Physical distance between diversity antennas

Answered Question
Aug 5th, 2008
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Before I get flamed for not checking the past posts, I did :) While I've read the bits about being one wavelength apart (and there is some debate whether this distance should be figured in wavelength or 1/2 wavelength measurments) there is no indication of where you take the measurement. What I mean is do you measure from the middle of the antenna, or the side of the antenna (or am I just splitting hairs?).


My particulars as follows:

1242AP + ANT2460P-R x 2.


Thank you in advance for the help.

Correct Answer by dennischolmes about 8 years 10 months ago

Rob,


The spacing can be in multiples but is best in multiples of odd numbers. 1x or 3x. This allows for the phase to be always 100% out for the opposing antennae. 2x could cause phase shift overlay and could result in both antennae receiving the same phase shift differentiation.

Correct Answer by Rob Huffman about 8 years 10 months ago

Hi Mike,


It's always good to be as accurate as possible :) I've always taken this measurement from edge to edge.


Here is the Cisco reference in question;


The 2.4 GHz wavelength is approximately 4.92 inches. Therefore, to support diversity on a 2.4 GHz radio with two separate antennas, the antennas should be spaced approximately 5 inches apart. The antenna pair could also be spaced at multiples of 5 inches, but the distance between should not exceed 4 multiples: reflected waves farther apart than that are likely to be so distorted and different in delay spread that the radio could not work with them.Because each antenna is selected by itself, both antennas must have the same radiation characteristics and be positioned to provide similar cell coverage.


From this good doc;


Multipath and Diversity


http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml


Hope this helps!

Rob


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Correct Answer
Rob Huffman Tue, 08/05/2008 - 16:19
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Hi Mike,


It's always good to be as accurate as possible :) I've always taken this measurement from edge to edge.


Here is the Cisco reference in question;


The 2.4 GHz wavelength is approximately 4.92 inches. Therefore, to support diversity on a 2.4 GHz radio with two separate antennas, the antennas should be spaced approximately 5 inches apart. The antenna pair could also be spaced at multiples of 5 inches, but the distance between should not exceed 4 multiples: reflected waves farther apart than that are likely to be so distorted and different in delay spread that the radio could not work with them.Because each antenna is selected by itself, both antennas must have the same radiation characteristics and be positioned to provide similar cell coverage.


From this good doc;


Multipath and Diversity


http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml


Hope this helps!

Rob


Correct Answer
dennischolmes Mon, 08/11/2008 - 05:58
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Rob,


The spacing can be in multiples but is best in multiples of odd numbers. 1x or 3x. This allows for the phase to be always 100% out for the opposing antennae. 2x could cause phase shift overlay and could result in both antennae receiving the same phase shift differentiation.

Rob Huffman Wed, 08/13/2008 - 05:00
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Hi Dennis,


Interesting info here for sure. We have only ever used 1x but I will keep this for future reference. +5 points for your always great tips!


Thanks again,

Rob

soularch23 Wed, 08/13/2008 - 07:19
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Hello Rob and Dennis:


Thank you both for the great insight regarding antenna spacing for diversity systems. I knew I would get great answers from this list. Rock On!


Mike

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