**THE
CROSSED-FIELD-ANTENNA
PART I**

Maurice C. Hately GM3HAT

& Ted Hart W5QJR

**PREFACE:** Please be
aware this article introduces a completely new concept in antenna theory. In fact, this is
considered the most important development relative to antennas in this century. It is so
pervasive that a series of articles are required to cover the concept and its applications
to the depth and extent it deserves. This is the first publication about the * Crossed-Field
Antenna* (CFA) in the U.S.A. Even as you read this, there are continuing
developments in the application of this concept.

**W**here
will this concept lead ? Let me tell you about one example, lest you think this is all for
naught: A CFA only 21 feet (6.5 Meters) tall, located at Tanta in the center of Egypt,
provides AM broadcast service at 1.16 MHz (258 Meters) to millions of people from Cairo
north to the coast. Certified measurements provide evidence that this small CFA produces a
radiated signal almost 6 dB stronger than the previous 1/4 wavelength vertical broadcast
tower which was 211 feet (65 Meters) tall. To express the performance a different way
>> with the tall tower, a 100,000 watt transmitter was required for the desired
coverage. With the miniature CFA the same coverage was attained with the transmitter power
reduced to 30,000 watts.

**BANDWIDTH GREATER THAN TALL TOWER!**

Unlike conventional small antennas, the CFA has greater bandwidth than the tall tower,
thus giving better fidelity to the broadcast signal. If that don't tug your heartstrings,
you need to go back to making mud pies. For all the rest—you ain't seen nothing yet.
In spite of this, the antenna "experts" have not widely accepted this concept. I
can only conclude that those who did not invent it don't want to admit that someone else
did. That is a common malady and is often referred to as the not-invented-here (NIH)
syndrome. I personally went through the same thing with the small loop antenna. It is the
purpose of * antenneX* to expose you to new concepts—whether you accept
them or not is your personal preference. Some people still don't think man has set foot on
the moon!

**INTRODUCTION**

While thinking about how to present this article, I (W5QJR) was
scanning the web and found the following definition of an antenna:* "An
antenna can be any conductive structure that can carry an electrical current.*

A number of years ago (1984) I (Ted Hart) wrote the book on small loop antennas and declared in that book, and several related articles, that the only way to build a small high efficiency antenna was to build a small loop. That statement was true until about 1988.

I am simply telling you that one doesn't have to have a wire
antenna—there is another way. The other way came about due to a College Professor by
the name of * Maurice Hately, GM3HAT*, in Scotland, and a student named

However, before giving you a history lesson, I do want to note that
Mr. Hately and Mr. Kabbary jointly own all rights to this invention. All rights are
reserved by them. If you have a commercial interest, contact the author. Mr. Hately
reviewed, modified and approved this article, so you are getting this information from the
horse's mouth. I, W5QJR, am merely a ghostwriter and take no credit for any of the
development. I have derived great pleasure in working with Mr. Hately for several years
and he is now in the process of bringing antennas based on this concept for sale thru * antenneX*.

**A HISTORY LESSON**

A long time ago, in a far away place, a fellow named Ampere and another fellow named
Faraday (1791-1867) independently developed the concepts and equations to define
electromagnetism. Then along came a fellow by the name of Maxwell (1831-1879) who combined
the works of Ampere and Faraday and developed the four (4) basic laws called * Maxwell's
Equations*. These equations are so fundamental that every Engineer considers them
to be

Although many authors have quoted Maxwell, and many a college
student has struggled trying to understand Maxwell, nothing interesting happened until
along came Professor Hately and Mr. Kabbary (now Dr. Kabbary due to this work). As is
prudent to do when tying to understand a concept, you go to the most fundamental version
of the concept that can be found. In this case, Maxwell's Equations were only an arm's
reach away in any good engineering reference book (for example see page 45-4 of * Reference
Data for Radio Engineers*).

Now, our time clock moves forward to March 1989, when * Electronics
and Wireless World* published an article entitled "Maxwell's Equations and the
Crossed-Field Antenna", by F.M. Kabbary, M.C. Hately and B.G. Stewart. To ensure you
get all of this picture in proper perspective, the following paraphrases that article. It
may get a little technical for some, but that is the essence of this new antenna concept.
We will endeavor to translate to simple terms wherever possible, so please continue to
read even if you are not an engineer. The picture would not be complete if the theoretical
portion of this puzzle was not included in this series of articles.

