RCS reduction of microstrip antenna using split square loop thin absorber

Abstract

This study proposes an electrically thin frequency-selective surface-based microwave absorber without using resistive surface and lumped resistors to make it simple and inexpensive. The ground plane of the microstrip antenna (MSA) serves as the metallic back of the absorber. The top two layers of the proposed absorber are printed on both sides of the top FR4 sheet in a square annular ring form to encircle the square patch. Both simulations and measurements are carried out to obtain the scattering parameters, which are used to retrieve the absorption coefficient, relative permittivity (ɛ r), and relative permeability (μ r). An equivalent circuit model for the proposed absorber is constructed and validated. The absorption performance is insensitive to the angle of incidence (θ) up to 50°. The absorption mechanisms are studied based on the surface current distribution, electric field distribution, and constitutive parameters. The absorber is then integrated with an MSA operating at 4.2 GHz, which gives a maximum monostatic radar cross-section (RCS) reduction of 15 dB. Numerical and experimental results of the radiation performance and the RCS of the absorber integrated antenna structure have been presented. A very good agreement between simulation and measurement results is observed.