Novel architecture of harmonic filter

Abstract

In this work we report a novel architecture for an harmonic filter with multi-track structure. The first example presented is a three-track structure. The displacement between two adjacent tracks is shifted /spl lambda//sub 0//6, where /spl lambda//sub 0/ is the wavelength at the fundamental frequency. The phase of the IDT in the middle track is inverse to that of the IDT's in the other two. Therefore, signals are cancelled at the fundamental frequency while enhanced at the third harmonic. For reducing the insertion loss of filters, the second example shown is a multi-track structure with a SPUDT transducer in each track. SPUDTs consist of third harmonic IDTs with /spl lambda//sub 0//8 width and strips with /spl lambda//sub 0//6 width as reflection arrays. Experimental results show that the sidelobe rejection is larger than 45 dB and fundamental response can be suppressed under -40 dB compared with the third harmonic. A filter at 1.4 GHz with an electrode width larger than 1 /spl mu/m on Y128/spl deg/X LiNbO/sub 3/ is also shown.