OTH Radar Antennas: 20th Century Behemoths

A dime in the antenna is worth a dollar in the transmitter any day.
— Anonymous

s we look back on the 20^th century, the first century of HF communications antennas, we may well be awed by the sheer size of many arrays. In the late 1920s, billboard arrays using screen or curtain reflectors with collections of 1-wavelength doublets gave a vertical dimension to antenna work, while long-wire arrays began to occupy considerable acreage. The long-wire era, largely dominated by competing RCA and Bell enterprises, reached its zenith just prior to World War II with large rhombics, the Bruce invention. In fact, some installations laid out rhombics end to end at slightly different angles to create different needle-width main lobes to various cities involved in the extensive message services of the era. Some of these HF antennas remain in service even today, although other more compact types have supplanted them. The required sidelobe suppression for security might in fact prove secondary in the demise of these antennas to the reduction in available land. Between the end of World War II and today, the U.S. population has virtually doubled, and the development of suburban living has gobbled land at an amazing pace. (We shall overlook some of the extensive MF and LF systems in various communications activities.)

Short-wave broadcasting turned to curtain arrays, which are available in designer sizes involving various combinations of vertical and horizontal elements. One advantage of the curtain array is that one can slew the beam electronically by changing the phase relationship among the vertical bays. These antennas are successors to the billboard arrays of the late 1920s, improved both by element development and by electronic control of energy distribution among the elements. For point-to-point communications and some broadcasting over very wide frequency ranges, fixed and rotatable LPDAs came into vogue. None of these antenna types could rival the older forms in raw size. That honor goes to the giant over-the-horizon (OTH) arrays developed by both the U.S. and the U.S.S.R. during the era of the cold war. The arrays of both nations from the 1970 to 1995 period share two features: the aim of detecting enemy bombers at very long range and very great size.

The photo above shows a small part of the OTH-B system at the eastern site. While technical details are skimpy, the tilted dipoles appear to be aimed at providing the equivalent of circular polarization. U.S. OTH-B installations occupied miles of linear space near Moscow, ME, and Christmas Valley, OR, picturesque location names to be sure, given their mission. These antennas covered both eastern and western approaches to the U.S., as shown in the map, while a set of radar installations in Alaska and Canada handled trans-polar regions. OTH-B operated in the 5-30-MHz range and employed perhaps the largest physical linear space of any antennas either before or since. Actually, at each installation, separate dipole arrays covered the numbered areas on the map.

The honor for area in OTH radar antennas goes to the Soviet DUGA-2 installations, of which the Pripyat-Chernobyl-Gomel antenna (often called the “Steel Yard”) may be the most famous for its reputation as the “woodpecker” that bothered shortwave listeners and amateur radio operators for 2 decades. Actually, the Pripyat installation consists of two separate arrays for transmitting (smaller) and receiving (larger). The frequency range for each array was about 6:1. The photograph shows both arrays. The reflector curtain is invisible in the photo, but the towers to the sides of each array apparently serve to support and stress the cables that make up the reflective surface. As well, the massive individual elements are too small to see in detail. However, the structures are about 690’ by 280’ for transmitting and 985’ by 445’ for receiving. Anyone who wishes may try to count the total number of elements in each array. The goal was a beamwidth of 0.5° or less.

The second Pripyat photo provides a sense of the complexity of the physical structure of these arrays. Each element cage is about 6’ to 8’ in diameter, which allows estimations of the supporting structural member sizes. Also evident is the rust that has set in since the de-activation of the station and the other events in the Chernobyl area.

The end of the cold-war era also meant the end of activity for both the U.S. and the Soviet OTH massive radar antenna systems. OTH radar remains widely used in both Russia and the U.S., but with far more compact antenna systems and with advances in electronic signal transmission, reception, and interpretation. The U.S. installation is in soft-storage, able to be reactivated if necessary. NOAA contemplated using the highly sensitive radar to study ocean currents and related phenomena, but the cost of operation and of maintenance have set aside these potentials. As well, advances in OTH art and science may well relegate these very large antenna systems to scrap. Of the many nations employing OTH radar systems, perhaps Australia is the most forthcoming with information on its Jindalee system’s development.

Despite the massive sizes of both U.S. and U.S.S.R. OTH systems, their defense missions largely obscure the names of key designers. F. Kuzmin was the chief designer of the Pripyat installation. In the U.S., William Thaler directed some of the early OTH research (in project Teepee). More generally, O. G. (Mike) Villard, Jr, W6YX, of Stanford University has received the title of “father of the OTH radar.” Mike’s call sign is now assigned to the Stanford University amateur radio station.

The 21^st century may not see HF antennas reaching the size of 20^th-century arrays. However, in the deserts of the U.S., we find radio-astronomy arrays composed of lines upon lines of parabolic reflectors, all working together to sum their signals and glean information about distant portions of the universe. Very large arrays have not disappeared. They have merely changed their shape, their operating frequency ranges, and their missions. Big antenna systems have an undeniable allure, despite our urge to shrink everything down to a nano-size.

