An Improved Stopband Dual-Band Filter Using Quad-Mode Stub-Loaded Resonators

In this paper, we present a dual-band microstrip bandpass filter (BPF) with an improved stopband, which was constructed by quad-mode stub-loaded resonator (SLR). Since the SLR is able to produce multiresonance within single unit, area saving significant. The proposed implemented two stubs allocated at symmetry places, thus even-/odd-mode can be applied analysis resonance. Moreover, shift spurious passband, step impedance structure harmonic resonance higher frequency. Design procedure for high performance BPF proposed, and examples were designed wireless local network (WLAN) of 2.4/5.2 GHz. measured insertion losses, return losses fractional bandwidths (FBW) are 1.43 dB, 10 14.8% 2.4 GHz 1.34 12.9% 5.2 applying quarter-wavelength on input/output ports, passband selectivity isolation 40 dB achieved. simulation measurement have close match, verifying design concept.