this was a qustion from my instractor in college

"tomerbr" wrote in message
oups.com...
this was a qustion from my instractor in college


short answer: there is no 'ideal' length.

long answer: an 'ideal length' is a metaphysical concept that has no place
in engineering. antennas of different lengths perform in different ways as
governed by the laws of physics, obviously the designers of those antennas
made some tradeoff in length vs signal strength vs distribution of energy in
azimuth and elevation vs installation location and physical limitations
including probably visibility, strength, produceability, and mounting method
to come up with a cost effective solution to the problem of letting a user
make phone calls from car. the concept of 'ideal length' assumes that there
is one length that gives the best of all those possible tradeoffs which is
highly unlikely to exist.

"tomerbr" wrote in message
oups.com...
this was a qustion from my instractor in college


As Dave said, there is no ideal length for an antenna.

The 1/4 wave antenna will have a radiation patern that sends much of the
signal at high angles from it. Not usually good for cell phones where they
are usually on short towers (if you call a couple of hundred feet short).
The longer (in wavelengths) antennas tend to put the signal more to the
horizon and not overhead. By modifying the radiation patern to put it
more where it is needed instead of where it is not needed you get gain in
that direction and hopefully longer range.

"Ralph Mowery" wrote in message
nk.net...

"tomerbr" wrote in message
oups.com...
this was a qustion from my instractor in college


As Dave said, there is no ideal length for an antenna.

The 1/4 wave antenna will have a radiation patern that sends much of
the
signal at high angles from it. Not usually good for cell phones
where they
are usually on short towers (if you call a couple of hundred feet
short).
The longer (in wavelengths) antennas tend to put the signal more to
the
horizon and not overhead. By modifying the radiation patern to
put it
more where it is needed instead of where it is not needed you get
gain in
that direction and hopefully longer range.



What an absolute load of blx.

The reason that car cellular antennae are longer than a 1/4 wavelength
is that almost all of them are centre loaded dual antennas or are 5/8
or 7/8 co-linears. The very short ones are often a little longer as
they are coupled through glass and have to be matched.

The wavelength of a signal and it's aerial have nothing to do with the
propagation pattern. A simple VHF or UHF folded dipole for the same
mounting and wavelength related structure spacing radiates the same
shape of pattern irrespective of frequency - roughly apple-shaped in
cross-section.

What you are getting mixed up with is the panel aerials used on most
base station sites. These are almost all multiple stacked element
arrays which are designed to project the signal more outwards and not
down/close in, and they amost always are spaced within the package to
make them directional after a fashion. Many of them have 5 deg or 10
deg of electrical downtilt to give the close-in coverage, hence why
you sometimes see the 'rabbit ears' tilted backwards where range is
important for that particular location.


--
Woody

harrogate2 at ntlworld dot com

On Sat, 24 Dec 2005 15:06:10 GMT, "harrogate2"
wrote:

The wavelength of a signal and it's aerial have nothing to do with the
propagation pattern.

Nonsense!
--

"What is now proved was once only imagin'd" - William Blake

Ralph Mowery wrote:


"tomerbr" wrote in message
oups.com...
this was a qustion from my instractor in college


As Dave said, there is no ideal length for an antenna.

The 1/4 wave antenna will have a radiation patern that sends much of the
signal at high angles from it. Not usually good for cell phones where
they are usually on short towers (if you call a couple of hundred feet
short).

A couple hundred feet is taller than most (all?) cell towers. Nextel used
to boast about having the tallest towers, around 110 feet max. Sprint's
towers were the shortest before Nextel bought them at around 60 feet. This
is why Sprint's signal really sucked balls before Nextel bought them out.

--
Paul Johnson
Email and Instant Messenger (Jabber):
Got jabber? http://ursine.ca/Ursine:Jabber

harrogate2 wrote:
"Ralph Mowery" wrote in message
nk.net...

"tomerbr" wrote in message
groups.com...

this was a qustion from my instractor in college


As Dave said, there is no ideal length for an antenna.

The 1/4 wave antenna will have a radiation patern that sends much of

the

signal at high angles from it. Not usually good for cell phones

where they

are usually on short towers (if you call a couple of hundred feet

short).

The longer (in wavelengths) antennas tend to put the signal more to

the

horizon and not overhead. By modifying the radiation patern to

put it

more where it is needed instead of where it is not needed you get

gain in

that direction and hopefully longer range.




What an absolute load of blx.

The reason that car cellular antennae are longer than a 1/4 wavelength
is that almost all of them are centre loaded dual antennas or are 5/8
or 7/8 co-linears. The very short ones are often a little longer as
they are coupled through glass and have to be matched.

The wavelength of a signal and it's aerial have nothing to do with the
propagation pattern.

Wha? surely you jest!


73 de Mike KB3EIA -

Paul Johnson wrote:

A couple hundred feet is taller than most (all?) cell towers. Nextel used
to boast about having the tallest towers, around 110 feet max. Sprint's
towers were the shortest before Nextel bought them at around 60 feet. This
is why Sprint's signal really sucked balls before Nextel bought them out.




One of the reason they don't make them much higher is because, if they
are over a certain height they have to get special permits and have to
notify the FAA.


--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com

tomerbr wrote:

this was a qustion from my instractor in college



Ignore the arguing going on here and suffice it to say that you could
get a PhD in antenna theory and spend a lifetime experimenting and just
begin to have a clear understanding of antennas. That may be
exaggerated, but only slightly.

A few general things to keep in mind. Many cell phones work on two
different bands, the antenna needs to work on both. When you are
interested in signals in a certain direction, in this case out and not
up, the longer the antenna the more gain and the more directional it
will be. Don't mistake that as an indication that you just want as long
as a wire as you can get, it is much more complex than that. For an
omni directional antenna where you want to limit the signal to out and
not up, stacking several antennas and hooking them all together in some
fashion, is one way to do that, but I doubt that any of the little cell
phone antennas do that. About the only time you would want an antenna
that also send the signal up is if you are communicating with low earth
orbit satellites that could be anywhere form the horizon to straight
above you. In that case, the antennas start looking more interesting,
that a vertical element.

--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com

On 24 Dec 2005 03:15:26 -0800, "tomerbr"
wrote:

If the ideal lenght of an antenna is 1/4 Wave lenght then way are the
Car Cellular antennas are longer then this ?

this was a qustion from my instractor in college

You have been sidetracked into answering the question, when the
premise that "the ideal length of an antenna 1/4 wavelength" is
unsupported and questionable?

On what basis does your instructor make this general assertion?

You could equally be trying to answer the question "If the ideal
length of an antenna is 1/4 Wave length then why Medium Wave broadcast
antennas commonly longer then this?"

What you learn in answering the question will be useful, but you will
also learn that, subject to the meaning of the term "ideal", the
assertion is unfounded, it does not apply in general.

It is equally valid to turn it around and ask that given so many
antennas are not quarter wavelength, is quarter wavelength really
ideal?

Owen

PS: several reasons come to mind why car cellular antennas are not
quarter wave ground plane antenns, they are (over here) multi-band,
they are often so-called ground independent designs (on-glass, gutter
mounts etc) with elevated feed points, they seek higher gain, some are
a metre long for rural coverage, they appeal to buyers who think
bigger is better.



--