Radar Cross Section Properties Research Articles

Measurements and analysis of the radar cross section of chaff dipoles

AbstractA free space test method to measure the Radar Cross Section (RCS) of single dipole elements is presented. The method is such that dipoles can be measured over a large range of frequencies, in free space and without the need of an anechoic chamber. The setup employs with a Vector Network Analyser (VNA) synchronised to a rotating turntable that controls the position of the transmitting and receiving antennas and the polarisation of the irradiated electric field. Measurements are collected for chaff dipoles made of copper wire, microwire and aluminised glass, from 5 to 11 GHz, to allow a comparison of chaff RCS properties with respect to chaff material and method of fabrication. Measurements of the copper wire chaff also allowed a comparison with existing theoretical predictions of chaff reflectivity. An analysis and a comparison of the results is presented. Results show that the experimental trends of the chaff RCS curves agree with the theoretical RCS curves for perfectly conducting wires. They also show that copper wire provides the strongest reflective chaff followed by the aluminised glass and the microwire.

Low-profile and wide-angle of a low RCS antenna based on a broadband polarization conversion metasurface.

A broadband and high-efficiency polarization conversion metasurface (PCM) is used to reduce the radar cross section (RCS) and improve the radiation property of a patch antenna. The PCM is arranged in a checkerboard configuration comprised of square split-ring unit cells. The polarization conversion ratio (PCR) of the PCM unit is greater than 90% over a frequency range of 8.9 GHz to 21.8 GHz. The proposed patch antenna (PPA) has a low profile of 0.06 λL and is designed with the PCM loading on the surface of a patch antenna. The -10 dB RCS reduction bandwidth of the PPA is from 8.5 GHz to 22.0 GHz under normal incidence, and the low RCS property can be maintained as the oblique angles up to 60° for x- and y-polarized waves. Additionally, the PPA has a 10 dB return-loss bandwidth of 11.5-12.6 GHz and a peak gain of 8.02 dBi. The measured and numerical results confirm that the PPA exhibits wide-angle and broadband RCS reduction properties, while also improving the radiation properties at a low profile.

Absorption-transmission-diffusion-type radar cross section reduction metasurfaces based on frequency selective absorber and polarization conversion chessboard structure

Absorption-transmission-diffusion-type radar cross section (RCS) reduction metasurfaces based on the frequency selective absorber and the polarization conversion chessboard structure are proposed in this paper. The RCS reduction metasurfaces consist of three parts, i.e. the top layer realized by a cross-shaped meander line loaded with lumped resistors for low-frequency absorption and high-frequency transmission, the mid-layer constructed by angular ring vias frequency selective surface (FSS) sandwiched with two square patches FSS for broadband transmission in mid-frequency zone, and the bottom layer employed chessboard metasurfaces composed of dual-arrow type polarization conversion units for scattering cancellation in high frequency zone. The physical mechanisms of the RCS reduction metasurfaces with multifunctional electromagnetic controlling including wave absorption, bandpass transmission, polarization reversal, and phase cancellation are also discussed and analyzed. Simulation and experimental results demonstrate a reflection of lower than −10 dB for normal incident linearly polarized waves over a frequency range of 2.5 GHz–18 GHz, with a relative bandwidth of 151.22%; transmission passband properties with insertion loss better to −3 dB in the frequency range of 5.62 GHz–11.0 GHz, with a relative bandwidth of 64.74%. Due to the resonance-coupling-resonance principle, the broadband transmission with low insertion loss was obtained. The RCS properties of the proposed multi-functional metasurfaces were further analyzed by numerical simulation and experimental measurement, and the results showed that RCS reduction of over 10 dB was achieved for normal incident different polarized waves at the frequency range of 2.5 GHz to 17 GHz. Even in the case of normal incidence, there was a deviation between the reflection characteristics and RCS reduction. The RCS reduction metasurfaces are expected to be employed in applications where multi mechanism collaborative control of electromagnetic waves is of extreme importance.

RCS reduction using embedded meta-structure absorber in X-band

One approach for lowering radar cross section (RCS) is by reducing reflection, which can be achieved by use of absorbers. Embedded meta-structure absorbers (MSAs) are void of metallic resonating structures, which minimize out-of-band reflections thus reducing the chance of detection by radar systems. Here, an X-band MSA is developed by embedding ionic deep eutectic solvent gel as subwavelength cuboidal resonant structures in flexible silicone rubber. The material properties and structural geometry of the gel combines to enhance the dB absorption bandwidth to more than . The fabricated Gel-Si MSA is sufficiently flexible with an overall thickness of . dB RCS reduction is evaluated in the range over the X-band. The RCS properties are insensitive to polarization angles up to and incident angle up to .

