A low-loss and compact size analog tunable filter on flexible organic substrate

This paper presents the design, fabrication and measurements of a low-loss and compact size 4-pole tunable filter based on open-loop resonators and operating in the X-band. This filter is fabricated on a flexible organic substrate and ferroelectric sapphire chips are mounted on it and used as tuning elements. This filter has a fractional bandwidth of 6-10% and an analog tuning range of 12.6%. Insertion loss of 5.4 dB to 1.8 dB is achieved while return loss is better than 10 dB on the covered frequency range. The presented topology allows a footprint size reduction of 50% compared to conventional open-loop resonator filters.