New Ultra-Wideband Filter With Sharp Notched Band Using Defected Ground Structure

Abstract

An ultra-wideband microstrip bandpass filter which operates from 3.1 GHz to 10.6 GHz, with high selectivity and sharp notched band is presented and experimentally verified. The filter is composed of a square loop shaped defected ground structure, metal faces, and microstrip lines. By adding two short stubs connected by a short circuit point on the microstrip lines, the filter achieves an attractive capacity in out-of-band rejection. By placing open stubs in microstrips, the filter realizes a notched band in passband. To illustrate the possibilities of the new approach, an ultra-wideband microstrip bandpass filter is designed and fabricated. Measured results agree well with the predicted counterparts. 1. INTRODUCTION Ultra-wideband (UWB) technology has been receiving tremendously increasing attention in high performance communication systems because it successfully overcomes the drawbacks of many classical communication technologies with its high speed, high immunity of noise, and low transmitting power [1]. Corresponding to this trend, various UWB filters with compact size, light weight, and adequate electrical characteristic performances have been extensively studied and explored [2]. One of the design techniques for obtaining high performance microwave filters is using defected ground structure (DGS) [3] resonators which are typically etched as various shaped breaks in the ground plane. DGSs act as parallel L-C resonators which resonate at certain frequencies depending on their dimensions and shapes for harmonic suppression [4-6]. UWB filters using DGS are always smaller than general UWB filters using multi-mode resonators in size and easy to manufacture. Moreover, rejection band is typically wider, and multi-pole characteristic can be set with combining several multimode resonators that have different sizes or shapes for harmonic suppression [7-10]. In this paper, a new UWB bandpass filter is proposed and implemented based on DGS. The proposed square ring shaped DGS is positioned symmetrically between the ports on the ground plane of initial filter. Hence, the filter itself is composed of dual metal faces and dual microstrip lines with short stubs to enhance out-of-band rejection and open stubs to create a notched band in passband. In the design process, the performance of BPF with the proposed DGS is investigated intensively to obtain the optimum design of overall structure. A UWB BPF with compact size and high performance is then presented, and predicted results are experimentally verified by testing the fabricated filter.

Application of a Stub-Loaded Square Ring Resonator for Wideband Bandpass Filter Design

“…Asymmetric SIR with only one-step discontinuity was thus proposed to achieve a wideband filter with low loss, wide stopband, and high selectivity. In [5], the defect ground structure (DGS) was used for wideband filter design, but the destruction of the ground plane would actually cause signal incompleteness. In [6], a wideband bandpass filter was reported using a multi-layer structure.…”

“…At present, most of the research and applications of the BPF still focus on the broadband and multi-band design [1,2]. In the past, several resonator structures have been proposed to achieve the wideband filter design, such as the use of the step impedance resonator (SIR) [3,4], defect ground structure (DGS) [5], multi-layer structure [6], multi-mode (MMR) [7][8][9], stub-loaded resonator (SLR) [10][11][12][13], coupled-line [14,15], multiple-mode split-ring resonators (SRR) [16,17], and so on.…”

Multimode HMSIW-Based Bandpass Filter with Improved Selectivity for Fifth-Generation (5G) RF Front-Ends

“…Bandpass filters, having this topology, achieve relatively small sizes with low fractional bandwidth. In [ 15 ], a UWB bandpass filter, based on a square-shaped defected ground plane and microstrip resonators, is designed. It covers the whole UWB band (3.1–10.6 GHz).…”

An Ultra-Wideband Bandpass Filter with a Notch Band and Wide Upper Bandstop Performances

“…In the past, several UWB-BPF design methods have been proposed [4][5][6][7][8][9][10][11][12][13][14][15][16]. In [4], the steppedimpedance resonator (SIR) was used to effectively obtain the wideband performance by controlling the spurious frequencies.…”

“…However, the design of ASIRs still suffered from design complexity. In [7,8], the defect ground structure (DGS) was used in the UWB design; however, the DGS would usually destroy the signal integrality. In [9][10][11], wideband BPFs with notched bands were designed using different open/shorted stub-loaded resonators.…”