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[TowerTalk] Isolated Mode Antenna Technology

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Subject: [TowerTalk] Isolated Mode Antenna Technology
From: "Ed Callaway" <>
Date: Sun, 20 Dec 2009 08:22:40 -0500
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I suspect that the article made little sense because the actual design of
the specific antenna is the "secret sauce" of the authors' company, and the
article is largely a commercial advertisement, not a true technical paper.
(Part 2 is available at , but doesn't add much
to the reader's understanding.)

However, the idea underneath is a sound one, and is well-known in the art:
Given an arbitrarily-shaped radiator, it's possible to feed it at multiple
points such that the feedpoints are isolated from each other.  Each feed
produces (in general) a different radiation pattern.  Having different
radiation patterns is useful in MIMO applications, which count on the
uncorrelated multipath propagation between multiple antennas (i.e.,
independently-fading signals arriving from multiple directions) to increase
throughput "above" the Shannon Limit for the channel.  In 802.11n
(Wi-Fi(tm)) and next-generation cellular systems, the developers are
counting on MIMO for this throughput increase but, as a practical matter,
having multiple, physically separated antennas on a cell phone is a
problem -- there's no room.  Having a single radiating structure but with
multiple feeds is a much more practical solution, so that's where the market
for this technology likely will be.

Although it doesn't involve feeding at multiple physical points, a simple
(perhaps degenerate) example of this concept most relevant to the Tower Talk
world might be two-wire Beverage receiving antennas, the patterns for which
move 180 degrees just by changing from differential to common-mode feed.

Note that for DXing this technique is unlikely to be as effective as true,
multiple-physical-antenna diversity:  The signal is likely to be coming from
only one direction, and the multiple-feed antenna will produce a DX signal
only on one feed (assuming independent patterns).  In a true diversity
system, both antenna patterns would be pointed in the direction of the DX,
so the DX signal would appear on both feeds, fading independently due to the
antennas' physical separation and providing diversity gain.  In the cell
phone MIMO case, the signals are expected to be scattered and arrive from
multiple directions, where the different antenna patterns can all be used to
collect the signal(s).

Meandering lines, or meanderlines, are runners on a substrate that are
physically shortened by having them go back and forth, like queues at
Disneyland.  They often look like little square waves when seen on circuit
boards, and are the 2-dimensional analogy of 3-dimensional helical
structures.  Like helices, they can be used as inductors, resonators, and

Ed Callaway N4II


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