Design and development of compact coaxial to coplanar waveguide directional coupler for HPM measurement.

A compact, high-directivity, weak-coupling directional coupler with coaxial-coplanar waveguide structure and diamond-shaped coupling slot was developed at L band for a high-power microwave measurement by both theoretical analysis and experiments. The relation between the dimension of the coupling slot and the characteristic parameters of the coupler was studied by the small-hole coupling theory and the infinitesimal method. According to the analysis results, the directivity could be better than 20 dB while the length of the slot is just less than a single λ because of the use of the diamond coupling slot. For demonstration, a 45-dB L band coaxial-coplanar waveguide directional coupler was designed and verified by test. The experiment results and the theoretical analysis are in good agreement, which indicates that in the range of 1-2 GHz, the coupling was approximately -45 dB and the directivity was better than 17 dB. The power-handling capacity was demonstrated to reach 2 MW with a length (150 mm) of less than λ and a cross section (46 mm × 55 mm) of less than one-twelfth of the BJ-14 waveguide directional coupler.

Research on calorimeter for high-power microwave measurements.

Based on measurement of the volume increment of polar liquid that is a result of heating by absorbed microwave energy, two types of calorimeters with coaxial capacitive probes for measurement of high-power microwave energy are designed in this paper. The first is an "inline" calorimeter, which is placed as an absorbing load at the end of the output waveguide, and the second is an "offline" calorimeter that is placed 20 cm away from the radiation horn of the high-power microwave generator. Ethanol and high density polyethylene are used as the absorbing and housing materials, respectively. Results from both simulations and a "cold test" on a 9.3 GHz klystron show that the "inline" calorimeter has a measurement range of more than 100 J and an energy absorption coefficient of 93%, while the experimental results on a 9.3 GHz relativistic backward-wave oscillator show that the device's power capacity is approximately 0.9 GW. The same experiments were also carried out for the "offline" calorimeter, and the results indicate that it can be used to eliminate the effects of the shock of the solenoid on the measurement curves and that the device has a higher power capacity of 2.5 GW. The results of the numerical simulations, the "cold tests," and the experiments show good agreement.