'Patch' Feed for S-Band

Dish Antennas


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Introduction
Some years ago (1992) when experimenting with S-band antennas I threw together a simple 2 turn helix dish feed in a couple of hours, well aware that this solution could be improved upon. It had always been my intention to 'productionise' a version of this for use with the AO-40 amateur satellite.

Recent experiments with an alternative feed based on the 'patch' principle showed it to be a better option both electrically and mechanically. Freddy de Guchteneire ON6UG used his formidable microwave antenna design skills to develop the feed electrically; then it was refined jointly with James Miller G3RUH who undertook production, manufacture and distribution. Together we offer you this ready-to-use design.

Description
This feed is a patch antenna for 2.4 GHz intended for use with a parabolic reflector dish. It is supplied fully assembled and tested.

 PATCH_PHOTO

[Note: downconverter not included!]

When installed in an f/d 0.35 60cm dish for example, the ideal beam pattern of this feed results in a G/T typically 1 db better than with the small helix often used for this application, and the axial ratio is almost perfect. The recommended f/d ratio for a dish using this feed is 0.3 to 0.5, the smaller values giving lowest noise reception (highest G/T), but the higher values a little more gain. SWR is better than 1.2:1 across 2.3 - 2.4 GHz. Any size dish may be used!

To realise the performance offered by today's lowest noise converters, you need a feed and dish system that together contribute less noise than the converter. This feed achieves that.

Feed polar plot:

 POLAR_PLOT

The feed has LHCP (left hand circular polarisation) so that when installed in a dish the resulting polarisation is RHCP, as used by Amsat spacecraft AO-40. The feed may be used for transmission or reception.

An N-male connector is used for direct coupling to typical S-band converters. The alternative N-female connector version can be supplied at no extra charge.

Mounting is via legs (not supplied) to three M5 (3/16") holes in the feed. The feed is weather-proofed to keep out direct rain, and is ventilated to prevent internal moisture build-up. All component parts are non-rusting.

The input is DC grounded; static charge cannot build up to damage converters.

Remember, the feed is an antenna in its own right, and can be used independently where a wide-beamed low gain system is needed.

Typical dish installation:

 TYPICAL_USE

Summary

  Frequency            2250-2450 MHz    [Option: 2150-2350 MHz]
  Gain                 8.5       dbic
  -3db beamwidth        85°
  -10 db beamwidth     125°
  SWR                  < 1.2:1
  Axial ratio          1.05:1
  Feed polarisation    LHCP             [Option: RHCP]
  Suitable dish f/d    0.3 to 0.5
  Connector            N-male    [Option: N-female]
  Impedance            50        ohm

  Overall diameter     120       mm
  Depth                 17       mm    excl. connector
  Weight               130       grams

Price

Price of the S-band feed is £95 plus insured carriage at cost, as follows:

Carriage

UK              £8.
Rest of world   £13, via air-mail.

Frequently asked questions

Feedback from users.

Photos of users' systems.

Methods of payment


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Last updated: 2014 Apr 02