.0λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> × 2.0λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> × 0.49λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> is the free-space wavelength referring to the lowest operational frequency) result in an impedance bandwidth of 17.1% (5.02 – 5.96 GHz) for 10-dB return loss and a high isolation of ≥ 45 dB. Moreover, the far-field measurements result in a good dual-polarized radiation with the peak gain of 13.0 dBi, cross-polarization level of ≤ –25 dB within the passband, and out-of-band suppression level of ≥ 20 dB.

Aperture-Shared Millimeter-Wave/Sub-6 GHz Dual-Band Antenna Hybridizing Fabry–Pérot Cavity and Fresnel Zone Plate

This article presents an aperture-shared dual-band large frequency-ratio high gain antenna for sub-6 GHz and millimeter-wave (mm-wave) bands applications. Initially, the partially reflective surface (PRS) of the Fabry–Pérot cavity (FPC) antenna operating at the sub-6 GHz band is realized by using single-layered periodic grid patches while the opaque region of the mm-wave bandwaveband Fresnel zone plate (FZP) lens antenna is implemented by using periodic double-screen dipoles. Then, the PRS and the FZP lens are hybridized together and upgraded into a kind of composite metasurface, which simultaneously functions as the PRS of the sub-6 GHz FPC antenna and the mm-wave bandwaveband FZP lens with little dual-band mutual interference. Thus, the FPC antenna and the FZP lens can share the same aperture with high aperture reuse efficiency. Because the principles are based on the FPC resonance and the collimating FZP lens, high gains are achieved at both bands without a feeding network. Meanwhile, a dual-band large frequency-ratio antenna is designed as the feed. A prototype working at 3 and 28 GHz bands is designed, fabricated, and measured to verify the idea.

Circularly Polarized FP Resonator Antenna With 360° Beam-Steering

A high gain circularly polarized Fabry–Perot (FP) resonator antenna with 360° beam steering property is presented in this communication. A linear to circular polarization conversion metasurface (PCM) based on a receiver–transmitter unit cell is designed to act as the partially reflecting surface (PRS) of the FP resonator antenna. The transmission phase of the unit cell can be tuned by rotating the radiator and transmission phase shift of the unit cell equal to the rotation angle of the radiator, indicating that the transmission phase varies over a range of 360°. Then, by manipulating the transmission phase of unit cells on the metasurface (MS), the antenna can realize 360° beam steering with an angle tilted range of 0°–75°. To further enhance the antenna performance, the compensatory transmission phase is added to each unit cell on the MS, which can make the antenna obtain higher gain while realizing tilted beam. The measured results of the fabricated antennas imply the feasibility of this design. The proposed MS provides a novel method to realize beam steering of the circularly polarized FP resonator antenna.

Novel Beam Scan Method of Fabry–Perot Cavity (FPC) Antennas

A new beam scanning method of a Fabry–Perot cavity (FPC) antenna is proposed. To obtain high gain in a target direction with a reduced sidelobe level (SLL), we devised a tapered partially reflective surface (PRS) as a superstrate. Moreover, to attain various beam scanning directions, a phase-controllable artificial magnetic conductor (AMC) ground plane with a broad reflection phase range and high reflection magnitudes was introduced. In the proposed method, a new formula to satisfy an FP resonance condition in a cavity for a scanned beam is also suggested. According to the formula, the FPC antenna can precisely scan the main beam in designed target directions with well-maintained high gain, which has been hardly achievable. In addition, our method demonstrates the potential of electrical beam-scanning antennas by employing active RF chips on the AMC cells. To validate the method, we fabricated a prototype FPC antenna for a scanned beam at θ = 30°. Furthermore, we conducted an additional simulation for a different beam scanning angle as well. Good agreement between the expected and experimental results verifies our design approach.

