Compact and Low-loss Stripline Bandpass Filters Made of Liquid Crystal Polymer for n257 and n258 Applications

We have designed two 6th-order canonical filters for n257 and n258 applications. They are made of liquid crystal polymer (LCP) with solder bump input and output transition to printed circuit board (PCB) and are optimized to have very compact size. The characteristics of the filters are estimated by the coupling matrix first. Then they are designed by electromagnetic simulation and are fabricated by PCB process. The size of the single bandpass filter is 4.2 × 3.4 × 0.33 mm
³
, and that of the dual bandpass filter is 4.2 × 6.0 × 0.33 mm
³
. Measurement demonstrates that the loss is about 3 dB in passband and suppression ratio of 2-GHz away from the passband is more than 30 dB. Variants of these two filters are also designed and fabricated by putting two of the same type on a common substrate for a practical module in which dual polarizations are applied.