A novel Ka-band bandpass filter using microstrip closed loop resonators

This paper presents a novel Ka-band bandpass filter with the center frequency of 35 GHz using microstrip closed loop resonators. The closed loop resonator features low radiation loss characteristics, and has an advantage over half- and quarter-wavelength resonators for its enabling the elimination of parasitic components which are usually induced at the open- and short-circuited ends. And the proposed bandpass filter has the merits of good passband characteristics and high stopband rejection. Experimental measurements on the fabricated filter agree well with simulated results. The novel filter will be suitable for high-performance microwave circuit applications.