Electronically tunable antenna

Claim 1

In a microwave receiving antenna assembly designated to operate over a broad band of frequencies, said antenna assembly including a pair of dipoles of fixed physical dimensions aligned end-to-end in spaced apart linear relationship, the improvement which comprises: means for maintaining said antenna assembly in resonance throughout the band of frequencies over which it is designed to operate, thereby avoiding the degradation in signal reception which would result from an out-of-resonance condition at frequencies other than the antenna tuned frequency; said means for maintaining said antenna assembly in resonance over said frequency band including an electrically-tunable ferrite member in the form of an yttrium-iron-garnet crystal of spherical configuration possessing gyromagnetic properties disposed intermediate said spaced-apart dipoles and electromagnetically associated therewith; a source of D.C. current; means for supplying D.C. current from said source to electrically tune said ferrite member; and at least one permanent magnet disposed adjacent said YIG crystal, the latter lying in the field of constant intensity developed by said magnet.