Fully reconfigurable evanescent mode bandpass filter embedded with metallic grid

Abstract

In this paper, an innovative bandpass filter design with both reconfigurable center frequency as well as controllable fractional bandwidth is presented. The main body of this bandpass filter is made of arrays of periodical metallic posts that known as electromagnetic bandgap (EBG) structure previously. Given that working frequency of such filter is targeted below cutoff frequency thus no propagation mode could be supported; therefore, more often this filter are also called evanescent (EVA) mode filter. Proposed is a three-pole reconfigurable EVA (RCEVA) filter that based on substrate of low loss Rogers material and consists of two arrays of metallic posts that either oriented in horizontal or vertical direction. In addition, all surfaces of the substrate of the filter are plated with 1/2 oz copper and with two sets of surface-mount lumped capacitors. One set of lumped capacitor on the top plate tunes the center frequency (CF) while another set on the side controls the fractional bandwidth. Both center frequency (CF) and fractional bandwidth are individually tunable. The center frequency (CF) of the three-pole filter is tunable from 4.44 GHz to 4.88 GHz and with reconfigurable 3 dB fractional bandwidth ranging from 6.8% to 8.4%; meanwhile maintains consistent insertion loss (IL) during tuning. It has very high potential for applications that require constant absolute bandwidth (ABW) during the center frequency tuning in order to meet more stringent wireless communication SPECs.