374~747 MHz digital tunable microstrip filter

Abstract

A novel digital microstrip tunable bandpass filter based on digitally tunable capacitor loading microstrip open ring resonators was proposed.The novel non-uniform open ring resonances with mixed coupling structure was used to make the coupling coefficient of the resonators increases with the decreasing of resonance frequency and achieve a con-stant absolute bandwidth tunable filter.Then the proposed digital tunable microstrip filters based on 5 bit digitally tunable capacitance was simulated and manufactured.The measurement shows that the −3 dB absolute bandwidth varies from 44~67 MHz while the central frequency of the passband varying from 374~747 MHz,the OIP3 is greater than 50 dBm.

Keywords

• constant absolute bandwidth;digitally tunable capacitor;bandpass filter;microstrip open ring resonators