[amsat-bb] Re: CP antenna from 2 WiFi panels

John Belstner jbelstner at yahoo.com
Mon Jun 7 07:37:17 PDT 2010

Hi Greg,

These panels are patch style antennas and as such you will not be able to place one behind the other to obtain circular polarization.  Placing one next to the other will at best produce an elliptically polarized pattern, and you should use a 50 ohm splitter to keep your impedance 50 ohms.  The shape of the patch and position of the feed point is typically how you obtain circular polarization with a patch antenna.

Or, you can obtain RHCP with the same or more gain and less trouble by making a Helix.  A sheet of aluminum, #8 copper wire and and a piece of PVC of the right diameter is all you need.

Or, you can try just a single panel and see how it performs for a while.

Good luck!

73, John W9EN

On Jun 6, 2010, at 1:15 PM, Greg D. wrote:

> Hi folks,
> Before I start nailing stuff together, I just want to verify what I'm doing...
> I want to make a 2.4ghz Right-Hand Circular antenna from two flat panel Wi-Fi antennas.  The idea is to mount them at 90 degrees from each other, with one 1/4 wavelength in front of the other.  Combine the two feeds with a simple Tee (the feeds are of equal length), and into the pre-amp.  Since I'm not transmitting, I'm not too worried about the resulting 25 ohm impedance (or should I be?).
> If it matters, the panels are from HyperLink Technologies, their model HG2414P, with a claimed 14dBi gain.
> So, the questions:
> 1.  1/4 wavelength at 2401 mhz is ((3 x 10**8 / 2401 x 10**6) / 4) meters, or about 1.23 inches.  Right?
> 2.  Most of our 2.4 ghz satellite downlinks seem to be either linear or RHCP, so I'm guessing that RHCP is probably the preferred construction.  (Yes?)  
> 3.  Looking at the Satellite Experimenter's Handbook (figure 7-10), I believe the panel rotated 90 degrees counter-clockwise as seen from behind the panels should be the one farther out in front, for RHCP.  (Their picture shows clockwise for LHCP.)  Is this correct?
> Thanks,
> Greg  KO6TH
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