This paper reports the investigations of a dielectric filled relativistic magnetron with diffraction output (MDO) on frequency agile. The mechanism of frequency agile is theoretically analyzed. Particle-in-cell simulations and preliminary experiments prove the analytics. In experiments, under the working conditions, 605 kV and 0.3 T, a microwave with 1.98 GHz, 200 MW is radiated from an A6 type MDO when the 95% Al2O3 ceramics with the total thickness of 0.9 cm are filled. Compared with the microwave of 3.72 GHz, 240 MW obtained without the ceramics filled, the frequency agile from S band to L band is achieved.

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Field analysis method is used to deduce the dispersion relation of rising-sun magnetron with sector cavities, which is proved correct by the high frequency field analysis software, and the influence of each structure parameter of the magnetron on the cutoff frequency of π mode and the mode isolation is investigated. The results show that the relative errors between the theoretical values and the simulation values of the dispersion relation are less than 3%, and the relative errors between the theoretical and simulation cutoff frequencies of π mode are less than 1%. Cutoff frequency of π mode is in direct proportion to the cathode radius Rc, anode radius Ra and big cavity angle 2θ1, but in inverse proportion to small cavity radius Rd0, big cavity radius Rd1 and small cavity angle 2θ0. However, these qualitative relationships are not entirely consistent with those of the same cavity magnetron. In radial orientation, the structure parameters, the influence of which on frequency is sorted in descending order, are as follows: anode radius, big cavity radius, small cavity radius and cathode radius. In angular orientation, the influence of big cavity angle on frequency is greater than that of small cavity angle. In addition, mode isolation γ is in direct proportion to big cavity radius Rd1, but in inverse proportion to cathode radius Rc, small cavity radius Rd0, and small cavity angle 2θ0, and it increases first and then decreases with the increase in anode radius Ra or big cavity angle 2θ1.

The physical mechanism of the radiation generation of all possible output modes of the relativistic magnetron (RM) with all cavity-magnetron axial extraction technique is theoretically analysed, and the necessary conditions for generating these modes are obtained respectively. Assuming that n 0 is the number of the electron spokes, N ≥ 4 as the total number of the cavities is an even number, and k is a nonnegative integer, some conclusions can be drawn as follows. If n 0 = kN is true, no mode can be excited in the coaxial waveguide; if n 0 = (2k + 1)N/4 is true, the linearly polarized modes can be excited in the coaxial waveguide; if n 0 = (4k + 2)N/4 is true, the TEM mode and the linearly polarized modes can be excited in the coaxial waveguide; if n 0 takes other value, the left and right circularly polarized modes can be excited in the coaxial waveguide and the directions of rotation of the circularly polarized modes can be reversed with the reversion of the direction of rotation of the electron spokes; in addition, some other regular characteristics of the corresponding mode excitation are presented in detail in this paper. Such unique attractive properties that have been verified by the cold and hot simulations in this paper make it possible for this type of RM to meet application requirements of various high power microwave (HPM) modes.