A Fabry–Perot antenna using a frequency selective surface layer with wideband and Low RCS for Mm-wave applications

In this article, a Fabry-Pérot cavity antenna operating in the K-band is introduced, offering wideband, high gain with low RCS properties. The design consists of a patch antenna serving as a feed antenna and a bianisotropic frequency selective surface (FSS) layer incorporated to create a Fabry–Perot antenna for expanding the bandwidth, intensifying the gain, and minimizing radar cross-section (RCS). The proposed Fabry–Perot antenna is fabricated and measured, showing good agreement between simulated and measured results. The results show an impedance bandwidth of 23.6 % and a 3-dB gain of 14.1% at the center frequency of 28 GHz.

Shape Optimization of an Integrated Mast for RCS Reduction of a Stealth Naval Vessel

In this paper, we analyze the radar cross section (RCS) of an integrated mast and present the optimized mast shape for RCS reduction. The RCS is simulated using commercial electromagnetic (EM) software based on the shooting and bouncing rays (SBR) method and the diffraction fields at the edges are also considered. Threat frequencies, threat regions and cardinal points are first defined considering the operational environments of a naval vessel. We calculate and analyze the RCS of the integrated mast in terms of the threat frequencies, the shapes of the integrated mast and the direction and polarization of the incident waves. The shape of the integrated mast is optimized based on the shaping technique. The optimized mast has low RCS properties in the primary threat sectors except for the exceptional angle regions.

A Mesh-Type Low RCS Reflectarray Antenna Based on Spoof Surface Plasmon Polariton

This letter presents a low radar cross section (RCS) reflectarray antenna consisting of a feed horn and a spoof surface plasmon polariton (SSPP) reflector. The mesh-type reflector, composed of ${\rm{14\ \times \ 14}}$ bandstop elements, is transparent in the optical band. Owing to the SSPP modes excited by the metallic grating structures (MGSs), each element has high reflectivity in its stopband and high transmittivity in its passband. Moreover, the reflection phase of each element can be adjusted by varying the length of the MGSs. Therefore, the reflector can convert spherical waves into plane waves in the working band and transmit the out-of-band incident waves, thus obtaining low RCS properties. The simulated results indicate that the proposed antenna has a maximum gain of 25.2 dBi, a maximum aperture efficiency of 44.5%, and a 1 dB gain bandwidth of 13.9% (9.4-10.8 GHz). Compared to the reference antenna, the RCS of the proposed antenna is obviously reduced in the frequency ranges of 1.0-8.5 GHz and 12.0-19.0 GHz.

Design of Tapered Periodic Meta-Surfaces for Suppressing Edge Electromagnetic Scattering

In this paper, a novel approach for designing tapered periodic meta-surfaces (TPMS) is proposed for suppressing electromagnetic scattering from a trailing edge of a square metallic plate with a given thickness. The TPMS is realized by periodic square metallic patches with tapered dimensions at the direction perpendicular to the considered edge but keeping its period unchanged. Based on the geometric phase interaction, the mechanism of suppressing electromagnetic scattering is analyzed. The lossy material is not required in this design, so it doesn’t generate thermal energy and benefits infrared stealth of military objects. The backscattering properties from the trailing edge with the proposed TPMS loading are analyzed and compared with that of original trailing edge. It is observed that wide angular trailing edge scattering suppressing can be obtained and the average value of mono-static radar cross section (RCS) reduction is 10 dB for L-band, S-band and C-band. Finally, the bi-static RCS properties and energy distribution of the proposed structure are also proposed to explain the mechanism of the electromagnetic scattering suppression of the trailing edge employed with the TPMS.

Metamaterial‐based patch antenna with wideband RCS reduction and gain enhancement using improved loading method

The simultaneous improvement of radiating and scattering performance of an antenna is normally considered as a contradiction. In this study, wideband radar cross-section (RCS) reduction and gain enhancement are both achieved for a conventional patch antenna by loading metamaterial in an improved way. First, two artificial magnetic conductor units are selected to construct a chessboard-like metamaterial surface (CLMS) which has wideband low RCS property. Then the CLMS is applied to a conventional patch antenna for the purpose of RCS reduction. Through a detailed investigation of three loading manners, a metamaterial-based patch antenna with both improved RCS and gain is proposed and experimentally validated. Both simulated and measured results show that, compared with the original antenna, the gain of the proposed antenna is enhanced almost over the whole operation band, and the wideband (in-band and out-of-band) RCS reduction is achieved concurrently.

