Comprod makes dipole arrays with a screen reflector, at least for VHF, not
sure about UHF.  I'm looking in the catalog and it shows a backside null
close to 20 dB down from the main lobe.

The screen reflector should be nominally about 1/4 wave behind the radiator
for maximum forward gain.  It could be modeled fairly easily. 

How wide of a forward beamwidth do you want?  Would a couple of corner
reflectors be a better way to go?

                                --- Jeff

> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com 
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Dan Hancock
> Sent: Thursday, November 19, 2009 11:43 AM
> To: repeater builders
> Subject: [Repeater-Builder] Antenna Pattern Question
> 
>   
> 
> I have a repeater that I need to have as tight a cardiod 
> pattern as possible. I have looked at the dipole antennas 
> such as the DB-411 and they don't really shut down the back 
> door quite enough. 
> Does anyone have any antenna modeling software that would 
> show the result of adding an 18" wide screen to the back side 
> of the mast on the DB-411? Does anyone have any experience in 
> home-brewing a modification like this?
> 
> Dan Hancock N8DJP
>       
> 
> 
> 
> 
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