basher_boy Posted April 29, 2002 Share Posted April 29, 2002 I am no expert on antennas, but find the basics very interesting. I was wondering if there is a site or someone that would like to expand upon the snippits of information on antennas that I have been reading in this site. What exactly is a patch antenna, a helix, double helix, etc. WHat are each type of antenna's stregnths and weaknesses? How does that relate to different GPS applications? Quote Link to comment
Davros Posted May 2, 2002 Share Posted May 2, 2002 A patch antenna is exactly what it implies a patch. A small square or circular patch consisting of two metalic patches. One patch is the active element. (where the signal is actually received)Which is isolated and mounted ditecly above the other patch which is the Ground Plane. (Basically where the signal is caught, and bounced onto the active element.) Helical or Helix means "Wound" in a spiral form usually verticaly however there can be some flat or horizontal helically wound antennas. A "Rubber Duckie" is an example of a vertically wound helical antenna. A double Helical antenna is 2 antennas side by side usually 180 degrees out of phase with eachother. This can be used to "Focus" the incomming / ougoing RF signals however the disadvantage is that it is directional. The advantage to this is that the directivity has a gain effect. If the antennas are not out of phase with eachother the way I see it they really don't provide any advantage at all. Single Helix, and Patch antennas are usually Omni-Directional which means they can receive signals 360 degrees (or near enough). The dis-advantage to omni-directional is that the lack of focused RF means that the received signals are not as strong. In marginal areas your reception is weaker. The advantage is that with omni-directional you don't have to be essentailly 'looking' right at the satalite. Naturally by focusing the recieved signals there is a bit more effective gain. Think of effective gain as that of a flashlight. With the beam wide open you can see a wider area, but the light degrades some areas off to the sides are dimmer than others that are closer to the center. Take the same flashlight and focus the beam as tightly as possible. Now you notice you don't see as much off to the sides but the visible part in the center of the beam is much brighter. Same amount of light. But the light signal is now focused more directly. Thus, it seems like you have more light when you really don't. You are still using the same amount of power, same amount of light in a more direct pattern. This is called "Effective Gain" That same principal applies to antennas. I hope this makes sense.. It's my feeble attempt to translate RF theroy into laymans terms I guess.. Does this help you any? I looked for a website but found mainly sales of antenas and minimal tech specs. So hopefully this sheds a little light on your quest for info.. Randall J. Berry davros@mdgps.net Quote Link to comment
Davros Posted May 2, 2002 Share Posted May 2, 2002 A patch antenna is exactly what it implies a patch. A small square or circular patch consisting of two metalic patches. One patch is the active element. (where the signal is actually received)Which is isolated and mounted ditecly above the other patch which is the Ground Plane. (Basically where the signal is caught, and bounced onto the active element.) Helical or Helix means "Wound" in a spiral form usually verticaly however there can be some flat or horizontal helically wound antennas. A "Rubber Duckie" is an example of a vertically wound helical antenna. A double Helical antenna is 2 antennas side by side usually 180 degrees out of phase with eachother. This can be used to "Focus" the incomming / ougoing RF signals however the disadvantage is that it is directional. The advantage to this is that the directivity has a gain effect. If the antennas are not out of phase with eachother the way I see it they really don't provide any advantage at all. Single Helix, and Patch antennas are usually Omni-Directional which means they can receive signals 360 degrees (or near enough). The dis-advantage to omni-directional is that the lack of focused RF means that the received signals are not as strong. In marginal areas your reception is weaker. The advantage is that with omni-directional you don't have to be essentailly 'looking' right at the satalite. Naturally by focusing the recieved signals there is a bit more effective gain. Think of effective gain as that of a flashlight. With the beam wide open you can see a wider area, but the light degrades some areas off to the sides are dimmer than others that are closer to the center. Take the same flashlight and focus the beam as tightly as possible. Now you notice you don't see as much off to the sides but the visible part in the center of the beam is much brighter. Same amount of light. But the light signal is now focused more directly. Thus, it seems like you have more light when you really don't. You are still using the same amount of power, same amount of light in a more direct pattern. This is called "Effective Gain" That same principal applies to antennas. I hope this makes sense.. It's my feeble attempt to translate RF theroy into laymans terms I guess.. Does this help you any? I looked for a website but found mainly sales of antenas and minimal tech specs. So hopefully this sheds a little light on your quest for info.. Randall J. Berry davros@mdgps.net Quote Link to comment
basher_boy Posted May 4, 2002 Author Share Posted May 4, 2002 I guess I was interested in the radiation patterns off of a patch and a quadrifilar antenna. I have found documents on the internet that show the pattern for a patch antenna, but have yet to find it for the quadrifilar. I also wonder what type of antenna the domed types are--you know the type on tractor trailers, and at some of the cell tower instilations. I realize in practice these patterns make little or no difference when using a GPS in the field, but I wonder if the theoretical patterns bear out the field experiences of users here. Quadrifilar antennas seem to outperform patch in the field. Patch antenna radiation pattern Quote Link to comment
Davros Posted May 5, 2002 Share Posted May 5, 2002 Well, If you understand that wrap sheet then you certainly don't need my help! I've been working with electronics my entire life never did get the hang of that W/XxY+Z=Headache for me! Glad you understand it! Randall J. Berry davros@mdgps.net Quote Link to comment
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