This paper proposes a new design of dual-band reactively loaded annular slot antenna (ASA) for dual-sense circular polarization radiation. Two concentric annular slots excited by a common microstrip feedline are employed to realize dual-band operation. Each slot can radiate a circularly polarized (CP) wave with a specified sense at its one or one-and-a-half wavelength resonance, given that an appropriately valued reactive component, i.e. capacitor or inductor, is introduced at a pre-determined location. A small frequency ratio (FR) can be achieved between the two oppositely-sensed CP bands when a capacitor and an inductor are loaded, respectively, onto the inner and outer annular slots. Contrarily, two oppositely-sensed CP bands that possess a large FR can be yielded when an inductor and a capacitor are loaded onto the inner and outer annular slots, respectively. For experimental verification, two antenna prototypes with FRs of 1.63 and 2.41 have been designed, fabricated, and measured. The measurement results exhibit a good agreement with the simulation ones. Details of design concerns and experimental results are presented and discussed.

This paper presents a radar cross-section (RCS) reduction technique by using the coding diffusion metasurface, which is optimised through a random optimization algorithm. The design consists of two unit cells, which are elements ‘1’ and ‘0’. The reflection phase between the two-unit cells has a 180° ± 37° phase difference. It has a working frequency band from 8.6 GHz to 22.5 GHz, with more than 9 dB RCS reduction. The monostatic RCS reduction has a wider bandwidth of coding diffusion metasurface as compared to the traditional chessboard metasurface. In addition, the bistatic performance of the designed metasurfaces is observed at 15.4 GHz, which shows obvious RCS reduction when compared to a metallic plate of the same size. The simulated and measured result shows the proficiency of the designed metasurface.

The design of a metasurface with low radar cross section (RCS) property is presented in this paper. The low scattering of the metasurface is achieved by applying the artificial magnetic conductor (AMC) unit cells in three different configurations. Two different AMC unit cells with an effective phase difference of 180 ± 37° are first designed to analyze the out of phase reflection in a wideband frequency range from 5.9 to 12.2 GHz. Then, the unit cells are placed in a chessboard-like configuration, newly constructed rotated rectangular-shaped configuration, and optimized configuration to study and compare the RCS reduction performance. All designs of the metasurface with different configurations show obvious RCS reduction as compared with the metallic plate of the same size. However, the relative bandwidth of the optimized metasurface is larger than the chessboard-like configuration and rotated rectangular-shaped configuration. To certify the results of the simulations, the metasurface with the optimized configuration is fabricated further to measure the RCS reduction bandwidth. The measured results are in good accordance with the simulated results. Therefore, the proposed metasurface can be a good option for applications where low RCS is desirable.

This article proposes a design of a microstrip patch antenna with reduced radar cross‐section (RCS) in a wide frequency band. The RCS of the patch antenna is reduced with the integration of an optimised coding metasurface. The coding metasurface is designed by placing artificial magnetic conductor (AMC) unit cells together to achieve a phase difference between 180 ± 37° within a wide frequency range. The out‐of‐band RCS for the proposed patch antenna is reduced >7 dB from 12.2 to 19.8 GHz, corresponding to a relative bandwidth of 48%, with a maximum reduction of 20 dB at 18 GHz. The operating frequency of the proposed antenna is 8.7 GHz and the RCS reduction is mainly in the Ku band. Both monostatic and bistatic RCS performance of the proposed patch antenna have been simulated and studied. The radiation performance of the proposed patch antenna is hardly influenced by the employment of the proposed coding metasurface. Details of the design considerations along with the simulation and measurement results are presented and discussed. The measured results are in a good agreement with the simulated ones, verifying the validity of the proposed antenna.

A low radar cross section (RCS) circularly polarized patch antenna array operating at the downlink S-band (2492 ± 5 MHz) of the Chinese Compass Navigation Satellite System (CNSS) is proposed. The low RCS is achieved by replacing the conventional metallic ground with an artificial magnetic conductor (AMC)-based metasurface. Two different AMC unit cells are designed having a phase difference within 180 ± 37° and combined in a chessboard-like configuration to realize the AMC-based metasurface. Furthermore, the AMC-based metasurface is utilized as the ground of the CNSS array for wideband RCS reduction. A wideband RCS reduction from 6 GHz to 17 GHz is achieved due to the wideband diffusion property of the AMC unit cells. The maximum RCS reduction is more than 14 dB at 13.3 GHz irrespective of the polarization direction of the incident waves. Moreover, the circular polarization (CP) performance is realized by embedding a circular slot on the patch radiator of the antenna element. The radiation characteristics of the CNSS array are hardly impacted by the inclusion of the metasurface-based ground. The proposed CNSS array has been fabricated and measured. The measurement results are in reasonable agreement with the simulations. The proposed CNSS array can be a good candidate for CNSS adaptive antenna applications where low RCS is simultaneously demanded.