MIL-DTL-5815H
4.7.4 Sampling probe attenuation measurements (see 3.9). Attenuation measurements may be made with a
network analyzer, or with the following method. A signal source shall be connected through a 50 ohm calibrated rf
attenuator to the antenna input connector and the output of the sampling probe shall be connected to a calibrated
receiving detector. The output of the probe shall be noted on the detector, after which, the antenna and probe shall
be removed from the circuit and a suitable connector-adapter substitute therefore. Without changing power or
sensitivity, the attenuator shall be adjusted to produce the reading noted previously on the detector. The difference in
reading, in dB, on the attenuators with and without the antenna and probe in place shall be the probe attenuation. All
rf interconnections shall be made by means of nominal 50 ohm coaxial cables (and connectors) and mismatch of both
the signal generator and the detector used for making the measurements shall be reduced as low as possible. The
attenuation of the antenna shall be measured over the frequency range (see 3.1) at interval no greater than 25 MHz.
(Sweep frequency techniques may be used.) The cable length between the antenna and the measuring equipments
shall not be greater than 6 feet. Each antenna shall be subjected to the attenuation tests both before and after
completion of the environmental tests.
4.7.5 Radiation pattern (see 3.10). The radiation pattern shall be measured with the antenna mounted in the
center of an eight-foot circular ground plane. The measurements shall be made on a continuously recording
automatic antenna range. Care shall be taken to avoid errors due to reflections from the earth and from nearby
objects (this does not prohibit the use of properly designed reflection ranges). The antenna under test shall be
considered as positioned at the origin of the standard right-handed spherical coordinate system shown in IEEE STD
149, with the plane of the antenna blade in the x-z plane and the long axis of the antenna blade along the z-axis. The
leading edge of the blade shall face the direction of increasing x and the top shall face the direction of increasing z.
The ground plane shall be in the x-y plane of the coordinate system. For each sample antenna, polar decibel
radiation patterns shall be recorded every 25 MHz from 225 to 400 MHz as follows:
a. Azimuth (conical) patterns (0° ≤ Ф ≤ 360°) for θ = 60° and 90°.
b. Vertical (great-circle) patterns (0° ≤ θ ≤ 90°) for Ф = 0°, 90°, 180°, and 270°.
Like vertical patterns shall be made for comparison, using the same frequencies and power levels, for a matched
quarter-wave stub antenna. The stub antenna shall be mounted in the same manner and location and with the same
polarization as the test antenna. Each comparison pattern shall be taken immediately after, and recorded on the
same sheet as, the corresponding test antenna pattern. There shall be only one test antenna pattern and one
comparison pattern per sheet. A separate and distinctive recording trace shall be used such that, on the original and
on any copies of the pattern recordings, it is possible to distinguish the test and the comparison antenna patterns.
There shall be no change of equipment, equipment settings, personnel, or operating technique that would affect the
consistency of the results. All patterns shall be clearly labeled with the sample number, the test frequency, and the
angles involved. The labeling of the angles shall be such that, for any pattern, the specific values of θ and Ф
associated with any measured point can be readily and unambiguously determined.
4.7.6 Polarization (see 3.11). The polarization performance shall be measured using the polarization-pattern
method (see IEEE STD 149). The antenna shall be positioned and oriented in the same manner as for the radiation
pattern measurements. The test frequency shall be 315 MHz. For each test sample, polarization patterns shall be
obtained and from them the axial ratio of the polarization ellipse determined, for the following directions (θ, Ф):
(60°, 0°), (60°, 90°), (60°, 180°), (60°, 270°)
(90°, 0°), (90°, 90°), (90°, 180°), (90°, 270°)
For comparison, like polarization patterns shall be obtained and the axial ratio of the polarization ellipse determined
for a matched quarter-wave stub antenna, using the same frequency and power level. The stub antenna shall be
mounted in the same manner and location and with the same polarization as the test antenna. Each comparison
pattern shall be taken as soon as practicable after the corresponding test antenna pattern such that there is no effect
on the consistency of the results. Each polarization pattern shall be clearly labeled with the sample number (when
applicable) and the direction involved. There shall be no change of equipment, equipment settings, personnel, or
operating technique that would affect the consistency of the results.
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