Design of High Order Cross-Coupled Constant Absolute Bandwidth Frequency-Agile Bandpass Filters

Novel high order constant absolute bandwidth (ABW) cross-coupled electrical tunable bandpass filters (BPFs) are proposed. Microstrip cross-coupled tunable resonators are designed and investigated to meet the coupling requirement of the tunable BPF with constant ABW. A thorough theoretical analysis is derived to determine the performance of the proposed filter and verify the initial values of design parameters. To verify the design concept, two prototypes are fabricated and measured. The measurements show that the proposed four-order filter has a -3 dB ABW of 119.5±2.5 MHz with 1.31~1.98 GHz tuning frequency. And the proposed six-order filter has a -3 dB ABW of 102±6 MHz with 1.39~2.07 GHz tuning frequency. High selectivity has been achieved in the proposed filter by TZs (transmission zeros) beside the passband, good agreement between simulated and measured results has been demonstrated.