Design of Broadband X-Band Subarray Antenna with Hybrid-Sequential Rotation Fed for Airborne CP-SAR

The design of a broadband circularly-polarized subarray antenna for airborne synthetic aperture radar is presented in this paper. The proposed antenna operates in X-band at the center frequency of 9.5 GHz with a bandwidth of 400 MHz. The subarray antenna employs 16 patches with 4×4 matrix formation and uniform patch separation of 0.7λ
s
. The hybrid sequential rotation technique on the feeding network is proposed to obtain a wide axial-ratio bandwidth and a balanced radiation pattern. The proposed antenna consists of two stacked substrates with identical specifications. Generation of circular polarization wave applies a curved-truncation patch on the radiator patch printed on the top layer bottom substrate. Broadening impedance bandwidth and gain enhancement are improved by an additional parasitic patch with circle-slotted printed on the upper layer. A floating copper on the upper layer is also attempted to improve the gain. Simulation results achieve the impedance bandwidth of 3.533 GHz (37.2%), axial-ratio bandwidth of 3.436 GHz (36.17%), the gain of 19.16 dBic, and the antenna size of 107 mm x 107 mm. The half-power beam-width in both azimuth and range direction is 16.4° and 15.9° at the center frequency of 9.5 GHz.