Investigation Of Problems Related To Power Measurement Of High Power Microwaves Using Far-field Method

The power measurement of high power microwave(HPM) is imprecise because of its features of short pulse duration(10's nanosecond), high power level(the order of gigawatt) and so on. Presented in this paper is the investigation of some problems existing in the far-field method widely used in HPM measurement. First, the errors are analyzed from the practical calculation of the directivity for the radiation of the TE11 mode in the circular waveguide. Secondly, the results obtained from simulation and experiments are compared with each other on the effective area of the receiving antenna of certain types, and the power capacity are calculated for these antenna. Finally, the effects of the pulse duration are measured on the performance of some microwave devices, such as coaxial detectors, attenuators and microwave cables.The comparison is made at certain given frequencies in the case of circular waveguides of diametersΦ242mm,Φ200mm,Φ174mm,Φ100mm andΦ90mm between the simulated directivity D and the approximated directivities DE at E plane and DH at H plane, which are calculated with the hypothesis of axially symmetric radiation patterns usually used in the power measurement of HPM in far-field zones. The results show that in the case of the radiation of the pure TE11 mode, DH is less than D with their difference ranging from 0.1dB~0.8dB, and DE is larger than D with a difference between -1.9dB and-1dB, and that in the case of the radiation of the mixed modes of TE11 and TM01 with power proportions from 5% to 30%, DH is still close to D with the maximum difference less than 1dB, while the difference between DE and D can be as large as -4dB. So the directivity at H plane is closer to the real directivity than the one at E plane. In the circumstances of the TE11 mode mixed with the given parasite modes, the errors from the practically used directivity can be corrected with the calculated difference between DH and D.The effective area of the receiving antenna is calculated with the established models, and measured at some points in the given frequency range. The comparison between the results of calculation and measurement shows that the two results are in good agreement for the broad band antenna in the L band and the waveguide-coax converter of BJ48 type used as antenna in the C band, with a difference of less than 0.7dB, and that the two results also agrees well in the X band for the waveguide-coax converter of BJ100 type used as antenna, with an error close to 1dB only at few points in the given frequency range. At the same time, the power capacity of the above mentioned antenna is preliminarily analyzed. The results show that in the pass band, their power capacities increase with the frequency on the whole, ranging from 10's kW to 100's kW.With the change of the pulse duration of microwaves, the measurement is carried out on the sensitivity of the detectors of the types WB-CD01 and 2087-6001-00, on the attenuation of the...