Multilayer broadside-coupled dual-band bandpass ring filter for WLAN applications

A two-layer microstrip dual-band bandpass filter with compact size is presented. The filter is constructed from the combination of two coupled-line sections and a ring resonator. The lines that are coupled to the ring are placed on the top layer while the ring is placed on the second layers to reduce the coupling gap. The centre frequencies of the two passbands are 2.5 GHz and 5.2 GHz. The dualband filter is realized using FR-4 epoxy-glass substrate of 1.6-mm-thick with dielectric constant equal to 5.4. Experimental results are found to be coherent with compared to the ones from simulation.