Quasi-harmonic interdigital transducers

This paper presents a quasi-harmonic interdigital transducer (QHIDT) utilized for SAW filters. The QHIDT consists of several single electrode transducers which serve as elemental transducers. The width and position of the electrodes in the elemental transducer was considered to eliminate the inter multi-reflection between the electrodes. Therefore, the center frequency of each element is not exactly the same as the operating frequency of the QHIDT. QHIDT is suitable for high frequency SAW filters because frequencies can be generated at the 2nd, 3rd and 4th harmonic etc. The fundamental frequency signals could be suppressed by using input and output QHIDTs with different order harmonic generation. An experimental prototype device, in which two transducers with different periods were applied, was fabricated on ST cut quartz substrate. The frequency response, at 242.94 MHz operating frequency, is shown. The insertion loss without tuner in a 50 Ω system is about 13.8 dB. The theoretical frequency response is also presented