Abstract: Comparator is widely used in radar field. The operational principle of eight-port comparator is introduced first, and a new concept called port quasi-symmetry is proposed, and the theoretical analysis and demonstration are carried out. An overall design scheme of ultra-wideband eight-port comparator is proposed based on port quasi-symmetry, which makes the number of de-sign parameters decreases from plurality to one. It simplifies the design largely. An ultra-wideband eight-port comparator based on double-sided parallel-strip line is actually fabricated whose center frequency is 3 GHz. Over the measured results, the operating frequency range is from 1. 5 GHz to 4. 5 GHz (the return loss is less than -10 dB), the relative bandwidth is 100%, the phase er-ror is less than ±4°. The measured results are consistent with the simulation results and theoretical analysis results, which verifies the correctness of the theory.