A low radar cross-section artificial magnetic conductor reflection screen covering X and Ku band

Based on the properties of the artificial magnetic conductor (AMC), a broadband low radar cross-section (RCS) reflection screen covering X and Ku band is designed and fabricated. The reflection screen is formed by combining two AMC cells, i.e., AMC1 with a dual band Jerusalem cross structure, and AMC2 with a wideband metal square patch structure. By optimizing the structures of these AMC cells, it is achieved that the frequency corresponding to the inversion point of the AMC1 reflection phase curve is equal or close to the frequency corresponding to the null point of the AMC2 reflection phase curve. Therefore, the valid reflection phase difference band is broadened and the RCS is reduced in a wider band. In addition, presented in this paper is a theoretical formula to calculate the reflection energy peak direction. When the incident angle, chessboard unit dimension and observed frequency are fixed, the reflection energy peak direction can be calculated by the formula. The calculation results from the theoretical formula are consistent with the HFSS simulation results, so the theoretical formula is valid. The simulation results indicate that, compared with the same-dimension metal RCS, the backscattering RCS is reduced by more than 10 dB in a frequency range of 7.4-17.0 GHz, except minority frequencies close to 9.8 GHz. The 10 dB-reducing RCS bandwidth covers the entire X band and most of Ku band, and the relative bandwidth is 78.7%. The largest reduction reaches 40.3 dB at 11.6 GHz. The simulations and the measurements are in good agreement. The results validate the broadband low RCS property of the reflection screen.

A broad-band gain improvement and wide-band, wide-angle low radar cross section microstrip antenna

A novel high-gain and low radar cross section (RCS) microstrip antenna is designed and fabricated. The proposed antenna obtained broad-band 3 dB gain bandwidth and wide-band, wide-angle low RCS properties after applying the frequency selective surface (FSS) as a superstrate of original microstrip antenna. The FSS cell is composed of two metallic layers separated by a dielectric substrate. A metallic square loop with four resistors mounted on each side of the loop is enched on the top layer and a metallic plane with a central cross slot and four fringe slots is enched on the bottom layer. The four resistors of top layer are mainly used to absorb radar incoming wave and reduce antenna RCS. The patch of bottom layer can constructe a Fabry-Perot resonance cavity with ground plane and improve the antenna gain. The reflection coefficient S22 and transmission coefficient S12 of top layer are all below -10 dB at 5.75-11.37 GHz. The reflection phase gradient of bottom layer is positive and the reflection magnitude value is above 0.86 from 11.21 GHz to 11.54 GHz. Measurement results show that the antenna gain is enhanced by about 3.4 dB at 11.73 GHz, and the half-power beam width of E-plane and H-plane is reduced 16° and 50° respectively. The 3 dB gain bandwidth is about 2.4 GHz which from 10.0 GHz to 12.4 GHz and well cover the impedance bandwidth. The proposed antenan achieved an RCS reduction of more than 3 dB in the normal direction at 4.10-11.30 GHz, the largest reduction reached 23.08 dB in comparison with the original antenna. The monostatic and bistatic RCS reduction are over 3 dB from -20° to 20° and -37° to 37° respectively at 4.95 GHz. The results proved the FSS superstrate can be applied to improve the radiation and scattering performance simultaneously.

Broadband low-RCS metamaterial absorber based on electromagnetic resonance separation

We have designed and fabricated a broadband low radar cross section (RCS) metamaterial absorber with polarization-independent characteristic based on electromagnetic resonance. The absorbing mechanism is investigated by means of electric as well as magnetic field distributions and retrieval algorithm. Absorbing and RCS properties of this absorber are performed by waveguide experiment and free space measurements, respectively. Theoretical analysis indicates that the absorber can produce electric and magnetic resonances in different locations for fixed frequency, while for different frequencies, it can provide energy losses in different dielectric layers, which effectively lowers the electromagnetic couplings and consequently keep the strong absorbing properties in a wide frequency range. Experimental results show that the designed absorber with 3-layer structure achieves a frequency range which is 4.25 times as that of 1-layer absorber with absorptivity above 90%, its relative bandwidth for RCS reduction above 10dB is 5.1%. The cell size and thickness of the designed absorber are very small, i.e., 0.17 and 0.015 of the working wavelength. Thus the low-RCS property of the absorber is wide-angle and polarization-independent. In addition, the working frequency range of the absorber can be adjusted by properly designing the layers.

