Wideband Diplexer With Narrow Channel Spacing Using Hybrid Bandpass-Bandstop Structures

Yan-Mei Xue,Xiu Yin Zhang,Jin-Xu Xu,Lian Yang,Xiao-Lan Zhao

doi:10.1109/access.2020.3012348

Abstract

In this paper, a wideband diplexer with narrow channel spacing is designed by using hybrid bandpass-bandstop structures. Two wideband bandpass structures are designed with the transmission zeros at the upper or lower passband edges to achieve high skirt selectivity. Two bandstop structures based on half-wavelength coupled lines are integrated to the two bandpass structures to introduce additional transmission zeros and thus the skirt selectivity is further improved. Accordingly, two channel filters with high skirt selectivity and high stopband rejection are designed to realize a wideband microstrip diplexer with very narrow channel spacing. For verification, a wideband diplexer operating at 1.71-2.17 GHz and 2.30-2.70 GHz is implemented, which covers multiple frequency bands for different mobile systems. The measured results show excellent performance of passband flatness, high in-band isolation of better than 35 dB and low minimum insertion losses of 0.46 and 0.50 dB for the two channels.

Highlights

Diplexers are essential components in wireless systems, which have been widely developed using the waveguide/ cavity, substrate integrated waveguide and printed circuit board (PCB) technologies [1]–[15]
Bandstop structures are integrated to the bandpass filter to generate transmission zeros at the passband edges to realize very high skirt selectivity and high rejection, which enable the realization of wideband diplexer with high isolation under narrow channel spacing applications
Design exhibits the advantages of wide bandwidths, flat passbands, narrow channel spacing and low insertion losses (0.46 and 0.50 dB), which is attractive in base station applications

Summary

INTRODUCTION

Diplexers are essential components in wireless systems, which have been widely developed using the waveguide/ cavity, substrate integrated waveguide and printed circuit board (PCB) technologies [1]–[15]. The high-Q waveguide/cavity [7]–[8], coaxial resonator [9] and organic liquid crystal polymer [10] are employed to realize diplexers with very narrow channel spacing These diplexers are implemented with 3-D metallic structures, which suffer from heavy weight and large size, and are limited in some certain applications. As the channel bandwidths increase, the frequency selectivity become worse It is more difficult for wideband microstrip diplexers to realize high isolation between two contiguous channels. Bandstop structures are integrated to the bandpass filter to generate transmission zeros at the passband edges to realize very high skirt selectivity and high rejection, which enable the realization of wideband diplexer with high isolation under narrow channel spacing applications.

LOWER CHANNEL FILTER

CONCLUSION