Compact microstrip ultra-wideband bandpass filter using short-circuited coupled-line hairpin resonator

This paper presents a compact topology of a very wideband bandpass filter intended for the use in ultra-wideband applications. Basic filter configuration consists of quarter-wave coupled-line units forming hairpin structure with short-circuited ends. To improve the out-of-band rejection, a compact couple-line hairpin bandstop filter is added. Design equations are derived using lossless transmission line model. A compact filter unit operating at 1.0 GHz is designed and implemented in microstrip. Theoretical results are validated using full-wave electromagnetic simulation. The results show an insertion loss below 0.74 dB, return loss better than 15.8 dB, and the up to sixth harmonic rejection better than 20 dB.