Zig-Zag Monofilar Spiral Shaped CRLH TL Based Compact Lowpass mono-/duo-/tri-/quad-bandpass Filter

Abstract

ABSTRACT Planar compact lowpass mono-/duo-/tri-/quad-bandpass filters design based on CRLH TL are presented. Filters are designed by cascading two unit-cells composed of Zig-Zag monofilar spiral lines (ZZMSL) and Zig-Zag open ring (ZZOR) loaded on the main transmission line. Only the length of ZZMSL which is housed within the fixed length of ZZOR is utilized to generate the multiple passbands, so all of the filters are of the same size. At the lowpass (LP) band of the filter’s −3 dB cut-off frequency of 0.71 GHz, the filter’s footprint area (excluding the feed line), is 0.083 λg × 0.034 λ g . The LP band's measured −3 dB cut-off frequency is 0.71 GHz, with a minimal in-band insertion loss of 0.22 dB and a return loss better than 20 dB from DC to 0.46 GHz. The measured center frequencies for four bandpass passbands are 1.3, 2.08, 3.37, and 4.6 GHz, with a −3 dB FBW of 76.15%, 10.57%, 8.6%, and 7.8%, respectively. The minimal insertion losses within the BPs are 0.26, 0.26, 0.39, and 0.4 dB, respectively, whereas the return losses are 33, 36, 19, and 37 dB. Lower in-band insertion loss, good band-to-band isolation, the controllable center frequency with good out-of-band skirts, higher compactness, and lower circuit complexity are all advantages of the proposed lowpass quad-bandpass filter. The Lowpass quad-bandpass filter is finally manufactured. A good agreement between electromagnetic simulation, circuit model simulation, and experimental measurement results validates the design process and filter performance.