NEW TYPE-13 MODELS
LB Cebik, W4RNL has made available numerous collections containing some 1210 of new Type-13 modeling files freshly compiled and uploaded to the server's download section of the Guest Rooms.

This is believed to be one of the best ways to obtain the most accurate propagation forecasts and analyses for a given amateur installation. Use these models within VOACAP of an antenna that closely resembles the actual station antenna at each frequency of operation. The resemblance need not be physical, but needs only to have a radiation pattern that closely fits the performance of the station antenna.

This is expected to be only a beginning of these files being made available free for download in the antenneX software section of the Guest Rooms. Our thanks for the generous effort LB has put into developing these new Type-13 files for your use.

To login, go to the URL below and then choose "Software Downloads" on the left side of the Welcome Page. That will take you to the software download page -- just scroll down until you reach Type-13 Files section. There is a brief introduction to the files. Each ZIP file contains 28 models plus a DOC file for further details. Shortly, we will be updating some software that contains VAOCAP and can direct call these files for your specific station.

THE PURPOSE OF THIS JOURNAL
In my column for September 2006, “The antenneX Mission,” I wrote about a subject close to my heart — the purpose of this journal. It had been quite some time since I had reminded our readers of our original purpose when we set out some 20 years ago.

More than anything else, this journal has always been a “labor of love” for me. It is the reason I founded the antenneX magazine almost 20 years ago, knowing that running a magazine is a tough business and especially so since I planned to do it without the traditional revenue support from advertisers or outside investors. I wanted this magazine to always be able to write about any issue without concerns of losing the support from any of those type revenues. I am pleased to say, we have never steered from that course one iota. And, as a consequence, we have covered some very controversial developments throughout the past two decades. In the process, we have provided valuable factual information to more than 200 countries, even to the most remote regions of the globe. Hence, our readers are much more informed about the truth about all of the “new” devices as their stories unfolded in the antenna and antenna-related field. For more details, you are encouraged to read my column from September 2006.

Additionally, we were pleased to receive and publish in the October 2006 issue, a very special editorial reaction to my column written by one of our long-term readers and contributors, Dr. Jef Verborgt. Those two articles are located by the following links below:

VISIT THE GUEST ROOMS
The relentless attacks on our web site by pirates and the like has made it necessary to add more security to protect our material against such piracy. It's only fair that we know who enters the House of antenneX, so our guests will need to provide some minimal information in the process of obtaining a login. This includes using your real active email address without which a login cannot be received. Do not confuse this login with a paid subscription login. They are not the same and your subscriber login will NOT work in the Guest Room areas. Of course, you may choose to create your own login to the Guest Rooms using the same login as your subscription, if the system will accept it.

Along with the continuing fight against spam/virii junk, protecting our material and valuable bandwidth against piracy takes up a great amount of our time—time we can't really spare. The Internet is simply not the friendly neighborhood it used to be in the "old days" and more and more security must be installed to counteract these intruders. Thus, we have made the access to the Guest Rooms as automatic as possible for you to manage your own login.

In view of the above, we have overhauled the numerous free and open-access sections that have always been wide open to all of our friends throughout the many years antenneX has been online. But, we must change with the times as the need dictates. I don't think the Internet will become more friendly in the near future and protected sites with logins are fast becoming the rule rather than the exception. To repeat, most would like to know who they invite into their house. The same applies at the House of antenneX. It's really worth the effort!

We have activated a new login system for access to the above guest rooms — and, the login can be totally managed by our guests. Above is a graphic of what you see as a login page to the new consolidated area, "antenneX Guest Rooms." This new page for logins is at this location now and available for your use:

As a result of this new programming, you will be able to obtain your own login, change it to update your info, change your password and delete membership if & when you desire without our help. Of course, the bottom link on the new page provides help if you still need it.

AN INVITATION TO CONTRIBUTORS
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antenneX thrives on the contributions of antenna experimenters, ranging from the informal home shop construction project to the theoretical investigation of basic antenna, feedline, and propagation phenomena. Over the years, we have published articles on the use of new or newly adapted materials, known antennas adapted to new circumstances, modifications of antenna structures, basic explorations of both common and unusual antennas, antenna modeling exercises, design improvements, antenna matching techniques from both a physical and mathematical perspective, evaluations of mini-antennas and their underlying theory of operation, new and patentable designs, propagation tutorials, and.... The list goes on, since no antenna-related topic is irrelevant to the readers of antenneX.

At the same time, antenneX has experienced continuous growth in its readership—for which we are appreciative. However, all readers can help us do even better. How? By submitting an article every now and then based on your current antenna work that may be useful at any level to other readers.

