Cubical Quad Notes ~ Volume 1
A Book Review
By Dan Handelsman, N2DT
have read just about every antenna book that is available. Some are arcane and full of mathematics and others are overly simplified. Some are poorly written while others are easily comprehended. As a reviewer, it is my duty to give you an objective analysis of the content and the author's style. With that said, it gives me great pleasure to review L.B. Cebik's new book, Cubical Quad Notes - Volume 1 - A Review of Existing Designs. But first, a little historical background.
Cubical Quads - History and Folklore
If one believes folklore or legends, Clarence Moore, the station engineer at HCJB in Quito, and some colleagues took along with them a stack of antenna and engineering texts and a Bible on a Sabbatical in 1942. Their urgent goal was to come up with an antenna that wouldn't consume itself by corona discharge when fed with high power, as was happening to their Yagi, at the high Andean altitude of their station.
Whether by divine engineering or by Divine intervention the Quad resulted and this full wave loop antenna has been with us for almost 60 years. The loop was the perfect design solution to the problem facing Moore. It was essentially a pair of dipoles, stacked 1/4 wl above each other, whose ends or high-voltage points were folded to meet each other half way. The result was no high-voltage point open to the atmosphere and hence no corona. As an added bonus the loop had a gain advantage over a dipole of about 1.2 dB.
Moore immediately got to work and constructed a parasitic array to replace the Yagi and patented the antenna. The two-element version was named the "Cubical Quad" since its appearance was, well, cubic.
Designs over the Years
After such a brilliant beginning quad design has stagnated since, although there have been sporadic efforts at improvements over the years. If one compares quad design to a game of chess then we have had random moves punctuating long time intervals. There has been no systematic investigation of the basics of the individual loop and how to combine quad loops into the multi-element and multi-band parasitic antennas that we have come to expect with Yagis.
Such an investigation is clearly warranted since the parasitic quads are valuable antennas for a host of reasons. First off they are more easily constructed than Yagis in many parts of the world where large diameter aluminum tubing is too expensive or unavailable. Second, they are more "compact" three dimensionally and require much shorter booms for the same gain as Yagis. Third they seem to be more amenable to multi-banding with fewer design sacrifices than with multi-band Yagis.
L.B. Cebik is a second generation loop experimenter. His Dad was experimenting with Loops way back in the 1920s. To the left is a partial image of an article written on a very early Loop by LB's father, James S. Cebik, 1ATG and published February 11, 1928 in the New York Telegram Radio section of the newspaper. Now in his nineties, I understand Mr. Cebik is in good health residing in Connecticut. There is a reprint of this entire article in the antenneX archives from their March 1999 issue.
A prolific writer and experimenter as well, LB has an extensive website on the Internet discussing antenna theory and design along with a tremendous collection of practical antennas. His particular interest is the quad and he has devoted much of his time to understanding and analyzing it.
What LB has done in Volume 1 is to gather together in one place the best designs that have arisen over the years and analyze them in a systematic manner. After perusing this book a reader can begin to get a deeper understanding of how these antennas "play".
LB writes clearly and logically and integrates his well-known expertise in antenna modeling with the design analyses. He has a knack for making technical concepts understandable to all. Some people are experts in their field and others are excellent writers and communicators. A rare few can combine both talents. Fortunately for us LB is one of those.
The introduction, and each succeeding chapter, leads one logically through all the elements of quad antenna design. Even if one is leery about antenna modeling the text is fine by itself. There is no complex mathematics and a beginner, as well as an expert, can be made conversant with the antennas.
LB begins with the full-sized two-element quad and then discusses its variations including "shrunken" or minituarized quads and multi-band quads. He also goes into the feed systems. Later chapters are devoted to larger quad arrays and stacking effects. It appears that he has managed to cull out all of the useful and interesting designs that have appeared in the literature since the quad's invention and uses them to make specific points.
What I found interesting and novel, even as an amateur who has been a student of loop antennas, are the designs that have somehow been "gotten right" over the years. I was surprised to find out that the "spider quads" where the element spacing (in wavelengths) for each band in a multi-band quad was held constant were inferior to some "planar quad" designs where the physical distance was made equal between all of the elements. It seems that the wires of the unused loops become parasitically excited and enhance the overall performance on many of the bands. Such surprises would never have seen the light of day had LB not done his modeling studies.
The book is good not only theoretically but also practically. A reader can come up with some very useful antennas for whatever the needs may be after getting an easily acquired understanding of the variables and compromises that go into quad design. To help with this, the book with over 220 pages, contains 125 illustrations and more than 80 Tables of information about antenna performance, dimensions and data essential to modeling the antennas discussed. Here is a lis of the titles for each of the 12 chapters in Volume 1:
|2||Full-Size 2- Element Quads||13|
|3||Variations and Comparisons Among 2-Element Quads||29|
|4||Shrunken 2-Element Quads||55|
|5||Multi-Band 2-Element Quad Beams||79|
Common Feed Systems
for Multi-Band 2-Element Quad Beams
|7||Stacking 2-Element, 5-Band Quads||119|
|8||Separately Feeding Multi-Band Quads||139|
|9||Monoband Quads of More Than 2 Elements||151|
|10||Special Notes on 3-Element Quads||175|
|11||Larger Multi-Band Quads||189|
|12||Where Do We Go From Here?||217|
The book is bound using the attractive plastic comb binding that allows it to lie flat and be easy to work with. The type size is easy on the eyes - even for a presbyopic guy like myself. It comes in three versions, and at $29.95 for the soft cover and $24.95 for a CD it is a bargain. For the convenience of those who want quick delivery, there is a download version for only $22.95. Both CD and download versions are in the popular "PDF" format and using Adobe Acrobat Reader one can zoom in to magnify for close-ups with amazing clarity because ot the high-resolution utilized. The book is published by antenneX and is available in the Shopping Shack BookShelf for immediate acquisition using a Credit Card on their secure online website order forms. Of course, you can opt to order by telephone or mail too.
As I understand it, Volume 2 will go into a systematic analysis of the fresher material which has now come to the fore. It will apply modern understanding of loop theory to ground-up design of multi-element and multi-band parasitic quad antennas.
To sum it up: Volume 1 is excellent and belongs on any antenna hobbyist's or serious antenna designer's bookshelf. I can't wait to read Volume 2. -30-
|Dan Handelsman, N2DT
Dan Handelsman, N2DT was first licensed as WA2BCG in 1957at age 13. He became interested in antennas at that time when he had to figure out a way to operate from the 6th floor of his apartment house. This resulted in a mobile whip being stuck out from a window without a counterpoise. At that point he became an "expert" in TVI. He was licensed as N2DT in 1977 and is a DX'er and contester. He is now playing with experimental antennas and low power.
Professionally, he is a Pediatric Endocrinologist and holds M.D. and J.D. degrees and is Clinical Professor of Pediatrics at the New York Medical College. As far as his antenna work he is an "amateur" in the truest sense of the word (Dan's words!).
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Last modified: December 31, 2010