Source: http://www.google.com/patents/US6255998?dq=2040248
Timestamp: 2016-08-30 17:21:53
Document Index: 445662168

Matched Legal Cases: ['arts 601', 'arts 602', 'arts 601', 'arts 606', 'arts 611', 'arts 615', 'arts 1409', 'arts 1411']

Patent US6255998 - Lemniscate antenna element - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsAn antenna element is disclosed that is a pair of approximately coplanar loops, having perimeters of approximately one wavelength, that are connected at one point. The loops are positioned so that a line through center of one loop and that common point also is the line through the center of the other...http://www.google.com/patents/US6255998?utm_source=gb-gplus-sharePatent US6255998 - Lemniscate antenna elementAdvanced Patent SearchPublication numberUS6255998 B1Publication typeGrantApplication numberUS 09/583,569Publication dateJul 3, 2001Filing dateMay 31, 2000Priority dateMar 30, 2000Fee statusLapsedAlso published asCA2303703CPublication number09583569, 583569, US 6255998 B1, US 6255998B1, US-B1-6255998, US6255998 B1, US6255998B1InventorsJames Stanley PodgerOriginal AssigneeJames Stanley PodgerExport CitationBiBTeX, EndNote, RefManPatent Citations (10), Non-Patent Citations (7), Referenced by (32), Classifications (19), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetLemniscate antenna element
US 6255998 B1Abstract
An antenna element is disclosed that is a pair of approximately coplanar loops, having perimeters of approximately one wavelength, that are connected at one point. The loops are positioned so that a line through center of one loop and that common point also is the line through the center of the other loop. The approximate shape of these loops is such that the distance from that common point to any point on either loop is proportional to the cosine, raised to some power, of a multiple of the angle between that center line and a line between the common point and the point on the loop. Compared to previous antenna elements constructed for the same purposes, antennas constructed with such loops can yield more directivity, particularly in the principal H plane, without producing large minor lobes of radiation. Several applications of such antenna elements in various arrays also are disclosed.
This invention relates to antenna elements, specifically antenna elements that are pairs of loops one-wavelength in perimeter. Such antenna elements can be used alone or in combinations to serve many antenna needs. One object of the invention is to achieve a superior transmitting and receiving ability, the gain, in some desired direction. Particularly, an object is to enhance that ability at elevation angles close to the horizon. Another object is to decrease the transmitting and receiving ability in undesired directions. Yet another object is to produce antennas that operate satisfactorily over greater ranges of frequencies.
There have been many antennas proposed in the literature based on loops approximately one wavelength in perimeter, but there seems to be less discussion of the reasons why some antenna elements are better than other ones. In order to understand the present disclosure, it is important to review and evaluate these previous elements. The following discussion will deal with the merits of single loops and pairs of loops, particularly pairs of triangular loops. Then it will be possible to show the merit of lemniscate-shaped loops.
Prior Art—Single Loops
The classical elementary antenna element, called a half-wave dipole antenna, is a straight conductor approximately one-half wavelength long. One of its disadvantages is that it transmits or receives equally well in all directions perpendicular to the conductor. That is, in the transmitting case, it does not have much gain because it wastes its ability to transmit in desired directions by sending signals in undesired directions. Another disadvantage is that it occupies a considerable space from end-to-end, considering that its gain is low. A third disadvantage is that it is susceptible to noise caused by precipitation. Yet another disadvantage is that if a high transmitter power were applied to it, in some climatic conditions, the very high voltages at the ends of the conductor could ionize the surrounding air producing corona discharges. These discharges could remove material from the conductor ends and, therefore, progressively shorten the conductor.
Prior Art—Pairs of Loops
More significant advances have been made using closely spaced pairs of loops. Examples of them have been disclosed by B. Sykes in The Short Wave Magazine of January, 1955, by D. H. Wells in U.S. Pat. No. 3,434,145, and by W. W. Davey in 73 Magazine of April, 1979. But mathematical analysis reveals that the best combination so far is John Pegler's pair of triangular loops, with one corner of each loop at the central point, which was disclosed by Patrick Hawker in Radio Communications of January, 1969. Mr. Hawker reported that Mr. Pegler had used Yagi-Uda arrays of such elements for “some years” on amateur radio and broadcast television frequencies. Because Mr. Pegler called them “double-delta” antenna elements, hereinafter that name will be used.
