TB 9-5985-314-24
7. Definitions. Explanation of terms peculiar to directional couplers are listed in a
through d below to ensure accurate interpretation of the measurement techniques used in
this procedure.
a. Nominal Coupling. The nominal loss between the primary input port and the
auxiliary side arm port, with the output port terminated, is called coupling. Normally
coupling is expressed in dB.
b. Coupling Variation. The maximum average deviation from the coupling value
resulting from manufacturing process, is called coupling variation and is normally
expressed in dB.
c. Frequency Sensitivity. The allowable deviation from the average coupling value
(coupling variation), resulting from the frequency characteristics of a directional coupler, is
called frequency sensitivity and is normally expressed in dB.
d. Directivity. The difference between the coupling value (in dB) and the insertion
loss (isolation) (in dB) measured between the output port and side arm port (reverse
direction) with the input port terminated is called directivity and is expressed in dB.
8. Equipment Setup
a. Use Appendix A to determine TI parameters as listed in (1) through (5) below:
(1) Frequency range.
(2) Coupling value.
(3) Coupling variation.
(4) Frequency sensitivity.
(5) Directivity.
b. Select appropriate equipment setup for TI frequency range from figures as listed in
(1) through (3) below:
(1) 10 MHz to 18 GHz, figure 1.
(2) 18 to 26.5 GHz, figure 2.
(3) 26.5 to 40 GHz, figure 3.
c. Determine and record a minimum of 10 evenly spaced test frequencies over the TI
entire frequency range.
d. Connect equipment as shown in figures 1, 2, or 3 and allow 1 hour for equipment