Contents I. Introduction
Broad-band[1] microwave circuits are very essential components for modern communication systems such as broadband wireless, satellite and radar systems application. The growth in this particular field has prompted rapidly the development of various broadband planar circuits. The major concerns of designing such microwave components include performance, bandwidth, selectivity, reliability, tunability, simplicity, compactness and cost effectiveness. Filters are the circuits which passes certain band of frequencies and attenuates out-of-band one. The most common and applicable among all type of filters is bandpass one. Edge coupled and Parallel-Coupled bandpass filter was the primary invention in the era of bandpass filter design [2]. Several bandpass filter have been proposed by the use of transformation techniques[l]. Later stepped-impedance resonators are synthesized with higher fractional bandwidth but low insertion loss[3]. Zhu et al. [4] developed the concept of broadband or UWB filters by the use of a MMR with a stepped -impedance configuration. Several MMR filters are developed for wide pass-band, good in-band and out-of-band performances [5]–[8]. Wideband ring resonators with loading of open circuited stubs [9] as well as a wideband band-pass filter using transversal resonator and using quadruple mode ring resonator [10] is also developed.
