Ultra-compact inductive coupled UHF tunable filter

In this paper, ultra-compact inductive coupled UHF tunable filters with two different coupling coefficients have been designed, fabricated, characterized, and compared. The relationship between the coupling coefficient and the filter´s performance has been investigated. The proposed filters were fully embedded into low cost multi-layered organic package substrate. The embedded filters were comprised of high Q spiral stacked inductors, high dielectric BaTiO₃ composite MIM capacitors, and varactor diodes. The fabricated two filters were operated in the frequency regime ranged from 500 MHz to 900 MHz for TV tuner receivers. The one with a coupling coefficient of 0.26 exhibited lower insertion loss of approximately -2dB, higher return loss of below -10dB, and larger tuning range of 56.3%. The other one with a coupling coefficient of 0.17 was more selective than that with a coupling coefficient of 0.26. The fabricated tunable filter exhibits extremely compact volume of 3.4 × 4.4 × 0.5mm³, which is the smallest in previously reported ones.