Antenna reception theory
 

Hi,

I am looking for an explanation of how an antenna receives a signal due
to the E-field of an electromagnetic wave.

I have looked in some books, and can understand transmission, but the
books I have looked in don't explain reception.

I have found an explanation of how the H-field induces a signal in a loop
antenna: a changing magnetic flux will induce a current.

But what about the E-field and a dipole antenna? I guess that the E-field
causes electrons to move in the antenna wire, because in a solid
conductor, electrons will move until the E-field inside the solid is
cancelled out?

I have googled but having difficulty finding a good explanation. Any
pointers?

Thanks & regards,

Paul.

--
Remove _rem_ before replying by email.

Antenna reception theory
 

"Paul Taylor" wrote in message
...
Hi,

I am looking for an explanation of how an antenna receives a signal
due
to the E-field of an electromagnetic wave.

I have looked in some books, and can understand transmission, but
the
books I have looked in don't explain reception.

I have found an explanation of how the H-field induces a signal in a
loop
antenna: a changing magnetic flux will induce a current.

But what about the E-field and a dipole antenna? I guess that the
E-field
causes electrons to move in the antenna wire, because in a solid
conductor, electrons will move until the E-field inside the solid is
cancelled out?

I have googled but having difficulty finding a good explanation.

===================================

It is impossible for an E-field to exist without an H-field.

Therefore, antennas of all sorts receive signals in the same way as a
simple loop. Calculations can begin using either the E-field or the
H-field but they both give the same answer.
----
Reg.

Antenna reception theory
 

Paul Taylor wrote:
Hi,

I am looking for an explanation of how an antenna receives a signal due
to the E-field of an electromagnetic wave.

I have looked in some books, and can understand transmission, but the
books I have looked in don't explain reception.

I have found an explanation of how the H-field induces a signal in a loop
antenna: a changing magnetic flux will induce a current.

But what about the E-field and a dipole antenna? I guess that the E-field
causes electrons to move in the antenna wire, because in a solid
conductor, electrons will move until the E-field inside the solid is
cancelled out?

I have googled but having difficulty finding a good explanation. Any
pointers?

Thanks & regards,

Paul.

Transmission and reception work essentially the same way -- if an
antenna induces a certain field pattern in space, then that same field
pattern will induce the same voltages going the other way.

Most books spend about that much space telling you about the principal,
then use the rest of the time telling you how antennas transmit, leaving
it to you to figure out how they receive.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Antenna reception theory
 

Paul Taylor wrote:
I have looked in some books, and can understand transmission, but the
books I have looked in don't explain reception.

This is another example of quantum physics being easier
to understand than Maxwell's equations. RF photons are
absorbed by free electrons in the copper antenna causing
RF currents to flow in the antenna wire.
--
73, Cecil http://www.qsl.net/w5dxp

Antenna reception theory
 

"Cecil Moore" wrote
This is another example of quantum physics being easier
to understand than Maxwell's equations. RF photons are
absorbed by free electrons in the copper antenna causing
RF currents to flow in the antenna wire.
========================================

So how does a dielectric antenna work?
----
Reg.

Antenna reception theory
 

Reg Edwards wrote:
So how does a dielectric antenna work?

I'm not sure since I don't find it in any of my
references including ARRL, Kraus, Balanis, and
the IEEE Dictionary. Is it a waveguide where the
inside air is replaced by a dielectric?
--
73, Cecil http://www.qsl.net/w5dxp

Antenna reception theory
 

Cecil Moore wrote:
Reg Edwards wrote:

So how does a dielectric antenna work?


I'm not sure since I don't find it in any of my
references including ARRL, Kraus, Balanis, and
the IEEE Dictionary. Is it a waveguide where the
inside air is replaced by a dielectric?

In the third edition of the _Antenna Engineering
Handbook_ there is an article on surface-wave antennas
which includes dielectric antennas starting on page
12-8.
73,
Tom Donaly, KA6RUH

Antenna reception theory
 

Tom Donaly wrote:
In the third edition of the _Antenna Engineering
Handbook_ there is an article on surface-wave antennas
which includes dielectric antennas starting on page
12-8.

I'll take a look the next time I'm over at Texas A&M.
In a nutshell, where does the radiation come from?
--
73, Cecil http://www.qsl.net/w5dxp

Antenna reception theory
 

"Tim Wescott" bravely wrote to "All" (24 Nov 05 11:49:57)
--- on the heady topic of " Antenna reception theory"

TW From: Tim Wescott
TW Xref: core-easynews rec.radio.amateur.antenna:220333

TW Paul Taylor wrote:
Hi,

I am looking for an explanation of how an antenna receives a signal due
to the E-field of an electromagnetic wave.

TW Transmission and reception work essentially the same way -- if an
TW antenna induces a certain field pattern in space, then that same field
TW pattern will induce the same voltages going the other way.

TW Most books spend about that much space telling you about the
TW principal, then use the rest of the time telling you how antennas
TW transmit, leaving it to you to figure out how they receive.


For antenna to receive it must also transmit part of the signal it
intercepts. Now that confuses this discussion a little more, doesn't
it?!

A*s*i*m*o*v

.... I like the word `indolence.' It makes my laziness seem classy.

Antenna reception theory
 

Most authors explain how a wave is generated, then resort to reciprocity
to explain the reception process. But a clear and simple direct
explanation appears in Bailey, _TV and Other Receiving Antennas_ (pp.
141-2), of what happens when an electromagnetic wave strikes a conductor:

"The second, and equally important effect [the first being reflection of
much of the incident energy] is that some energy /does/ enter the outer
skin of the conductor. That part of the energy, which is not reflected,
must enter the conductor. The conditions at the surface of the
conductor, as we have already seen, give rise to a small resultant
electric vector and a large resultant magnetic vector. The presence of
these at the conductor is direct evidence that power is entering the
conductor. The small electric vector acts on the internal electrons of
the conductor and impresses a direction force, tending to drive the
electrons along the skin of the conductor in the direction of the
electric vector. But from experience we know that /no/ electrons can
ever be caused to move without gradually establishing their own magnetic
field, and this usually takes /time/. The motion of electrons (which is
electric current by definition) never takes place without the magnetic
field. How, then, is the electric vector from the electromagnetic wave
going to put these electrons in motion? It can only do so because the
electromagnetic wave /also supplies a magnetic vector/ as well as an
electric vector. And the value of this magnetic vector is exactly
proportioned to supply just the right amount of magnetic field energy
which the electrons require for immediate motion. Thus the electrons do
not have to establish their own magnetic field, since this field is
supplied by the electromagnetic wave. Hence, electromagnetic wave energy
entering the conductor establishes immediate motion of electrons /along/
the conductor, the direction of motion at any instant corresponding to
the direction of the electric vector. If the electric vector changes
direction, the electrons will follow suit."

Other posters have correctly pointed out that an antenna doesn't and
can't receive a signal solely due to the E field; a time-changing E
field can't exist without an accompanying time-changing H field.

Roy Lewallen, W7EL

Paul Taylor wrote:
Hi,

I am looking for an explanation of how an antenna receives a signal due
to the E-field of an electromagnetic wave.

I have looked in some books, and can understand transmission, but the
books I have looked in don't explain reception.

I have found an explanation of how the H-field induces a signal in a loop
antenna: a changing magnetic flux will induce a current.

But what about the E-field and a dipole antenna? I guess that the E-field
causes electrons to move in the antenna wire, because in a solid
conductor, electrons will move until the E-field inside the solid is
cancelled out?

I have googled but having difficulty finding a good explanation. Any
pointers?

Thanks & regards,

Paul.