Design of Dual Bandpass Filter Using Parallel Coupled Lines

Abstract

In this report two techniques are used to design dual bandpass lter. First technique is based on the frequency transformations of prototype lowpass lter to the desired bandpass and band reject lters and arranging them in series and shunt con gurations in such away to meet the desired speci cations. Di erent possible combinations have been considered and presented the best possible con guration to validate this new design. Emphasis is given for dual bandpass lter while this can be extended to multi bandpass lters. The design of dual bandpass with di erent orders is presented in this paper for maximally at and equal ripple lters. In second technique the behavior of single port coupled line is analyzed using di erent con- gurations. Using single port coupled line di erent resonant frequency lters is obtained. A conventional four port parallel coupled lines on microstrip has ten canonical forms. Of these ten forms, two port parallel coupled lines are used in the design of bandpass lters. From the frequency characteristics of this single port parallel coupled line in open and short circuit con gurations, the design of dual bandpass lter is proposed by connecting this single port network in the shunt con guration for the conventional bandpass lter at the mid points. After this hairpin coupled line lter is analyzed based on di erent struc- ture and dual bandpass lter is obtained with shunt coupled lines connected in between hairpin lines.