What's in a Name? 
The antenna owes its name to a certain visual similarity that some kinds bear to the "movable, segmented organ of sensation on the head of insects, myriapods, and crustaceans." We rarely confuse the two generic types of the antenna for plural reasons. An insect has two antennae, but an amateur radio operator often has two (or more) antennas. (Many British experts preserve the alternative name, aerial, perhaps because the term is less arcane and captures something of the antenna's lofty position in the air and something of its ethereal role in radio communications.) "What's in a name?" wrote Shakespeare. An antenna by any other name would radiate as well--and confuse the heck out of amateur radio operators.
Confusion reigns within the field of antenna names largely due to history--more specifically, the history attached to how each antenna type received its name. Some antennas have received the names of their creators or developers, such as the (W)8JK. Others have received names because of what they look like, such as the J-pole. Still others received names from their original uses, such as the Zepp(elin). Some few antennas hide technical information behind their names, such as the dipole. Since the history of antennas includes strong elements of mixing, matching, and adaptation, the result has become almost a free-for-all of naming that can leave us breathless, wondering what a name really means.
We can obtain some useful information--or at least a bit of entertainment--by looking at the names of antennas apart from most of our normal concerns for their performance under the circumstances of their installation. Ultimately, the option that we shall face is whether to call an antenna by its common name--often a misnomer--or by a technical description that best places the antenna within the total body of antenna types. Shall we refer to a certain antenna as an endfire bi-directional array of a pair of horizontal center-fed collinear 2-half wavelength wires 180° out of phase or simply as a W8JK flattop? The answer seems obvious until we explore some of the ways in which common names can get us into trouble.
So let's explore some of the types of names that we give antennas. This space is too small for detailed histories of names, but along the way, we can suggest avenues of further exploration for those interested. As a convention, I shall italicize each antenna name that we consider. Mercifully, I shall omit from consideration most merely cute names, such as the myriad of antennas that have borne the name "signal squirter." ("Squirt," however, once had a common use in amateur radio to designate newcomers who usually used lower power than more experienced hams.)
Antennas Named for People
In earlier radio days--say the late 1920s through about 1940--antenna designs emerged largely from two sources: Bell Labs and RCA. Engineers would publish their developments--after their companies obtained patents--in the Proceedings of the IRE (later supplanted by the array of IEEE publications) or in a house organ, such as the RCA Review. Both are excellent sources of information on antenna developments, and most college libraries have collections. If you wish to look at the original papers, you may obtain specific references by looking at the footnotes or references in any of the standard college texts, such as Kraus' Antennas.
If an antenna design took hold, users would tag the antenna with the developer's name. Such was the case for Bruce and Sterba, whose antennas appear in outline form in Fig. 1. Both antennas are bi-directional arrays in which the beamwidth and gain emerged from the number of bays in the system. The feedpoints shown varied, with a more central feedpoint removing a slight azimuth tilt produced by end wire or corner feeding.
Both antennas have interesting histories. Although both have passed from commercial use, the Bruce array has found renewed interest among amateurs, especially in the Northwest corner of the U.S, with its tall supportive Douglas firs. However, Kraus is reputed to have reported that Edmond Bruce himself confessed that he would have preferred his name be attached to another of the many types of antennas that he developed in his distinguished career.
Sterba's work has also passed from use, but not from legend. It also illustrates how easy it is to confuse categories of antenna names. We shall soon look at the naming of antennas in terms of what they resemble. The Sterba curtain is not one of those antennas--although it sort of looks like a curtain. Nonetheless, as the diagram shows, the antenna has some specific requirements, such as the 1/2 wavelength dimensions and the vertical parallel sections that form phasing (transmission) lines. However, I have seen on the web an "all-band Sterba curtain." Yes, the antenna will load up on all HF bands, even when cut for 10 meters. However, the phase relationships that make the antenna a Sterba curtain hold only for the narrow band of frequencies for which the basic properties hold. Just because an antenna looks like a Sterba curtain does not mean that it is a Sterba curtain. Off the design frequency, it may become simply a random tangle of wires with dubious radiation properties.