Among the engineering and researching readers, there are undoubtedly a number of unclassified and non-proprietary findings that antenneX readers would like to know. Among the practical antenna designers, there are ideas, tests, and numerous other practical findings to benefit our readers. Antenna builders very likely have some techniques to share with other readers. Besides the regular articles, we always have the home work shop column for shorter practical ideas and we always have the invited news and editorial column for information about new technologies, future advances, lost old but good ideas, and personal views on the good to bad things that are happening in the world of antennas and propagation.

If you are uncertain about whether your ideas merit an article, please feel free to send an outline to the general editor/publishers at manuscripts at antennex.com . Do not feel that you must be ready to be a regular submitter to write for antenneX, because we welcome the individual contribution as much as monthly articles. As well, do not believe that the slots in each issue are already spoken for—we shall always make room for a worthy article.

Appreciating Current Trends in LPDAs
By L. B. Cebik, W4RNL

Modern log-periodic dipole arrays (LPDAs) serve a wide variety of applications throughout the RF spectrum. Wherever the user requires a wide operating frequency range with relatively equal performance across the passband, LPDAs find service. LPDAs belong to a class of “frequency-independent” antenna designs, wherein the geometry of the antenna is the crucial factor in setting the performance level and the frequency span covered. The apex angle, α, together with length and spacing factors τ and σ, provide much of what one needs to design an LPDA. In fact, the process is amenable to computer-based design.

Despite the title of these notes, our goal is not to survey contemporary LPDA designs. The expression “current trends” refers to the progression of current magnitude along the series of elements forming an LPDA. Those currents have much to tell us about the anticipated performance of the antenna at all frequencies. After some preliminary reflections on the electronic portions of the typical set of design equations, we shall explore just what those current progressions tell us about potential performance and what adjustments may be wise to make to the initial design.

Voltage Across the Terminals of a Receiving Antenna
By Kirk T. McDonald, PhD
Joseph Henry Laboratories, Princeton University

Our problem here is to deduce the no-load (open-circuit) voltage V_oc across the terminals of a short, center-fed linear dipole antenna of half height h when excited by a plane wave of wavelength λ >> h whose electric field is parallel to the dipole antenna.

One may assume that the antenna conductors have a diameter small compared to the height h, and that they are perfect conductors. The gap between the terminals is also small compared to h.

By dimensional analysis, the no-load voltage has amplitude of order E₀h, where E₀ is the amplitude of the incident wave. The problem is to show that to a good approximation the voltage is actually E₀h. This problem can be addressed using techniques that are simplifications of those appropriate for antennas comprised of thick wires with complex geometries.

A 6:1 Balun and My Antenna System
By Fred M. Griffee, N4FG (EE Retired)

I recently completed an exercise using an antenneX-supplied 6:1 balun that surprisingly, showed overall efficiencies greater than 90 percent but no less than 70 percent. This article includes the design result with included HF frequencies of most interest.

Improving the Versatility of the Autek VA1 Vector Analyst
By Anselmo Stiffan IZ3BGJ

Serious experimenting with antennas requires, on top of a minimum understanding of AC basics and possibly of the RF basics, some instrumentation somewhat more complex than an SWR meter. The SWR meter is very useful and very often is an integral part of the transceiver. Its reading can prevent damages to the power RF amplifier by letting the operator to adjust the line and the load in such a way that the transmitter sees a safe load. This however doesn’t tell anything about the antenna (load) impedance or its resonant frequency.

BALUNS, WHAT DO THEY DO?
By Jack Althouse, K6NY
Palomar Engineers

The most popular, simple, and effective antenna is the horizontal dipole. It is a balanced antenna, that is, the wires on both sides of the center insulator are of equal length. In the early days of radio it was fed with "ladder-line," two wires in parallel spaced by insulators. It too is balanced. Feeding a balanced antenna with a balanced feeder works well. Many amateurs still use this method because of the very low loss of ladder-line.

But back around the time of World War II coaxial cable was introduced. It has certain advantages over ladder-line: It is self-shielded and so does not radiate; it can be routed next to metal objects or even buried in the ground with no affect on is operation. But it has a major defect in that it is unbalanced.

"Balanced feed" and feedline radiation - Part 2
By Jan Gunmar SM0AQW

A preliminary conclusion from Part 1 is that the most effective measure to obtain a “balanced” antenna system which remains “balanced” over a wider frequency range is to actively suppress common mode current on the feed line using good grounding principles and suppression devices like current and voltage baluns. Other measures like moving the feed point, changing the antenna position, or rerouting the feed line may perhaps be helpful, but the author believes that they belong to the “trial and error” category of methods. This part contains a study of how unbalance currents on an asymmetrically located feed line to a dipole are distributed when different suppression measures are applied.

Well, there you have it, folks—thanks for listening and remember, the reading lamp is always on for you in the reading rooms. If I can be of further help, I'm just a Stone's Throw! away.-30-

Best reGARDS, Jack L. Stone, Publisher
jack@antennex.com
August 2007 antenneX Online Issue #124