Compact dual-band bandpass filter using simply hybrid structures

A novel compact dual-band bandpass filter (BPF) using a hybrid structure of microstrip patch and coplanar waveguide (CPW) is proposed, designed, and implemented. The dual-band response can be realised by embedding two CPW structures in the microstrip square patch, which can not only disturb two fundamental degenerated modes, TM₁₀₀ and TM₀₁₀, but also adjust the resonant frequency of the TM₁₁₀ mode. The two degenerated modes are used to form the first passband while the TM₁₁₀ mode and two CPW resonators are used to generate the second passband. The first and second passbands have two and three poles, respectively. The dual-band BPF has a simple structure and good performance.