Perhaps the most famous and still widely used antenna-naming event has been the Yagi, one version of which appears in Fig. 2. The original work on parasitic element relationships appeared in the late 1920s as a joint publication of Yagi and Uda. Hence, one historically correct name for the antenna is the Yagi-Uda parasitic array. It is unclear just why the name was shortened to simply the Yagi. A number of engineers are bothered by references to the antenna by its shortened name, since Uda may have been more central to the development of ideas that are still in use today. They appear to fear that the shortened name reflects our bad habit of the giving of credit to or the taking of credit by an academic or staff senior member, when the work is actually the product of a younger creative mind. However, the more probable reason for the truncation is that it is simply easier to say the first of the two names--and what is easiest to say often sticks as a label.
I must confess to a small contribution to the name-by-development enterprise. In the 1990s, I began examining Les Moxon's development of the VK2ABQ square into a rectangle with more reliable performance characteristics. (The antenna has precedents in the 1930s, but it appears that both VK2ABQ and G6XN were unaware of them.) As I developed the outlines of the rectangular antenna that used both parallel-element and element-tip coupling to yield some useful properties, I called the antenna the Moxon rectangle. Les' contributions to understanding antennas among radio amateurs seemed to warrant the label for the antenna. See his HF Antennas for All Locations. The name for the rectangular antenna appears to have gained some currency.
Some antenna names appear to have been either self-generated or self-promoted by individual developers. Perhaps the classic case appears in Fig. 4. John Kraus, W8JK (or simply 8JK in some older circles), has never avoided any opportunity to promote his own work, which was highly creative over his long career. In his works, you will find innumerable self-references, even in texts that we might expect to take a more objective or remote perspective on matters.
The (W)8JK array is a bi-directional horizontal endfire array consisting of 2 elements, each of which is anywhere from 1/2 wavelength to 1.25 wavelengths long. The elements are 180 degrees out of phase with each other, as suggested by the center main feed line and the fact that one of two connecting lines to the elements has a half twist. The antenna appears in many variations of element spacing and length, and some versions have used multiple-wire elements. The antenna still has numerous applications.
At the opposite end of the scale are antennas with only partial names, so that the name of the developer has been lost, except among those with enough interest to dig out the information. The ZL Special, shown in 3 variations from the 1950s in Fig. 5, is a case in point. Many folks view this antenna simply as a development from down under rather than as the work of an individual. The antenna emerged in 1949 from the work of George Prichard, who was ZL3MH at the time and later became ZL2QQ. F. C. Judd, G2BCX dubbed the antenna the ZL Special in 1950 in his article describing his initial experimental results. Specific identifying marks to indicate Pritchard as the originator simply disappeared after that. (There are some similar developments during World War II, but they were not accessible to--or usable by--radio amateurs at the time.)
The ZL Special is a basic version of a 2-element horizontal phased array with principles of operation similar to those used by its Swiss counterpart, the HB9CV. Unfortunately, the sad state of affairs in the development of amateur Yagi beams of the period gave the simpler 2-element antenna an unwarranted reputation for very high gain (over 9 dBi in modern terms) to go with an excellent front-to-back ratio. (It deserved the latter judgment.) Variations on the design still appear today.
Naming antennas for their developers is a long, honored, and honorable tradition in radio communications work. However, we should remember that such names tell us virtually nothing about the antenna itself--unless we happen to be familiar with the antenna by having studied it--however briefly. Hence, as we saw with the Sterba curtain, the combination of a named antenna and too little information about what the antenna really is (and how it does its work) carries the danger of perpetuating either wrong labels or--worse yet--faulty impressions and information.
Still, we find a persistent ego-borne effort by some writers to name antennas after themselves. In amateur circles, the naming usually involves a call sign. There are occasions on which the practice is appropriate. For example, if one is comparing an already named antenna design to some variation or refinement of one's own devising, then distinguishing the comparators may require something like a pair of calls, one of which will be the author's. Apart from such circumstances, I prefer to let history take its toll. Understanding what an antenna is and how it works is more significant than giving the antenna a catchy name.
Antennas Named for What they Look Like
Antennas often received names based on their appearance. What they look like determines the label, which comes in one of two general forms: alphabetic and geometric. Fig. 5 shows typical examples of each kind of name. The J-pole not only resembles the letter J, but originally made use of pipe sections to result in a self-supporting VHF vertical antenna.
