US3696430A

US3696430A - High gain two bay unidirectional broadband antenna

Info

Publication number: US3696430A
Application number: US146764A
Authority: US
Inventors: Terry S Cory; Roger A Markley
Original assignee: Collins Radio Co
Current assignee: Collins Radio Co
Priority date: 1971-05-25
Filing date: 1971-05-25
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03

Abstract

A unidirectional broadband horizontally polarized HF two bay antenna with an upper bay and a lower bay using a larger Alpha angle than the upper bay. Both bays also employ substantially the same Tau ratio even though the bay Alpha angles are different. These result in an optimized antenna structure of minimum size for the frequency range of operation, and with resultant points of equal radiated phase from the two bays lying substantially in a vertical line for any one particular operational frequency.

Description

[ 51 Oct. 3, 1972 United States Patent Cory et al.

[54] HIGH GAIN TWO BAY Primary ExaminerEli Lieberman UNIDIRECTIONAL BROADBAND Attorney-Warren H. Kintzinger and Robert J. Craw- ANTENNA ford [72] Inventors: Terry S. Cory; Roger A. Markley,

[57] ABSTRACT A unidirectional broadband horizontally polarized HF two bay antenna with an upper bay and a lower bay using a larger 0: angle than the upper bay. Both bays both of Richardson, Tex.

[73] Assignee: Collins Radio Company, Dallas,

Tex.

221 Filed: May 25,1971

21 Appl.No.: 146,764

also employ substantially the same 1' ratio even though the bay 0: angles are different. These result in an optimized antenna structure of minimum size for the frequency range of operation, and with resultant g mm""mm343/792'5 256 Points of equal radiated phase from the two bays lying substantially in a vertical line for any one particular operational frequency.

[58] Field of Search....343/792.5, 811

Reierences Cited UNITED STATES PATENTS 14 Claims, 16 Drawing Figures 3,271,774 9/1966 Justice....................343/7925 PAR PATENTEDHBIEI I972 3.696.430

sum 1 OF 7 TERRY S. OORY ROGER A. MARKLEY BY M ATTORNE PKTENTED m 3 I973 INVENTORS TERRY 3. com ROGER A. MARKLEY Wm ATTO NEY PATENTEM I973 3.698430 TERRY S. CORY ROGER A. MARKLEY BY 7/ ATI E NEY PATENTEDnma 1912 3.6963430 SHEEI 5 0F 7 FlG. 8

REFLECTION AREA RADIATING ELEMENT 8 w FlG. 9

INVENTORS TERRY S. CORY ROGER A. MARKLEY ATTORKIEY PATENTEDUCT 3 1972 SHEET 6 OF 7 s 4 m 2 T V v m m 2 2 A m /l F \V w FREQUENCY IN MHZ O TERRY S. CORY BY ROGER A. MARKLEY IV Afl NEa 7 20.5 MHz PATENTEDnc-m m2 3,696,430

sum 1 or 7 IN VENTORS TERRY S. C ROGER A. MARKL BY m ATTORNEY HIGH GAIN TWO BAY UNIDIRECTIONAL BROADBAND ANTENNA This invention relates in general to antenna systems and, in particular, to a horizontally polarized high gain two bay unidirectional broadband HF antenna using a larger angle for the lower bay than for the upper bay.

Pre-existing two bay log periodic and horizontally polarized HF antennas with similar radiation characteristics to applicants present antenna generally require towers much higher than the maximum height of the rear lowest frequency radiating elements. The use of equal length upper and lower bays results in the longest dimension of the bays, measured from a common apex, lying on the arc of a circle with a center at the common apex. These prior art antennas, having upper and lower bays constructed with identical log periodic parameters, have radiation phase centers lying substantially on circular arcs measured from the common apex of the antenna. With some two bay broadband HF antennas excitation phase difference has been accomplished to some degree with log periodic scaling that increases the physical size of the lower bay with respect to the upper bay. This, however, further compounds size difficulties pointed out hereinbefore with respect to tower size required for supporting bays arranged physically on circular arcs from an antenna common apex or projected apex substantially on the ground. This means that with many of these structures that the lower phase center is closer to any vertical line to the rear of the array than is the upper phase center for the upper bay. If the vertical line mentioned represents one of the rear supporting towers for the antenna, the tower height is given by X sine A where A is the angle of the upper bay curtain with respect to ground and X is the distance that the tower is located away from the apex. For a fixed A, X is determined by the lower bay curtain because of its smaller angle with respect to the ground. Scaling the lower elements to obtain phase shift has the effect of increasing the tower height even more as pointed out hereinabove. It is obvious, then, that if the curtains or bays could be designed so as to position the phase centers and elements of equal length of the curtains in a vertical line; i.e., directly above and below one another, X would be a lesser distance and the required tower height would be less and essentially determined by the length of the upper curtain only. This is not exactly the case, however, since factors such as constant factor due to mutual coupling but it is quite close to actual conditions. The actual lower bay, designed by using different a angles, is short of reaching the rear tower; a facet which aids in achieving improved performance with smaller overall antenna size when the proper phasing is achieved.

