A Simple Patch Antenna Feed

From the Design by Tim, K3TZ

In an effort to optimise the antenna system for AO-40 receive on 2.4GHz, several feeds where trialled starting with a Helix and a G3RUH patch. Following the experience of other operators the number of turns on the helix were adjusted for reported optimum performance.

A G3RUH patch was purchased and used as a bench mark for further tests. From the start the Patch generally outperformed the Helix. Ultimately, when the K3TZ design was tested, the ease of construction and consistency of results demonstrated the worth of this antenna.

As part of the tests, circularity of polarization was checked against a local known source and the signal from AO-40, since this was the ultimate use for the antenna, it seemed the best target for the trials.

Fig 1. G3RUH Dish and Patch with DEM 13ULNA pre-amp.

Three antenna were trialled, a 600mm G3RUH dish, a flatter 600mm dish of about .5 F/D and a commercial 640mm off-set satellite dish. For the G3RUH dish and the off-set unit, the patch units consistently gave >0.5db better results than the Helix, however, on the flatter 600mm dish there was no real measurable improvement between the patch and a 3.5 turn helix. It is felt that this could result from the over illumination of this dish by the patch and probably the resultant increase in back ground noise from “splash-over.”

Fig 2. K3TZ dimensions and construction details – note measurements in millimetres.

From a practical point of view, and after constructing several of the K3TZ units, the patch proved its worth by its consistent performance, ease of construction and ease of mounting.

It is important that the patch is protected from the elements as any water between the patch element and the ground plane will affect performance. In one application a small plastic pale covers the Patch and the DEM 13ULNA pre-amp protecting both units.

  Fig.3AO-40 Receive antenna.  Note the small pail covering the Patch and pre-amplifier.