A Simple Method to Design a Compact Triple-passband Filter Using Novel Coupling Scheme and Multi-Layered Substrate

Abstract

In this paper, a simple method to design a compact triplepassband filter is presented. The proposed filter structure is mainly composed of two half-wavelength input/output (I/O) terminated microstrip lines and three open-loop uniform impedance resonators (UIRs), which are designed for three different passbands. By properly selecting the coupling position between I/O open-ended microstrip lines and each desired resonator, three passbands can be integrated, and the insertion loss can be improved. In order to achieve compact size, the three UIRs are placed on different layers of the substrate. A filter example operated at 1.575 GHz, 1.8 GHz, and 2.4 GHz for GPS, GSM, and WLAN applications is designed using the proposed concept and then fabricated. Experiment results show a good agreement with the simulated performances.