V.А. Kolomejcev, А.V. Ezopov, A.E. Semenov
Pulsed mode of RTM operation depends on parameters of sequential rectangular pulses: period Т; pulse width τим; duty cycle Q. Specific density of thermal sources in the pulse qv = q0vQ. In finding maximum allowable radiated microwave power the steady state is the regime of interest, where the temperature of RTM's active element reaches its maximum value. The feature of the steady state in pulsed mode is that the temperature tуст is not constant and periodically changes with the period Т changes. The temperature reaches its maximum at the end of the pulsed action τ = τим (heating mode) and drops to its minimum value at τ = nT (cooling mode). RTM's pulsed mode's specifics is the constancy of thermal power in the pulse. This means that the value of the non-uniform part of the thermal equation is constant.
It is shown that the decrease of pulses' width τим increases the range of heating temperatures ∆t = tmax – tmin due to increase of microwave power in the pulse with increasing of duty cycle Q. The temperature in the heating mode nT ≤ τ ≤ (nT+Tим) changes faster than in the cooling mode (nT+τим) ≤τ≤ (n+1)T. If Q > 2, the deviation of maximum temperature increases from the established temperature when τим decreases, and the minimum temperature decreases from tуст. This position is crucial because it reduces RTM's power output and therefore the range of target detection.
Results of tmax, tmin, tср calculation for monolithic scheme of RTM for various durations of the thermal pulse are shown in the output area of MMIC. A comparative analysis of the data is done. It shows that the copper base of MMIC leads to sharp decrease in the temperature model tmax and the average temperature tср. It is concluded that for the RTM the most appropriate mode is pulsed mode with short pulse duration of 5 ms. Listed data were received as result of internal boundary value problem solution of RTM's two-layer model solving, which takes into account thermal processes in MMIC and metallic base.