The advantages of using 1 kW generators, similar to microwave oven magnetrons (7kW), have already been reported in the literature [3]. Such generators are presently mass produced for the microwave oven market at a very low cost. In addition, the frequency of operation is suitable to minimize diffraction effects in the ionosphere. Six-Port Junctions Six-port junctions have been used for the measurement of reflection coefficients, S-parameters, impedances, power flow, etc., for many years [5-7], More recently, a six-port junction setup was used to measure the relative amplitude and phase of two oppositely directed waves on a transmission line where the reflected wave was launched by a signal generator rather than by an impedance mismatch. This principle has also been applied for automated multiharmonic load-pull measurements and for antenna polarization measurements [8-9], The six-port junction can generally be built by connecting together a number of components (power dividers, hybrids, etc.) or by using special compact circuits such that the three Q points are defined and well separated at each operating frequency as illustrated in Figure 1. [4-5] Once the six-port junction is calibrated, i.e. the position of the Q points in the complex plane are known, it is possible to determine the reflection coefficient of a DUT by measuring the relative power levels P3, P4, P5, and P6, at each of the four output ports as shown in Figure 2. [8, 10], Calibration and Interface The calibration procedure to determine the position of the Q points is very important. Different methodologies were used to relate the four power readings to the complex reflection coefficient including linear and non linear formulations [ 10-12]. The number of standard loads and the computational effort to calibrate the six-port reflectometer are the most important criteria in the selection of any calibration method. One of the most convenient methods was proposed in [10]. For the purpose of controlling a large number of channels , it is best to convert the RF power readings from each junction into a digital format for control and measurement by a central computer via a bus (e.g. IEEE-488) using optical fiber transmission lines. Such an arrangement can facilitate the gathering of the numerous readings at a central computer for numerical processing and beam control purposes. Configuration for an "NxM" Channel Array Configuration with Modulation Figure 3 shows a block diagram of an NxM channel array where each channel contains a microwave power generator, a module for amplitude and phase control, a six-port junction, and a radiating clement.
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