Uniplanar hybrid couplers using asymmetrical coplanar striplines

This paper presents four new uniplanar 3-dB hybrid couplers using asymmetrical coplanar strips (ACPS's) for microwave integrated circuit (MIC) and monolithic MIC (MMIC) applications, Experimental results show that the standard (1.5 lambda(g), circumference) uniplanar 180 degrees hybrid-ring coupler has 3.5 +/- 0.4 dB coupling, greater than 21-dB isolation, and greater than 23.4-dB return loss over a 25% bandwidth centered at 3 GHz. The 180 degrees reverse-phase hybrid-ring coupler (1.0 lambda(g) circumference) provides better performance as compared to conventional microstrip hybrid couplers, This circuit has a bandwidth of more than one octave from 2 to 4 GHz with +/-0.4-dB power dividing imbalance and +/-4 degrees phase imbalance, The 180 degrees reduced-size reverse-phase hybrid-ring coupler (0.8 lambda(g) circumference) maintains the performance of the 180 degrees reverse-phase hybrid coupler with the advantage of smaller size, This circuit also has a bandwidth of more than one octave from 2 to 4 GHz with +/-0.3dB power dividing imbalance and +/-3.1 degrees phase imbalance, A new 90 degrees 3-dB branch-line hybrid coupler is also introduced, Experimental results show the insertion loss of this component to be 0.5 dB at 3 GHz, and also greater than 15.3-dB isolation and 17.1-dB return loss over a 10% bandwidth centered at 3 GHz. The circuits were designed and simulated with Sonnet electromagnetic-circuit solver software, The measured results agree well with the simulations.