Mutual Coupling Reduction of a Circularly Polarized Four-Element Antenna Array Using Metamaterial Absorber for Unmanned Vehicles

A double-layer metamaterial absorber is proposed to suppress the mutual coupling within a circularly polarized (CP) four-element antenna array operating at the Chinese Beidou navigation satellite system (BDS) B3 band, wherein four miniaturized patch antenna elements are positioned in a rotationally symmetric distribution. The single-feed antenna element utilizes simultaneously a thick air substrate to widen the achievable CP bandwidth, four parasitic grounded strips to reduce the size occupation, and a capacitive probe feed to enhance the impedance matching. A wall of the double-layer metamaterial absorber using slotted cross patch structure is introduced in between the four CP antenna elements. An antenna array prototype with an overall footprint size of 0.81λ
₀
× 0.81λ
₀
(λ
₀
denotes the free-space wavelength at 1268 MHz) is implemented and validated experimentally. The measured results in a good agreement with the simulated ones demonstrate a mutual coupling reduction of 11 and 8 dB, for the parallel-directed and orthogonal-directed antenna element pairs across the entire operation band, and meanwhile a good CP performance is also achieved. Details of the design considerations as well as the simulation and measurement results are presented and discussed. The proposed antenna array can be well suited for BDS anti-jam antenna applications in unmanned vehicles.