Dual-Band Filtering Balun Using Dual-Mode Resonators

In this paper, a compact dual-band bandpass filter (BPF) and its balun filter are proposed. Initially, a dual-band bandpass filter is designed, and later it is extended to design a balun filter. The design includes one pair of square open loop resonators loaded with an open-circuited stub to obtain dual-band filtering properties and enhance matching. The properties of the balun filter and the dual-band bandpass filter are investigated. The simulation results of the proposed balun bandpass filter (BPF) show effective filtering at 2.4 GHz and 4.32 GHz as the center frequencies, which can be suitable for WLAN applications. The output ports of the Balun filter show an exact 180° phase difference, and it has a great amplitude imbalance with values of about 1.03 dB and 0.61 dB, respectively.