ELECTRONICALLY TUNABLE YIG FILTERS WITH ELECTRONICALLY VARIABLE BANDWIDTH.

The purpose of this work is to develop an electronically tunable YIG bandpass filter with electronically variable bandwidth. The center frequency is to vary from 2.0 to 4.0 Gc and the bandwidth from 5 Mc to 50 Mc independently of the center frequency. In this report a theoretical background is presented for the method of varying the bandwidth of a YIG filter by changing the angle between the dc biasing field H sub dc and the incident rf magnetic field h sub rf. The results are then used to analyze single and double-resonator YIG filters. Experimental results agree with the theory for a single-resonator circuit. A two-resonator YIG filter has thus far yielded a 3.21 change in bandwidth but at the expense of a 12 db insertion loss at the narrowest 5 Mc bandwidth. The role of the coupling coefficient K between the YIG resonators is analyzed since the rapid increase of insertion loss and the failure to obtain larger changes in bandwidth is felt to be due to variations in K such that the product KQ sub e does not remain constant. Experimental results are presented for a two-resonator YIG filter using a number of differently shaped coupling apertures. Author