Making a Circular Polarized antenna
Hi folks,
Just curious...
One of the ways to make a circularly polarized antenna is to feed two linearly polarized antennas in-phase, but mount one them 90 degrees rotated from the other, and 1/4 wavelength ahead of it.
Couldn't one also mount the two antennas 180 degrees rotated and 1/2 wavelength ahead?
The reason I ask is that I have some flat panel 2.4 ghz "Wi-Fi" antennas, and the mounting holes work out best that way.
The only effect I can think of is that the array will probably pick up signals from both left and right polarizations, which could actually be handy.
Greg KO6TH
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http://www.enzim.hu/~szia/emanim/emanim.htm
Above link has a wonderful 3D graphic display of waves. Give it a try.
You can adjust V, H, phase, and then display sum of the 2 waves.
I use it mainly to show how circular polarization comes about.
The sum of 2 waves in the same plane ( 180 degrees rotated ), 180 degrees out of phase ( 1/2 wavelength ) is a nul which probably would be out performed by a rubber ducky.
Interesting visual program! But, I don't see a way to offset the two antennas in space, only in phase. I agree that if you put two antennas in the same plane and 180 degrees out of phase, they will nicely cancel each other out. But if they are offset, then the linear signals will cancel, while a CP signal will have rotated 180 degrees in passing through that offset, and will be in-phase at the second antenna. No?
Greg KO6TH
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Hi Greg, KO6TH
You are right.
Imagine to get two folded dipoles horizontally mounted over the same boom at a distance of 1/2 wave in space (180°) They are feed in phase and we are looking along the boom in one direction.
First case: The rear dipole has the inner conductor of the feed line connected to the right stud and the front dipole has the inner conductor of the feed line connected to the left stud. At time-1 with maximum positive voltage the maximum current in the rear dipole is flowing right of you and for the same reason in the front dipole the current is flowing left of you. After 180° the maximum current in the front dipole reverses direction and actually flow right of you but at the same time the field radiated by the rear dipole has propagate up to the front dipole and having the same right direction both field reinforces linearly and horizontally polarized.
Second case: The rear dipole has the inner conductor of the feed line connected to the right stud and the front dipole has the inner conductor of the feed line connected as well to the right stud. At time-1 with maximum positive voltage the maximum current in the rear dipole is flowing right of you and for the same reason in the front dipole the current is flowing right of you. After 180° the maximum current in the front dipole reverses direction and actually flow left of you but at the same time the field radiated by the rear dipole has propagated up to the front dipole and having opposite directions right and left at the same time both fields cancel out.
73" de
i8CVS Domenico
----- Original Message ----- From: "Greg D." ko6th_greg@hotmail.com To: ve4yz@mts.net; amsat-bb@amsat.org Sent: Sunday, October 25, 2009 8:45 PM Subject: [amsat-bb] Re: Making a Circular Polarized antenna
Interesting visual program! But, I don't see a way to offset the two
antennas in space, only in phase. I agree that if you put two antennas in the same plane and 180 degrees out of phase, they will nicely cancel each other out. But if they are offset, then the linear signals will cancel, while a CP signal will have rotated 180 degrees in passing through that offset, and will be in-phase at the second antenna. No?
degrees
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Alan VE4YZ -
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