Compact multi-band bandpass filters based on parallel coupled split structure multimode resonators
J.Luo, K.B. Shi, S. S. Gao
Abstract: In this letter, a novel sext-band bandpass filter (BPF) using two split-type multiple-mode resonators is proposed. The filter is composed of two sets of resonators which are respectively designed to realize Filter 1 with two passbands and Filter 2 with quad passbands. Then the two BPFs are combined by parallel coupling feed lines for sext-band responses, and each of the six centre frequencies in the proposed sext-band BPF is able to be controlled due to the design freedom. To validate the design and analysis, a prototype filter has been fabricated with six passbands centered at 1.88/2.59/3.48/5.26/5.82/6.75 GHz. The measured result of the fabricated filter agrees well with the simulation, which shows that the proposed structure is a good candidate for sext-band BPF designs and validates the proposed design flow well. Key Words: Sext-band, bandpass filter, split-type multiple-mode resonator, parallel coupling feed lines. This document gives you guidelines on preparing manuscripts for
Introduction: In the recent years, developments in microwave multi-band bandpass filters (BPFs) have been gaining much attention for multi-service wireless communication systems, such as GPS, WLAN, WiMAX and RFID applications. However, it is still a challenge to carry out high-performance multi-band BPFs with compact size, closely spaced passbands, low insertion loss, high return loss and sharp skirt to satisfy the whole WLAN application demands.
Recently, many approaches to multi-band BPF design have been reported to address that problem[1]–[6]. In [1], Yan T F used two sets of short-stub-loaded E-Type resonators to realize a quad-band BPF. In [2], Bukuru D investigated quad-mode stepped impedance resonator (QMSIR) to achieve a compact quad-band bandpass filter. In [3], Li X realized novel quad- and sext-band bandpass filters on a basis of multimode resonator (MMR) using SIRsloaded tapered-line (SIRTL). In [4], Kamma A used T-shaped stubs loaded with a modified ring resonator (MRR) to realize a quad-band BPF. In [5], Chen F C used six pairs of semi-lumped resonators to achieve a sext-band BPF. In [6], Hsu K W realized a quint-band BPF using five tri-mode stub-loaded SIRs among the common input/output (I/O) ports. These papers show good electrical performance, but because of the use of many pairs of resonators, the size is relatively large.
In this letter, a novel sext-band bandpass filter (BPF) using two split-type multiple-mode resonators is proposed. The filter is composed of two sets of resonators which are respectively designed to realize Filter 1 and Filter 2. Filter 1 generates two passbands, meanwhile, Filter 2 generates other four passbands. The proposed filter has compact size, low insertion loss. Moreover, there are multiple coupling paths between different stubs, resulting in controllable bandwidths.
Filter design procedure: Fig. 1 shows the equivalent transmission line model for the proposed sext-band BPF.
Fig.1. The equivalent transmission line model for the proposed sext-band BPF
Fig.2 shows that Filter 2 generates four passbands. And Filter 1 generates two passbands obviously. The two BPFs are then combined by parallel coupling feed lines for sext-band responses.
Fig.2. EM simulated frequency response of quad-band Filter 2
Fig. 3 displays the equivalent transmission line model for the proposed three-band BPF in Filter 2.The center frequencies of the three passbands are f 1, f 2 andf 3, respectively.