In-band Radar Cross Section Research Articles

An In-Band Low-Radar Cross Section Microstrip Patch Antenna Based on a Phase Control Metasurface

An in-band low radar cross section (RCS) microstrip patch antenna based on a phase control metasurface is proposed. As the size of the phase control metasurface changes, it will have different phase adjustments to the incident electromagnetic wave. Two kinds of phase control metasurfaces with a 90° reflection phase difference are arranged in a checkerboard configuration and loaded above a microstrip array antenna. The metal of the microstrip array antenna can fully reflect the electromagnetic wave, so the incident wave passes through the metasurface again and forms a reflected wave with a phase difference of 180° ± 37° when passing through the phase control metasurfaces of different sizes. Thus, the microstrip array antenna can achieve in-band RCS reduction. The metamaterial forms a transmission window in the microstrip patch array antenna band to maintain the radiation performance. Finally, a reasonable agreement is obtained between the measured and simulated results.

In-band dual-polarization RCS reduction of waveguide slot array antenna integrated with AMC and PEC chessboard structure

An in-band low radar cross section (RCS) waveguide slot array antenna (WSAA) is proposed by using a chessboard structure composed of artificial magnetic conductor (AMC) and perfect electric conductor (PEC), which serves as the antenna radiator. The method for RCS reduction is the reflection energy cancellation. Standing wave array is used to achieve higher energy efficiency and more compact antenna structure. Experimental results show that the in-band monostatic RCS is sufficiently reduced with the chessboard structure application for both co- and cross-polarized incident waves, where 10-dB RCS compression is realized among the frequency range of 9.7–9.91 GHz for co-polarization and 9.5–9.85 GHz for cross-polarization with maximum RCS reductions of −13.3 dB and −11.9 dB, respectively. Meanwhile, the designed WSAA maintains the high gain characteristics of the original WSAA. The paper provides a simple, practical and effective strategy for stable RCS compression in the operation band of waveguide antenna array, which has potential applications in stealth platforms.

A Low-Scattering Vivaldi Antenna Array With Slits on Nonradiating Edges

To reduce in-band scattering over a large angular range, this communication presents a low-scattering Vivaldi antenna array with cutting slits on the nonradiating edges of each antenna element. Over-concentrated overlap between structural modal and antenna modal scattering currents motivates the novel slit design over the nonradiating edges. These slits separate the structural modal and antenna modal scattering currents in the largest extent. The structural modal scattering is then suppressed through a cavity like structure in the nonradiating portion, while the antenna modal scattering currents keep unchanged as they are crucial for the radiation performance. The design features with a simple structure, while effectively reduces the in-band radar cross Section (RCS) in a wide angular range of ±70° and achieves ±60° scanning in the E-/H-planes over the entire X-band. Prototypes for the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 Vivaldi antenna array and a reference conventional Vivaldi antenna array are fabricated, assembled, and measured. Both measured and simulated results demonstrate the effectiveness of the low-scattering Vivaldi antenna array design.

Antenna Array Design With Self-Adaptive In-Band Radar-Cross-Section Reduction and Beam Scanning

In this article, a novel antenna array with self-adaptive radar-cross-section (RCS) reduction has been proposed for the first time. The design mechanism of the proposed array is based on Van Atta retrodirective array and orbital angular momentum (OAM) vortex wave. By inheriting the adaptive beam tracking ability of the Van Atta array, the scattering beam of the proposed antenna can be automatically steered toward the incident wave direction without any prior knowledge of the incident wave. By reasonably designing the connection line lengths in the Van Atta array, the OAM scattering beam with null amplitude along the arbitrary incident direction is generated for the RCS reduction. As the demonstration, a dual-ring array with dual-polarization characteristic has been designed. By choosing a part of the antenna elements as the Van Atta array and the remaining part of the antenna elements as the radiation array, the designed antenna array can simultaneously achieve the beam steering and the low in-band RCS performance without the increase in the antenna array size. The prototype of the proposed array is fabricated, and good agreement between the simulation and the measurement verifies the proposed design.

