MIL-DTL-15370J
4.7.5 Coupling (see 3.5.1). The coupling of directional couplers shall be determined by obtaining the midpoint
between the maximum and minimum coupling over the specified frequency range. The coupling of unidirectional
couplers shall be determined as the ratio, expressed in dB, of the power input to the primary line to the power
available at the output of the secondary line, with the output end of the primary line properly terminated. The coupling
of bidirectional couplers shall be determined separately for each secondary line.
4.7.6 Coupling variation (see 3.5.2). The coupling variation of directional couplers shall be determined over the
specified frequency range (see 3.1). The coupling variation of unidirectional couplers shall be determined by taking
the difference between the maximum and the minimum coupling over the specified frequency range. Such difference
shall be taken as a positive number or zero. The coupling variation of bidirectional couplers shall be determined
separately for each secondary line.
4.7.7 Effective directivity (see 3.5.3). The effective directivity of directional couplers shall be determined over the
specified frequency (see 3.1). The effective directivity of unidirectional couplers shall be computed from the ratio,
taken as greater than unity and expressed in dB, of the available power at the output of the secondary line for the two
directions of excitation, at equal power levels, of the primary line; the secondary line shall be terminated in a matched
termination. The effective directivity of bidirectional couplers shall be determined separately for each secondary line.
The alternate test (see 4.7.7.1) may be used as a substitute test with the prior approval of the preparing activity.
4.7.7.1 Alternate test. The effective directivity of directional couplers shall be determined over the specified
frequency range. The effective directivity shall be computed from the difference between measurements of minimum
and maximum outputs of a secondary line, when a short circuit is displaced through one-half a wave-length in the
primary line. The generator at the primary line shall be matched to the primary line. The effective directivity of
bidirectional couplers shall be determined separately for each secondary line with the remaining secondary lines
terminated by an impedance equal to the characteristic impedance of the secondary line.
4.7.8 Insertion loss (see 3.5.4). The insertion loss shall be measured by a substitution technique using radio,
audio, or intermediate frequency (RF, AF, or IF). An average of three test runs shall be used as a final result. The
insertion loss (dB) to be applied shall be determined from the following formula:
(dB) Insertion loss = P(in) - P(out) - coupling split loss
4.7.9 VSWR (see 3.5.5).
4.7.9.1 Primary line (see 3.5.5.1). The VSWR of directional couplers shall be measured over the specified
frequency range (see 3.1). The VSWR of unidirectional couplers shall be measured at the input end of the primary
line, with the output end of the primary line and the secondary line terminated in matched loads. The VSWR of
bidirectional couplers shall be measured at one end of the primary line, with the other end terminated in a matched
load; the secondary lines shall be terminated in matched loads.
4.7.9.2 Secondary line (see 3.5.5.2). The VSWR of directional couplers shall be measured over the specified
frequency range (see 3.1). The VSWR of unidirectional couplers shall be measured at the output of the secondary
line with both ends of the primary line terminated in matched loads. The VSWR of each secondary line of
bidirectional couplers shall be measured at the output of the secondary line with the other secondary line and both
ends of the primary line terminated in matched loads.
4.7.10 Power dissipation of secondary-line termination (see 3.5.6). The power dissipation of the secondary-line
termination shall be determined over the specified frequency range (see 3.1). The power (P) to be applied shall be
determined from the following formula (see 6.8 for expanded discussion):
[ -α/10 ]
[ -α/10 ]
[ -d/10 ]
P = (Pr) (10
) + (Pi) (10
) (10
)
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