X-Band Low-Probability Intercept Marine Radar Antenna Design With Improved Bandwidth and High Isolation

A series-parallel hybrid-fed microstrip array antenna design is presented for X-band low-probability intercept (LPI) marine radars. Contrary to traditional counterparts, the proposed antenna has improved impedance and radiation bandwidth from 9.1 to 9.6 GHz to accommodate pulse compression and frequency diversity for LPI radars. The antenna structure consists of
$24\times4$
patch elements with horizontal polarization. The two halves of the structure are fed in parallel and each arm is fed in a series-series feed network to achieve low sidelobe level (SLL) of −26.5 dB. The manufactured antenna has a gain of 24.0 dBi with half-power beamwidth (HPBW) of 4.5° and 21.5° in azimuth and elevation, respectively. The measured gain flatness is ±0.3 dB over the radionavigation band and ±1.0 dB over the entire band. A novel grid baffle structure with capacitive surface impedance is proposed and implemented to provide high isolation over the target bandwidth. The maximum and average isolations between transmit and receive antennas are measured as 65 and 62 dB, respectively. The proposed antenna is very suitable for dual-mode pulsed and continuous-mode LPI marine radars.