Design of Substrate Integrated Waveguide Filters

Abstract

Substrate Integrated Waveguide (SIW) technology is a promising alternative to conventional metallic Waveguides. Because, relatively it has low loss, its low cost, compactness, very low insertion loss and high performance. Its integration with planar circuits is very easy, because it can be easily fabricated on Printed Circuit Board (PCB). A normal dielectric waveguide generally suffers from two basic problems. One is radiation loss because of discontinuity and the other one is difficult transition to planar circuits. In this work, we have mainly focussed on microwave filters. A microwave filter is nothing but a frequency selective network, works in frequency range (300MHz-300GHz).It allows the signals which have frequencies in the passband and attenuates the signals which have frequencies in the stop band.
In this thesis, Substrate Integrated Waveguide (SIW) Band pass filters and Half mode Substrate Integrated Waveguide (HMSIW) Band pass Filters have been designed. These types of filters have been extensively used for satellite Communications. A wide band Substrate Integrated Waveguide band pass filter is proposed. The proposed filter has a percentage bandwidth of 75% and insertion loss of 1.5dB. U shaped slots have been etched to create a new Multiple-mode Resonator and also to achieve wideband operation. The proposed filter operates in frequency band(6.4GHz-10.9GHz).Another wide band Half Mode Substrate Integrated Waveguide(HMSIW) band pass filter is proposed. The proposed filter has a percentage bandwidth of 82% and insertion loss is less than 0.9dB. This filter operates in the frequency band (5.44GHz-13.43GHz). The above two filters are designed using a substrate of dielectric thickness 2.55 and thickness 0.8mm. A Half Mode Substrate Integrated Waveguide (HMSIW) filter for X-band applications is proposed. In this filter, the feed line has been tapered and tapered metallic vias are used to provide smooth transition between Microstrip line and HMSIW. The speciality of this filter is its compactness and its structure’s complexity is also very less. The filter is designed using low cost FR4 substrate which has a dielectric constant of 4.4 and thickness of 0.8mm. The foot print of the filter is 23.2×15.46𝑚𝑚2 . This filter is designed on Printed circuit board (PCB) and the proposed band pass filters are easy to fabricate. Another HMSIW band pass filter for Ku band applications is proposed. Similar procedure which is used for the above filter is used for this proposed filter. The foot print of the proposed filter is 17.4×15𝑚𝑚2 .The proposed filters have constant group delay. Software used is HFSS v.15.