Dual-mode Planar Resonator Based Balun BPF for Bluetooth Applications

In this paper, a multifunctional balun band-pass filter (BPF) circuit for Bluetooth application is reported. Two multimode resonators and open-circuited transmission line have been utilized to obtain balun BPF response. Theoretical and full-wave EM simulations are discussed in detail along with the even-odd mode analysis. Even and odd mode frequencies as well as transmission zero frequency can be flexibly controlled through structural parameters. Based on the principle of open-circuited transmission line and dual-mode resonators, a compact Balun BPF circuit has been designed and validated through measured results. The designed balun BPF has insertion and reflection loss better than 3 dB and 40 dB respectively in the operating band. Measured isolation of 10 dB is obtained in between both the unbalanced output ports. The two output ports have an amplitude imbalance of 0 dB and a phase imbalance of 180 degrees at the design frequency of 2.4 GHz.