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.
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.
[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:
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:
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 of the S-band feed is £95 plus insured carriage at cost, as follows:
UK £5. Rest of world £10, via air-mail.
Frequently asked questions
Feedback from users.
Photos of users' systems.
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Last updated: 2010 Oct 06