The Invention—Smooth Embodiments
Since this prior art of pairs of triangular loops performs well, it is reasonable to investigate shapes of loops that are somewhat similar to triangles. If the central acute angles were kept, to reduce the radiation from the central high currents, but the outer sides were bowed outward and, perhaps, the outer corners were rounded, the performance would be improved. Particularly, it is possible to increase the directivity of the element while still having the FIG. 1B type of radiation pattern. Pegler's triangles also can produce such directivities, but they are accompanied by minor radiation lobes as in FIG. 1C. That is, with Pegler's triangles, the FIG. 1B type of radiation pattern is available essentially with only one combination of gain and bandwidth. With the present invention, the FIG. 1B type of radiation pattern is available with a variety of combinations of gain and bandwidth. However, with either loop shape, as usual, higher gains are accompanied by smaller bandwidths.
It is necessary to limit the angle to values around zero and π radians because it is possible, with some values of the multiplying constant, to obtain more than two loops from the above expression. Because the purpose of the expression is only to represent the real invention approximately, it is legitimate to limit the expression to whatever adequately represents the invention.
The Invention—Angular Embodiments
As was stated above, the use of the lemniscate cosine curve is an analysis convenience, not a definite requirement. If the shape of the loop were substantially the same as a lemniscate curve, the results should be substantially the same. FIG. 6, with parts 601 to 618 illustrates such a shape. If the straight parts 602, 603, 607, and 608, adequately simulated parts of a circle, the loops formed by parts 601 to 604 and parts 606 to 609 would perform substantially the same as the sectors of a circle produced by the power constant equaling zero.
The Invention—Construction Tactics
The Invention—Matching Tactics
Because it is unlikely that the impedance of an antenna element will equal the impedance of the transmission line leading to the associated electronic equipment, some kind of matching system usually is required. To match a balanced antenna element, a T match is a traditional choice. Because the lemniscate antenna element has two loops, two T matches are appropriate. FIG. 6 shows such a system with T parts 611 to 614 and the shorting parts 615 to 618. The transmission line typically would be connected at the feeding points, F, through tuning capacitors and, if the transmission line were unbalanced, through some kind of balanced-to-unbalanced transformer. Except for the fact that there are two loops, these are all conventional tactics for connecting a transmission line to a balanced antenna element. Because they are conventional and, therefore, they would unnecessarily complicate the diagram, the capacitors and transformer were omitted from the diagram.
The Invention—The Double Loop Embodiment
For some applications, a variation of this basic lemniscate antenna element can be beneficial. When antenna parts are close to each other or when antennas are close to the ground, in terms of wavelengths, the terminal impedances can be rather low. This might produce a problem of efficiency if the loss resistance of the parts became significant relative to the resistance that represented the antenna's radiation. To raise the impedance, one tactic is to use multiturn loops, as in Moore's patent.
These lemniscate antenna elements may be used in the ways that other antenna elements are used. That is, they may be combined with other lemniscate antenna elements to produce larger arrays. For broadcasting or for networks of stations, a horizontally-polarized radiation pattern is often needed that is omnidirectional instead of unidirectional in the horizontal plane. To achieve this, an old antenna called a turnstile array sometimes has been used. It comprises two half-wave dipole antennas oriented at right angles to each other and fed 90 degrees out of phase with each other. FIG. 10 shows the equivalent arrangement of lemniscate antenna elements that would serve the same purpose. Hereinafter, this arrangement will be called a turnstile array of lemniscate antenna elements.
Applications—Broadside and Collinear Arrays
Another application of lemniscate antenna elements arises from observing that half-wave dipoles traditionally have been positioned in the same plane either end-to-end (collinear array), side-by-side (broadside array), or in a combination of those two arrangements. Often, a second set of such dipoles, called reflectors or directors, is put into a plane parallel to the first plane, with the dimensions chosen to produce a somewhat unidirectional pattern of radiation. Sometimes an antenna element is placed in front of a reflecting screen (1111), as in FIG. 11. Such arrays have been used on the high-frequency bands by short-wave broadcast stations, on very-high-frequency bands for television broadcast reception, and by radio amateurs.
Application—Nonlinear Polarization
Yet another application of lemniscate antenna elements concerns nonlinear polarization. For communications with satellites or for communications on earth through the ionosphere, the polarization of the signal may be elliptical. In such cases, it may be advantageous to have both vertically polarized and horizontally polarized antennas. They may be connected together to produce a circularly polarized antenna, or they may be connected separately to the associated electronic equipment for a polarity diversity system. Also, they may be positioned at approximately the same place or they may be separated to produce both polarity. diversity and space diversity.
Yet another application, commonly called an end-fire array, has several lemniscate antenna elements positioned so that they are in parallel planes and the central points and outer points of the loops are all aligned in the direction perpendicular to those planes. One lemniscate antenna element, some of them, or all of them could be connected to the associated electronic equipment. If the second lemniscate antenna element from the rear were so connected, as in FIG. 13, and the dimensions produced the best performance toward the front, it could logically be called a Yagi-Uda array of lemniscate antenna elements. Hereinafter, that name will be used for such arrays.
