Klystronmicrowave Cylindrical Coaxial Cavity Loaded With Rectangular Output Waveguide Filter

The characteristic of TM_n10-mode in cylindrical coaxial cavities of klystron isstudied. By increase the number of drift tubes in cavity and the external radius of drifttubes that will pass the electron beam and decrease the external radius of other drifttubes, mode rotation is restrained and fields’ uniformity at each gap improvedeffectively. A single gap X-band output circuit of cylindrical coaxial cavity klystronoperating at transverse magnetic TM₃₁₀-mode with low external quality factor isdesigned. Characteristic impedances at the positions of six longitudinal electric fieldpeak values i.e. shift tubes center are simulated with CST at the resonant frequency.Higher order TM₃₁₀mode in single gap coaxial resonator cavity loaded with rectangularwaveguide with a pair of diaphragms is analyzed and the gap impedances at six drifttubes center are simulated and calculated based on the cold test simulation method. Thepeak value of gap impedance is about3,500ohm, and the bandwidth is narrow. Theresonant frequency of resonator cavity output circuit is calculated by the group delaycharacteristic, and the external quality factor is calculated.The gap impedance imaginary part and real part of output circuit is calculated withequivalent circuit method. Only the length between equivalent gap center of drift tubesand the transverse diaphragms in output waveguide is unknown in the gap impedanceformulas. The simulation calculation method of the length in traditional cylindricalcavity output circuit is not applicable for the cylindrical coaxial cavity. So a newmethod to calculate the length according as the gap impedance imaginary part is zero atthe working center frequency is put forward, which is also applicable for studyingoutput circuit of high order transverse magnetic mode in the cylindrical cavity outputcircuit. Equivalent gap impedance of cylindrical coaxial cavity coupled with waveguidefilter is calculated based on the length with MATLAB programming, and the result isapproximating with that of the cold test. It shows that the equivalent length calculation method of is right. The real part of gap impedance is also calculated based on fieldanalysis method; the two group results are approximating the same，just slightlysmaller.A double gap cylindrical coaxial resonator cavity operating at center frequency9.8GHz loaded with two pairs of diaphragms rectangular waveguide filter is designedwith cold test and field analysis method respectively. The impedance peak value withcold test method is at the center frequency, however field analysis method isn’t. Thismay be due to the limitations of the method itself.A double gap cylindrical coaxial output cavity operating at center frequency9.8GHz loaded with empty and one pair of inductance diaphragms rectangularwaveguide filter output circuit is designed. The3dB bandwidth of output circuit withempty waveguide is about0.98%, By adjusting the diaphragms, the gap impedancefrequency characteristic curve of3db bandwidth （saddle） increased to6.6%and6.6%respectively （flat）. Compared with two groups of diaphragms situation, relativebandwidth increase approximately30times, gap impedance peak values fell about6times.