A novel compact LC resonator-based bandpass filter design with tunable transmission zeros

In this paper, the proposed LC resonator-based bandpass filter embedded in a two-layer substrate is presented to achieve both miniaturization and transmission-zero creation for 3.5 GHz WiMAX applications. There are two extra transmission zeros generated near the passband for a 2nd order design without introducing either a cross-coupling mechanism between adjacent resonators or a source-load coupling configuration in the input and output ports. The proposed LC resonator-based bandpass filter is compact in size and can achieve excellent insertion and return loss characteristics in the passband. A novel approach for tunable transmission zeros is also proposed. This approach is to groove a slot of rectangular C shape on the ground plane without additional components or devices.