Subject: RE: [NEXTEL-1] Re: Antenna theory

From: Anderson John-P29444 <[email-masked]>
Date: Thu, 3 Jul 2003 08:05:21 -0700

The Department of Defense uses circularly polarized systems on all kinds of mobile platforms.  The basic tradeoff is robust performance over all conditions vs. peak gain under certain conditions.  Linearly polarized systems are more an artifact of history than anything else.  Just like 50 ohm cable.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Wednesday, July 02, 2003 11:46 PM
To: [email-masked]
Subject: [NEXTEL-1] Re: Antenna theory

------- Original Message --------
From: Jack Daniel <[email-masked]>
Subject: Re: Antenna theory

Interesting. We have taken different forks in the same road. ha ha.

I agree 100% with your assesment that using a circular polarized TX and
antenna and a linear RX antenna will result in some less-than-optimum
reception in any case. 

My point was when the RX antenna is also circular polarized in the same
rotational direction as the transmit antenna multipath (i.e reflections)
will reverse rotation and be attenuated by the rotational selectivity of
the receiving antenna. Perhaps easiest way to visualize this is a
reflected signal immediatly behind the receiving antenna. If the
direct/desired signal is CCW the reflected signal will be CW relative to
the recivunbg antenna. Since this scenario uses selectivity instead if
cancellation mechanisms, I suspect the desired signal level would always
be greater than in the cricular-to-linear set-up.

This is an interesting discussion because we are using different
mechanisms to resolve the same problem. Now I wonder which would be
superior in differnt applications? 

Instinct tells me your linear antenna (mobile whip) would be most
practical on a moving receiver and a circular polarized might be better
for a stationary receiver. But I'm not sure.

Hmmmmmmm.... gotta dust off some books.....

Jack Daniel
(I WILL trim, I WILL trim,..)
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---

From: Jack Daniel <[email-masked]>
Date: Thu, 03 Jul 2003 12:42:24 -0700

Thanks John.

Are these used while the paltform is in motion?

If so, is antenna steering required. 

Jack Daniel
===============================

Anderson John-P29444 wrote:
> 
> The Department of Defense uses circularly polarized systems on all
> kinds of mobile platforms.  The basic tradeoff is robust performance
> over all conditions vs. peak gain under certain conditions.  Linearly
> polarized systems are more an artifact of history than anything else.
> Just like 50 ohm cable.
> 
>      Your use of Yahoo! Groups is subject to the Yahoo! Terms of
>      Service.
> 
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> 
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