measurements is greater than for the diode. For one set of measurements the circuit loss was set at 2.37%± 0.4%. A novel method for accurately measuring diode losses was developed under this contract. The method made use of a ground-plane test fixture in which the balanced rectenna element is simulated by splitting the element into two halves and then locating one half of the element above a ground plane. This permits the use of a thermistor bridge to measure the temperature rise in the diode as the result of power dissipated inside the diode. The bridge is calibrated in terms of power dissipated in the diode by injecting and accurately measuring DC power into the diode. However, the measurement technique is insensitive to whether the heating source is DC power or microwave power since both are dissipated within the diode semiconductor chip. Hence when the diode is operating normally in the rectenna element as a microwave power rectifier the power dissipation is determined from the thermistor bridge and assumed to be the total loss in the diode as it is normally used. 4. Mathematical Modeling and Computer Simulation The rectenna element, although it has the mechanical appearance of being a simple device, and in the half wave rectifier configuration is indeed the simplest electrical device, is nevertheless an electrically very complex device when it is examined in detail. This complexity is caused by the high non-linearity of the device, which generates harmonic power which greatly complicates the waveforms of the voltage and current within the element. To analyze the behavior of the device in detail it is necessary to resort to computer simulation based upon a reasonable mathematical model of the element. Under this contract, a successful effort in mathematical modelling the element and simulating its performance on a computer has been successfully carried out and has resulted in a technique that is certain to be of great importance in further refinement of the rectenna element. The computer simulation program has generally given results that confirm the experimental results, but upon occasion has indicated differences which have led to investigations to resolve the differences. For example the diode losses were first computed on the basis of the theoretical design of the diode and found to be less than those measured. It was found that the forward voltage drop as measured by DC voltage measurements was greater than that predicted from theory leading to the conclusion that the ohmic contact is not purely ohmic but retains some Schottky barrier characteristics which contribute to the voltage drop.
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