A Double Helix Antenna for AO-40 Mode L/S  (the DNA - Dualband New Antenna)


A dual helix antenna for A0-40 Mode L/S is being developed for use as a dish feed, to allow the same dish to be used for Mode L uplink and Mode S downlink.  This will not be marketed by the MCCS, but in due course articles on this design will be published when the development is complete,  and if it works in practice.

A test antenna has been built and a photo is shown below.  The inner helix is the standard G3RUH design for 2401MHz, while the outer is a direct scale from the S-Band one to 1269MHz. 


DNA.jpg (9361 bytes)

The prototype exhibits better than -16dB return loss at 1269 and 2401MHz for the two separate helices and the coupling between the two helices is -15.4dB at 1269 and -26.0dB at 2401MHz.

To prevent the expected desense with this level of coupling, two microstrip filters have been designed and built.  These are described on another page on this website.

It is hoped to try this antenna out over the next few weeks - initially the plan is to measure sun noise with this feed on two dishes  (5ft 0.4f/D and 10ft 0.3f/D)  on both 1269 and 2401MHz and compare the levels with those measured with known good feeds on both dishes.  I will report the data here when it is available.