In-Band Radar Cross Section Reduction and Enhancement of Gain for a Patch Antenna Array by Using a 1-D Periodic Metasurface Reflector

Abstract: Based on far-field cancellation, a low-profile metasurface (MS) for both x- and y-polarizations is created. This concept uses a 1-D MS instead of a typical MS with a low RCS that uses checkerboard architecture. The proposed MS can be integrated more freely in various applications because it does not require periodicity in two dimensions. A patch antenna array is proposed based on the proposed MS. Under normal incidence, full-wave calculations and measurements demonstrate that integrating the proposed MS reduces the scattering of the antenna array by more than 5 dB over the antenna working frequency band of 10.7 to 12 GHz (11.45 percent). Moreover, when the array radiates, parasitic radiation from the slots of the MS can be activated, increasing the array's boresight gain.

In-band Radar Cross Section reduction for electromagnetic window by simultaneously enhancing transmission and coding reflection

For electromagnetic windows (EWs), although the in-band transmission is satisfactory, reflection always exists at interfaces, which leads to considerable in-band RCS, especially for large-size EWs. The conventional manner of reducing the in-band RCS is focused on enhancing transmission, which is always limited by the unavoidable impedance mismatch at interfaces. To overcome this limit, in this paper, we propose to reduce the in-band RCS of EWs by simultaneously enhancing transmission and coding reflection using dimer metasurfaces. The dimer structure is composed of two unidentical meta-atoms patterned on the front and back surfaces of the EW, respectively, which can enhance the transmission in the band of interest. More importantly, when the dimer structure is flipped, the transmission is unaffected due to reciprocity, whereas the reflection will be different. Therefore, by coding the reflection phase, the in-band backward reflection can be further reduced due to scattering cancellation. Proof-of-principle prototypes were designed, fabricated and measured to verify this strategy. The experimental results are consistent with the simulation results, which proves the feasibility of this strategy. This work provides an alternative way of reducing the in-band RCS of EWs and may find practical applications in radomes, lenses and other areas.

Dual‐mode dual‐polarization orbital angular momentum metasurface antenna with in‐band radar cross‐section reduction

In this paper, an orbital angular momentum (OAM) metasurface antenna is proposed. Based on the idea of controlling the radiation and scattering simultaneously, the metasurface unit cells play two roles of radiating and scattering energy. For radiation, the metasurface unit cells are excited by two carefully designed phase shift networks (PSNs) at two orthogonal directions. Thus, OAM vortex waves with topological charge l = ±1 are generated at 7.48 GHz band. For scattering, the incident wave is deflected through the phase canceling scheme due to the anisotropy property of the metasurface unit cells. As a result, the in-band radar cross section is reduced. A prototype of the antenna was fabricated and measured. The measurement results agreed well with the simulations.

In‐band dual‐polarization radar cross section reduction of patch array antenna using hybrid resistive metasurface

In this article, a hybrid resistive metasurface (RM) based on the different field distributions of radiation and scattering is designed and realized for dual-polarization radar cross section (RCS) reduction of patch array antenna without enlarging its original dimensions. The hybrid RM is composed of two RMs located on the same plane, which is both transmissive for electromagnetic waves from antenna below at resonant frequency of 12.3 GHz. The combination of the RMs and the metal ground of antenna form absorbers, which absorb in-band co-polarized (RM1) and cross-polarized (RM2), waves respectively. The hybrid RM is arranged by RM2 placed directly above the radiation patches while RM1 placed elsewhere. Therefore, the radiation performance of antenna is basically unaffected meanwhile realizing the in-band dual-polarization RCS reduction. Simulation results demonstrate that the hybrid RM exhibits RCS reduction of co-polarization and cross-polarization reaches 10.7 and 3.3 dB respectively by the window-like layout, and main lobe gain achieves to 18.0 dB, which is 2.2 dB lower than that of reference antenna. The experimental results are consistent with the simulation results in the main.

