科研之友
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摘要
Two ultra-wideband balanced bandpass filters based on transversal signal-interference concepts are proposed in this paper. By employing the two structures: microstrip/slotline transition, and quarter-wavelength shorted coupler lines, 180 degrees phase shift can be easily implemented for each design. In addition, due to the different transmission paths, wideband common mode rejection and differential mode transmission bandwidth can be achieved. Two balanced filters centered at 3 GHz are calculated, fabricated and measured successfully. For the differential mode, the 3-dB fractional bandwidths are 102% from 1.47 GHz to 4.53 GHz and 103% from 1.52 GHz to 4.61 GHz, respectively, and the return loss are both greater than 20 dB. For the common mode, signals are suppressed below -20 dB and -15 dB over the whole frequency band.
