Broadband PCML bandpass filter with rectangular middle resonator

Abstract

In recent years, compact broadband filters compatible with printed circuit boards (PCB) are required in many communication systems. The filter size is usually constrained by the number of resonators and size of the resonator structures employed in the design. Various techniques were proposed to design broadband bandpass filter [1]-[2]. One of the simplest and easiest methods to achieve broadband is by employing resonators with multiple poles within passband region [3]. In these studies multiple poles within passband were achieved by employing two types of resonators. One is a pair PCML with tight coupling factor and the other is rectangular middle resonator which connecting the both PCML structure. By varying the physical parameters of PCML and middle resonators multiple poles can be achieved which will lead to design of broad band bandpass filter. The filter bandwidth is mainly limited by the achievable maximum coupling between these resonators. A broadband bandpass filter of PCML structure can be realized by employing high coupling parallel coupled line of narrower width and gap. The overall PCML coupling factor can be further enhanced by using feeding network with small characteristics impedance.