Wideband Gain Enhancement of High-Isolation Fabry–Pérot Antenna Array With Tandem Circular Parasitic Patches and Radial Gradient PRS

A high-isolation Fabry–Pérot (FP) antenna array with wide bandwidth and high gain is proposed for <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</b> -band vehicle satellite communications. Each antenna element consists of a pair of tandem circular parasitic patches (TCPPs), a radial gradient partially reflective surface (PRS), and a reflector, respectively, separated from the ground plane with a double-dumbbell-shaped slot (DDSS) by air layer and foam dielectric. The slot radiator steers the TCPPs to create multiple resonant frequencies and then the impedance bandwidth is widened. The impedance matching could be improved by adjusting four circular slot diameters of the DDSS. The gain is raised by TCPPs and radial gradient PRS, which function to guide the electromagnetic field and uniformize the aperture near-field, successively. The reflector with several resonator elements is used to reduce the backside radiation. As proof of concept, the FP antenna array prototype with a height of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.613\lambda _{0}$ </tex-math></inline-formula> has been fabricated and measurements confirming simulations are provided. Experimental results show that the impedance bandwidth ranges from 13.48 to 16.95 GHz [22.8% fractional bandwidth (FBW)], and the realized gain is up to 21.59 dBi. A decoupling metallic strip could achieve over 40.8 dB isolation. The proposed antenna element is easily extended for the multiple-input multiple-output (MIMO) and beamforming antennas, further improving the directivity.

Multifunctional Partially Reflective Surface for Smart Blocks.

In general, a partially reflective surface (PRS) is mainly used to increase the gain of an antenna; some metallic objects placed on the PRS degrades the antenna performance because the objects change the periodic structure of the PRS. Herein, we propose a multifunctional PRS for smart block application. When a passenger passes over a smart block, the fare can be simultaneously collected and presented through the LED display. This requires high gain antenna with LED structure. The high gain characteristic helps the antenna identify passengers only when they pass over the block. The multifunctional PRS has a structure in which an LED can be placed in the horizontal direction while increasing the antenna gain. We used the antenna’s polarization characteristics to prevent performance deterioration when LED lines are placed in the PRS. We built the proposed antenna and measured its performance: At 2.41 GHz, the efficiency was 81.4%, and the antenna gain was 18.3 dBi. Furthermore, the half-power beamwidth was 18°, confirming a directional radiation pattern.

A multifunctional ultrathin flexible bianisotropic metasurface with miniaturized cell size

In this paper, a flexible bianisotropic metasurface possessing omega-type coupling is presented. The designed metasurface behaves differently when excited from either forward (port 1) or back (port 2) sides. It provides an absorption of 99.46% at 15.1 Gigahertz (GHz), when illuminated from port 1, whereas, on simultaneous illumination from port 2, it behaves like a partially reflective surface (PRS). Furthermore, the presented metasurface not only acts as an in-band absorptive surface (port 1) and partially reflective surface (port 2), but it also provides 97% out-of-band transmission at 7.8 GHz. The response of the presented metasurface remains the same for both transverse Electric (TE) and transverse magnetic (TM) polarized wave or any arbitrary linearly polarized wave. Additionally, the response of the metasurface is angularly stable for any oblique incidence up to 45º. The proposed ultrathin flexible metasurface with absorption, partial reflection and out-of-band transmission properties can be used in the Fabry Perrot cavity antenna for gain enhancement with radar cross-section (RCS) reduction both for passband and stop-band filtering, and conformal antenna applications.

Dual-Band and Shared-Aperture Fabry–Perot Cavity Antenna

This letter presents a novel dual-band and shared-aperture Fabry-Perot cavity antenna (FPCA) with high aperture efficiency (AE) and high port isolation, which operates in both S- and C-bands with a frequency ratio of 1:1.45. This antenna is composed of a partially reflective surface (PRS), a frequency selective surface (FSS), and a ground plane. A microstrip patch working at 3.45 GHz and a dipole working at 5 GHz are acted as primary radiator, respectively. To form two separate FP cavities, the FSS layer shows passband characteristic for low frequency and stopband characteristic for high frequency. Since two resonant cavities share the same PRS layer, the utilization rate of the proposed antenna has been significantly improved. This scheme can be used to design shared aperture antenna with any frequency ratio. To verify this design concept, an antenna prototype is designed, fabricated, and measured. The measured results demonstrate that the proposed dual-band shared-aperture FPCA has -10 dB impedance bandwidth of 3.42-3.47 and 4.94-5.05 GHz with the peak gain of 13.7 dBi (at 3.45 GHz, 77% AE) and 16.8 dBi (at 5 GHz, 74% AE), the isolation between two ports is better than 30 dB, which agrees well with the simulated ones.

