Summary
International Symposium on Antennas and Propagation
2009
Session Number:1E1
Session:
Number:1E1-1
Broadband PCML Bandpass Filter with Rectangular Middle Resonator
Jayaseelan Marimuthu, Mazlina Esa,
pp.193-196
Publication Date:2009/10/21
Online ISSN:2188-5079
Summary:
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. In this paper, a simple broadband bandpass filter with PCML structure was designed by placing a rectangular single line resonator of specific length and width between two identical PCML sectors. Basically a simple PCML structure with high coupling factor can produce two poles near to each other. The enhancement of PCML structure coupling over the wide frequency range can be realized by using microstrip transmission line with narrow width and gap of the parallel structure. Due to fabrication constraint in real world, the microstrip line width and gap of the parallel structure as the minimum value which cannot be further reduce. In these studies, a technique was proposed by employing a feeding network with small value of characteristic impedance. This technique shows that the PCML structure coupling factor can be further enhanced and two poles can be achieved. In order to further increase the number of poles, a rectangular middle resonator between two PCML structures with specific dimension introduced. This will produce multiple poles in periodical at overall electrical length of 180°, 360° and etc. By carefully selecting the length and width of the resonator the poles at 180° and 360° can brought nearer to two poles of PCML structure. The overall filter performance such as insertion loss, return loss and suppression of harmonic response was further improved by adjusting the length and width of the middle resonator. The middle resonator width was adjusted accordingly to improve the insertion loss and return loss performance at passband response. The length of resonator was adjusted for harmonic cancellation by transmission zero frequency. Details of the compact broadband filter design are presented and measured results are given to demonstrate the performance of the proposed filter. The proposed design is further optimized by adjusting the length and width of the middle resonator. Overall the simulated and measured results of insertion and return loss show good agreement with BW > 80%, ｜S11｜< -16dB, ｜S21｜ > -0.1dB and 200% wide upper stop-band.