Clarence Moore, W9LZX, holds the patent for the cubical quad antenna. The closed loop structure originally overcame coronal discharge problems at HCJB in Quito, Ecuador in 1942. The name obviously derives from the appearance--virtually a cube using 4-sided elements. An X-brace supports the 4 corners and allows the loops to have a square (shown) appearance or to take on a diamond shape. Because the basic name applies to a 2-element version of the antenna, individual elements often bear the name quad loop, while arrays with 2 or more elements become quad beams.
Alphabetic names are perhaps the most numerous, since many basic antennas resemble common letters. To the alphabet, we may add another piece of U.S. history that plays a role in antenna naming: cattle branding. Brands had to be simple to meet the capabilities of frontier blacksmith shops, but maintain a unique identity for each rancher. From those origins have emerged a few antenna names, such as the pair in Fig. 7.
The lazy-H is a relatively old bi-directional beam consisting of 2 collinear elements spaced originally 1/2 wavelength in a vertical arrangement. The cross bar of the H is the phase line, which feeds the two elements in phase. Other feeding schemes are possible for monoband versions of the antenna using 1 wavelength element lengths and an electrical half wavelength phase line (taking the velocity factor into account). However, the 1960s brought the realization that if the elements are 1.25 wavelengths long and spaced 5/8 wavelength apart, the beamwidth will be narrower and the gain higher. As well, the antenna will operate reasonably down to the point where the elements are only 1/2 wavelength long, with a spacing of 1/4 wavelength. With a wide-range antenna tuner, the lazy-H became a multi-band bi-directional broadside array.
Much younger than the lazy-H is the lazy-N. The tilted N structure is all part of the radiating element (unlike the lazy-H that combines elements and phase lines to make its letter shape). The antenna zigzags the element with angular fold-backs to reduce the total height of the vertical. To overcome the lowered feedpoint impedance of this arrangements, the antenna uses an offset feedpoint experimentally determined to be close to 50 Ohms.
Both the lazy-H and the lazy-N tell a sad tale from the historical perspective. With such easy names, few--if any--people remember who the developers may have been or where to find the original articles describing the first incarnations.
Alphabetic antenna names very quickly become alphabet soup. Fig. 8 shows us why. Consider a resonant half wavelength antenna fed at the center. Rather than creating a linear element, we shall bend the antenna at the center to form a 90-degree angle. What do we get? Fig. 9 shows us some of the territory.
At the bottom left are 4 views of antenna with our eyes parallel to the ground plane. Hence, the antenna extends vertically. We may make an L or an inverted-L. (We often bring the latter antenna to the ground and feed it at that point, sometimes using a radial system.) The next two views shows us a V (rarely used except for TV rabbit ears) and the very common HF inverted-V. The last entry allows us to suspend an HF wire with only one high support. Although the Ls require a 90-degree angle, Vs and inverted-Vs often use wider angles. If we change our viewing point to a position above the antenna and arrange it parallel to the ground, we obtain a horizontal V, also called a quadrant antenna. The last name seems to apply only to single element horizontal wires.
The upper part of the sketch shows a bit of the terminological morass created by the letter V (a part of the letter's story intentionally omitted by Sesame Street). On the upper left is a long-wire V-beam. The end wires return to ground or to just above ground with a terminating resistor to create a directional traveling wave antenna. Each leg may be from 2 to n wavelengths long, depending upon the available wire and terrain. At the center is a second V beam, this time composed of elements that are swept forward to form the V shapes. V-ing elements tends to degrade rather than enhance the performance of 1/2 wavelength elements, but may provide some pattern control of 1.25 wavelength elements. (In some designs, the 1.25 wavelength dimension is between the element end points and results in a need for physical elements totaling close to 1.5 wavelength.) Just to add to the potential confusion in the V name, the right-hand V-beam consists of inverted-V elements. In most cases, the seeming simplicity of a letter name leads to its use for antennas that may have very distinct arrangements and properties.
Geometric shapes are not without their own oddities of use or of history. Fig. 9 shows 3 vertically polarized self-contained verticals. On the left in each case is the electrically simpler version. The delta is any triangle, although equilateral and right triangles are the most common shapes. The side feed point is 1/4 wavelength from the apex to provide a vertically polarized pattern. Below it is the side-fed rectangle, again vertically polarized given the feedpoint.
