[MLB-WIRELESS] Downpipe Antenna??

[Rob Clark]

Mark,

You are correct. Double the slots ==> 3dB extra gain.

Practical Limit?
- The more slots you add, the thinner the beam. The 'problem' with
slotted waveguides is that the signal (gain) drops off as you move the
receiving antenna up/down in elevation ... away from the center of the
pizza-shaped beam. So...for client antennas that are perfectly along the
beam (ie at the same elevation)...yes more slots = more gain. But for
client antennas higher/lower...they get less signal.

- 8-slots is the most common as it gives a pretty good compromise. An
8-slotter will go to the horizon anyway (with say a Hills 25 dBi dish as
the client). But - I have seen designs for 16 slots. 

This page: http://www.freenet-antennas.com/Waveguide has an excel
spreadsheet that includes the designs for 8+0, 8+8, 16+0, and 16+16 slot
waveguide antennas.

Cheers

Rob Clark (The Downpipe Guy)



-----Original Message-----
From: owner-melbwireless at wireless.org.au
[mailto:owner-melbwireless at wireless.org.au] On Behalf Of Mark Aitken
Sent: Tuesday, November 11, 2003 2:40 PM
To: melbwireless at wireless.org.au
Subject: [MLB-WIRELESS] Downpipe Antenna??


Just a few quick questions about Downpipe Antenna's and gain.......

If one doubles the the number of slots on a single sided antenna, say
from 
8 to 16, does this act like a colinear antenna where a double of the
number 
of elements gives an extra 3db gain?

Is there a finite limit on slots in this type of antenna?

And finally, how well do they perform over something like a "planar" 
antenna (which seem to give good gain charastics!?!?)

Many thanks for your time in reading/replying.

Mark


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