CP patch design

[IBCrazy]

I am opening this thread for suggestions and help in designing a better circularly polarized patch antenna. Currently all units that I know of are "trimmed corners" patches. These have less than ideal axial ratio and are very critical to their dimensions. Out of spec dimensions result in loss of circularity as well as huge drops in SWR.

Thus I would like some assistance in developing a dual feed patch.

There are two ways to do this:

1. feed a square 50 ohm patch 90 degrees apart and do impedance transformations with 75 Ohm coaxial cable and add a 90 degree 50 ohm phase shifting stub.

This method is easiest to design.

2. Feed a square patch at its 100 Ohm impedance points at different sides and use a 90 degree, 50 ohm phase shifting match.

This is a bit hard to design, but will be easier to build.

I leave this open for discussion. I will provide my research and calculations. If anyone has any helpful input, please post it.

-Alex

[Mictronics]

So what design do you prefer, metal sheets with air or a printed board, probably FR4 as substrate (or even a Rogers)?

[GregSilver]

Not sure is these are any good ideas...and im sure you have seen them before.
They are however all buildable without needing special tools.

[Mictronics]

Here is a link to the page where the images are from: http://www.qsl.net/va3iul/Antenna/Pr...p_Antennas.htm
With images in original size. Seems the attached GIF's were resized as well, same happened when I tried to attach PNG's yesterday.

[SENTRY]

Just click them twice and they open to orig size.

[IBCrazy]

I am trying to stay away from trimmed panels as they have some difficulty with frequency variation.

Michael - Can you find the 100 Ohm feed point for the following panel at 1280MHz?:

Air type patch, back feed. Dimensions are as follows:

Ground plane size: 225mm square
Active element size: 106.5mm square
Height: 6.3mm

The 50 Ohm point should be about 26mm from center. Therefore I think the 100 Ohm point should be around 38mm or so?

Can you experiment with this a little?

[IBCrazy]

Here's another panel if someone will model it:

Same dimensions as above.

Here's the trick: Feed points 90 degrees apart. One feed has 1/4 wavelength of RG179 cable. The other feed has 1/4 wavelength of RG179 followed immediately by 1/4wavelength of RG316. Both feeds are then joined to the same cable at that point.

The feedpoints are 26mm from center 90 degrees apart.

This should have a good axial ratio and fairly wide bandwidth (I hope).

-Alex

[IBCrazy]

I just realized something: We're here developing (or at least trying to develop) a better antenna specifically for FPV. As of now, it only appears in text books and theory, but nobody has discovered how to make it work. This is the theoretical "best" patch antenna. If we can get it designed and developed, how cool would that be?

-Alex

[SX_]

Legen........
DARY!
thats how cool
Wish i could help

[ssassen]

Already working on something, none of the above applies, think microstrip and PCB material

Cheers,

Sander - ImmersionRC