MIL-DTL-23971D
4.7.4 VSWR (see 3.5.2). The VSWR of each port shall be measured across the full frequency range (see 3.1)
using sweep frequency technique and the test setup of figure 2 or equivalent. Each unused port shall be terminated
in a matched load. VSWR may be measured at fixed frequencies using figure 3 or equivalent, at seven equally
spaced points across the frequency range (see 3.1). The accuracy of each measurement shall be within .1 dB.
4.7.5 Insertion loss (see 3.5.3). The insertion loss shall be determined by subtracting the nominal value of the
divider from the measured average coupling value (see 4.7.3).
4.7.6 Isolation (see 3.5.4). The isolation (in dB) shall be measured using the sweep frequency technique across
the full frequency range (see 3.1) of the item, using the test setup of figure 4 or equivalent. The isolation may be
measured at 7 equally spaced points across the frequency range of the items (see 3.1). The accuracy of each
measurement shall be within .1 dB. The procedures for measuring the isolation of the various items are as follows.
4.7.6.1 Power divider, quadrature. The isolation shall be measured between any selected port and adjacent
isolated port with the opposite output ports terminated with matched loads (VSWR of 1.02). Repeat the
measurement for each remaining port.
4.7.6.2 Power combiner. The isolation shall be measured between two input ports with the output port and any
additional input ports (if any) terminated with matched loads (VSWR of 1.02). Repeat the measurement for each
additional input port.
4.7.6.3 Power divider-combiner. The isolation shall be measured between the symmetric and anti-symmetric ports
with the output ports terminated with loads matched to each other (VSWR of 1.02) or in open circuits if matched loads
are not obtainable. Next, the isolation shall be measured between two output ports with the remaining output ports, if
any, and symmetric and anti-symmetric ports terminated in matched loads (VSWR of 1.02).
4.7.7 Phase balance (see 3.5.5). The phase balance shall be measured at the low end, middle, and high end of
the frequency range (see 3.1) using the test setup of figure 5 or equivalent. Suggested test procedures for the
various items are as follows.
4.7.7.1 Power divider, quadrature. The phase balance of the item shall be measured between the output ports
with the other co-linear output port and the adjacent isolated port terminated in matched loads (VSWR of 1.02).
Repeat the measurement for any remaining ports.
4.7.7.2 Power combiner. The phase balance of the item shall be measured as the difference at the output
between in-phase signals at two input ports with the remaining input ports terminated in matched loads (VSWR of
1.02). Repeat the measurement for each remaining input port.
4.7.7.3 Power divider-combiner. The phase balance of the item shall be measured between the symmetric port
and an output port with the anti-symmetric port and remaining output ports terminated in matched loads (VSWR of
1.02). Repeat the measurement for each remaining output port. Next, measure the phase balance between the anti-
symmetric port and an output with the remaining output ports terminated in matched loads (VSWR of 1.02). Repeat
the measurements for each output port.
4.7.8 Amplitude balance (see 3.5.6).
4.7.8.1 Power divider, quadrature. Use the test procedure of 4.7.7 and 4.7.7.1 except read the amplitude balance.
4.7.8.2 Power combiner. Use the test procedure of 4.7.7 and 4.7.7.2 except read the amplitude balance.
4.7.9 Power level (see 3.5.7). The specified peak and average power shall be applied simultaneously at any
frequency within the specified range (see 3.1). When no peak power is specified, apply 1.5 times rated average
power. Power shall be maintained for a period of 15 minutes after the item has reached thermal equilibrium. It is
considered that thermal equilibrium has been reached when the temperature of the item has not changed by more
than 5°C over a period of 5 minutes. For pressurized items, the internal pressure shall be as specified (see 3.1).
Following the exposure, the VSWR, insertion loss, and isolation shall then be measured as specified in 4.7.4, 4.7.5,
and 4.7.6, respectively.
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