About Us

July 17th 04, 09:55 PM

On 17 Jul 2004 13:27:03 -0700, (J. Harvey) wrote:

Roy Lewallen wrote:
The sum of LHCP and RHCP fields of equal magnitude
is a linearly polarized field. The orientation of
that linearly polarized field depends on the
relative phases of the LHCP and RHCP fields.

...and...

Walter Maxwell wrote:
Without giving the problem any serious mathematical
or physical thought, only knee-jerk intuition, IMO,
if a radiator suitable for radiating CP of either
hand were fed with equal signals leading to both
RHCP and LHCP simultaneously, I agree with the
poster above that complete cancelation would result,
and there would be no radiation.
This is why a linearly-polarized antenna could not
receive any energy. (har har)

One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. DBS satellites (for example) use
RHCP and LHCP to double their bandwidth, just like FSS satellites use
H and V. I have not heard anything about the DBS RHCP transponder
having to worry about the LHCP transponder. I haven't heard any
mention of nulls suddenly appearing and disappearing in the downlink
passband as the two senses happen to coincide, out of phase. I haven't
heard about the CP being converted to linear and causing interference
(at -3dB) in the other CP mode.

I assume that the two CP signals have no knowledge of each other. The
hardware can be designed (easily) to maintain that isolation - imagine
the two transmitter hidden from each other and the signals just happen
to be headed in the same direction. In other words - for purposes of
argument - it doesn't have to be the same antenna.

It just so happens that, for this 'dual-CP' concept, the two CP
signals happen to be the same but one is inverted. They don't have to
'know' about their evil mirror-image twin.

If they cancel out, then where does the energy go? Make it a mega-watt
each and follow the smoke. If they combine in the vacuum of space,
where is the smoke?

Appreciate your comments...

de VE1BLL

Hi Jeff, my age is showing. In my knee-jerk reaction I stupidly thought of
applying the RH and LH sigs from the same source. Of course your concept works
when the signals are supplied from two different sources. The two signals are
totally oblivious to each other.

I know this is true, because it's exactly the method I used in developing the
antennas for TIROS 1, the World's first weather satellite. The circuit concept I
used there comprised a four-port hybrid ring, or rat race. The two transmitters
fed two opposite input ports. Each of the ouput ports fed a two-port balun, each
balun port feeding one terminal of a dipole. However, the line from one of the
output ports had a 1/4wl extra length, and the dipole fed from this output port
was oiented 90Â° from the other. With this arrangement, the radiation of the
signal entering one input port of the hybrid is inherently RHCP and from the
other is LHCP. The signals from each transmitter were received on a
linearly-polarized antenna at any orientation angle, with no mutual
interference.

If you'd like I can send you a copy of the circuit diagram in jpg format. This
coupling system was fabricated in stripline, so if you'd like, I'll also send
you a copy of that. Actually, the total system comprised the use of four
transmitters, with each pair operating in two different frequency bands. The
total coupling system fed all four transmitters simultaneously into one antenna.

Please let me know if you'd like me to send the stuff.

Walt, W2DU

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search
Display Modes
Switch to Linear Mode Switch to Hybrid Mode Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Comet Dual Bander question	Dan	Antenna	2	March 11th 04 04:16 AM
Help, Digital TV UHF antenna needed for 21-69 channels	ja	Antenna	3	February 10th 04 12:22 AM
Poor quality low + High TV channels? How much dB in Preamp?	lbbs	Antenna	16	December 13th 03 03:01 PM

Menu

About Us