It is, therefore, a principal object of this invention to provide a high gain two bay unidirectional HF broad band antenna capable of producing maximum power gain from an antenna of minimum size for a specific radiation beam maximum angle through a predetermined HF frequency range of operation.

Another object is, with respect to any particular frequency throughout the range of operational frequencies, for points of equal radiated phase from the two bays to be in substantially vertical alignment and to develop a radiated field vertical phase front.

A further object is to achieve a balanced transmission line feed to the upper and lower antenna bays in the sense that no unbalanced feed system current flow occurs in any ground leads that would either upset the antenna impedance or shunt any radiated power into ground. This is achieved with a balanced transmission line feed to the antenna bays having different a angles since the bays are not perfect geometric complements of one another.

Features of the invention useful in accomplishing the above objects include, in a high gain two bay unidirectional broadband HF antenna a two bay array of two horizontally polarized log-periodic curtains designed and arranged in a manner such that maximum gain is achieved for a given size. The two curtains are stacked vertically and arrayed with respect to the common apex on the ground. Actually, the curtains of the two bays are truncated arbitrarily with a feed system including an unbalanced coax line feeding a balun having a balanced transmission line output connection to the two bays of the antenna with the lowest portion of the balun being approximately 9 feet above ground.

A specific embodiment representing what is presently regarded as the best mode of carrying out the invention is illustrated in the accompanying drawings.

FIG. 1 represents a perspective of applicants high gain two bay unidirectional broadband HF antenna;

FIG. 2, a horizontal plan projection of the two bay antenna of FIG. 1;

FIG. 3, a side elevation view of the antenna of Fig. 1;

FIG. 4, a partial side elevation view showing feed detail;

FIG. 5, a perspective view of the unbalanced coaxial line input to two sided balanced transmission line output balun with the two balanced transmission lines sides feeding the upper and lower bays of the antenna;

FIGS. 6 and 7, plan views of the lower and upper bay curtains, respectively;

FIG. 8, a side elevation showing of the direct and reflected radiation emanating from a radiating element (or tuned frequency activated zone of the antenna);

FIG. 9, a horizontal plan view of a radiating element and the ground reflection area therefor;

FIG. 10, a VSWR to frequency in MHz diagram for the antenna;

FIGS. 11, 12, and 13, elevation H-plane patterns for the antenna at 8 MHz, 16 MHz, and 20.5 MHz respectively; and

FIGS. 14, 15, and 16, azimuth E-plane voltage patterns for the antenna at 8 MHz, 13 MHz, and 22.5 MHz, respectively.

The horizontally polarized unidirectional broadband HF antenna 20 of FIG. 1 is shown to be a two bay array of two horizontally polarized log-periodic curtains 21L and 22U designed and arranged in such a manner in the antenna structure that maximum gain is achieved for a given antenna size. The lower curtain 21L and the upper curtain 22U are stacked vertically and arrayed with respect to a common apex such as indicated in FIGS. 2 and 3 with, however, the curtains truncated arbitrarily and fed by a balanced feed section 23. Maximum broadband gain is achieved by virtue of spacing the broadband log-periodic curtains 21L and 22U apart and with respect to ground so as to achieve the optimum spacing of the curtain phase centers in height and also by positioning of the curtain phase centers in substantially the same vertical line (or alternatively, making the array radiation phase front a vertical line by retarding the phase of the upper curtain with respect to the lower). This phase shift is obtained on a broadband basis without requiring special phase shifting devices in the antenna 20 with the two bay curtains 21L and 22U being at angles 32 and 47, respectively, relative to the ground plane from a common apex ground point. The rear most end of the curtains 21L and 22U are mounted on