To the right of each single antenna is a doubled version. Since each of the left-side shapes forms a pair of vertical monopoles fed in phase (roughly), the doubled versions act like a bank of 3 vertical monopoles fed (roughly) in phase. The bi-directional pattern is broadside to the plane of the wires.
At the top of the figure we find the half square, so named because it seems to lack the bottom half that would make a full square. To the right is the doubled version, called in a mixed metaphor the bobtail curtain by its developer. Each antenna uses true vertical elements properly spaced for maximum gain. However, to achieve this goal, the half-square is somewhat out of square, with a 5:8 ratio between vertical and horizontal sections. The bobtail curtain requires significant elongation of the horizontal sections and shortening of the legs for maximum broadside gain. Whereas the simple delta and rectangular shapes predate their doubled versions, the bobtail curtain historically precedes the half square. See Woodrow Smith, W6BCX, "Bet My Money on the Bobtail Beam," CQ (March, 1948), 21-23 and 92-95, and Ben Vester, K3BC, "The Half Square Antenna," QST (March, 1974), 11-14, for the seminal articles on each antenna. In place of the upper high-current, low voltage feedpoints shown, one may bring the tip of one vertical to ground and use standard voltage-feeding methods.
The odd name of the doubled half-square results from combining two different look-alike ideas. The idea of a curtain goes back to the 1920s and rests on the resemblance of the array of elements (and support lines) to a curtain. The verticals do not reach the ground, giving rise to the idea of bobbing the tail of a horse. The composite picture of a horse's tail covering a living room window, however, is not a pretty sight. When we stray from using strictly alphabetic or geometric names, we often open the door to confusion. Fig. 10 shows a different kind of example.
The sketches show 3 different kinds of bow-ties. In the left, feeding across the center points of the top and bottom wires yields a vertically polarized signal. We find such bow-ties ahead of many planar reflectors in UHF FM repeater service. If we feed across the center horizontally, the wings of the bow-tie act like very fat horizontal element halves. This configuration also bears that name fan, but it should not be confused with fans of dipoles for two or more frequencies, fed at a common point. On the right is an alternative shape for the horizontal bow-tie. Both the center and the right versions may have a straight horizontal section running across the overall shape and supporting lighter spread wires in the HF region. UHF bow-ties sometimes consist of solid surfaces.
The bow-tie at the right is a bow-tie only if we feed it horizontally, as shown. If we separate the upper and lower wire structures and feed across the two at the center--following the system used at the far left, then the bow-tie becomes a vertically polarized double diamond. However, diamonds have their own foundations for confusion.
Fig. 11 shows the outline of a terminated long wire array. In 1931, Bruce called this a diamond. However, others preferred a more purely geometric name and called it the rhombic. Bruce adopted this label in his 1935 article, co-authored by Beck and Lowry. The dimensions of the antenna combined the leg length and the angle called alpha in various equations to result in a highly directional array with a very narrow beamwidth. Matching the terminating resistor of this traveling wave antenna to the feedpoint impedance yields a wide-band array with consider performance--but also with very strong sidelobes. Although few remain in use, the antenna served point-to-point communications across the oceans for several decades. Incidentally, this is the array that Bruce apparently would have liked his name attached to instead of the array shown in Fig. 1.
Although many other geometric labels exist, these suffice to show the simplicity--and therefore the danger--of using names that rest simply on what an antenna may resemble. Merely calling out the alphabetic or geometric name of an antenna does not yet tell us anything significant about the antenna itself in most cases.
I have vowed to omit from these notes labels that are merely cute. However, there is a trend in antenna labels that has an alphabetical flair. It occurs when we mix antenna types and try to come up with a unique name for the hybrid result. Perhaps no basic antenna has seen more variations than the Yagi (or Yagi-Uda, if you prefer). Fig. 12 shows some of the labeled hybrids.
