Antenna - Radiation pattern measurement - Angle uncertainty

[MathieuChalnot]

Hello everyone,

Suppose you have an antenna with a narrow pencil-beam radiation pattern pointing broadside.

Well, at least you designed the antenna to behave that way.

Then, when you measure its radiation pattern, instead of having a maximum at 0° (for example), you notice that the maximum is at 3°.

How can you determine whether this error comes from improper positioning of the antenna inside the anechoic chamber or from the antenna design itself?

Thank you very much in advance.

 

[BradtheRad]

A plumb line, bubble-level, a mirror hanging vertically... in short, surveyor's instruments seem likely to be able to check physical alignment of a physical antenna.

There's a question what spectrum of electromagnetic waves emanates as a narrow pencil-beam radiation? The first thing that comes to mind is lasers which is visible or near-visible light. Maybe X-rays too. Maybe microwaves.

Because as I understand it, rf photons propagate (multiply) and bounce off one another as a beam travels... so that a narrow beam expands wider with distance. Even a concentrated laser spreads to a disc several inches wide by the time it reaches the moon.

 

[vfone]

I assume is about an array antenna.
Beam steering in phase array antennas occurs not only changing the phase of the antenna elements, but also just varying the frequency signal. Is named frequency scanning. At one frequency, all antenna elements are in phase. As the frequency is changed, the phase across aperture tilts linearly, and the beam of the array is scanned.
So, if your array was designed to get a broadside pencil beam at 5GHz, if you change slightly the frequency to 5.1GHz, the beam will no longer be pointed to 0°, but to other angle.