Design of compact tri and quad band band-pass filters using stub loaded resonators for wireless applications

A compact tri and quad band band-pass filters (BPFs) utilizing stub loaded resonators is presented for wireless applications. The proposed resonator has been designed and analyzed using even-odd mode analysis due to its symmetrical geometry. Open-ended stubs are loaded at an appropriate position in the dual-mode resonator to achieve tri and quad passbands. To reduce the circuit size and create transmission zeros at our desired frequencies, a symmetrical meandered shape resonator is loaded with open-ended identical stubs which are bent towards each other. The proposed BPFs are tune to operate at GSM (900 MHz), LTE (2300 MHz), WiMAX (3.5 GHz), and WLAN (5.4 GHz) bands. Significant improvements are observed in terms of circuit size, 3-dB fractional bandwidth, insertion loss, and transmission zeros. To check the validity of the proposed tri and quad BPFs, these are simulated, fabricated and measured. The simulated and measured results are compared and strong agreement is observed. The proposed filters can be prospective candidates for wireless communication applications.