Hello All,
should the antenna ground be connected to the transmitter circuit
ground? i saw a microstrip antenna that has only a feed pad but no
ground pad .
Regards

redhat wrote:
Hello All,
should the antenna ground be connected to the transmitter circuit
ground? i saw a microstrip antenna that has only a feed pad but no
ground pad .
Regards

The short answer is yes. But such a connection isn't usually
infinitesimally short, so current will flow along the path and the path
will become part of the antenna and radiate.

An antenna is a circuit, and like any circuit it has two terminals. Our
calling one of these "ground" doesn't give it any special or magical
properties -- it's simply one of the two connections. However much
current flows into one of the antenna terminals must flow out of the
other. If we connect, for example, a piece of coax from a transmitter to
an antenna and connect only the center conductor to the antenna, then
the outside of the coax becomes the other half of the antenna. If one
amp flows into the antenna, one amp flows along the outside of the coax
shield. This would be the case for the microstrip antenna you describe,
if you're really describing it accurately.

Follow the current from the "hot" side of the transmitter to the
feedline, along the feedline to the "antenna", back from the other
terminal of the "antenna" to the "ground" side of the transmitter.
Anywhere the current is flowing right beside an equal current going in
the other direction (to simplify a bit), like it does on the inside of a
coaxial cable, there won't be any significant radiation. But anywhere a
current is flowing where there isn't a very nearby, opposite current,
the conductor is actually part of the antenna and will radiate.

Roy Lewallen, W7EL

i was talking about this u-strip antenna
http://export.farnell.com/productima...d/42265868.jpg
,where the center pad is the feed but has no ground pad (the other pads
are for mounting),here is the datasheet:
http://rocky.digikey.com/WebLib/Yage...-118-00918.pdf
so, when you mount it to the pcb and connect it to a microstrip line
for example, the antenna ground (internal) will not be connected to the
circuit's ground
http://www.geocities.com/aezzat3/antenna.jpg
so , this means that the ciircuit's ground will radiate and not all the
power will be fed to the antenna. is that right?
Regards

The key here is the "Suggested layout" diagram in the .pdf file. The
transmitter ground is connected to the ground plane, so the 50 ohm
microstrip line is one conductor of the feedline and the upper surface
of the ground plane is the other. There will be very little radiation
from the feedline because return current will flow on the ground plane
directly beneath the top side trace.

Right at the antenna is the only place where the microstrip line will
physically move away from the ground plane -- the other conductor of the
feedline. So only that part will radiate. Typically, you'd have a
conductor which goes vertically straight up from the end of the
microstrip line to the patch. Only that very short part of the feed
system will radiate.

Roy Lewallen, W7EL

redhat wrote:
i was talking about this u-strip antenna
http://export.farnell.com/productima...d/42265868.jpg
,where the center pad is the feed but has no ground pad (the other pads
are for mounting),here is the datasheet:
http://rocky.digikey.com/WebLib/Yage...-118-00918.pdf
so, when you mount it to the pcb and connect it to a microstrip line
for example, the antenna ground (internal) will not be connected to the
circuit's ground
http://www.geocities.com/aezzat3/antenna.jpg
so , this means that the ciircuit's ground will radiate and not all the
power will be fed to the antenna. is that right?
Regards

With mobile verticals what is ALWAYS forgotten about is that the car
body is just as much a part of the radiating system as the antenna.

The body is just the lower half of a somewhat off-centre-fed,
mishaped, vertical dipole.

It is ridiculous to describe its operation in such laymen's terms, but
the body radiates as much useful power as the antenna itself. And it
is fed with coax whereas, according to perfectionists, to prevent
radiation from the feedline, it ought to be off-centre fed with
450-ohm ladderline. But from wherever it supposedly comes radiation is
never wasted.

I've often thought of modelling a mobile loaded whip in a computer
program. Input data would include body dimensions and height above
ground. With a lot of patience you could do it with an EZNEC type of
program.
----
Reg, G4FGQ

Thanks for your reply. what about this patch antenna
http://rocky.digikey.com/WebLib/Toko...K1575MS50T.pdf
it has a feed pin at the center, the ground is the whole area around
the pin , they say it has an adhesive tape for ease in mounting to the
ground plane , is this adhesive tape a good conductor so that it
connects the antenna ground to the circuit's ground or what? so,in the
pcb design should i make a rectangular copper area under this antenna
connected to the ground?
Regards,
Redhat

I guess you could buy one of those square cars like the Scion to make the
modeling easier.

"Reg Edwards" wrote in message
...
With mobile verticals what is ALWAYS forgotten about is that the car

In article ,
Reg Edwards g4fgq,regp@ZZZbtinternet,com wrote:

With mobile verticals what is ALWAYS forgotten about is that the car
body is just as much a part of the radiating system as the antenna.

The body is just the lower half of a somewhat off-centre-fed,
mishaped, vertical dipole.

Some people refer to mobile verticals as "short tuned counterpoises,
working with a large untuned radiator".

I've often thought of modelling a mobile loaded whip in a computer
program. Input data would include body dimensions and height above
ground. With a lot of patience you could do it with an EZNEC type of
program.

There are probably some not-quite-obvious gotchas to be considered.

I've observed that a significant number of vehicles (e.g. my Ford
Aerostar minivan) don't weld the body panels to the frame. Instead,
the side panels and roof are _glued_ to the framework using a
structural adhesive, and there's no DC connection at these points...
just a capacitive one (probably with high capacitive reactance).
There's DC continuity in some places, but not at all contact points.

Depending on how the vertical is grounded to the vehicle (to the
panels, to the frame, or to both), the RF "ground" currents are likely
to vary quite a bit.

Similar issues are likely to exist in recent-model cars which have a
lot of fiberglass or other composite-plastic panels and structure.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Reg Edwards wrote:
With mobile verticals what is ALWAYS forgotten about is that the car
body is just as much a part of the radiating system as the antenna.

I've always considered the vehicle body as a funny looking
large diameter elevated radial. :-)
--
73, Cecil http://www.qsl.net/w5dxp

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On Wed, 08 Jun 2005 17:57:21 -0000, (Dave Platt)
wrote:


Similar issues are likely to exist in recent-model cars which have a
lot of fiberglass or other composite-plastic panels and structure.

Back in the good old days, I was the proud owner of a 1956 Corvette,
one of only 3467 built and along with the '57s, the prettiest ones
ever buit. (damn I wish I had that car back). As are all Corvettes,
it was fiberglass.

The soft top was stored under a flip up hatch behind the seats and
there were two toggle clamps that secured the rear of the top when it
was up. These penetrated the hatch cover so that it was possible to
snake a vertical whip through them. I used a 17" aluminum
transcription disk (common in broadcast stations of the day) with the
coating stripped off for a ground plane under the hatch.

Best DX using a Heathkit "Twoer" was from the driveway of a friend in
Tempe, AZ back to another friend in Tucson; about 100 miles.

This wasn't long after QST magazine had breathlessly reported that the
"difficult path" between Tucson and Phoenix had been bridged.