Analytical Design of Wire-Bonded Multiconductor Transmission-Line-Based Ultra-Wideband Differential Bandpass Filters

A systematic design process of ultra-wideband differential bandpass filters based on wire-bonded multiconductor transmission lines is presented. The topology is thoroughly analyzed by means of analytical design equations that provide some insights into the physical behavior of the proposed structure. Single- and double-section configurations are introduced and exact closed-form design equations are derived to design differential filters with either a Butterworth or Chebyhsev frequency response. To validate the design procedure, two differential filters are designed and fabricated with an equal-ripple fractional bandwidth (FBW) of 100% and 60% (3-dB FBW of 145% and 97%), respectively. The measured differential-mode responses show a good in-band flatness with insertion losses lower than 1 dB and with high common-mode rejection levels greater than 20 dB. Experimental results demonstrate a good agreement with theory and prove that the proposed design methodology is useful for accurate and fast ultra-wideband differential filter synthesis.