Miniature Quasi-Lumped-Element Wideband Bandpass Filter at 0.5–2-GHz Band Using Multilayer Liquid Crystal Polymer Technology

Miniature wideband bandpass filters are proposed using multilayer liquid crystal polymer (LCP) technology to cover the very low-frequency band of 0.5-2 GHz. To reduce the filter size at such low frequencies, lumped-element theory is used for the filter design and a value extraction process is developed to accurately get the capacitive or inductive values of different multilayer microstrip quasi-lumped elements. These elements are used to produce the required filter response, and thus the overall design process relies less on the time-consuming EM optimization. A filter with the size 0.058 λ_g ×0.026 λ_g ×0.004 λ_g is demonstrated as an initial design. To further improve the stopband performance, an improved design is then developed while still maintaining the compact sizes within 0.065 λ_g ×0.026 λ_g ×0.004 λ_g. Both filters are fabricated on a five-metal layer LCP construction, which has not been done before, with robust via connections using the newly developed laser-aided fabrication technique. Good agreements between simulation and fabrication are observed, which has proven both the success of the design methodology, as well as the fabrication technique.