© 2020 Virginia Diodes, Inc.
—All Rights Reserved
7 October 2020
Tapers and their Role in
High Frequency Measurements
When measuring signals of frequencies higher than the WR10 waveguide band, but within
standard higher bands, best accuracy is obtained by inserting a linear waveguide taper between
the source and the meter input. Such tapers between WR10 and all higher bands are available as
standard microwave components from VDI, and typically have a length of about 1 inch. These
tapers need not be very long or optimally shaped for low mode conversion, since the sensor load
responds well to higher waveguide modes.
Using Horn Antennas
For free space beams at any frequency, a gradually flared horn (beginning with WR10) should couple radiation into the sensor
waveguide with good efficiency. Within the WR10 band the horn must precisely match the beam properties since the waveguide
carries only one mode in band. At much higher frequencies, the horn should be sized so that the aperture is somewhat larger than
the expected beam size, and a precise beam match is not needed, since the waveguide can carry several modes. DO NOT use a
horn tapering down to single mode size, and then a taper up to WR10, since this adds greatly to the waveguide loss, and makes
mode matching much more critical.
Flange Details
The UG387 waveguide Flange is nickel plated copper and its tapped
holes can be stripped very easily compared to waveguide parts
constructed of different metals. Repair of the waveguide Flange is difficult
once threads are damaged. Do not over-tighten these screws since this
leads to progressive thread damage. There is no advantage to tightening
these screws beyond initial snug contact between flanges. VDI has supplied a 1” section
of WR10 waveguide to help prevent damage to the sensor Flange. VDI recommends the
use of this section for all measurements. Please see information about tapers at the top
of this page and Appendix Two
: “VDI’s Power Correction Factors.”
Caution
Tapped holes
in the nickel
plated copper
waveguide
Flange can be
easily stripped.
Using Tapers and Horn Antennas
Section
Five
Figure 2:
Interface Flange for 1-inch and 2-inch waveguides. WR10
waveguide is shown above. All dimensions are in inches.
