Hairpin microstrip bandpass filter for millimeter-wave applications

A compact microstrip bandpass filter is proposed in this paper for millimeter-wave applications. The filter consists of three new non-uniform coupled-line modified hairpin resonators. The filter is designed to exhibit a fractional bandwidth of about 5.0 % at a center of frequency of approximately 34 GHz. The shapes of the hairpin resonators are modified to suppress the unwanted spurious harmonic response. As a result, the filter exhibits very wide stopband with a rejection level better than 10-dB. In addition, the filter shows a transmission zero close to upper edge of the desired passband which enhances the selectivity of the passband. The filter design is successfully realized on a RT/Duroid 6002 with a dielectric constant of 2.94 and a thickness of 127μm. The filter is simulated, and fabricated to demonstrate the proposed technique where excellent agreement is obtained.