Microwave Components Using Ferrimagnetic Pastes

Abstract

Ferrimagnetic pastes have been developed using Mg-Mn, Mn-Ni, Li, and Cu-doped magnesium ferrite aluminate and YIG powders. Isolators and circulators fabricated using these pastes on alumina substrates have been partly reported earlier. These devices exhibited higher insertion losses compared to those on YIG/ferrite substrates. Photomicrographs of Li-ferrite have been taken and these reveal cracks which may be responsible for high loss. The thermal co-efficient of expansion has also been found for this paste.Thick-film dual directional couplers have been fabricated using the field-displacement phenomena in wide microstrip lines. The coupling from one auxiliary line to the other on either side of the wide line can be changed by switching the polarity of the magnetic field. The performances of these devices have been compared with those on ferrite substrates over the frequency range from 2 to 8 GHz. A bandwidth of 600 MHz for a 15-dB coupler has been obtained with Li-ferrite paste.