Quad‐Band Bandpass Filter Using Asymmetric Short Stub Loaded E‐Type Resonators

In this study, a quad‐band bandpass filter (BPF) with high selectivity and independently controllable passbands is proposed. The proposed BPF is achieved by employing two pairs of asymmetric short stub loaded E‐type resonators. Each pair of E‐type resonators achieves a dual‐frequency filtering characteristic. One pair of E‐type resonators operates at 1.57 and 3.0 GHz, and the other pair operates at 2.4 and 3.5 GHz, respectively. The three lines parallel coupling (TLPC) structure is employed between the source and load to generate eight transmission zeros (TZs), which greatly improves the selectivity of the filter. To verify the feasibility of the proposed model, a prototype was designed and fabricated, whose simulations and measurements are in good agreement.