# Is a patch antenna symmetrical?

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#### flanello

##### Advanced Member level 1
Hello,
I'm a little confused about symmetrical and non-symmetrical antennas.
I know that a dipolantenna is symmetrical, but is a patch antenna also symmetrical?
An is it possible to connect a symmetrical RFID Tag Chip to a patch antenna?

#### rezna

##### Newbie level 6
It depends on antenna feeding/excitation
(usually ... In some cases it means geometry of the antenna too. You must know what is the point of asymmetricity).

For example: If you need to drive antenna by "+/-" signal (like dipole antenna), you have usually symetrical one because you must drive one side of antenna by "+" signal from the source and the second side by "-" signal.
(One thing - "+" and "-" source means that the "+" source is shifted from "-" source by 180 degrees - no DC ! )
Example: dipole antenna is symetrical (you need "+" and "-" source). But monopole antenna is non-symetrical. You drive it only by one source (the second side is "mirrored through the ground")

If you want to know what type of antenna you have, you must know 2 things.
1. what is your source? (are you feeding antenna by two signals that are shifted to each other? Or you use only one signal?)
2. Is there some sort of conversion before the antenna itself? (e.g. balun or 180 phase loop)

(I hope that it help you and my answer is not more confusing for you - read some articles, on wiki for example, there are basic principles you need to know and they are easy to understand)

EDIT: vfone is right, patch Antenna is not symmetrical (2nd post below)
(I mixed up ordinary planar with patch antenna). Moreover, he is right that "symetry is related o the current/phase distribution on the antenna" ... geometry is product of desired current distribution (it is much better explanation than mine ).

#### FvM

##### Super Moderator
Staff member
Most baisc patch antennas have single ended feeds. Although some designs may allow a differential feed, I think it's easier
to use a simple LC balun to connect a differential chip output to a single ended antenna.

#### vfone

##### Advanced Member level 5
Just to answer to your question: Patch Antenna is not symmetrical, whatever feeding topology you use. Symmetry is related to the current/phase distribution on the antenna.

#### flanello

##### Advanced Member level 1
Ok.
Thx for the information.

Then it is not easily possible to connect a symemetrical RFID Chip to a patch antenna?

And what you mean with ordinary planar antenna?

#### rezna

##### Newbie level 6
flanello said:
Ok.
Thx for the information.

Then it is not easily possible to connect a symemetrical RFID Chip to a patch antenna?

And what you mean with ordinary planar antenna?

By "ordinary planar antenna" I mean antenna that did not fit to description of patch antenna.
Patch antenna is planar antenna. However not all planar antennas are patch antennas.
Patch antenna has metalic patch over the ground plane (usually is some substrate between patch and ground).

for example see:
www.ansoft.com/converge/High-performance-UWB-Planar-Antenna-Design-ProWong-NSYSU.pdf
www.ansoft.com/DeliveringPerformance/NSYSU2.pdf

#### GaffarEEE

##### Member level 2
all it depends on the configuration of feed, slot-cut, superstrate as well as symetrical perturbation makes the antenna symmetrical........

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