To The Editor:
The article in the January 2010 issue of Microwaves & RF entitled "Match Loop Antennas Via Mutual Inductance" is a rehash of the old loop-coupled loop. This was invented by Dunlavy and patented in 1971. Both loops have small radiation resistances and individually low efficiencies. The overall efficiency is essentially the product of the two loop efficiencies, and this number will be very small. A loop-coupled loop was manufactured for some time by Antenna Research Associates (ARA), but no longer. A careful analysis of the loopcoupled loop is given by R. C. Hansen in section 1.5.3 in the engineering text, i, published by John Wiley & Sons in 2006.
R. C. Hansen
Consulting Engineer
R. C. Hansen, Inc.
P. O. Box 570215
Tarzana, CA 91357
(818) 345-0770
FAX: (818) 345-1259
Internet: www.rchansen.com
Editor's Note:
Mr. Hansen's work in antennas is certainly well known in this industry, and we would like to express our appreciation for his taking the time to actually pen a letter to the magazine to express his thoughts on this matter. The article in question, written by Alan Bensky of Ateret Radio Engineering and appearing on p. 78 of the January 2010 issue of Microwaves & RF, was a short exercise in designing loop antennas for frequencies between 300 and 1000 MHz, notably for compact portable wireless products. The designs are not new, nor presented as new. The article intended to help simplify the impedance matching of miniature printed-circuit loop antennas and to design and manufacture these antennas as simply and inexpensively as possible. An example fabricated for the article shows a loop antenna with resonance at 318 MHz using mutual inductance coupling.