The microwave signals at each radiator need to be at the same frequency and the only variables are the signal phases and amplitudes. The "pseudo-reflection coefficients" measured at each channel by the six-port correspond to the ratios of reflected waves to the incident wave generated by the reference channel generator. The reflected waves can originate from the actual physical reflections within the transmission line itself, Go, and the various signals generated by mutual coupling between a radiating element and its nearest neighbors. Thus, in a reference channel (0), one can measure four reflection coefficients GOE, Gow, Gos, and GON, which correspond to the reflection coefficients of the various waves coupled into the reference channel from the nearest radiators (E, W, N, and S). In addition, a reflection coefficient, Goo corresponding to the reference channel mismatch can also be obtained. In all cases, the six-port junctions can provide all of the above reflection coefficients if the signals are coded, e.g. by low frequency amplitude modulation [12]. Thus, a change in the reflection coefficient GOE corresponds to a change in phase between the reference channel (0) and the adjacent eastern channel (E). It is thus possible, when all the channels of the array contain a six-port, to measure and control the relative phase differences between channel (0) and a given E, W, N, or S channel. Signal code patterns for the array can be used for channel identification such that the various reflection coefficients between channel (0) and adjacent channels can be identified from the measurements as illustrated in Figure 4. In the case where the coupling with the second closest antennas is not negligible, an appropriate signal code pattern for the array must be used for proper channel identification. Configuration without Modulation In this configuration, the six-port junctions is placed between each pair of radiating elements as shown in Figure 5. In a given array, the arrangement of the system is illustrated in Figure 6. The total number of six-port junctions needed for an array of NxM radiating elements is (N-I)M + (M-I)N, which is almost twice the number needed in the first configuration. In this situation, no modulation is required because we do not have to distinguish between multiple signals. The ratio of two signals feeding a pair of radiating elements, as shown in Figure 5, can be calculated from the calibration parameters and the four relative power readings P3, P4, P5, and P6, of the six-port junction. The measurement of the relative phase and amplitude of the signal of each radiating element allows the use of analogue phase shifters and attenuators (or variable gain amplifiers) without a need to precalibrate those devices. In addition, the measurement data obtained by the six-port junctions can be used by the central control system of the array to detect a malfunction of one radiating element when such elements cannot be adjusted. This last consideration also applies to the configuration with modulation. Conclusions In this paper it was shown that six-port techniquescan be used for the control of an NxM phased array antenna on microwave power satellites. Two configurations,
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