On the design of equal division single-band filtering dividers with an extended transmission line and resistor as isolation elements

Abstract

This paper introduces a new scheme for effective output port isolation and return loss in RF-filtering divider design. The proposed design incorporates an extended transmission line and a conventional resistor as isolation elements. The technique has a simpler microstrip circuit implementation when it comes to the integration of a single-band band-pass filter with a Wilkinson power divider to achieve simultaneous filtering-dividing action. It is established that if a band-pass filter with a certain fractional-bandwidth is matched to 70.7 $\Omega $, a transmission line section and isolation resistor are sufficient for achieving reasonable output port return loss and isolation in the resulting filtering divider. In experimental validation, two single-band band-pass filters, namely a coupled-line filter and an open-loop coupled resonator triangular filter with center frequencies of 3 GHz and 1 GHz, respectively, effectively replace the conventional quarter-wavelength transformers for equal division of power. The proposed filtering divider structures were fabricated and a reasonable agreement was observed between respective simulated and measured S-parameter responses. The experimental results for a coupled-line filtering power divider and an open-loop triangular filtering power divider were as follows: 1 dB fractional-bandwidths of 15.3% and 12%, port isolations better than 31 dB and 20 dB, and good out-of-band performances up to 2.67f$_{0}$ and 2.85f$_{0}$, respectively.