..

jopl wrote: ???

In a standing wave antenna, like a dipole, the power wave hits
the end of the antenna and voltage and current are reflected.
The standing wave pattern on 1/2 of a dipole looks somewhat
like the standing wave pattern for a lossy 1/4WL open stub.
In the case of a traveling wave antenna, the power wave hits
a resistor with close to the same value as the Z0 of the
antenna and is dissipated in the resistor.

So, a traveling-wave antenna is essentially one without
reflections.
--
73, Cecil http://www.qsl.net/w5dxp

On Thu, 15 Apr 2004 09:20:59 -0700, jopl wrote:

.
A Traveling-wave antenna is used for satellite up-link communication.
The signal is a microwave frequency up into the (multi) GHz region of
radio waves. The transmitting tube is a traveling-wave tube, which is
powered by a special pulsed amplifier.

A familiar use for this set-up is to relay telephone signals (from U S
Sprint, etc.) up to the satellite and then down load to another ground
station where the signal is converted back into a telephone signal and
sent (over land line) to the person you called. This eliminates the
use of land-lines most of the way for your long-distance telephone
calls.

There are also many military uses for this type of technology.

By the way, the signals are fed from the amplifier through Wave-guides
(a hollow rectangular cross-section sections that are held together by
flanges), rather than by wires. It would be similar to a squared-off
hose section, connected to other hose sections, if this makes the
concept easier to understand.

Waveguides have much less loss than wire or cable and because of the
ultra-high frequencies involved, are much more efficient.

Hopes this gives you some idea of this type of communication.

Regards

warren

warren wrote:

On Thu, 15 Apr 2004 09:20:59 -0700, jopl wrote:

.
A Traveling-wave antenna is used for satellite up-link communication.
The signal is a microwave frequency up into the (multi) GHz region of
radio waves. The transmitting tube is a traveling-wave tube, which is
powered by a special pulsed amplifier.

A familiar use for this set-up is to relay telephone signals (from U S
Sprint, etc.) up to the satellite and then down load to another ground
station where the signal is converted back into a telephone signal and
sent (over land line) to the person you called. This eliminates the
use of land-lines most of the way for your long-distance telephone
calls.

There are also many military uses for this type of technology.

By the way, the signals are fed from the amplifier through Wave-guides
(a hollow rectangular cross-section sections that are held together by
flanges), rather than by wires. It would be similar to a squared-off
hose section, connected to other hose sections, if this makes the
concept easier to understand.

Waveguides have much less loss than wire or cable and because of the
ultra-high frequencies involved, are much more efficient.

Hopes this gives you some idea of this type of communication.

Regards

warren

And here's a site that talks about power waves:

http://www.thepowerwave.com/

:-)

ac6xg

Jopl wrote:
"What is a traveling-wave antenna?"

A traveling-wave antenna has only weak if any reflections. So, it is
defined.

A traveling-wave antenna is the opposite of a standing-wave antenna. In
a standing-wave antenna, the wave reaches the tip end to find an
impedance significantly different from the characteristic impedance of
the wire or wires carrying the wave.

In the standing-wave antenna, the wave often encounters a short-circuit
or an open-circuit at the antenna tip which reflects 100% of the energy
remaining in the wave after its trip from the feedpoint. This produces a
standing wave pattern on the anternna wire just as a short or open would
cause on a lossy trannsmission line. In the standing-wave antenna case,
most of the energy escaping from a good antenna is radiated as r-f in
place of being converted to heat at the wire.

A traveling-wave antenna is usually equipped with a resistor or
resistors to absorb energy which is not radiated on its trip to the end
or ends of the wire or wires (if it is a balanced antenna). To absorb
100% of the remaining energy and to produce no reflection requires the
chosen load resistance to match the charcateristic impedance of the
wire, or wires in a balanced configuration, of the antenna.

The ideal horizontal rhombic antenna, for example, is a balanced
traveling-wave antenna which is terminated at its far end with a
resistor equal to the characteristic resistance of the antenna at its
far end so that no energy will be reflected at the far end to travel
back toward te feedpoint and produce radiation toward the feedpoint end
of the antenna. Well constructed and with the proper termination
resistor, the rhombic is unidirectional. Without the resistor, the
rhombic is bidirectional and its front to back ratio depends on how many
wavelengths are in a side of the antenna.

