Two-dimensional cyclotron-resonance maser array: Spectral measurements with one and two electron beams

The cyclotron-resonance-maser ~CRM! array is a device in which separate electron beams perform simultaneously a cyclotron interaction with a single Bloch wave in an artificial lattice. The CRM array has the capability of generating high-power microwaves with relatively low-voltage electron beams. The low-voltage operation reduces the system overhead and leads to a relatively compact device. In future schemes, the CRM array may radiate directly to free space as an active phased-array antenna. Furthermore, the phase of each element output, and therefore the antenna far-field radiation pattern, can be varied by the electron-beam voltages. This paper presents an experimental demonstration of a CRM array. In this experiment, a twodimensional CRM array is operated with one and two electron beams ~;10 keV, 0.1 A each!. Microwave output signals are observed in frequencies around 7 GHz in an axial magnetic field of ;3 kG. Spectral measurements of the CRM outputs reveal frequency sweeps along the CRM pulses. These are associated with electron-energy variations, in accordance with the theoretical CRM tuning condition. The synchronism of the cyclotron-resonance interaction with a backward spatial harmonic is confirmed. These results promote the efforts toward the realization of large CRM arrays. @S1063-651X~99!02002-4#