doubts in Patch antenna basic plz clarify it - RF Cafe Forums
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Post subject: doubts in Patch antenna basic plz clarify it
Posted: Fri Oct 29, 2004 11:35 am
Joined: Fri Oct 29, 2004 11:22 am
Location: India , mumbai
I am Mtech student from India DA-IICT(reliance). I am persuing my
reserch in microstrip patch antenna. I heva few basic doubts regarding patch antenna & will be very thankful if you can solve them.
1. Whats the reason of narrow bandwidth in case of Patch Antenna.
2. how can i exicte A patch antenna in TM30 mode
I'll be really greatful if you can clarify these doubts.
Post subject: Patfch antenna- narrow bandwidth
Posted: Sun Oct 31, 2004 3:15 pm
Joined: Sun Oct 31, 2004 3:01 pm
Regards Shashi Bala,
I do not have exacxt to your exact questions but will be happy to try and help resolve them and am interested in your problem.
1. Are you using a reference document (if so what is it so I can get a copy and we are on the same page) to design from. Or is your source of expertise your own reseach?
2. Not clear about a narrow bandwidth requirement from a physics perspective. How narrow? Have you measured the antenna performance in a calibrated environment?. If so what are the 3 dB sidelobes and front to back ratio? I am also not clear on how you are defining "patch". Many years ago we replaced a loop antenna in a hand held product with an F type patch antenna and got very good coverage in a 360 degree radius.
3. I am not clear on TM30 mode, please give me more to go on for a definition.
Antennas I do professionally sometimes, and while not an expert, I have practical experience that may help you. I have a background in physics so am pretty good with the theory too. Often it is the matter of findig the right reference book or app note. While I can start from Maxwells equations, I find that is not typically helpful and makes most people want to throw up.
Post subject: patch antenna
Posted: Wed Dec 01, 2004 6:32 am
The reason for the extremely narrow bandwidth of the patch antenna is its ground plane. Whenever you place a ground plane close to a radiating system, the bandwidth goes down. You can see this by checking any antenna book, when they compute the equation for the dipole impedance above a ground plane: there is a graphic that shows in the x-axis the distance from the gnd plane (related to the wavelength, it is normalized) versus the impedance. You ll see that for small distances the derivative of the impedance is very high, which means, very small changes of frequency result in great changes in the impedance, i.e., the bandwidth is narrow. I am pretty sure balanis book contains this picture.
For the way to excite this other mode in a patch antenna, I sincerely do not know. I dont remember having seen this before in the literature.
Posted: Sat Dec 11, 2004 1:35 am
From what I remember when I built a 2.4GHz patch antenna, the larger the epoxy thickness is, the the larger the bandwidth, so yes, it is the GND plane that limits your BW. I also remember reading a paper that increases your bandwidth if you etch circular gaps in the GND plane, don't ask me why, I don't know ...something to do with releasing EM from between signal plane and GND palne.
anyways, good luck.