Compact diplexer with slotline resonators for wideband and WLAN applications

In this article, a compact diplexer is proposed using the U-shaped slotline resonator (U-SR) and dual-mode slotline resonator (DM-SR) for wideband and WLAN applications. The filter using the U-SR has three transmission poles in the passband and two transmission zeros near the passband edges. The wide upper-stopband can be realized for the second mode of the U-SR is well suppressed. The DM-SR has two resonant frequencies (odd- and even-modes) in the desired passband. And the odd-mode resonant frequency can be flexibly controlled by the slotline stub, whereas the even-mode one is fixed. Due to the main path signal counteraction and source-load coupling, the filter using the DM-SR possesses two transmission zeros in the upper-stopband. The mutual loading effect of two filters can generate new transmission zeros, which are mainly applied to improve the isolation. Compact size can be obtained without extra matching network. A diplexer prototype is designed, and good agreement can be obtained between measured and simulated results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2480–2484, 2014