Design of Low Cross Polarization Phased Antenna Arrays for X-band Spaceborne SAR Applications

In this paper, a type of low cross polarization phased antenna arrays for X-band spaceborne synthetic aperture radar (SAR) applications is presented. The horizontal polarization radiation performance is realized with ridged-waveguide longitudinal slotted antenna arrays. The arrays are divided into several subarrays according to the scanning requirements of the phased array antennas, and V type slot is employed in ridged-waveguide wide wall as radiation unit. Excellent capacities such as matching characteristics, high efficiency and low cross polarization are achieved by adjusting the penetration angle and depth of the V slot. In the azimuth direction, the slotted waveguide antenna is designed as a linear array, and the low profile characteristics of antenna is realized by adopting stereoscopic coupling feeding technology. In the range direction, the narrow-wall dimensions of the ridged-waveguide is compressed by the ridged-waveguide to optical-waveguide mode conversion technology, and the preferable grating lobe performance is assured. A panel of 10 × 32 ridged-waveguide slotted antenna arrays with the active transceiver module are designed and fabricated, which are composed with 10 subarrays in azimuth direction and 32 subarrays in range direction, and each subarray contains 20 V slotted radiators, the total size of the phased antenna arrays is 121.6λ
0
× 23.4λ
0
. The measured result shows a good agreement with the designed and calculated values, the normal efficiency exceeds 80% and the cross polarization level is lower than −30 dB in working band-with, and the modular design and compact structure, it is suitable for sapceborne SAR system, and the arrays in orbit is in good use.