Broadband RCS reduction for both microstrip array and Fabry‐Perot antenna based on the quasi‐ AMC superstrate

This article presents a new type of quasi-AMC superstrate (QAMCS), which can achieve wideband RCS reduction (RCSR) for both the microstrip array and Fabry-Perot (FP) antenna. The proposed QAMCS comprises of two-layer metallic patterns with a thin air gap. The top-layer consists of two types of frequency selective surfaces (FSSs) in a checkerboard layout, and the wideband RCSR is realized based on the phase cancelation principle. The bottom-layer consists of the slotted FSS, to reflect out-of-band signal while allowing the in-band signal to pass through with a low insertion loss. Besides, the reflection phase of the proposed QAMCS is about −180° around higher frequencies. Therefore, it can be regarded as a partially reflecting surface (PRS) to construct the FP antenna with a highgain and low-RCS. The simulation and measurement results show that the bandwidth of 10-dB RCSR is more than 76% (7.2-16.1 GHz). The 10-dB impedance bandwidth of the array antenna is ranging from 16.6 to 18.6 GHz. For the FP antenna, its aperture efficiency is 31.5% and the peak gain is 17.5 dBi at 20 GHz.

Magnetoelectric Dipole-Fed Fabry–Perot Antenna With Wideband RCS Reduction Based on Multilayer Metasurface

This letter presents a novel superstrate composed of multilayer metasurface (MM), which is characterized by wideband monostatic and bistatic radar cross section reduction (RCSR) for Fabry-Perot (FP) antenna with magnetoelectric (ME) dipole-fed. The proposed MM consists of four layers, the top three layers form a polarization-selective absorber (PSA), and the bottom layer is a polarization conversion metasurface (PCM). The copolarized incident waves are absorbed by the PSA, while the cross-polarized waves pass through with a low insertion loss. Then, it is reflected by the PCM with 90° polarization rotation and absorbed by the upper PSA. Additionally, the bottom layer of the PCM unit is an improved pattern instead of the ground plane. It is capable of polarization conversion and partial reflection. Therefore, the MM and ME dipole are respectively utilized as the partially reflecting surface (PRS) and the primary source to construct an FP antenna. Simulation and measurement results show that the bandwidth of monostatic RCSR is more than 80%. The FP antenna also achieves a high aperture efficiency of 51%, which is due to the benefit from the widebeam characteristics of the ME dipole.

Study on the Velocity Analysis Method of Low SNR Seismic Data

When the signal to noise ratio of seismic data is very low, velocity spectrum focusing will be poor., the velocity model obtained by conventional velocity analysis methods is not accurate enough, which results in inaccurate migration. For the low signal noise ratio (SNR) data, this paper proposes to use partial Common Reflection Surface (CRS) stack to build CRS gathers, making full use of all of the reflection information of the first Fresnel zone, and improves the signal to noise ratio of pre-stack gathers by increasing the number of folds. In consideration of the CRS parameters of the zero-offset rays emitted angle and normal wave front curvature radius are searched on zero offset profile, we use ellipse evolving stacking to improve the zero offset section quality, in order to improve the reliability of CRS parameters. After CRS gathers are obtained, we use principal component analysis (PCA) approach to do velocity analysis, which improves the noise immunity of velocity analysis. Models and actual data results demonstrate the effectiveness of this method.

Fabry-Pérot Resonator Antenna in Equivalent-Medium Metamaterials

In this communication, a wideband Fabry–Perot resonator antenna (FPRA) is proposed. An optimized partially reflective surface (PRS) with a transverse permittivity gradient (TPG) composed of four nonrotationally symmetric sections is employed in the design of the antenna. The use of nonrotationally symmetric PRS results in more than 31% improvement of the 3 dB gain bandwidth compared with the traditional rotationally symmetric PRS. Furthermore, two types of nonresonant metamaterials (metallic-ring and etching-hole unit cells) are used to implement the equivalent permittivity of PRS. In this way, the equivalent permittivity value covers a broad range (3.5–9.5) for the same dielectric. As a result, the restrictions imposed by the use of only commercially available dielectrics and the errors that occur during the fabrication and assembly progress of different materials can be avoided. The primary radiator of FPRA is a double-ridge waveguide horn, which ensures wideband antenna operation. An FPRA prototype is fabricated and measured, which exhibits a broad bandwidth (5.2–11.5 GHz) with the return loss |S11| of less than −10 dB. The measured 3 dB gain bandwidth is 73.8% (in the frequency range of 5.3–11.5 GHz) with a peak gain of 17.1 dBi at 7.8 GHz.