LOW RCS METAMATERIAL ABSORBER AND EXTENDING BANDWIDTH BASED ON ELECTROMAGNETIC RESONANCES

A low radar cross section (RCS) metamaterial absorber (MMA) with an enhanced bandwidth is presented both numerically and experimentally. The MMA is realized by assembling three simple square loops in a three-layer structure according to the idea of separating electric and magnetic resonances. Difierent from one- layer MMA, the proposed MMA can efiectively couple with the electric and magnetic components of the incident wave in difierent positions for flxed frequency, while, for difierent frequencies, it can trap the input power into difierent dielectric layers and absorb it in the lossy substrate. Experimental results indicate that the MMA exhibits a bandwidth of absorbance above 90% which is 4.25 times as that of one-layer MMA, and 10dB RCS reduction is achieved over the range of 4.77{5.06GHz. Moreover, the cell dimensions and total thickness of the MMA are only 0:17‚ and 0:015‚, respectively. The low RCS properties of the MMA are insensitive to both polarization and incident angles.

Using Scaled Models for Wind Turbine EM Scattering Characterization: Techniques and Experiments

Characterizing the Radar Cross Section (RCS) wind turbine structures is the first step to mitigate the impact of wind farms on radar operations. An efficient technique based on scaled wind turbine models in both laboratory and computer environment is studied. The scaled 3-D computer model is used in different electromagnetic solvers to predict the RCS properties, given radar parameters. The scaled laboratory model is placed in a controlled laboratory environment, and accurate RCS measurements of the scaled models are used to emulate wind turbine radar signatures. Comparisons between approximate numeric model prediction and measurement results are presented, and a method for predicting full-size wind turbine scattering properties based on scaled models is discussed.

An Outdoor Bistatic Scattering Assessment Using Array Antennas

Passive coherent location (PCL), which is also known as passive radar, is of in- creasing interest lately. In a passive radar system, the transmitting and receiving antennas are placed at difierent locations. Therefore, it detects targets' bistatic scattering instead of monos- tatic scattering in conventional radars. In this work, we conducted experiments that evaluate the bistatic radar cross section (RCS) from targets in the UHF band. The variation in the amount of bistatic scattering was examined and analyzed by changing the parameters which include the target's shape, orientation, distance to antenna, and antenna polarization. 1. INTRODUCTION In 1936, German deployed radio frequency radar at warship Graf Spee for the flrst time. Since then, the radar technology has dramatically evolved and played an important role on the battle- fleld. Among the many difierent types of radar, the air surveillance radar is of crucial importance. However, the conventional air surveillance radar, which continuously emits strong radiation in the order of hundreds of kilowatts or even megawatts, is likely to expose its location. Therefore, the concept of passive radar has been brought up and implemented. Unlike tradition active radars, passive radars do not require high power transmitters and come with receivers only. Passive radar receivers continuously monitor the background radio signals, such as commercial TV broadcasting, mobile telecommunication or satellite signals. The presence of air targets may perturb the magni- tudes, phases and even frequencies of background signals. A passive radar may therefore be able to detect the perturbation and determine if an air target is present. In the passive radar operation scenario, the transmitting and receiving antennas are not placed at the same position. Unlike traditional radars, which detect the monostatic back scattering from the target, passive radars exploit the bistatic RCS property of targets (1{4). In this paper, we designed a series of experiments that measures the bistatic RCS values of elevated targets in the UHF band. The experiment set-up includes two antennas, one is for transmission, and the other is for reception. Because the signal magnitude may be very weak due to propagation, an RF transmitter of 10 watts at the UHF band was assembled to conduct measurements. The components used in the transmitter include two stages of amplifler, attenuators, a power supply, a circulator and a termination. The mock-up targets that scatter impinging radio frequency waves are placed in front of directive antennas. A network analyzer was employed to provide radio source and measure the properties of scattered signals. In order to minimize scatterings from background clutters experiments were conducted on a roof top. The design and performance improving measures of the antennas used in experiments are pre- sented in Section 2. The measurement range set up as well as measurement results and analysis are provided in Section 3. A conclusion and future work topics are drawn in the end. 2. DIPOLE ARRAY ANTENNA FOR BISTATIC RCS MEASUREMENTS