There are several possibilities for all-driven end-fire arrays but, in general, the mutual impedances make such designs rather challenging and the bandwidths can be very small. The log-periodic array, as illustrated by FIG. 14, is a notable exception. A smaller, feasible all-driven array would be just two identical lemniscate antenna elements that are fed 180 degrees out of phase with each other. The distance between the elements would not be critical, but one-eighth of a wavelength would be a reasonable value. This would be similar to the dipole array described by John D. Kraus in Radio of March, 1937, which is commonly called a W8JK array, after his amateur-radio call letters. Since the impedances of the two elements are equal when the phase difference is 180 degrees, it is relatively easy to achieve an acceptable bidirectional antenna by applying such tactics. If a balanced transmission line were used, the conductors going to one element would be simply transposed. For coaxial cable, the use of an extra electrical half wavelength of cable going to one element might be a better tactic to provide the desired phase reversal. If the space were available, such a bidirectional array of lemniscate antenna elements could be very desirable in the lower part of the high-frequency spectrum where rotating such large antennas may not be practicable.
The log-periodic array of lemniscate antenna elements is similar in principle to the log-periodic dipole antenna disclosed by Isbell in his U.S. Pat. No. 3,210,767. Hereinafter, that combination will be called a lemniscate log-periodic array. Log-periodic arrays of half-wave dipoles are used in wide-band applications for military and amateur radio purposes, and for the reception of television broadcasting. The merit of such arrays is a relatively consent impedance at the terminals and a reasonable radiation pattern across the design frequency range. However, this is obtained at the expense of gain. That is, their gain is poor compared to narrow band arrays of similar lengths. Although one would expect that gain must be traded for bandwidth in any antenna, it is nevertheless disappointing to learn of the low gain of such relatively large arrays.
Applications—Log-Periodic Design Tactics
Whether equal-height lemniscate antenna elements or proportional dimensions are used, the design principles are similar to the traditional principles of log-periodic dipole arrays. However, the details would be different in some ways. The scale factor (τ) and spacing factor (σ) usually are defined in terms of the dipole lengths, but there would be no such lengths available if the individual elements were not half-wave dipoles. It is better to interpret the scale factor as the ratio of the resonant wavelengths of adjacent lemniscate antenna elements. If the design were proportional, that also would be the ratio of any corresponding dimensions in the adjacent elements. For example, for the proportional array of FIG. 14, the scale factor would be the ratio of any dimension of the second largest element formed by parts 1409 and 1410 divided by the corresponding dimension of the largest element formed by parts 1411 and 1412. The spacing factor could be interpreted as the ratio of the individual space to the resonant wavelength of the larger of the two lemniscate antenna elements adjacent to that space. For example, the spacing factor would be the ratio of the space between the two largest lemniscate antenna elements to the resonant wavelength of the largest element.
λmax=9.84�108/fmin ft or
λmax=3�108/fmin m
σ=[L(1−τ)]/[λmax(1−fmin/fmax)]
Once a mechanical design was revealed by these calculations, it should be tested for electrical performance by an antenna simulating program. The largest lemniscate antenna element would be designed using the maximum wavelength (λmax). The resonant wavelengths and dimensions of the remaining elements would be obtained by successively multiplying the wavelengths and the dimensions by the scale factor. The spaces between the elements would be obtained by multiplying the wavelength of the larger adjacent element by the spacing factor. An additional factor needed for the program would be the distance between the feeder conductors. For good operation this distance should produce a relatively high characteristic impedance. Unless the scale factor were rather high, a minimum characteristic impedance of 200 ohms perhaps would be prudent. Because the boom (1427) is a part of the feeding system in FIG. 14, that criterion would be at least 100 ohms between either feeder conductor and the boom.
Both Yagi-Uda arrays and log-periodic arrays of lemniscate antenna elements can be used in the ways that such arrays of half-wave dipoles are used. For example, FIG. 12 shows two end-fire arrays that are oriented to produce elliptically polarized radiation. For another example, FIG. 13 shows two Yagi-Uda arrays oriented so that the corresponding lemniscate antenna elements of the two arrays are in the same vertical planes. In this case, there is a collinear orientation, because the array is extended in the direction of principal E plane. The arrays also could be oriented in the direction of the principal H plane (broadside), or several arrays could be arranged in both orientations.
Except for the restrictions of size, weight, and cost, lemniscate antenna elements could be used for almost whatever purposes that antennas are used. Beside the obvious needs to communicate sound, pictures, data, etc., they also could be used for such purposes as radar or for detecting objects near them for security purposes. Since they are much larger than half-wave dipoles, it would be expected that they would generally not be used at the lower end of the high-frequency spectrum. However, they may not be considered to be too large for short-wave broadcasting because that service typically uses very large antennas.
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