towers

24 and 25 and the ground apex end of the curtains 21L and 22U are anchored in place with catenary end connections to concrete

ground anchor pads

26 and 27. Further, a center concrete anchor pad 28 has a guy 29 connection to an antenna apex end post 30 mounting balun feed system 23 and having additional guy connections to the feed system 23 and the forward center of the two bay curtains 21L and 22U. The two bays of the two curtains 21L and 22U array are fed in a balanced manner without the exitation of a high and/or lossy ground return current in the vicinity of the balun transformer 31. The towers 24'and 25 that are mounted on concrete

ground support pads

32 and 33 are each provided with three two wire

guy wire pairs

34L and 34U, 35L and 35U, 36L and 3611, 37L and 37U, 38L and 38U, and 39L and 39U connected to the

towers

24 and 25, respectively substantially at the locations of curtains 21L and 22U connections, respectively therewith and extend to duplicate concrete ground guy wire pads 40, respectively. A working embodiment of this invention covering a frequency range of approximately 8 through 24 MHz gives substantially a 15:1 DB1 gain at effectively a 15 elevation angle that is quite suitable for long range HF signal propagation in the order of 1,5000 miles in an antenna structure with VSWR to frequency of less than 2 to 1 over the entire operational frequency range.

The antenna 20 is an array of two triangular tooth log-periodic antenna bays that are horizontally polarized with the bays inclined over the ground at angles of 32 and 48, respectively, and extending from the area of a truncated feed point approximately 9 feet above ground, as shown in FIG. 4, to the

towers

24 and 25 spaced at approximately 90 feet and extending from the ground to a height of approximately 150 feet. Referring also to FIGS. 5, 6, and 7, each of the bay curtains are equipped with radiating tooth elements 42U through 60U in the

upper bay curtain

22U, and 42L through 61L in the lower bay curtain 21L. Tooth 60U of upper bay curtain 22U is a truncated tooth as opposed to all the other teeth thereof being triangular radiating element teeth with a truncating crossover connective line 62U to a rear radiating element line 63U. Line 63U extends from the element 62U to connection with the center feed line 41U and further to end termination connection with an insulating jumper 64U with the conductive jumper line 62U and the end termination connection with jumper 64U being at the limits of a 17 at angle. The 17 angle for the upper bay curtain 22U is defined by radiating element tooth tip ends and also by the

outer lines

65 and 66 of the upper bay curtain 22U three wire feed. The upper bay curtain three wire feed with the lower bay curtain 21L three wire feed with

outer feed wires

67 and 68 and center fee wire 41L and the respective

triangular feed sections

69 and 70, respectively connected to

output lines

71 and 72 of balun 31, provide a balanced feed for the two bay curtain antenna 20. It is significant that

outer feed wires

67 and 68 are tapered at, and that the radiating element tooth 42L through 61L ends of the lower bay curtain 21L define an a angle of 23 an appreciably larger angle than the 17 (1 angle of the upper bay curtain 22U.

Radiating elements and feed lines are made of stranded Alumoweld (aluminum covered steel) cables. The lower and

upper cantenaries

73L and 73U and 74L and 74U, extended, respectively, from concrete ground anchor pad 26 to tower 24 and from concrete ground anchor pad 27 to tower 25 in order to support the lower and upper bay curtains 21L and 22U, are made of Alumoweld cables that are broken with insulators 75 to prevent distortion of the antenna radiation pattern. Jumpers from the radiating element tip ends to the catenaries such as

jumpers

76, 77, and 78 are made of glass reinforced polyester rods compounded with titanium dioxide to resist ultra violet radiation. The feed to the antenna is through a 50 ohm unbalanced coax line 79 connected to radio equipment (not shown) to balun 31 having a two

line

71 and 72 balanced output that with the six wire transmission line shown for a particular antenna built in accord herewith is a 235 ohm balanced transmission line. With this balanced transmission line feed the lower bay triangular feed portion is 3.5 feet long and the three wire transmission line section with wire 67 is 14 feet long, while in the transmission line feed to the upper bay, the triangular feed section 69 is 3.37 feet long and the transmission line section with line 65 is 20 feet long.

The larger, lower frequency end

triangular radiating elements

57L, 58L, 59L, and 60L of lower curtain bay 21L are provided with outer end to center feed line 41L

connective lines

80, 81, 82, and 84, respectively.