The ideal dipole antenna, for example, is a balanced standing-wave
antenna which is terminated at its far end in an open-circuit in the
usual case, or it is terminated in a short-circuit if the dipole is the
"folded-dipole" type. Both types radiate identically. Only the
drivepoint resistance is different between the two types of dipoles.
Both dipoles have energy left over from the first trip between feedpoint
and antenna tip and this is nearly 100% reflected at the tip. If the
dipole has a 1/4-wave length between drivepoint and tip, the open or
short is inverted and at the feedpoint the open-circuit tip appears a
low impedance. On the contrary, the short-circuit at the tips of the
folded dipole appear as a high impedance back at the feedpoint when the
elements are 1/4-wavelength.

The usual horizontal balanced rhombic looks like a transmission line of
600-900-ohm Zo. It is pulled apart for extremely wide-spacing which
allows radiation. This widening as distance from the drivepoint
increases also raises the Zo to a high value but this is symmetrically
reduced back to the drivepoint impedance by the reduction in spacing
between the rhombic wires toward the far end. Ideally the whole assembly
just looks like a transmission line terminated in its Zo, which happens
to have a wide spot within which allows radiation in and out. At high
frequencies where the rhombic has many wavelengths per side, much of
energy fed a rhombic will be radiated before reaching the termination,
often a dissipation line made from stainless steel resistance wire.

Best regards, Richard Harrison, KB5WZI

I think my beverage, a traveling wave antenna, would be rather poor for
satellite use.

"warren" wrote in message
...
On Thu, 15 Apr 2004 09:20:59 -0700, jopl wrote:

.
A Traveling-wave antenna is used for satellite up-link communication.
The signal is a microwave frequency up into the (multi) GHz region of
radio waves. The transmitting tube is a traveling-wave tube, which is
powered by a special pulsed amplifier.

A familiar use for this set-up is to relay telephone signals (from U S
Sprint, etc.) up to the satellite and then down load to another ground
station where the signal is converted back into a telephone signal and
sent (over land line) to the person you called. This eliminates the
use of land-lines most of the way for your long-distance telephone
calls.

There are also many military uses for this type of technology.

By the way, the signals are fed from the amplifier through Wave-guides
(a hollow rectangular cross-section sections that are held together by
flanges), rather than by wires. It would be similar to a squared-off
hose section, connected to other hose sections, if this makes the
concept easier to understand.

Waveguides have much less loss than wire or cable and because of the
ultra-high frequencies involved, are much more efficient.

Hopes this gives you some idea of this type of communication.

Regards

warren

Warren wrote:
"A traveling-wave antenna is used for satellite up-link communication."

The similarity between the "traveling wave tube" and the "traveling wave
antenna" is that both are wideband devices.

The helical beam antenna is not considered a traveling wave antenna,
though it does enjoy a wideband response. The traveling wave tube also
employs a helix and enjoys a wideband response but is not usually an
antenna.

Many microwave amplifiers are capable of only 1% of the center frequency
bandwidth. The traveling wave tube was developed to give more than 10%
bandwidth. It was invented in England in 1943.

The traveling wave amplifier generates an electron beam similar to that
of a CRT, but the beam is confined within a long helix. The signal input
is to the electron gun end of the helix. The signal output is taken from
the collector end of the helix.

The traveling wave amplifier electrons are modulated by the signal
traveling along the surface of the helix. Interaction between electrons
in the cathode beam and signal on the helix promotes signal growth and
accumulation as the signal travels to the output end of the helix.

John D. Kraus, inventor of the monofilar axial-mode helical antenna
(helical beam antenna) notes that it: "---has inherent broadband
properties, posessing desirable pattern, impedance and polarization
characteristics over a wide frequency range." (page 268, 3rd edition of
"Antennas")

Kraus` 1948 helix had a pitch angle of 14-degrees, 6 turns, 0.31
wavelength diameter, and a center frequency of 400 MHz. Its pattern was
satisfactory over the 300 to 500 MHz range.

Kraus says:
"Although the helical beam antenna consists of a continuous conductor
carrying a traveling wave, it is also a periodic structure with period
equal to the turn spacing as considered in Sect.8-8. (page 271, 3rd
edition of "Antennas)

Best regards, Richard Harrision, KB5WZI

an online RF book -- checkout page 519

http://www.ece.rutgers.edu/~orfanidi/ewa/ch15.pdf

@

"Cecil Moore" wrote in message
...
jopl wrote: ???

In a standing wave antenna, like a dipole, the power wave hits
the end of the antenna and voltage and current are reflected.
The standing wave pattern on 1/2 of a dipole looks somewhat
like the standing wave pattern for a lossy 1/4WL open stub.
In the case of a traveling wave antenna, the power wave hits
a resistor with close to the same value as the Z0 of the
antenna and is dissipated in the resistor.

So, a traveling-wave antenna is essentially one without
reflections.
--
73, Cecil http://www.qsl.net/w5dxp