An m-derived ladder high pass SAW filter

Surface acoustic wave (SAW) filters are widely used as RF filters for GHz-band in mobile communication terminals. Recently high performance SAW filters are required as the frequency is higher and the frequency band is wider in mobile communication systems. Above all low insertion loss SAW filters are required, which make mobile communication terminals sensitive and low power consumption. In this paper, a new structure of a low loss high pass filter with SAW resonators, a design method, and fabricated results are reported. This filter is composed of one port SAW resonators as series elements and series resonant circuits as shunt elements. We call it an m-derived ladder high pass SAW filter. The m-derived ladder high pass SAW filter has good features of low insertion loss and high attenuation in wide frequency range although the pass band frequency is apart from the rejection band frequency. We fabricate the new structure of the filter. The resonant circuits as shunt elements consist of chip capacitors and chip inductors and the one port SAW resonators as series elements are fabricated on 128°YX-LiNbO₃ substrates. Consequently, the insertion loss of the fabricated filter is less than 0.5 dB at the frequency of 940-958 MHz, and the rejection band attenuation is more than 33 dB at the frequency of 810-828 MHz.