Wideband BPF using quadruple-mode ring resonator loaded with short-circuited stubs and Γ-shaped band-stop sections

Abstract

In this letter, a compact, wideband bandpass filter with 31% 3-dB bandwidth, with very sharp roll-off characteristics, low insertion loss of 0.45 dB, high return loss greater than 25 dB, and improved out-of-band performance, suitable for 2.4 GHz WLAN applications is presented. The developed prototype filter is based on a quadruple-mode square ring resonator, connected to two λg/2 short-circuited stubs. In order to improve the out-of-band performance and achieve a wider stopband response, two Γ-shaped band-stop sections are connected on the feeding lines without disturbing the geometric symmetry along the diagonal. Measurements of the fabricated prototype provide experimental verification of the theoretical and simulated behaviour of the proposed filter. © 2017 Wiley Periodicals, Inc.