In-band RCS reduction antennas using an EBG surface

AbstractThe paper has proposed a multilayer, polarization rotation featured, low radar cross-section (RCS) antenna using electromagnetic band-gap (EBG)-based frequency selective surface (FSS) at 8.25 GHz. Cross-shaped EBG unit cells offer zero reflection phase and −25 dB reflection magnitude at 8.25 GHz. The FSS layer consists of eight cross-shaped EBG unit cells sandwiched between two substrates to offer high absorptivity at the desired band. The circular patch antenna resonating at 8.25 GHz is placed on the top substrate having a lower dielectric constant. Four circular-shaped patches are etched at the four corners of the top layer and are coupled with two feed lines which are aligned 90° to each other at the bottom layer and interconnected diagonally to achieve polarization rotation. The proposed antenna offers a gain of 6.72 dB and an in-band RCS of −21.4 dBsm. Incident energy is backscattered into eight directions separated by angle ϕ = 45°. The proposed antenna has the RCS reduction band of 7.7–9.4 GHz. It offers normalized polarization rotation ratio more than 0.8 within the −40° to 40° angular region at the frequency band 8–8.5 GHz. The measured result using the fabricated prototype agrees well with the simulated one.

Superstrate-based patch antenna array with reduced in-band radar cross section

AbstractTo design a low radar cross section (RCS) antenna, the major concern is not only to reduce scattering, but also to maintain its radiation parameters, viz. gain, voltage standing wave ratio (VSWR), etc. This paper presents a simple configuration of low RCS microstrip patch array with a periodic structure-based superstrate. The ground of the array is designed as reduced ground plane with high impedance surface elements, viz. rectangular patch and Jerusalem cross. The configuration of superstrate consists of multilayered, viz., two-layered and three-layered structures having partially absorbing and reflecting surfaces. In both the proposed configurations, the array gain of 12.5 dB is maintained with reduced structural RCS over the entire in-band frequency range. The reflection coefficient (~ −20 dB) and VSWR (~ 1.1) of the array are maintained. It is shown that the proposed superstrate-based patch array design has significantly reduced in-band RCS (−18 dBsm) at its resonant frequency.

Wideband, low radar cross section circularly polarized array antenna based on metasurface and sequential phase feed

A planar circularly polarized (CP) array antenna based on polarization conversion electromagnetic band-gap (PCEBG) and sequential phase (SP) feed network with wideband circular polarization and low radar cross section (RCS) is presented. The array is formed by 2 × 2 PCEBG elements. The CP performance is obtained due to the PCEBG, and the SP feed network contributes to the wide bandwidth and symmetric radiation pattern. The proposed array antenna, with an overall size of 64 mm × 64 mm × 2.008 mm (1.6 λ0 × 1.6 λ0 × 0.05 λ0 at 7.5 GHz) has been fabricated and measured. The measured results are as follows, an impedance bandwidth of 42.90% (6.61-10.22 GHz), a 3-dB axial ratio bandwidth (ARBW) of 28.3% (6.65-8.83 GHz) and a 3-dB gain bandwidth of 23.7% (6.7-8.5 GHz). The antenna exhibits left-hand CP(LHCP) characteristics with a peak broadside gain of 14.1 dB. The proposed antenna achieves an in-band and out-band RCS reduction more than 8 dB under normal incidence. The measured results are in agreement with the simulated results.

A Low Cost, Low in-Band RCS Microstrip Phased-Array Antenna With Integrated 2-bit Phase Shifter

In this article, we present a low-cost microstrip phased-array antenna, which is composed of electronically reconfigurable elements. The p-i-n diodes' integrated elements have various functions, such as tunable polarization characteristics and adjustable radiation phases. The high sidelobe level (SLL) due to the 2-bit phase shifter can be reduced by a randomly rotated (RR) array element. It is shown that the array can realize electronic beam-steering capabilities and keep -10 to -14 dB sidelobes without tapering. To verify the above theory, an eight-element linear array prototype working at 3 GHz was designed, fabricated, and tested. Numerical simulations and experimental results show that, by controlling the “ON” and “OFF” states of p-i-n diodes, the radiation beam can be controlled to steer in a circular polarization (CP) mode, wherein the scanning angle is up to ±45°. Furthermore, the principle of suppressing the vector scattering field by the opposite phasing cancellation method can achieve in-band radar cross section (RCS) reduction. Simulation results show that approximately 15 dB in-band RCS reduction can be realized for both bistatic and monostatic RCS reduction with an 8×8 array.

