A Fully Packaged Bandpass Filter on Stripline Patch Resonator With Wide Upper Stopband

In this letter, a fully packaged dual-mode bandpass filter (BPF) with wide upper stopband is presented. The stripline patch resonator loaded by the shorting slabs is adopted to achieve the dual-mode bandpass performance under operation of TM00 mode and TM01 mode. To remove other harmonic resonances of the stripline patch resonator, a common-mode double-point inset-feeding technique is proposed at the very beginning to prevent the excitation of high-order modes. To verify the design concept, a prototype packaged dual-mode BPF working at 4.0 GHz with the fractional bandwidth (FBW) of 8.2% is designed and fabricated using the multilayer liquid crystal polymer (LCP) circuit technology. Final results theoretically demonstrate and experimentally confirm that a wide stopband rejection up to $4.3f_{0}$ is obtained, well verifying the feeding method.