A compact dual-band bandpass filter using folded quarter-wavelength resonators

In this work, a very compact dual-band filter based on folded quarter-wavelength resonators is proposed. Specific configuration of the filter results in four independently controlled transmission zeros which provide very high selectivity of the passbands. The proposed configuration is analysed in detail and a design procedure is presented. To demonstrate the feasibility of the proposed approach, two dual-band filters operating at WLAN frequencies of 2.4/3.5 GHz and 3.5/5.25 GHz are designed, fabricated and measured. To the best of the authors´ knowledge, proposed 2.4/3.5 GHz dual-band filter is the most compact solution presented so far that at the same time exhibits high-selectivity and low losses.