Design of Miniaturized Equal-Phase Dual-Band Branch Line Coupler for GNSS Applications

In the paper, a miniaturized dual-band branch line coupler (BLC) with equal phase difference is designed for GNSS applications. The dual-band equal phase response is realized by replacing the BL in the coupler by open/short stub loaded transmission line (TL). Besides, by using the stub loaded TL, small frequency ratio of around 1.3 can be realized. Parameter relationships between the BL and the open/short stub loaded TL are given and a prototype operating at dual GNSS bands was designed. For easy integrated with the antenna, the BLC is folded without affecting the original performance, and mender lines are used for implementing the open/short stub loaded TL. The size of the fabricated prototype is 0.3λ
g
× 0.3λ
g
. Measurement results show that the bandwidths at lower and higher GNSS frequencies are 14.1% and 15.4%, respectively, under the criterion of 10- dB return loss. For 1-dB amplitude imbalance and 10° phase difference error, the measured bandwidths are 14.9% and 9.6%, separately.