Compact etched ground structure ultra-wideband bandpass filter with adjustable bandwidth

Abstract

A bandwidth adjustable ultra-wideband (UWB) bandpass filter is investigated using a simple meander-typed etched ground structure (EGS) unit on the lower ground plane. On the upper layer, the feed line of characteristics 50Ω is modified by attaching a two-directional open-circuited stub to form a modified symmetrical T-shaped microstrip line, which is proposed to achieve wide upper stopband. Three similar EGS morphologies with different dimensions are designed for comparison. We will show that a novel compact EGS UWB filters with adjustable bandwidth can be easily investigated. The center frequency and the bandwidth increase with decreasing effective length of EGS unit. The experimental results show that a EGS unit with an effective length of 23.6 mm yields a UWB filter with the bandwidth of 3.01 ∼ 10.6 GHz. The measured results also show that the fabricated UWB filter has a high out-of-band rejection and a low group delay variation.