Reducing the radar cross section while maintaining the performance of a coplanar waveguide-fed antenna with an absorptive metasurface

The paper presents, for the first time, an analysis of the optimum arrangement of a coplanar waveguide-fed monopole antenna and a metasurface absorber (MSA), aiming to reduce the antenna’s in-band radar cross section (RCS) without perturbing its radiation properties. The proposed arrangement will show that the efficiency of the antenna, of great interest in many applications (such as the internet of things), can be preserved, contrary to results of previous papers focused on combining these structures. Moreover, the final structure will be easily embeddable (with an optimum number of unit-cells) as well as conformable. A proper analysis of the losses and currents on the structure will be provided for a better understanding of the interaction phenomena that arise. Good agreement between simulation and measurement results can be observed, corroborating the proper performance of the structure. Furthermore, bistatic reductionis obtained as well as monostatic RCS reduction, due to the angular stability of the employed MSA. Finally, it will be shown that the introduction of loaded resistors will be preferable to the use of a lossy dielectric to improve the RCS reduction whilst maintaining the antenna performance.

In-Band RCS Reduction and Isolation Enhancement of a 24 GHz Radar Antenna Using Metamaterial Absorber for Sensing and Automotive Radar Applications

A triple-band low radar cross-section (RCS) high isolation antenna is proposed for 24 GHz ISM band sensing and automotive radar applications. The proposed design consists of 2 x 2 patch array that acts as transmit and receive antennas. Low RCS and high isolation are achieved at 24 GHz by designing a metamaterial absorber (MA), which consists of a square ring with a resistor connected in its diagonal arm for the absorption of electromagnetic waves. The proposed MA shows near unity normalized impedance at 24.1 GHz with 90% absorptivity bandwidth of 1 GHz. An array of MA is placed in between and around the transmit/receive antennas to suppress surface current and reduce in-band RCS of the radar sensor. The −10 dB impedance bandwidths of the triple-band sensor antenna are 20.8 to 21.24 GHz, 23.94 to 24.55 GHz, and 27.18 to 27.5 GHz. The proposed sensor antenna achieves isolation of 34 dB between the transmit and receive ports, and peak RCS reduction of 11 dB, as compared to the reference antenna. The half-power beamwidth of the proposed sensor antenna is 38° for E-plane and 52° for H-plane at 24 GHz.

A High-Performance Rectenna for Wireless Power Transfer in CubeSats

This letter presents a high-efficiency circular-polarized (CP) rectenna at 5.8 GHz within wide input power range featuring low profile and radar cross section (RCS) reduction. Originating from the connection to a branch-line coupler, two identical subrectifiers in parallel combination are capable of extending the input power range and enabling the stability of dc output. The contribution of this combination in the performance of rectenna is experimentally demonstrated and a solution to RCS reduction by means of defected ground structure and complementary split-ring resonators is devised. The measured results show that the rectenna achieves a conversion efficiency of more than $60\%$ within the input power range from 2.2 to 17.6 dBm, and an in-band RCS reduction of 5.1 dB, verifying the applicability of wireless power transfer for CubeSats.

Low-RCS Holographic Antenna With Enhanced Gain Based on Frequency-Selective Absorber

This article presents a low radar cross-section (RCS) holographic antenna with enhanced gain based on a frequency-selective absorber (FSA). The proposed antenna consists of a feed monopole antenna, a holographic metasurface using slotted patches, and a two-layered resistive metasurface. Within its operating band, the holographic metasurface manipulates the surface wave into a $y$ -polarized broadside plane wave and vice versa, which simultaneously realizes high gain and in-band low RCS for $y$ -polarized incidence. In addition, slotted patches are utilized as unit cells of the holographic metasurface to further enhance the antenna gain. The resistive metasurface used in the proposed antenna has a transmission window for the $y$ -polarized waves. After integration with the proposed holographic metasurface, it exhibits absorption–reflection–absorption and wideband absorption responses for the $y$ - and $x$ -polarized waves, respectively. Thus, not only is good radiation performance maintained but also the in-band RCS for $x$ -polarized incidence and out-of-band RCS for both polarizations are significantly reduced. Compared to a conventional holographic antenna, the gain of the proposed antenna was enhanced by 1.4 dB at 10 GHz. Both the monostatic and bistatic RCS were significantly reduced in the frequency range 4–17 GHz. The measured results of a fabricated prototype of the proposed antenna were in good agreement with simulations.

