A Defected Ground Structure without Ground Contact Problem and Application to Branch Line Couplers

Jongsik Lim,Dal Ahn,Haiwen Liu,Sang-Min Han,Yongchae Jeong

doi:10.1155/2013/232317

Abstract

A new defected ground structure (DGS) microstrip line that is free from the ground contact problem is described together with its application example. The proposed DGS microstrip line adopts a double-layered substrate. The first layer contains the microstrip line and DGS patterns on the top and bottom planes as with the conventional DGS line. The second substrate, of which upper metal plane has already been removed, is attached to the bottom ground plane of the first layer. This structure prevents the ground plane of the first substrate with DGS patterns from making contact with the metal housing. The proposed DGS microstrip line has advantageous transmission and rejection characteristics, without the ground contact problem of DGS patterns, which has been a critical problem of previous DGS lines. A 10 dB branch line hybrid coupler is designed and measured, as an example of application of the proposed DGS microstrip line.

Highlights

IntroductionIt has been extensively known that if perforating patterns, such as photonic bandgap (PBG) and defected ground structure (DGS), are inserted on the ground plane, the transmission characteristics change severely from those of normal transmission lines [1, 2]
Normal microstrip lines theoretically have all pass characteristics
In the previous microstrip lines with defected ground structure (DGS), hereinafter “DGS microstrip line” or “DGS line,” there has been a serious problem when they are packaged in metallic housing because the bottom ground plane of microstrip lines, where DGS patterns are realized, makes direct contact with the metallic package

Summary

Introduction

It has been extensively known that if perforating patterns, such as photonic bandgap (PBG) and defected ground structure (DGS), are inserted on the ground plane, the transmission characteristics change severely from those of normal transmission lines [1, 2]. In the previous microstrip lines with DGS, hereinafter “DGS microstrip line” or “DGS line,” there has been a serious problem when they are packaged in metallic housing because the bottom ground plane of microstrip lines, where DGS patterns are realized, makes direct contact with the metallic package. It is definite that the advantageous effects of DGS are removed, when the inner bottom of the housing and the lower plane of microstrip lines make contact with each other. DGS patterns are realized on the ground plane of microstrip lines as in previous cases. As an example of application, a 10 dB branch line hybrid coupler is designed and measured

DGS Lines Using Double-Layered Substrate

Characteristic Impedance Analysis

Isolation

Application to Branch Line Hybrid Couplers

Conclusions