MIL-DTL-83517A
4.5.11 Voltage standing wave ratio (VSWR) (see 3.14). The VSWR shall be measured in accordance
with the following procedure or a method acceptable to the Government. In the event of dispute the
method outlined herein shall be used. Diagrams for the swept frequency VSWR system check out and
measurement procedures are shown on figure 1.
In the basic measurement setup on figure 1 detector 1 provides a feedback signal to the swept RF source
in order to normalize the output signal of detector 2. The frequency-amplitude characteristics of detectors
1 and 2 should be matched within 0.5 dB.
To measure VSWR several sweeps are made with the slotted line probe incrementally positioned over at
least a half wave length at the lowest frequency of interest. In this manner an X-Y display is generated
whose upper and lower envelope limits represent maximum and minimum amplitudes of the standing
wave for each frequency in the test band. A base line may be generated by making a sweep with no
input to the measurement channel amplifier. The resultant X-Y display is calibrated according to the
characteristics of the measurement channel detector and amplifier, e.g., linear, square law, logarithmic,
etc.
The VSWR test system is checked out by successively terminating the slotted line with the elements
shown in steps 1, 2, and 3 and sweeping the frequency over the specified test band (see 3.1). In step 1
the system VSWR shall be less than 1.02 + .004 frequency (frequency measured in GHz). In steps 2 and
3 the system VSWR shall be as specified (see 3.1).
The hermaphroditic connector (see figure 1) for the standard precision adapter (item 11) and standard
precision test fixture (item 12) shall conform to IEEE 287. The standard test connector interface on
precision adapters shall be in accordance with the appropriate connectors in MIL-STD-348.
Refer to Appendix (see A.3.4) for precision adapters and precision test fixture design parameters.
NOTE: Transition end is considered as part of the complete connector and must be included in all
tests with the surface launch stripline connector. The enlarged terminal end of the contact ("nail
head") is a mechanical feature to attach to the stripline. Its effect is determined by impedance
matching techniques incorporated by the user. Thus, contact modification to adapt to a test fixture is
specified. All situations specifying transition end is covered by one of the specified test methods.
For qualification inspection the connector under test is measured with the slotted line terminated as
in step 4. The VSWR shall be as specified (see 3.1).
NOTE: For steps 1, 2, 3, and 4, see figure 1.
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