Editing Microwave (section)

== Frequency measurement ==

[[File:Ondamtr.JPG|thumb|upright=0.75|[[Absorption wavemeter]] for measuring in the K<sub>u</sub> band]]
Microwave frequency can be measured by either electronic or mechanical techniques.

[[Frequency counter]]s or high frequency [[heterodyne]] systems can be used. Here the unknown frequency is compared with harmonics of a known lower frequency by use of a low-frequency generator, a harmonic generator and a mixer. The accuracy of the measurement is limited by the accuracy and stability of the reference source.

Mechanical methods require a tunable resonator such as an [[absorption wavemeter]], which has a known relation between a physical dimension and frequency.

In a laboratory setting, [[Lecher lines]] can be used to directly measure the wavelength on a transmission line made of parallel wires, the frequency can then be calculated. A similar technique is to use a slotted [[waveguide]] or slotted coaxial line to directly measure the wavelength. These devices consist of a probe introduced into the line through a longitudinal slot so that the probe is free to travel up and down the line. Slotted lines are primarily intended for measurement of the [[voltage standing wave ratio]] on the line. However, provided a [[standing wave]] is present, they may also be used to measure the distance between the [[node (physics)|nodes]], which is equal to half the wavelength. The precision of this method is limited by the determination of the nodal locations.