In this article, a compact and low-profile beam steering circularly polarized folded reflectarray antenna (CPFRA) with low scan loss for wide-angle coverage is proposed and designed. In order to obtain lower scan loss over a wider beam coverage range (BCR), a multibeam optimization method considering the illumination weighting factor is introduced to obtain minimum phase errors for the designed beam direction. To improve antenna compactness and alleviate the mutual couplings among multiple feeding sources, small-size substrate integrated waveguide (SIW) cavity-backed slot antennas are employed as the feeding sources, which are integrated with the single-layer reflector board. An incident-angle-insensitive circular polarizer is designed and integrated over the antenna aperture to achieve circularly polarized (CP) radiation over a wide BCR. Finally, a 15-beam CPFRA working at the Ka-band with a size of 140 mm $\times140$ mm is designed, manufactured, and measured to validate the proposed design method. Measurement results show that the designed CPFRA can achieve a rather flat gain, with only a 2.1 dB scan loss, across the wide 3 dB BCR of ±29°. The good CP beams are formed over the entire coverage range without any blind zone. With the advantages of wide-angle coverage, low scan loss, and high integration, the proposed beam steering antenna is promising in applications such as 5G communication, radar imaging, and target recognition.

A new design method for ultrabroadband radar cross section (RCS) reduction by exploiting characteristic complementary polarization conversion metasurfaces (PCMs) is proposed and validated. The proposed method lifts the conventional bandwidth limitation enforced by the performance of a single PCM and expands the RCS reduction bandwidth. A systematic strategy for ultrabroadband RCS reduction design is developed and an effective reflection coefficient amplitude of the composite surface ( $\Gamma _{ {eff}}$ ) is derived as a new RCS reduction indicator. Based on this indicator, complete polarization conversion (CPC) frequency points of PCM are identified as important characteristics, and PCM pairs with interleaved CPC points, termed as initial PCM (I-PCM) and complementary PCM (C-PCM), are designed to compensate each other for ultrabroadband RCS reduction. A scaling-and-tuning two-step method for designing the C-PCM of a specific I-PCM is developed and validated. To further improve RCS reduction performance, taking the ${\Gamma _{ {eff}}}$ as an indicator, the particle swarm optimization (PSO) algorithm is used to select the optimal I-PCMs, C-PCMs, and their area ratios. Finally, an ultrabroadband RCS reduction surface is designed, fabricated, measured, and validated. It realizes 10-dB monostatic RCS reduction ranging from 7.6 to 26.2 GHz (110.7% relative bandwidth) which exceeds the polarization conversion bandwidth of each individual PCM. Besides, good polarization insensitivity and bistatic RCS reduction performance are also obtained. The proposed method provides a new route for designing broadband RCS reduction surface based on PCMs with unsatisfactory characteristics and greatly alleviates the performance requirement for PCMs.

A novel electronically controlled (EC) leaky-wave antenna (LWA) based on Corrugated Substrate Integrated Waveguide (CSIW) with fixed-frequency beam-steerable capability is presented in this letter. This structure is based on a CSIW structure with rectangular ring slots and metallic vias to the ground, which realizes two isolated DC equipotential planes. Each slot of the rectangular ring is loaded with a varactor diode, and thus the series and shunt capacitance are tunable by adjusting the DC bias voltage, which eventually results in beam scanning at a fixed frequency. The proposed antenna is a single-layer structure and has a simplified DC bias network, which merely needs an inductor and a short microstrip line. An electronically controlled beam-steerable CSIW LWA is designed and experimentally validated. It is experimentally demonstrated that the radiation angle ranges from -40.66° to 31.32° as the bias voltage is tuned from 32 V to 7.5 V at 4.5 GHz.

A novel forward method to establish the three-dimensional(3-D) parametric scattering center models is developed to extract scattering centers from the combined target/rough surface models. Both scattering centers from ship including single-order and higher-order scattering contributions, and from the multiple interactions between ship and random rough sea surface, would be described concisely with physically relevant parameters by this proposed method. Due to the statistical nature of the random rough surface for the Monte Carlo simulation, we acquire a large number of realizations for estimations of the amplitude and position parameters to overcome the problem that single realization cannot extract scattering centers effectively. This method is validated through parametric models of the ship in free space and on the sea surface and good agreement has been demonstrated between the constructed and simulated radar characteristics. Further, we analyze the composite target/surface model's physics and feature stability in visually spatial range and direct connections between scattering centers and scattering sources, which would be valuable to future target recognitions and classifications. Finally, we quantitatively calculate and analyze the coupling scattering centers from interactions between ship and the ocean-like surface that provide more abundant contour information of the ISAR image to facilitate contour detections.

A super diffuse broadband radar cross section (RCS) reduction surface design method based on rotated phase coding polarization conversion metasurfaces (PCMs) is proposed. Multiple PCMs with coding phases are employed for wideband RCS reduction, and the spatial locations of the PCMs are utilized for bistatic RCS reduction since it arouses spatial phase. Further, it is derived that the Pancharatnam-Berry (P-B) phase provides extra design freedom for bistatic RCS reduction. These three types of phases are combined for optimal wideband bistatic RCS reduction. To facilitate bistatic RCS reduction design. the variance of the scattered field (δ _E ) is derived as an indicator for the evenness of the whole space electric field distribution, and an optimal design method is developed thereafter. For comparison, two RCS reduction surfaces, termed as MS1 and MS2 respectively, composed of phase coding PCMs are designed, fabricated, and measured to demonstrate the effectiveness of the proposed method. The MS1 is designed by only using spatial phase, and multiple coding phases, while MS2 is designed by further exploiting the P-B phase. The MS2 achieves 10-dB monostatic RCS reduction ranging from 8.8 to 25.4 GHz (97.1% relative bandwidth, which is 2.2% better than that of the MS1). More importantly, the MS2 realizes super diffuse characteristic under different incidences. It achieves 10-dB bistatic RCS reduction ranging from 9 to 25 GHz (94.2% relative bandwidth), and the maximum bistatic RCS reduction can reach upto 20 dB. The proposed broadband super diffuse RCS reduction design method is particularly desirable for both monostatic and bistatic RCS reduction of various complex coupling structures.

This article presents a forward modeling method for the scattering center (SC) model of coated targets on rough ground, tailored for remote sensing and target recognition applications. The methodology initiates with the geometric model and coating impedance parameters of the ground target, employing a forward approach to decompose overall scattering into multiple component-level sources. Integrating high-frequency electromagnetic (EM) theory, quantitative computation, and derivation of SC parameters constructs a parameterized 3-D model for coated targets on rough ground. Illustrated through the example of a T72 tank and considering the effects of coated media and ground coupling, a forward SC model for the tank target on rough ground is developed. The model’s statistical characteristics are meticulously analyzed, and its accuracy is validated using real measurement data from publicly available datasets. The proposed model offers several advantages. First, it directly reflects the local geometry and coated material characteristics of target components, providing detailed information about component shapes and materials. Second, the modeling process meticulously considers and segregates the contributions of the target’s complex coupled SCs with the ground. A statistical analysis demonstrates consistent parameter convergence, aligning with theoretical expectations. Third, this research extends the forward modeling approach to coated targets on rough ground, enabling the model not only for component-level identification but also for rapid target synthetic aperture radar (SAR) echo reconstruction. In conclusion, this cost-effective approach provides a practical means for the rapid estimation and analysis of radar characteristics, target detection and recognition, target remote sensing, and other applications in complex environments.