Purpose: to measure the spectrum of a short-term pulsed high-power microwaves (HPM) distributed over a large cross section.
Operational principle: cut-off waveguides reflect microwaves with frequencies below certain value, and are transparent to microwaves with higher frequencies. An ensemble of circular waveguides packed together (so-called "microwave cut-off filter") operates similar to a stand-alone waveguide.
I. L. Bogdankevich, P. S. Strelkov, V. P. Tarakanov, et al. "A calorimetric spectrometer measuring single pulses of relativistic microwave generators". Instruments and Experimental Techniques, vol. 43, No. 1, 2000, pp. 82-87.
Main components: calorimeter(s), cut-off filter(s).
2-piece configuration: ring-shaped calorimeter to measure the fraction of lower frequencies reflected from the filter; disk-shaped calorimeter to measure the fraction of higher frequencies penetrated through the filter; two electronic blocks, one for each calorimeter; a set of cut-off filters; container.
Typical parameters: are determined mainly by that of calorimeter(s) (e.g., diameter 56 cm, sensitivity 0.15 J and frequency band 1.5 GHz - 60 GHz) and the set of filters.
Area of application: effective in case of bad reproducibility of microwave power from pulse to pulse.
Advantage: all the HPM power is registered irrespectively to its particular distribution. The ratio of the signals from the two calorimeters (which corresponds to the spectrum) varies less than the power.
1-piece configuration: ring-shaped calorimeter is absent, the gap between the horn and the filters is substantial (~ the longest wavelength emitted). The configuration is recommended in case of good reproducibility of HPM power from pulse to pulse. The configuration comprises one calorimeter, a set of several filters and the container.
Advantage: more simple in use and cheaper comparatively to the 2-piece configuration.
Drawback: it does not provide the information about the total HPM pulse power.