A microwave phase shifter that can be tuned by varying both electric and magnetic fields has been developed. This device combines all the advantages of prior electrically and magnetically tunable microwave devices, but in comparison with them, it is smaller and cheaper and it performs better. Devices like this one are suitable for use in monolithic microwave integrated circuits.
This microwave phase shifter is a thin-film ferroelectric/ferrite device. One can alter the propagation of electromagnetic waves in such a device by (1) varying an applied electric field and thereby varying the permittivity of the ferroelectric layer and/or (2) varying an applied magnetic field and thereby varying the permeability of the ferrite layer.
Figure 1 depicts the device as a layered structure and as the main component of a phase-shifting circuit. The substrate is a polycrystalline yttrium iron garnet (YIG) ferrite material. In the fabrication of the device, buffer layers of Si3N4 and MgO were deposited on the substrate, then the ferroelectric layer was formed by ion-beam-assisted deposition of Ba0.6Sr0.4TiO3 on the MgO. Then a transmission line comprising a central strip and two lateral ground-plane strips was patterned on an electron-beam-evaporated gold film.
In tests of this device, significant phase shift was observed at frequencies up to 18 GHz when an electric bias or a magnetic field was applied. For example (see Figure 2), at a bias of 250 V, phase shifts of 20° and 34° were observed at 7 and 9 GHz, respectively. When an externally generated magnetic field of 800 gauss was applied in tests at 5 and 6 GHz, phase shifts of about 230° were observed. As the magnetic field was increased beyond 800 gauss, the phase shift gradually saturated at about 300°.
This work was done by Hua Jiang of NZ Applied Technologies for Glenn Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4 -8
21000 Brookpark Road
Refer to LEW-16762.