Multilayer interdigital ultra-wideband filter

A miniature ultra wideband (UWB) bandpass filter that uses a multilayer interdigital structure is presented in this paper. The quarter-wavelength resonators including microstrip line resonator and coplanar waveguide (CPW) resonator are vertically stacked to achieve a strong coupling for the designed UWB filter. By adopting multilayer configurations, a miniature footprint is achieved. A seven-pole UWB bandpass filter is designed and fabricated using the multilayer liquid crystal polymer (LCP) lamination process, and is measured by using a vector network analyzer. The measured and predicted results are presented with good agreements. The fabricated prototype has a 10 dB return loss bandwidth from 2.8 GHz to 11.0 GHz and a compact size of 9.3 mm by 3.6 mm (0.38 λg by 0.15 λg, where λg is the guided wavelength of 50 Ω microstrip line at centre frequency).