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Satellite Communications/Antenna Pattern Cut & Boresight Test Measurement

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Question
Hi Sir,

Thanks for your very informative reply to my earlier post on 50 ohm vs 75 ohm impedance. Really appreciated & thanks.

My next questions are related to ground antenna performance and measurement where manufacturer always ask us to perform antenna pattern cut. There are a lot of literature/theory are being made available over the internet. But as a ground field engineer, we're more concentrate on the practicality of it.

Could you please enlighten us on the correct approach how to perform the antenna pattern cut using 5-meter dish antenna? What are the objectives of performing such measurement? And how does this differ to boresight test?

Thank you.

Answer
John:

Thanks for the positive feedback regarding my response to the 50 ohm vs. 75 ohm question. I am glad that it helped.

Regarding these questions…

BORESIGHT TEST

A boresight test is used to measure the extent of misalignment, if any, between the mechanical boresight – where the antenna is pointed – and the antenna’s maximum gain. This is not a big problem with a broad antenna beams (small diameter antenna and low frequencies), but it can be a major problem with narrow antenna beams (large diameter antenna and high frequencies).

The boresight test requires a minimum of two sets measurements: one set on the x-axis and another on the y-axis to determine vector offset of maximum gain.

A boresight test can be thought of as a subset of the antenna cut test. The boresight test makes small excursions – plus/minus a few decibels about the maximum gain.

A boresight test is conducted on an antenna range. The antenna under test is physically aligned using a laser with a target. The signal strength at the target is measured. The antenna is stepped incrementally along both the plus/minus X-axis with signal strength measured at each increment. The test is repeated along the plus/minus Y-axis. In both cases, gain measurements are made only in the vicinity of the peak of the main beam. The two set so results are combined to calculate the misalignment.

ANTENNA CUT TEST

The process for conducting an antenna cut test is the same as for conducting a boresight test. In the antenna cut test, gain measurements are taken on both sides of the main lobe, extending out to several sidelobes.

If properly set up, one test can provide all the data needed for both purposes: misalignment and off-axis gain.

I hope that this is helpful. If not, please get back to me for additional discussion. If it was helpful, I would appreciate it if you would complete the satisfaction survey.

Regards,
Thomas E. Burke, Ph.D., PMP

Satellite Communications

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Thomas E. Burke

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Experience

Forty years of experience with satellite communications. Have held roles as system engineer on JPL Mariner 9 program and a program manager for a number of classified communication satellite programs. Served as head of TRW / Defense Communications Division / Engineering Development Operation, a 1,400-person organization responsible for all aspects of classified communication satellite design and development.

Education/Credentials
Ph.D. Chemistry, California Institute of Technology (1969) B.A. magna cum laude Chemistry, University of Minnesota (1962)

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