Based On Bst Varactor Tube Of Electrically Controlled The Development Of The Bandpass Filter

With the development of multi-mode and multi-band communications technology, tunable band-pass filters take more and more attentions for its fast response, small size, low control voltage. Barium strontium titanate (BaxSr1-xTiO3) is largely used in microwave device due to their large field dependent dielectric constant.The dielectric nonlinearity of barium strontium titanate is used on the basis development of BST ferroelectric capacitors, combline tunable bandpass filter and monolithic integration of open loop coupling bandpass filter are designed, simulated, producted and tested respectively.the main contents of this article is:(1) BST thin films which have high dielectric adjustable approximately rate of55%(40V) and low dielectric loss of about0.08%is produced by magnetron sputtering. BST ferroelectric capacitors with adjustable rate of about50%and dielectric loss of about1.0%are fabricated by micro-fabrication techniques.(2) Combline tunable band-pass filter is developed on FR-4substrate using BST ferroelectric capacitors as tuning elements. The measure results show that:With the bias voltage from0V increased to35V, the return loss are above13dB, so the ports achieve a good match; center frequency f0of band-pass filter moves from2.10GHz to2.39GHz and tuning bandwidth is280MHz, the tuning rate is about15%; band insertion loss of it from11dB down to7.3dB,1dB bandwidth is reduced from270MHz to210MHz; In the passband of it has good group delay.(3) Monolithical integrated open-loop coupling bandpass filter is developed on the Al2O3substrate by using micromachining technology.The results show that:when no bias voltage is applyed, the center frequency of the bandpass filter is1.55GHz. bandwidth of1dB is200MHz, the return loss is about12dB. Passband insertion loss is9.1dB. Increasing voltage from0V to50V bias, return loss is above13dB, the center frequency of open ring coupling bandpass filter moves from1.55GHz to1.75GHz, the tuning bandwidth is200MHz, the tuning rate is13%. In-band insertion loss tunes from9.1dB down to5.2dB,1dB bandwidth is reduced from200MHz to180MH.