Slotted Line

a device for measuring parameters in devices that have distributed constants (such as feeders or wave guides). It is used to find the standing-wave ratio (SWR) and the displacement d of the nodes or antinodes of the electric field intensity along the line; other physical quantities (total resistance, amplitude, and phase; coefficient of reflection) are found in terms of the SWR and d.

Slotted lines in the form of a section of coaxial or wave-guide line connected between a generator G and object being measured Z_l (see Figure 1) are used most frequently; a dial gauge head with a contact probe and a tuning oscillatory circuit (resonator) moves along a section of the line. The voltage from the circuit is fed to the detector and then to the indicator (in many cases, through an amplifier). The electromotive force induced in the probe is proportional to the electromagnetic field intensity at the point of probing. Slotted lines are usually used in the frequency range from hundreds of megahertz to hundreds of gigahertz; the error of a slotted line is 2–5 percent.

Slotted lines are made with fixed probes (squeeze lines), in which the nodes of the standing wave are displaced with respect to the probe by changing the cross section of the wave guide, and with rotating probes, and also as automatic types, with readout on the screen of a cathode-ray tube.

REFERENCES

Valitov, R.A. Radiotekhnicheskie izmereniia. Moscow, 1963.
Tischer, F. Tekhnika izmerenii na sverkhvysokikh chastotakh. Moscow, 1963. (Translated from German.)
Figure 1. Diagram of a slotted line: (P) probe, (H) dial gauge head (carriage), (D) detector, (I) indicator, (S) reference scale for movement of dial gauge head, (G) SHF generator, (A) attenuator, (Z_t) load