Rectangular-Cavity Bandpass Filters With Large Metal Cylinders and Different Fillets

This letter proposes a class of rectangular-cavity bandpass filters (RCBPFs). First, an initial tri-band RCBPF is designed by feeding an empty rectangular cavity (RC) with two orthogonal probes. Second, a dual-band RCBPF is designed by loading two large metal cylinders (LMCs) into the RC. The LMCs change the electric field distributions and resonant frequencies of six resonant modes. Moreover, by increasing the radii of two fillets on the RC, the two transmission zeros (TZs) between two passbands are eliminated. Therefore, a wideband RCBPF is realized. Both proposed RCBPFs exhibit wide stopband due to the effective suppression of out-of-band spurious modes. The performance of these RCBPFs is validated through fabrication and measurement.