Ring Hybrid Balun with Good Amplitude and Phase Balance

We present a ring hybrid balun with additional two lambda/4 short stubs, which offers excellent amplitude and phase balance characteristic. In the proposed scheme, the phase and amplitude imbalance essentially occurred in the conventional ring hybrid is alleviated by a lambda/4 shorted stub and the second stub with a series resistor respectively. The measured data shows that phase imbalance is less than 2.5deg and magnitude imbalance is less than 0.2 dB over a 1.75-2.25 GHz.