The quagi combines some quad loop elements--usually the driver and the reflector--in an effort to improve performance by at least the level of a quad loop over a dipole. Results have been mixed, although the idea continues to attract experimenters in VHF and UHF antenna work. The zagi is a yagi with zigzag elements that use linear compression to shorten the width of at least small beams. The zigzagging may use triangular or square sections. Since a Yagi does not care much about its driver, we may use a J-pole to drive a vertical beam. The result is the jagi. Finally (at least for the moment), we may drive a Yagi with two drivers, phase-fed, in order either to increase gain over a narrow bandwidth or to increase the natural bandwidth of a driver-director array. The result becomes the phagi (also called the log-cell Yagi). The quest for short memorable names is almost as unstoppable as the effort to name an antenna after oneself.
Antennas Named for Their Initial Use
Of all the antennas named for their original applications, we need only one example to show what can happen to a name, once we give it some currency. Consider the Zeppelin, a hard-frame lighter-then-air ship of the 1920s and 30s. For radio communications, the simplest HF antenna that we might use would be a long wire trailing from the ship. Of course, we would have to feed it at one end of the wire. We might use an antenna tuner today to match the high-impedance of the wire's end, but in earlier days of high-impedance vacuum-tube amplifiers, we might also find a way to connect the antenna directly to the transmitter. The top sketch in Fig. 13 shows the antenna itself.
The feasibility of this antenna gave rise to ground-based applications. Two modifications emerged. First, to keep the antenna as high as possible, we employed a high impedance transmission line between the equipment and the antenna end. Second, we shortened the antenna name to the Zepp. With a wide-range antenna tuner, we found that we could operate the antenna over a considerable span of frequencies if the wire was at least 1/2 wavelength long at the lowest frequency. At high frequencies, the antenna wire became longer as measured in wavelengths.
Eventually, the center sketch in Fig. 13 acquired a longer name: the end-fed Zepp. Given its origins, we should not have needed the label expansion. What occasioned the enlargement was a curious turn of linguistic events. If we take the same length of wire, we can also feed it in the center. This arrangement is convenient for many home installations where the house and the operating room may be centered on the available property. Unfortunately, many folks began calling the mid-point feeding arrangement the center-fed Zepp. The original use that gave rise to the name for the antenna had disappeared, lost in the human penchant for short snappy names. However, if you are prone to mental pictures, consider a Zeppelin trying to use a center-fed arrangement with very long wires on either side of the feedpoint. Pictures aside, one center-fed antenna has permanently acquired a Zepp association. If the element is about 1.25 wavelengths, then we have an extended double Zepp (or EDZ--in some literature, a DEZ), even though the vertical monopole version (at 0.625 wavelength) is not called an extended Zepp or any kind of Zepp at all.
Like all of the antenna names or labels that we have so far considered, a name based upon an initial application tells us almost nothing about what the antenna is technically. Such names obscure rather than reveal where an antenna fits within the overall set of structures that we use to radiate and receive signals. Indeed, it sometimes amazes me how few antenna names actually do reveal what the antennas do and how they do it. Even those antennas that do bear technical names are subject to dangers of label misuse.
Antennas Whose Names Carry Technical Information
If we look closely at a few of the basic antenna names, we can find some technical information. To find the information, we must treat the label as a noun with a meaning and not just as a convenient name. Radio amateurs tend to have difficulty in this regard because they enter antenna studies in the middle. Basic licensing requirements tend to insist that the individual undergoing a test recognize some antenna shapes, not that they understand basic antenna principles.
Consider the dipole. At the most rudimentary level, this antenna serves both theoretical and practical purposes. The most rudimentary dipole is very short and has the general properties shown in Fig. 14. The level of charge increases constantly from the centered feedpoint outward, reaching a peak value at the element ends. In contrast, the current distribution is maximum at the feedpoint and decreases toward zero at the wire ends.
If a dipole is to be a dipole, then it must preserve its basic properties as we lengthen it to a value that is practical. Current must be highest at the center and decrease once along the wire length toward the wire ends. Essentially, the maximum length of a true dipole is an electrical half wavelength. This antenna is perhaps the most common and fundamental antenna used by radio amateurs if we combine a number of properties to form a label for the antenna that is truly accurate. What we normally call a dipole is actually a center-fed resonant (or nearly resonant) 1/2 wavelength dipole. The term "dipole" indicates the current (and the charge) distribution. The term "center-fed" indicates where along the wire that we place the energy source, that is, the feedpoint. (Other feedpoints for the length of wire involved will produce the same current distribution as the center feedpoint.) The reference to being "resonant" indicates that at the feedpoint, the measured impedance shows no reactance, but is instead purely resistive. (The note on being nearly resonant recognizes that a small amount of reactance at the feedpoint is acceptable under normal conditions of use.) The wire length (1/2 wavelength) may seem redundant, but it does give us information needed to replicate the conditions on other frequencies. The combination of ingredients that make up the commonly used dipole are very convenient. It allows us to use a coaxial cable as a feedline for monoband operation, and the impedance of a well-matched system coincides closely with the output or input impedance of standard transmitting and receiving equipment used for many decades.
