Compact Microstrip Balanced Bandpass Filter with Stepped Impedance Resonator for Wireless Application

In this paper, a compact balanced Bandpass Filter (BPF) using stepped impedance resonator is presented. The proposed balanced BPF can reject common-mode signals and noise, which affect both input lines equally. This structure is composed of simple stepped impedance resonators and open stubs. The proposed balanced BPF has a center frequency of 8.1 GHz, operating frequency from 7.3 GHz to 8.9 GHz, which provides 1600 MHz bandwidth equal to 20% Fractional Bandwidth (FBW). The return loss and insertion loss in the passband for the proposed balanced BPF are less than 12 dB and 0.4 dB, respectively. The filter is designed based on RT/duroid 5880 with a relative dielectric constant of 2.2, thickness of 31 mil and loss tang of 0.0009. The designed BPF has a compact size and the size of the presented filter is 7.5 mmx14.8 mm. The presented design offers desirable prospects for applications in compact and efficient communication systems, where size constraints, low unwanted radiation levels, and high noise immunity are critical considerations.