Design of a UWB Bandpass Filter with a Notched Band and Wide Stopband

A novel ultra-wideband (UWB) bandpass filter (BPF) is proposed and implemented in this article. The proposed UWB BPF has a highly rejected notched band and improved out-of-band performances. It is composed of two cascaded interdigital hairpin resonator units and four semicircle defected ground structures (S-DGS). The interdigital hairpin resonator unit and S-DGS with different dimensions are theoretically analyzed. The equivalent circuit of S-DGS is also presented. The working frequency band of the proposed UWB BPF is 3.1 to 10.6 GHz and the notched band is 7.5 to 7.6 GHz. Good insertion and return losses and high out-of-band rejections are achieved as demonstrated in both simulation and experiment.

From: Vol. 52 | No. 11 | November 2009 | Page 96

by L. Chen, Y. Shang and Y.L. Zhang, Xi’an Technological University, Xi’an, P.R. China; F. Wei, Xidian University, Xi’an, P.R. China

Research into ultra-wideband technology has risen dramatically since the US Federal Communications Commission (FCC) authorized the frequency band of 3.1 to 10.6 GHz for commercial purposes.¹ A bandpass filter is a key component of a UWB wireless communication system. Many BPFs have been developed based on various kinds of methodologies, such as non-periodical shunt-stub loading,² composite low pass/high pass topology,³ cascaded broadside-coupling,⁴ circular resonator⁵ and multiple-mode resonator (MMR).^6-9 Most of these BPFs have good in-band frequency performance, but the out-of-band performance is poor. Due to the existing radio signals such as wireless local-area network (WLAN) signals, which may interfere with the UWB users, a small BPF with a notched band is needed to reject these interfering signals. A UWB BPF with a notched band was realized using an embedded open-circuited stub,¹⁰ which is an effective way to reject any undesired radio signal. However, this structure has poor out-of-band performances.

In this article, a novel UWB BPF is proposed and implemented. It exhibits good frequency performances and a highly rejected notched band in the passband and achieves a wide stopband. The designed UWB BPF consists of two cascaded interdigital hairpin resonator units and four semicircle defected ground structures (S-DGS) along with the microstrip line. This structure is simple and flexible for the purpose of blocking any unwanted existing radio signals that may appear in the UWB band. S-DGSs are used to improve out-of-band performances. Measured results agree well with the simulated results.

Analysis and Design

Interdigital Hairpin Resonator

Figure 1 Geometry of interdigital hairpin resonators: (a) 3 fingers and (b) 5 fingers.

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Analysis and Design

Interdigital Hairpin Resonator