Tunable microwave oscillators employing narrowband MSSW delay lines

A recently reported experimental study of microwave tunable oscillators employing narrowband magnetostatic-wave (MSW) delay lines is reviewed. The narrowbanding was achieved by using lifted transducers with magnetostatic surface waves (MSSWs) which yielded a bandwidth of 10 MHz with an insertion loss of less than 20dB. This approach at delay-line narrowbanding does not work as well with the other MSW wave-types because of increased insertion loss. The mode-hopping problem which beset earlier studies of MSW delay-line oscillators was overcome in the present work but now a different problem arose, viz., frequency jumping, which occurred every time the electrical length of the circuit external to the delay line changed by 360 degrees. A maximum tuning range of about 600 MHz was obtained, with this range limited primarily by the Avantek GaAs FET amplifier that was used whose electrical length was equivalent to about 45 cm of air transmission line. It was concluded that, if the electrical length of the external circuit is sufficiently reduced (ideally made zero), singlemode operation over an octave bandwidth or more is possible.