Compact Triple-mode Bandpass Filter Based on a Capacitive-loaded Isosceles Right-Angled Triangular Patch Resonator

A compact triple-mode bandpass filter (BPF) is proposed in this paper based on a capacitive-loaded isosceles right-angled triangular (IRAT) patch resonator. In order to realize triple-mode response, metallic vias array is introduced along the symmetrical axis. An additional mode nominated as LC mode is generated, making the perturbed IRAT resonator operate below its former fundamental resonate frequency, and thus miniaturization has been achieved. Through the metallic vias array and the capacitive-loaded patch, the first mode (LC mode) and the third mode (TM
₀₁₀
) are shifted toward the second mode (TM
₁₁₀
) to form a passband. Moreover, three transmission zeros (TZs) can be obtained in the upper stopband. As a result, the designed filter has featured both compact size and high selectivity characteristics with three TZs. For validation, a triple-mode filter centered at 3.04 GHz was fabricated, and the measured return losses are better than 27 dB and the minimum in-band insertion loss is 0.65 dB.