WiZeus
> Biography
| Education
| Scientific
| Archive
(Demjanjuk,
Suslensky, Harasymiw, etc.) >
Measurement of the Gain of
a Horn Reflector Antenna
by
William W. Zuzak
A thesis submitted in partial fulfilment of the requirements for the
degree of
Bachelor of Science in
Engineering Physics
in the Faculty of
Engineering,
University of Saskatchewan
April, 1963
SYNOPSIS
The objective of the project was to measure the on-axis gain of an 80
square foot aperture horn reflector antenna to an accuracy of one
percent at three frequency bands: S-band (3000 MC/S), J-band (6500
MC/S), and Ku-band (13,500 MC/S). Usually the gain of antennae
are measured to an accuracy of ten percent or at the most five percent.
As far as is known this was the first attempt to measure the gain of a
large horn to such accuracy. The difficulties were rather prohibitive.
First,
it was decided that the gain of the horn reflector antenna would be
compared with that of an accurately known standard. This forced the
construction and measurement of the gain (to within 0.5 percent) of a
set of standard gain horns. Three pairs of identical standard gain
horns of convenient size were constructed and their gains measured at a
15 foot range. Temperature of the bolometer detectors was controlled,
reradiation was investigated and near-field effects taken into
consideration in the measurements. The results had a maximum estimated
error of plus or minus 0.03 db and compared quite well with theoretical
values.
The horn reflector antenna and the standard gain horn
were mounted on a 50 foot tower to shield them from excessive
reflections. Transmitting antennae, stationed at 500 and 1000 feet,
were small E-plane (electric field horizontal) sectoral horns less than
one foot above a plane reflecting surface, 12 by 40 feet and
covered with aluminum foil.
Field probing apparatus was mounted on the opposite side of the
horn reflector so that by rotating the turntable on which the horn
reflector was mounted through 180 degrees the field occupied by the
antennae apertures could be investigated.
Field probing with a
small horn mounted on a movable carriage was necessary to ensure that
the field at the horn aperture was uniform or at least varied evenly.
The transmitting horn was adjusted until the field was considered
satisfactory.
The horn reflector was then aligned for maximum
gain and its gain compared with the standard gain horn using an
accurately calibrated waveguide variable attenuator. Also, the two
horns had to be isolated from each other by absorber and the horn
reflector antenna pressurized to 0.14 psig (pounds per square inch
above atmospheric pressure) to prevent movement of its polyester
fibreglass covering.
The measured gain was corrected for
near-field effects and taper of illuminating field. These corrections
were of the order of 0.10 db to 0.50 db and up to 0.07 db respectively.
When
allowance was made for reflection from the fibregalass cover, the
results obtained agreed quite well with the theoretical values. The
probable errors for the S-band, J-band and Ku-band gains were plus or
minus 0.04 db, plus or minus 0.03 db and plus or minus 0.06 db
respectively.
The horn reflector antenna was built in Germany by
Siemens and Halske and transported to Canada. It was of parabolic
design and the aperture face was approximately eight by ten feet. A
photocopied drawing is given in appendix Axv.
This accurately
calibrated horn reflector antenna was to be used to measure the gain of
much larger antennae (the 150 foot diameter dish to be built at
Algonquin Park in Ontario in 1963) and also to pick up microwave
signals from the outer galaxies.
The
above-described project was carried out during the summer of 1962 under
the direction of Dr. E.V. Jull and technician E.P. Deloli at the
National Researh Council in Ottawa, Ontario. Further acknowledgements
are given to Dr. A. Kavadas for guidance in preparing the thesis and to
Maurice R. Zuzak and Peter Stoll for typing the manuscript and drawing
the sketches therein.
A report on the project by E.V. Jull and
E.P. Deloli titled "The Precise Calibration of a Horn Reflector Antenna
for Radio Astronomy" has been published in
IEEE Transactions on Antennas and Propagation AP-12, 439 (1964).