Substrate Integrated Waveguide (SIW) Bandpass Filter with Novel Microstrip-CPW-SIW Input Coupling

Augustine O Nwajana,Amadu Dainkeh,Kenneth S K Yeo

doi:10.1590/2179-10742017v16i2793

Abstract

A Substrate integrated waveguide bandpass filter is presented with a novel CPW-to-SIW transition at both the input and output ports which also served as the input and output couplings into the filter. The CPW-to-SIW transition structures presented here exploited the step impedance between the 50 ohms input/output feedline and the transition to control the input/output couplings of the filter. The SIW filter is also shown to have very minimum milling or etching requirement which reduces the fabrication error. The proposed SIW filter has been validated experimentally and results presented. The results show that a simulated return loss of 15 dB and an initial measured return loss of 16 dB were achieved. An improved measured return loss of 22 dB was later achieved after some tuining adjustments were performed on the filter input and output couplings. A minimum insertion loss of 1.3 dB was also achieved across the band.

Highlights

Substrate integrated waveguide (SIW) is a new type of transmission line that has evolved since the inception of the twenty-first century
The SIW inherits the advantages of the microstrip, i.e. compact size and easy integration, but maintaining some of its waveguide characteristic, i.e. low radiation loss, high unloaded quality factor (Q-factor), as well as the high power handling characteristics
All electromagnetic (EM) simulations were carried out using the finite-element method (FEM) of the Keysight electromagnetic professional (EMPro) 3D simulator

Summary

INTRODUCTION

Substrate integrated waveguide (SIW) is a new type of transmission line that has evolved since the inception of the twenty-first century. This new technology has become popular in the past decade as it has opened new doors to the design of efficient microwave and millimetre-wave circuits at low cost. Various authors have reported bandpass filters (BPFs) implemented with different transmission line technologies including: microstrip [3], waveguide [4], and SIW [5]. The transition employs a step impedance from 50 Ohms microstrip to a low impedance GCPW before coupling into the filter using the short low impedance GCPW transmission line. This transition as an input/output coupling for filter is shown to be very efficient as it allows two degrees of freedom in controlling the input/output coupling, i.e. the input/output coupling or the external Q-factor can be varied by either changing the step impedance of the CPW or the length of the short CPW transmission line

SIW DESIGN

DESIGN AND SIMULATION

FABRICATION AND MEASUREMENT

CONCLUSION