IMPROVED COMPACT SPURIOUS PASSBAND SUPPRESSION RAT-RACE COUPLER USING ASYMMETRIC T-SHAPED UNITS

摘要

A compact rat-race coupler (RRC) using asymmetric tapped-stub units for wide-range spurious passband suppression is presented. The main advantage of the present approach is that, under similar conditions, asymmetric T-shaped unit exhibits slow-wave and stopband effects, superior to those of traditional symmetric T-shaped unit; this result in extra size reduction and extended harmonic suppression within the fabrication limit of high impedance line. Design equations along with graphs are presented. A fabricated prototype RRC, at f_0 = 0.5 GHz, has circuit area only 28% of that of the conventional one and no harmonic passband up to 10 f_0. The method also features good 20-dB input matching bandwidth and sharp-harmonic rejection (>30 dB at second harmonic) performances.