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# calculating beamwidth

## calculating beamwidth

(OP)
Hi everybody,
I'm running a matlab code for a planar array antenna. I just want to know how I can calculate the half-power beamwidth of the main lobe if it is pointing at a given angle such as theta = 30 degrees and phi = 30 degrees. I know how to find the half-power beamwidth if it is pointing at theta = 0, and phi=0 but not one that is pointing at a different angle.

Thanks

### RE: calculating beamwidth

I'm not knowledgable in Matlab, but I've done similar things in MS-Excel. My approach was to calculate the gain pattern of the antenna array over the entire sphere (displayed in a Mercator projection). My application was calculating the maximum possible gain at any point so we could trade-off various options.

For your application, you would need a little GUI to enter the parameters to aim the array. Once you've used this generalized bottom-up approach, then it becomes simple to layer-on a dynamically calculated beamwidth. And then another loop would allow you to plot beamwidth versus anything - probably running overnight...

Obviously there are higher-level approaches that would be much faster, both in terms of implementation and run time.

### RE: calculating beamwidth

a first cut would be just the projected aperture reduction giving rise to a wider beamwidth. Simple Cosine formula. If you need more accuracy than that, you'd have to calculate the pattern and just look at it.

If you scan too far off boresight with your array, the beam won't actually peak at the calculated scan angle due to individual element rolloff, it'll peak closer to antenna boresight by a few degrees. So be careful just running array factor calculations and showing it to customers. Later comparison to measured will show that you forgot the antenna element factor in the array calculations. A common oops for array designers. You only make that oops once though.

kch

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