Help with horn antenna dimensioning

The dimensions for horn antenna in 4-8Ghz 84x69x80, was specified by one of the manufacturers.I cannot comprehend this way of specifying dimension. The antnna datashet also does not help.As far as i kno the antenna parameters are:

1. a,b the dimansions of waveguide
2. A the aperture size in H plane
3. B the aperture size in E plane
4.pE and pH

Can anyone tell which of the above parameter is specified by 84x69x80 dimension?

As you give no information, do no expect to get any in return.
Antennas including horns are defined by their gain and radiating pattern, both derived from aperture size measured in wavelength.
If you have no knowledge, go and find some antenna books for study.

Here are the antenna specs...

Nominal Gain: 17 - 20.9 dBi
3dB Beamwidth: 22° - 11.3°
Connector type WRD350 Flange, N-type, SMA
VSWR < 1.7:1 with transition to coaxial connector
Power Handling :2 kW c.w (waveguide flange)
Dimensions: as mentioned wd the querey

Plzzz help

The dimensions are apparently not correct as the beam width is concerned.

If you study an antenna book, you can see that the horn beam width is linked to aperture size by the equation:

a = 70 L/A where a is the beam width in degrees, L is wavelength and A is the

aperture size, L and A in the same units. If you try to find A for 8 GHz and 11.3 degrees, the aperture size (one of horn opening dimensions) must be ~232 mm.

Therefore either the dimensions you show or the beam width are not matching.
The WRD-350 is the M-type ridged waveguide; it can transmit 4 to 8 GHz.

We studied Antenna theory by Balanis for the horn antenna.The equation you hav mentioned is not given in that book.Could you please refer us the book you have taken the formula from?

I have studied Balanis' book long ago but my best source is Kraus, J.D. Antennas, McGraw-Hill 1950; in this edition, page 344, Eq. 12-31 gives exactly the equation I used above.
The formula a = 70 L/A is generally used for any aperture antenna and a refers to the beam width to -3 dB from a maximum gain.