Abstract: A filter comprises a shallow bulk acoustic wave (SBAW) longitudinally coupled double mode resonator (LCR) and a reactance coupled between an input and an output of the resonator. Due to its use of a piezoelectric substrate with high electromechanical coupling and an orientation for propagating SBAWs, the resonator has a relatively poor stop band attenuation in a shoulder region on a high frequency side of its pass band. At frequencies in the shoulder region, a signal coupled via the resonator from the input to the output is reduced by a signal of opposite phase coupled via the reactance with a similar attenuation, thereby improving attenuation in the shoulder region. The reactance can be a capacitance formed on the substrate surface.

Abstract: A SAW device has tapered trasnsducers each of which is divided into two or more tapered transducer parts, which are arranged in line with one another in one or more SAW tracks with the tapers of adjacent tapered transducer parts complementary to one another to provide a compact arrangement. The tapered transducer parts can be symmetrically or asymmetrically tapered to provide different frequency bands for band or bandwidth switching of the SAW device. Input and output impedances of the SAW device can be maintained during such switching by switching of dummy transducer parts also provided on the same piezoelectric substrate.

Abstract: A double mode surface wave resonator comprises two IDTs (inter-digital transducers), arranged side by side between reflection gratings, on a surface of a piezoelectric substrate to provide for coupling of surface waves therebetween, each IDT having interleaved electrodes extending from a common rail between the two IDTs and from a respective outer rail of the IDT. One or each of the IDTs and its outer rail is divided into two halves for providing a differential signal connection to the resonator. The electrodes of the IDTs can be arranged in spatial synchronism with adjacent fingers of the reflection gratings to reduce spurious longitudinal modes.

Abstract: A SAW (surface acoustic wave) device tapped delay line comprises a continuous pattern of bifurcated inter-digital fingers having a constant pitch of .lambda./2 and forming a first IDT (inter-digital transducer), a plurality of second IDTs, substantially identical to one another and arranged with a predetermined pitch P for consecutively receiving a SAW propagated from the first IDT with respective propagation delays, and grounded dummy fingers in regions between adjacent IDTs. The first IDT is apodized in accordance with a Hermitian response to provide it with a pass band centered at a first frequency, and .lambda. is the wavelength of a SAW at a second frequency different from the first frequency and within the pass band. P is an integral multiple of .lambda./2, so that there is a constant finger periodicity throughout the SAW device whereby reflections between the second IDTs are avoided.

Abstract: A SAW device tapped delay line includes an apodized input IDT (inter-digital transducer) and a plurality of substantially identical unapodized output IDTs arranged to receive, after delays which successively increase by an amont T, a SAW propagated from the input IDT. Each output IDT is terminated with a low impedance which is constituted by the low input impedance of a buffer amplifier, to minimize acoustic regeneration by the output IDTs. Grounded dummy fingers with the same metallization ratio as the output IDTs are provided between adjacent output IDTs to provide a constant SAW velocity. The delay line is particularly suited to use in an equalizer of a microwave radio transmission system, in which the delay T is the inverse of the symbol rate of the system. Intermediate frequency automatic time domain equalizer (IF ATDE) arrangements using the SAW device tapped delay line are described.