What happens if we make the center-fed wire longer? We do not need to do any physical work, but only to increase the operating frequency. Then the wire can be several wavelength long, even though it is 1/2 wavelength at the initial or lowest frequency. Typical of the results is the current distribution curve shown in the lower part of Fig. 15.
With many transitions of current from maximum to minimum and back again, we no longer have a dipole. Instead, we have a 4 wavelength center-fed antenna whose feedpoint may or may not be nearly resonant. Indeed, the only trait that the antenna has at the listed frequency with the original dipole is the fact that both antennas have a centered feedpoint. For a half century, we have called such antennas doublets. The name only tells us where to find the feedpoint. The rest we shall have to add to arrive at a reasonable technical description of the antenna.
There is an unfortunate tendency among radio amateurs especially to label an antenna by what it looks like and not by what the antenna is doing. Even seasoned antenna veterans persist in calling any center-fed wire a dipole, except for some few who call it a center-fed Zepp. However, the antenna shown in the lower part of Fig. 15 is a doublet and requires further specification to capture its functioning. Now let's make the story just a bit more complex. In the 1930s, we likely could not have used the term "doublet" as a label for the antenna. In that decade, some handbooks used the term for a very specific antenna. If we use parallel feedline as the line to a 1/2 wavelength center-fed wire, we do not obtain a close impedance match between the antenna and the feedline. To effect a match, builders would spread the feeder ends and connect them to the wire at a distance from the wire center and eliminate the gap that we might ordinarily find at the center point. Within a decade or so, handbooks gave this arrangement a more specific name: the delta match, because the spread of the feedline formed an inverted Greek letter in shape. The term "doublet" had been freed to indicate a center-fed wire of indeterminate length, but certainly one that is longer than a strict dipole.
The 4 wavelength center-fed wire at 28.4 MHz that we viewed in Fig. 15 is not only longer than a strict dipole, it qualifies as a long-wire antenna. You may ask fairly the following question: How long must a wire antenna be to qualify as a long-wire antenna? The answer is not illuminating: we are not sure. Most antennas that we classify as long-wire antennas do not begin to show desirable properties until they are at least 2 wavelengths long--sometimes 3 or more. Practical long-wire antennas used in the 1930s through today tend to be at least 5 wavelengths long. However, I know of no text that sets a dividing point between the long-wire antenna and the antenna that is not a long-wire. (However, note that we do not divide the world of antennas into 2 classes: the dipole and the long-wire. The two terms do not form a true contrasting pair.)
Most long-wire antennas also use end feedpoints. With the feedpoint at one end, we can add a terminating resistor at the other end of the wire array to convert a standing-wave antenna with bi-directional properties into a traveling-wave antenna that is highly directional. Fig. 16 shows three commonly used long-wire arrays: the simple 1-wire long-wire, the V beam, and the rhombic. All three use terminating impedances to arrive at the sample azimuth patterns that I have overlaid on the antenna sketches. Both the V beam and the rhombic make use of the angles of the single wire's main lobes to arrive at the correct wire angle to achieve the high gain and narrow beamwidth of their main lobes.
"Long-wire" then is both a generic label for any antenna that is numerous wavelengths long and a more specific label for one kind--the simplest kind--of generic long-wire antenna. So the 4 wavelength center-fed unterminated doublet of Fig. 15 is a generic long-wire antenna, but not specifically a long-wire antenna of the end-fed sort.