Low In-Band-RCS Antennas Based on Anisotropic Metasurface Using a Novel Integration Method

Radar cross section (RCS) reduction in the working band of antennas, likely leading to radiation performance change or deterioration, is quite difficult for both antenna elements and arrays. Aimed at this problem, this article presents a novel design strategy of microstrip patch antennas with low in-band RCS. This strategy combines metasurface with antenna from the perspectives of both structure and electrical performance. To be specific, anisotropic metasurface is proposed to replace the conventional patch and behave as the radiating structure of the antenna directly, which does not increase the original antenna size. Through proper connection of the metasurface units, the novel antenna has the same radiation performance with conventional microstrip antenna but low in-band RCS for any polarized incidence. The radiation and scattering mechanism of the novel antenna is carefully elaborated, from which a frequency reconfigurable antenna is also derived by loading varactors. Furthermore, different design strategies of low in-band-RCS antenna element and array are clarified. On the basis of which, a $4 \times 4$ array is developed to achieve in-band-RCS reduction with radiation performance kept. Both numerical and experimental results are demonstrated, and the reasonably good agreements verify the effectiveness of the proposed strategy.

In-Band Scattering Control of Ultra-Wideband Tightly Coupled Dipole Arrays Based on Polarization-Selective Metamaterial Absorber

With the polarization-selective metamaterial absorber (PSMA), a unique approach for reducing the in-band radar cross section (RCS) while preserving the radiation performance of a tightly coupled dipole array (TCDA) is proposed. The proposed PSMA structure is comprised of resistive films, dielectric layers, and polarization gates. In detail, the resistive films are loaded on the surface of a TCDA, and the polarization gates are utilized to broaden the absorption bandwidth of PSMA as well as to improve the polarization purity of the array. Moreover, the process of the co-design of the phased array with PSMA is presented. The designed infinite array is able to achieve a 3:1 bandwidth from 6 to 18 GHz with the active VSWR $10 \times 10$ single-polarized prototype array is fabricated and measured. Measured results are in good agreement with simulated ones, thus demonstrating that the PSMA structure is able to reduce the scattering significantly throughout the operating band of the array under normal and oblique incidence.

Microstrip array antenna in-band RCS reduction using polarization reconfigurable elements

ABSTRACTAn efficient approach for in-band radar cross section (RCS) reduction of microstrip patch array antenna without employing extra-low RCS artificial materials is proposed and analysed. The element of the array has a simple structure, consisting of a corner-cut square patch and two tiny perturbation elements. By controlling two independently biased PIN diodes, it can produce linear polarization (LP), left- and right-handed circular polarization (LHCP/RHCP) radiation waves. The backscattering RCS reduction of the array can be achieved by changing the polarization status of array elements. For verification, the performance of a polarization reconfigurable microstrip array with different polarization modes is designed, compared and analysed. From the simulation and measurement results, the peak RCS of the array can be reduced by more than 7 dB without affecting its radiation performance.

Analysis and Reduction on in-Band RCS of Fabry-Perot Antennas

In this article, a method is proposed to reduce the in-band radar cross section (RCS) of the high-gain Fabry-Perot antenna (FPA) based on the cancellation between the antenna mode RCS (AM-RCS) and structural mode RCS (SM-RCS). The ports of the two back-fed microstrip array antennas are connected to form the partial reflective surface (PRS) with a high reflectivity. The phase delay line (PDL) is proposed to control the AM-RCS to cancel out the SM-RCS. The AM-RCS is used to further reduce the in-band RCS of the low RCS high-gain FPA instead of being eliminated by the matched load. The measured results show that the FPA has a great impedance matching within the band of 9.8-11.2 GHz, and the maximum realized gain of the FPA reaches 10.7 dBi. The simulated bistatic RCS of the FPA is less than -14 dBsm within ±90 degrees angle domain at the center frequency. The minimum monostatic RCS of the proposed FPA is reduced by 17.9 dB compared with the reference FPA. Furthermore, this article provides a design basis for the feed line length of the FPA from the perspective of scattering performance.