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The receive antenna was installed in its permanent location inside the chamber
A spectrum analyzer was used to monitor the receive antenna, the frequency span set to zero, and the sweep time equal to the time of one full paddle revolution
A known signal was injected into the chamber (this was the same frequency and power as was used during the calibration) and verified with a directional coupler and power meter
The paddlewheel was rotated continuously while the spectrum analyzer took one sweep
A calculation of the field strength was made from the peak power sampled across one tuner rotation using the equation below:
Comparison with E-field probe
The field strength calculated from the peak receive antenna was then compared against the average of the nine peak e-field probe resultants taken during the chamber calibration at that frequency, and a dB delta between the two calculated and shown in the graph below
If the calculated field strength from the receive antenna was lower than the average peak resultant measured, then it is indicated by a negative number, if it was higher, the number is positive
Multiple receive antennas were used to create the comparison in the graphs below
Using the data above it was determined the antennas were in general a worst case style of measurement. The only exception being the 400 MHz – 1 GHz range.
The discone antenna demonstrated a closer match to the isotropic probe readings, and it was therefore decided to use the discone antenna for testing.
In all cases, the dB delta of the peaks seen above the e-field probe were within the total error tolerances of the measurement equipment
Receive Antenna Uniformity
The receive antenna calculated peak field was integrated into the uniformity measurements for an evaluation of the impact it will have on the uniformity, for a total of ten measurement points for the uniformity