B737 Weather Radar Antenna Diameter

[Hank Birofski]

Does anyone know what the diameter of the B737 weather radar antenna is? I'm on holiday at the moment so no friendly engineers to ask on the ramp I've just been watching an ancient video of Archie Trammell (American Airbourne Weather Radar Guru) and based on this information can work out the radar beam width in degrees.

Cheers

[NSEU]

"based on this information can work out the radar beam width in degrees."

I'm not sure if you can work out the beamwidth with antenna diameter alone. Mr Trammell is probably assuming that the antenna is an old parabolic style antenna and not like a modern flatplate antennae(?). Even so, on the older parabolic systems, you could have a variable beamwidth. If my memory hasn't failed me, I recall some commercial airliner radar systems had a "pencil" beam for ground mapping (as well as the wider, weather mapping beams). Can't remember how the different beams were generated though.

For interest, the antenna width of a flat plate 737NG antenna is 23" wide with a beam width of 5.4 degrees (Does this match his formula?).

Rgds.
NSEU

[Captain Stable]

NSEU is correct - the calculation will only work for an old parabolic dish, not a modern flat-plate synthetic aperture radar.

[Hank Birofski]

Thanks NSEU

In the video he displayed a table of Antenna Size vs Beam Width depending on it being X Band or C Band (it is an old video).

I understand the 737 to have an X Band radar (that's all the information I've been able to find published - Bill Bulfer's 737 Cockpit Companion)

So in his table an 18" antenna has a beam width of 5 degrees and a 24" antenna = 4 degrees.

Not quite the same figures as you've given but as you say his table may be based on the older style parabolic dish. Could you provide me with a source for the 737NG numbers as that's the type I'm most interested in.

Best regards

[Shaka Zulu]

Mate I thought you were on HOLIDAY!

[Hank Birofski]

Touche (knocks the top off another beer and thinks 'It really is better to be down here wishing you were up there...)

[NSEU]

"Could you provide me with a source for the 737NG numbers as that's the type I'm most interested in."

I found this dimension in the Boeing 737NG Maintenance Manual, Hank. For airline engineers' eyes only, I'm afraid.

Rgds.
Q.

[Rudi Zarsoff]

The RTA-4A WX radar fitted to the B737-300's that we fly have a 30 inch flat plate antenna with a beam width of 3.4 degrees.
This is useful in determining the beam width in feet at any given distance.
The formula for calculating this is :
number of degrees of antenna beam x distance (nm) x 100 = beam width dimension (feet)
ie 3.4 degrees x 50nm x 100 = 17,000 feet.