Compact High-Selectivity Tri-Band Bandpass Filter for WLAN Applications

This paper presents a compact tri-band bandpass filter (BPF) with controllable frequency and high selectivity for WLAN applications. A stepped impedance resonator with a shorting stub and a uniform impedance resonator with an open stub are applied in the design. Several techniques that can generate transmission zeros are combined to improve the frequency selectivity. The resonators and the proposed filter are characterized by full-wave simulations. To validate the design strategies, The tri-band BPF centered at 2.4 GHz, 5.2 GHz and 5.8 GHz was developed. Both simulations and measurements were carried out to demonstrate the effectiveness of the design. Good agreements are achieved.