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Equipment: Two antenna stands, one of them should have a turntable on the top.
Antenna stands' heights should reach the using conditions of antenna's design. In
principle, it should be larger than two operating wavelengths. The distance between
the two stands should be longer than 10 times of the operating wavelength
(short-wave antenna and other antennas which the operating wavelengths are very
long, shortening the spacing is acceptable). If necessary, user can do several meas-
urements with different distances and take the average value among the results to
remove the influence which is from the ground reflection. Prepare the cable which is
long enough according to the distance between the stands. Try to make that the dis-
tance between the instrument and the user can be more than 10 times than the
wavelengths. If the gain needs to be tested, prepare another reference antenna which
the gain is already known.
Method: install the testing antenna and the antenna which is under the test on
the stand (Chart 4-3). Testing antenna's main lobe should align the antenna which is
under the test. Make the under-the -test antenna's certain direction (a predicted
main-lobe direction or just mark a direction) align the testing antenna. Set the in-
strument in S21 mode and enter the testing frequency. In normal situation, choose
the small span, 1MHz for example. Do the user calibration in S21 mode to make the
curve return to zero. Turn the under-the-test antenna within a certain angle and rec-
ord the corresponding S parameters (dB) of every angle. Finally, mark the points on
the angle-gain coordinate graph to get the directivity diagram of the under-the-test
antenna.
The measurement mentioned above can also be done in insertion loss mode.
Firstly, enter FIELD mode and choose Insertion to start the insertion measurement.
Then press Auto CAL to make the insertion reading return to zero. Its insertion read-
ing shares the same meaning with the S parameter in S21.
Chart 4-3: Measuring Antenna Gain in an Open Field
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