The present invention relates to tunable selective devices based on the transmission and receiption of progressive magnetostatic volume waves. These waves are normally propagated by a magnetic layer deposited on a non-magnetic substrate. The selective characteristics are obtained by forming resonant cavities at the surface of the magnetic layer which are delimited by grids or networks of grooves or filamentary regions having been exposed to an ionic implantation. The ondulatory cascade coupling between two resonant cavities, each equipped with a microstrip permits selective transmission of an electrical signal at high frequency being performed within a very narrow frequency band. This band may be displaced to perform a tuning action by altering the intensity of a magnetic field perpendicular in direction to the plane of the magnetic layer.
The progressive magnetostatic volume waves have isotropic propagation characteristics in the plane of the magnetic layer and as compared to the magnetostatic surface waves they offer the advantage of a higher saturation level. If it is contemplated to produce a tunable selective device by installing a transmitting microstrip and a receiving microstrip within a resonant cavity, a resonance peak may well be obtained at a given frequency, but the direct coupling formed between the microstrip has the result that the insertion losses observed close to resonance are barely greater than those observed at the apex of the resonance peak.
By arranging in cascade two resonant cavities delimited by parallel reflector networks and each equipped with a microtape, a common mode may be isolated by filtering action, so that a single resonance peak is observed within a substantial frequency range. Nevertheless, the insertion losses at either side of this resonance peak display a comparatively small drop compared to the apex of the resonance peak. This results from insufficient decoupling between the microstrip for the frequencies differing from the resonance frequency.
In order to secure a reduction of the insertion losses, the coupling of the two resonators is provided by a reflector network of which the lines are disposed obliquely with respect to the axes of the resonators. The spacing between the lines of the reflector network is selected in such a manner as to reflect the maximum of energy from one resonator to the other at the wavelength required.
It is observed, however, that the overall transfer function may have interference signals, corresponding to other longitudinal modes of the resonators, close to the resonance peak intended to assure the single-mode operation.