Compact PCB embedded tunable filter for UHF TV broadcasting

In this paper, fully embedded tunable bandpass filter (BPF) with inductive coupling circuit was newly designed and demonstrated for UHF TV tuner applications ranged from 500 MHz to 900 MHz. Conventional RF tunable filter with an electromagnetic coupled tuning circuit has several problems such as large size, high volume, and high cost, since the electromagnetic coupled filter is comprised of several passive components and air core inductors to be assembled and controlled manually. To address these obstacles, compact tunable filter with inductive coupling circuit was embedded into low cost organic package substrate. The embedded filter was optimally designed to obtain high performance by using high Q spiral stacked inductors, high dielectric BaTiO₃ composite MIM capacitors, varactor diodes. It exhibited low insertion loss of approximately -2 dB, high return loss of below -10 dB, and large tuning range of 56.3%. It had an extremely compact volume of 3.4 times 4.4 times 0.5 mm³.