Two-channel cascading of transversely coupled resonator filters

Transversely coupled resonator filters (TCRF) usually form a cascade of two single filters accompanied by additional loss. As known, this loss can be compensated by so-called coupling coils. However, those coils give rise to additional costs. The first try to diminish the cascade loss is to widen the aperture of coupling transducers at the expense of the remaining transducers. As a result the mean cascade coupling is hardly increased. As an alternative, the coupling IDTs are divided into two IDT components. Each IDT component has an input of its own and two inputs of different single filters are connected with each other forming a cascade connection. Thus the total TCRF has two cascade connections called channels. The sum of apertures of coupling IDT components is wider than that of the remaining IDTs of the respective single filter. Simulations show that the splitting of both resonances gets wider. As a result, the mean coupling is clearly increased and the cascading loss is reduced. This effect is confirmed experimentally.