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doubts in Patch antenna basic plz clarify it - RF Cafe Forums
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shashi_bala
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Post subject: doubts in Patch antenna basic plz clarify it
Posted: Fri Oct 29, 2004 11:35 am
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Joined: Fri Oct 29, 2004
11:22 am Posts: 1 Location: India , mumbai
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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. Doubts: 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.
Reagrds Shashi Bala
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garylsmith2k |
Post subject: Patfch antenna- narrow bandwidth
Posted: Sun Oct 31, 2004 3:15 pm
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Joined: Sun Oct 31, 2004
3:01 pm Posts: 5 Location: N/A
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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.
_________________ Cheers, Gary Smith
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guest |
Post subject: patch antenna
Posted: Wed Dec 01, 2004 6:32 am
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Hello, 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.
cheers, brazilian
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Edstroyer |
Post subject:
Posted: Sat Dec 11, 2004 1:35 am
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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.
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Posted 11/12/2012
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