Some technically informative labels become so long that we create abbreviations. Then we proceed to use the abbreviations in antenna writings, often assuming that the reader can translate the label. Hence, we find articles and specification sheets on LPDAs, sometimes further abbreviated to LPDs. LPDA stands for log periodic dipole array, and some writers believe that the word "array" (and its abbreviating letter) are superfluous. (We also have LPMAs or LPMs, meaning log periodic monopole arrays.) The LPDA label indicates not just a set of antenna properties, but as well an entire design procedures for creating antenna of the required type. Fig. 17 shows some of the basic design elements as well as the general outline of an LPDA.
The elements of the LPDA are substitutes for short sections of arc in a circle. By using initial values that define the angle formed by the element outlines, the relative length of any two adjacent elements and the spacing between adjacent elements, and the initial spacing of the rearmost two elements, we can design a complete LPDA. The design will include a transmission line between elements that undergoes a single half-twist at each new element working from the forward feedpoint to the rear. The line partly determines the antenna's properties and also the feedpoint impedance, which will be close to resonant in adequate designs. In fact, the antenna falls into a class of antenna called frequency-independent antennas. However, practical LPDAs set upper and lower frequency limits in normal applications. Entire books exist on the design and properties of LPDAs--and their cousins, the LPMAs. However, this brief overview may suffice to indicate just how much technical detail a very specific antenna label may indicate.
Now let's become complex again. Many practical designs for LPDAs may add a parasitic director at the forward of the array to raise the gain at the high end of the operating passband without the need for numerous short elements. Sometimes, practical designs will also use a parasitic reflector to aid low-end performance. Now we have a quandary. Is the resulting antenna a supplemented LPDA or something else.
The "something else" might be a log-cell Yagi, as illustrated in Fig. 18. In this antenna, we find a driver section that answers to LPDA rules, plus a pair of parasitic elements. The driver section usually does not enhance gain, but it can yield an improved front-to-back ratio over a Yagi with a single driver element. Most significantly, the log-cell can broaden the operating bandwidth of the antenna allowing relatively even performance over all of the widest amateur bands, such as 10, 6, and 0.7 meters.
In fact, we often distinguish between a supplemented LPDA and a log-cell Yagi by reference to the frequency coverage. If the parasitic elements aid performance at very disparate frequencies but are inert for other parts of a wide operating spectrum, then we generally have a supplemented LPDA. If the parasitic elements are effective across the entire passband (usually restricted to a single band, such as 10 or 20 meters), then we have a log-cell Yagi. However, like all separations between labels, the distinction is not absolute. For example, there are pure LPDAs designed for single bands, such as 10 or 6 meters.
Let's add one final complexity. Fig. 12 showed one sample of a phagi, a Yagi using a pair of phased driver elements. Now we can pose a further fair question: When do we have a phagi and when do we have a log-cell Yagi? The most general answer will die a death of a thousand qualifications. Usually, a true log-cell Yagi will design the driver section using LPDA design procedures. In contrast, most simple phased driver sections tend to find their dimensions experimentally, that is, by trial and error. As well, the phagi driver section might use a common feedpoint with transmission line section going both forward and rearward (with the half-twist only on the rearward section). A true log-cell always places the feedpoint at the forward element in the cell.
So much for generalities. In practice, the phased driver section of a phagi may result in values that would meet LPDA rules. The log-cell that originates using LPDA design procedures may require modification to meet the needs of the overall log-cell Yagi. In the end, we do not find a sharp dividing line between the two antennas and their labels. Instead, we find only a fuzzy gray area of indeterminacy. Such is the life of labels and names.
Conclusion--of Sorts
We certainly might extended our list indefinitely. Among abbreviated antenna names is the DDRR. Antennas named for developers include the Windom, the Beverage, and the Adcock. Geometrically based names include the bi-square and the four square. Common antennas taking their names from various everyday shapes encompass the fishbone and the bazooka, not to mention whips, folded elements in various forms and antenna elements with hats. As the list of labels grows longer, the more we realize just how uninformative most of them are.
If these notes have a conclusion, it might be in the form of a rule. Antenna labels, when properly used, mask a wealth of information about what the antenna does and how it does it. Labels are not for simple visual recognition, since visual appearance can deceive as often as it enlightens. When you encounter a new (or old) antenna label or name, take time and devote energy to learning everything that you can about the antenna. Only then will the antenna's name become truly meaningful.
What's in a name? Everything--or nothing at all, depending upon the effort you put into learning about the thing named.
Updated 12-26-2005. © L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.
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