**A LOT OF HEAVY THEORY**

All electrical and communications engineers are in some way acquainted with Heavyside's
differential form of the third and fourth Maxwell equations, viz.

In these equations,** '** is the derivative with
respect to time, **E** represents the electric field strength, **H** magnetic field
strength,** J** current density, **B** magnetic flux density = **µ H**,
and** D** electric displacement =
is called the displacement current. Equation 1) is Faraday's law, while equation 2) is
credited to Maxwell for adding **D'** to Ampere's law, which is to maintain charge conservation or charge continuity and thus
obtain** J + D'** as the true or total current.

Unfortunately, the understanding of these equations still poses many conceptual difficulties for many people which inevitably lead to shortcomings in the basic understanding of their engineering applications (and you thought you were alone?). One reason for this lack of insight is perhaps the inability to appreciate the physical meaning of the vector operations curl, div and grad. Many texts and research papers often detail the mathematical intricacies of these vector operations but few describe in practical simple terms their physical interpretation.

In addition to the above, it is often not realized that contained in
equations 1) and 2) is the following extremely valuable information: (a) a time-varying
magnetic field creates an electric field (or back EMF) and, importantly, (b) a current __or__
a time-varying electric field

The essence of Maxwell's equations, conveyed through points (a) and (b), is that fundamentally they are reactive or field-production equations. The physical , mathematical and engineering importance of the field-production nature may be more readily relayed and understood if the forms of equations 1) and 2) are reversed:

The reversal leads not only to a greater understanding of Maxwell's equations (which is hidden in the non-reversed form) but to a greater appreciation of the nature of time-varying electromagnetics and their associated engineering applications.

One significant engineering application, only fully realized through
the reversed form of Maxwell's 4th equation, has been the recent development of
revolutionary antenna systems called crossed-field-antennas (CFA) which synthesize
directly the Poynting vector **S = E X H** from separately stimulated **E**
(electric) and **H** (magnetic) fields.* ***S** is electromagnetic radiation,
thus this says there are two (2) components to the radiated field, **E** and **H**.
The **X** is defined as the cross product, meaning that they must be properly related
both in time, phase, and position.__ In other words, if you can separately create the
two fields and properly combine them, you don't have to have a piece of wire carrying a
current.__ Because of this,

The principle of Faraday's Law (equation 1) as detailed by most
textbooks, is that an electric field can be related to the rate of change of a magnetic
field. This electromagnetic feature can be expressed in a more elegant and informative way
by reversing equation 1) to give which is
interpreted as a time varying magnetic flux, **B'** creating an electric field** E**
such that the negative of the curl of the induced** E **field distribution is equal to
the source **B'**. The directive arrow is present in the relationship to indicate that
the left-hand-side causes or creates the right-hand-side. The negative sign is a
manifestation of Lenz's law. In fact, the application of the reversed form of Faraday's
law is fully deployed in transformer theory, where a time varying magnetic flux creates,
i.e., induces, a back EMF. Note that the **E** field in the reversed form of Faraday's
law is the induced **E** field from **B'** and is not in anyway related to the
independent electric field created from free charge through Gausse's law.

Consider now equation 2). In magnetostatics, it has always been
accepted that current produces a magnetic field though the phenomenon called Ampere's law.
To get across the importance of this statement in a more meaningful physical and
mathematical form, Ampere's law should be expressed as: i.e., **J** (current density) creates a
magnetic field **H**, such that the curl of **H** is equal to the source **J.**
It is also known (though often ignored) that a magnetic field may be related to either a
current as above* or* a time varying electric field. The latter source of
magnetic field is sometimes refereed to as the Maxwell Law, and may be expressed in the
more informative form as: i.e., displacement current

__Unfortunately, many people fail to realize that an H field
may, at any time, be the combination of two separately induced fields from independent
types of sources, i.e., charge motion and displacement current.__

The editor says we are out of space, so we will pick up here next
month and apply what we have learned to create a magnetic field without running current
thru a wire. This will be accomplished by a simple demonstration. That is essential to the
process of building this type of Crossed-Field-Antenna. The heavy theory is behind us so
it is down hill from here. Stay tuned. **-30-**

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Last modified:
April 06, 2008