[Antennas] Broadbanding an antenna...

Tue May 22 20:39:41 EDT 2012

There's a lot of professional literature on broadband impedance matching. Look up H. A. Wheeler and you might find some of it. A parallel circuit broadbanding a series resonant antenna is referred to as "double tuning", and it will roughly double the VSWR bandwidth. In essence, a single tuned impedance locus will pass through the center of the chart, with increasing reactance (and VSWR) off frequency. When double tuned, the impedance locus circles the center of the chart, with a nearly constant VSWR within the band. More complexity is possible but rarely practical. However, it's not trivial to do the double tuning and get the right impedance levels out. My employer has done a lot of research on tuning, and built a lot of multituned antennas.
The need for Smith chart calculations or computer codes mostly kept this out of the ham arena. It may be more feasible for hams to use circuit design software these days.
Ed W2EMN
-----Original Message-----
From: Ray <w4byg at att.net>
To: antennas <antennas at mailman.qth.net>
Sent: Tue, May 22, 2012 5:28 pm
Subject: [Antennas] Broadbanding an antenna...
Charles Michaels, W7XC, (someone else has this call now), designed and 
built an interesting network to successfully broadband his short 160 
meter vertical. He called it a "Load Tracking Network". It was 
published in the April issue, 1992, QST.
I've not seen any other reference materials or articles on his 
approach. It involved designing a series inductance plus a shunt "L-C" 
network. The shunt network resonated at about 3.4 Mhz thus had the 
reverse reactance characteristic of what occurred as he tuned off of his 
optimum frequency. It seems like a valuable approach to broadbanding 
and antenna.
Has anyone else has expanded or written on such a "Load Tracking 
Network" that it could be more easily utilized in other narrow banded 
applications such as HF mobile antennas or other bands?
Thanks for your attention.
73,
Ray, W4BYG
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