QKS6177, a 2-watt CW C-Band magnetron, is saw-toothed, frequency-modulated for use in an altimeter. There are also a number of ways of electronically tuning a magnetron as a backup approach. The circuit schematic for the new design is shown in Figs. 6 and 7. Figure 6 shows the circuit schematic of all of the low power microwave components that are mounted either on the slotted face of the antenna or in the voids between the waveguides. These components connect with the high-power, high-temperature side of the module shown in Fig. 7 by coaxial cable. The phase comparison of the output of both magnetrons with respect to the drive reference is made with phase comparators mounted on the surface of the slotted waveguide module. The output phase information is brought to them from directional couplers attached to the two arms of the “Magic T” by small coaxial lines. A portion of the input signal is sampled and fed into the other input arm of the comparators. The DC output of the comparators is fed through amplifiers of appropriate design and returned to the voice coils of the tuners of the respective magnetrons. It is likely that additional coils attached to the tuner to sense the velocity of the tuner will be needed for feedback control purposes, and this information will be conducted back to the amplifier on the waveguide surface. The microwave transmission lines that provide phase information also provide amplitude information so that the output amplitudes of the two magnetrons can be compared, and any error signal fed back to one (not both) of the buck-boost coils to increase or decrease the power in that tube to match the other tube. It is noted that the microwave load attached to the third port of the circulator will absorb any reflected power, and that this location is also the most sensitive indicator of any reverse directed power. However, an amplitude sensor at this point is insensitive to which of the two tubes has the higher or lower power. The physical separation of the sensors and solid state circuitry from the microwave power generation makes necessary somewhat involved interconnections, well
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