Locking of magnetrons by an injected RF signal

The ability to lock the frequency of magnetron oscillators with an injected RF signal allows these high-efficiency devices to be utilized in modern radars which require electronic frequency variation or pulse-to-pulse phase coherence. Furthermore, this ability allows magnetrons to be cascaded in order to obtain an output power greater than a single tube. An equivalent circuit has been used to compute the locked performance of composite magnetrons containing up to ten sections. The required equivalent circuit parameters may be determined, for example, from the Rieke diagram of the prototype section. Both reciprocal and non-reciprocal (circulator) coupling schemes have been studied. Circulator coupling provides better gain-bandwidth and stability. Reciprocal coupling offers lower dissipation and a more compact structure, and by proper circuit techniques "reflectionless" operation is possible. Both types of coupling may be used to advantage in the same array. Experimental verification of the concepts has been obtained at X-band with peak powers of several hundred kilowatts using packaged magnetrons. A single tube with circulator coupling and arrays of up to three magetrons using reciprocal coupling have been tested.