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VHF/UHF Antenna [hlp]

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No one

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Hello Everyone;
I need a VHF/UHF antenna which must have a very good null near itself (about 3-5 meters apart from it). How I can design it? Is there any such antenna in the RF market? Please help.
 

salam2000

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I think you use from 2 design. 1- the Yagi antennas have a from like trapezium that support all two band where shorter section cover UHF and longer cover VHF. 2- The Yagi antennas have two sided horseshoes like (semi circle) where connect to a central axis.
 

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Azulykit

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You pose an interesting question. I do not have a solution. If I were faced with this problem I would attempt to examine the near field field structure of a number of antennas to see if I could find something suitable. HFSS may be helpful in this situation although I suspect that you will need a machine with a bucket of RAM.

I would imagine that you are attempting to place two different antennas very close yet have high isolation requirements. I wonder if shielding or microwave absorber would help. Active cancellation might be another avenue to consider.

How much rejection do you need (define: very good null)? What are the basic antenna parameters? Is it omni or directional? Bandwidth etc.?
 

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vfone

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From all antenna types the Loop Antenna (due to its configuration) have the smallest Near Field region (in VHF region ~150MHz is less than 1m).

The Near Field is divided in two regions, Reactive Near field and Radiated Near field.

The Loop Antenna inductance, which is the main contributor for Reactive Near field, is determined by the circumference, the enclosed area, the conductor thickness and the magnetic permeability.
 

atul_microwaves_antenna

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Actaully all the HF antennas can be used for this purpose.About loops, they are inefficienct transmistters at HF & MW though they are good receivers.
The best choice could be a Yagi,J Pole or Quab Beam antennas.Refer to Les Moxon book for the same.
 

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Hello;
Azulykit wrote:
I would imagine that you are attempting to place two different antennas very close yet have high isolation requirements. I wonder if shielding or microwave absorber would help. Active cancellation might be another avenue to consider.
What's active cancellation?
 

Azulykit

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Active cancellation is when you add a signal that is out of phase to another. They destroy each other. It is the principle behind noise canceling headphones. It can be very effective if the conditions are right.
 

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Hello Azulykit;
You wrote:

Active cancellation is when you add a signal that is out of phase to another. They destroy each other. It is the principle behind noise canceling headphones. It can be very effective if the conditions are right.
Can this method be used in situations that two separate receive and transmit antenna are present and should work together?
 

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