A new two-layer bandpass filter using stepped impedance hairpin resonators for wireless applications

In this paper, we propose a new compact two-layer band-pass filter using stepped impedance hairpin resonators. This structure is composed of four resonators located on two microstrip stacked layer substrates, and the couplings between the resonators on the upper layer and those on the lower one are obtained by using two coupling apertures etched on a common ground plane placed between the two layers. A full-wave simulator is used to design the proposed structure and calculate the aperture coupling coefficients. To demonstrate the proposed design, a four-order band-pass filter prototype was fabricated and measured. The simulated results are compared with the measured data, and a good agreement is reported.