Compact Differential Wideband Bandpass Filters Based on Half-Wavelength Lines

Abstract
A compact differential wideband bandpass filter is proposed based on three half-wavelength transmission lines. The main advantages of small size and simple configuration are achieved. The improved design with two cascaded quarter-wavelength coupled lines can further improve the bandwidth of common-mode (CM) suppression and frequency selectivity. Two prototypes centered at 1.8 GHz with the size of 0.07λ g 2g is the guided wavelength at the center frequency f 0 ) and 0.056λ g 2 are designed, fabricated, and measured. The measured results of Design I (Design II) exhibit the minimum insertion loss of 0.27 dB (0.6 dB), 3-dB fractional bandwidth of 57.8% (52%), and the bandwidth of 20-dB CM suppression of 0.67 f 0 (4.1 f 0 ).
Funding Information
  • National Natural Science Foundation of China (61471209, 61271136, 61501263)
  • six types of Talents Project of Jiangsu Province (2013-XXRJ-010)
  • Nantong University-Nantong Joint Research Center for Intelligent Information Technology
  • Nantong Science and Technology Planning Project (GY12016023)