Focus dimensions for Prodelin 1.2m dish 0.8 f/D with mode matched feed

This web page provides the dimensions of this new high performance VSAT as used for the HX50 VSAT services by Bentley Walker in Europe, Middle East and Africa. The antenna uses a mode matched feed which cancels the cross-pol interference which is a feature of all single reflector, offset fed dishes. The only comparable performance antennas are Gregorian designs with dual reflectors. The cross-pol cancellation requires that the fat part of the feed throat is directly towards the feed arm in all circumstances. Horizontal nominal polarisation is shown and adjustment to any polarisation is possible by rotating the entire dish through 360 deg using a 3-axis positioner behind the dish. You can also change the polarisation by specific angles 0, 30, 60, 90 deg using the flange with 12 holes between the spacer tube and the filter assembly.

Prodelin Dish 0800-3264

There are no markings on the dish so use the following to determine if you have the correct part:

Overall height = 137 cm
Overall width = 123 cm

Parabolic curved surface:
Vertical diameter = 126.5 cm
Horizontal diameter = 120.7 cm
Max depth = 9.1 cm at 64 cm up, approx in line with the upper pair of fixing holes (use straight edge or fishing line up the front) .

There are 6 hemispherical reference holes, 0.25 inch diameter; 4 around the edges of the curved surface and two either side, near the middle.

Feed support strut and side arms

Side arms marked "323", length = 106.5 cm

Feed support boom length = 121.5 cm

Feed horn diameter

Overall diameter = 14.2 cm

Focal length (by calculation)

By calculation using width = 120.7 and f/d=0.8 (as stated). Focal length = 96.56 cm

The focal length is the distance from the phase centre of the feed (approx where the throat transitions to the cone) and the apex of the parabola which is probably just below and off the lower edge of the curved surface.

Prodelin 1.2m VSAT antenna f/D=0.8 with mode matched feed

Focus dimensions (white lines):

D: Top of curved surface to top of feed                           123.2 cm
C: Top of curved surface to lower edge of feed              131.2 cm
B: Lower edge of curved surface to top of feed               90.36 cm
A: Lower edge of curved surface to lower edge of feed   85.6 cm

All distances measured using the dish loaned to me by Bentley Walker Ltd

Page started 24 July 2008