Gain and AR Improvements of the Wideband Circularly Polarized Fabry-Perot Resonator Antenna

A method to improve the performance of a wideband circularly polarized (CP) Fabry–Perot resonator antenna (FPRA) is presented in this communication. First, a wideband CP FPRA composed of a partially reflective surface (PRS) with a positive reflection phase gradient and a wideband CP patch antenna is proposed. Then, a transmission metasurface (MS) with a high transmission magnitude and tunable transmission phase in a broadband range is proposed to correct the electric field phase above the antenna. This MS has the ability to independently tune the transmission phases of two orthogonally polarized waves. On the one hand, the nonuniform phase distribution on the aperture field of the antenna can be transmitted to be nearly uniform, so the gain of the antenna will be enhanced. On the other hand, the transmission phases of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -polarized waves are corrected to maintain a 90° phase difference at every position, which leads to a wider axial ratio (AR) bandwidth. Therefore, after the phase correction of the MS, the gain and AR performances of the antenna are both improved significantly. The measured results suggest that the overlap of the 10 dB return loss bandwidth, 3 dB gain bandwidth, and 3 dB AR bandwidth of the antenna is 9–11.1 GHz (21%). The peak gain of 18.3 dBic is achieved at 10.2 GHz. The results indicate that the proposed MS can achieve excellent performance improvement of the CP FPRA.

High-Gain Compact Circularly Polarized X-Band Superstrate Antenna for CubeSat Applications

In this letter, a concept of a high-gain circularly polarized X-band antenna employing a partially reflecting surface (PRS) has been presented. In the initial antenna analysis, the influence of parasitic element size in the PRS structure on antenna radiation pattern parameters has been investigated and the optimal arrangement of the elements has been identified. The proposed antenna provides a wide bandwidth of return loss above 10 dB of 20% (8–9.8 GHz) and circular polarization (CP) in a frequency range 8.35–8.95 GHz. The final design is compact (62 × 62 × 22.2 mm) and lightweight (29.7 g), which makes it suitable for use not only in CubeSat X-band communication systems but also in drones and high-altitude pseudosatellite applications.

Gain bandwidth enhancement of microstrip antenna fed half wavelength Fabry Perot cavity antenna

In this article, gain-bandwidth of microstrip antenna (MSA) fed half wavelength Fabry-Perot cavity (FPC) antenna is enhanced by modifying partially reflecting surface (PRS) and artificial magnetic conductor (AMC) surfaces. Two methods are considered to analyze the resonant condition of FPC antenna. In the first method phase correction is applied, to take into account the modification in AMC layers, while in second method the entire AMCs and PRS surface of the structure is taken as a unit cell. The proposed antenna provides S11 < −10 dB, peak gain of 17.7 dBi with gain variation < 2 dB, side lobe level < −19 dB, cross polarization level (CPL) < -16 dB and front to back lobe ratio > 20 dB over 5.66 to 6.4 GHz, which covers ISM and satellite uplink C band. The overall antenna dimensions are 2.7λ0 × 3.1λ0 × 0.5λ0; here λ0 is the wavelength in free space corresponding to 5.8 GHz, center frequency of the ISM band. The measured results agree with simulated results.

Wideband and Compact Fabry–Perot Resonator Antenna Using Partially Reflective Surfaces With Regular Hexagonal Unit

A wideband and compact Fabry–Perot resonator antenna (FPRA) employing two layers of partially reflective surfaces (PRSs) is presented in this letter. The proposed PRSs with regular hexagonal units are used in wideband FPRA for the first time. Based on the compact arrangement of regular hexagon units and the addition of tripod branches, the size of FPRA is greatly reduced. Furthermore, the regular hexagonal units are arranged periodically along three directions on the 2-D plane, which means that one regular hexagon unit has six identical units around it. Therefore, there is a strong coupling between the PRS units, and units obtain a positive phase gradient in a wide range of 9.1–13.5 GHz, which is the basis for the formation of the wideband FPRA. The FPRA with dimensions of (2.2×2.2×0.6) λ03 (λ0 is the wavelength of the center frequency) has a 3 dB gain bandwidth over 9.2–13 GHz, relatively 34.2%, with a peak gain of 14.2 dBi. The prototype has been fabricated and tested, and validate the simulated results.