Novel architecture of harmonic filter

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 λ₀/6, where λ₀ 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 λ₀/8 width and strips with λ₀/6 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 μm on Y128°X LiNbO₃ is also shown