Alumoweld extensions

85, 86, 87, and 88 of the

wires

80, 81, 82, and 84, broken with insulators, interconnect the center feed line 41L and the

catenaries

73L and 74L, respectively, for center feed line 41L and radiating element support. In like manner, tooth end to center feed

line 41U wires

89, 90, and 91 and Alu moweld jumpers, broken with insulators, 92, 93, and 94 are extensions to

catenaries

73U and 74U, respectively, provided in the upper curtain bay 22U.

The requirement in HF communications for antenna systems having good radiation patterns and input impedance characteristics that are essentially frequency independent has resulted in the design of log periodic antennas. Generally, the geometry of log-periodic structures is so chosen that the electrical properties repeat periodically with the logarithm of the frequency and the operational bandwidth may be arbitrarily large by proper extension of the geometry of the structure. If the defining parameters of the antenna are adjusted so that the variation over any one period is relatively small, then the variation will be small over all periods with frequency independence being thereby obtained. The log-periodic antenna of finite length operates in an essentially frequency independent manner over a finite range of frequencies that depends primarily on the lengths of the longest and shortest radiating elements. The low frequency cut-off occurs when the longest element is approximately one-half wavelength long/At any frequency between cut-off frequencies, the antenna currents are largest in the elements that are approximately one-half wavelength at the excitation frequency with these elements contributing most of the radiation and forming the most active region of the antenna.

Applicants antenna is formed with generally horizontal elements in the respective array curtain bays with length and spacing determined by log-periodic principles. The arrays produce a horizontally polarized unidirectional beam radiated in the direction of the shortest elements. In each of the triangular toothed logperiodic antenna bays the teeth are spaced along the center feed line in log-periodic progression. The spaces between teeth get larger as the distance from the apex is greater. The ratio of the length of the adjacent similar teeth is such that the teeth are longer as the distance from the apex gets greater. This occurs in such a way that the tips of the radiating elements describe a constant angle with the apex being common to the apex of the two curtain bays. These properties are known as the 7 ratio and at angle, and are the basic properties of a log-periodic antenna that account for the constant gain and impedance characteristics that a good log-periodic antenna will have over a broad range of frequencies.

In the subject antenna, it is significant that while each bay has the same 1' ratio that the lower curtain bay has a wider at angle than the upper curtain bay. This advantageously allows the longest elements of each curtain bay to be located substantially directly vertically in line. Structural advantages inherent in this a angle variation may be appreciated by considering a structure with at angles equal in upper and lower array curtain bays so that a much greater tower height would have been necessary to keep the same angles of inclination since the lower bay would have its longest element much behind the longest element of the upper curtain bay. Further, with an antenna sealed for the same low frequency limit as with the new antenna herein described and claimed the tower height reduction achievable using the new structure is approximately 37 percent. In order to understand this distinction better, consider that if the array curtains were identical and arrayed to a common apex on the ground the curtain phase centers would lie on the arc of a circle whose center is at the array apex. This means that the lower phase center is closer to any vertical line to the rear of the array than is that for the upper curtain. If the vertical line represents one of the rear supporting towers for the antenna a tower height is given by X sine A where A is the angle of the upper curtain with respect to ground and X is the distance that the tower is located away from the apex. For a fixed A, X is determined by the lower curtain because of its smaller angle with respect to the ground. Scaling the lower element to obtain phase shift has the effect of increasing the tower height even more. It is obvious, then, that if the curtains could be designed so as to position the phase centers (and elements of equal lengths) of the curtains in a vertical line (i.e., directly above and below one another) that X would be a lesser distance and so, the tower height would be less.

Applicants HF antenna uses the ground to help form the desired radiation pattern with it being necessary that a relatively smooth area be in existence where ground reflection occurs. Further, height of buildings near the reflection area must be limited so as not to block the ground reflected rays. Actually, the optimum antenna height for a given angle of radiation is with reference to FIG. 8 h (M4 Sine A) with the distance d from the ground point under the active center of the antenna to the reflection point being d (h /Tangent A). Actually, reflections occur over an area instead of just at a single point such as indicated by FIG. 9 with the area over which reflections occur being defined by the concept of a Fresnel zone. This Fresnel zone ground area is elliptically shaped with the distance to the far edge of the ellipse being d (h/Tangent A) and the distance the nearer edge being d (h/Tangent A). Further the width of the ellipse is W= 5.66 h. The subject antenna has an effect takeoff angle equal to 15 and equivalent height of 0.965 wavelengths. The following table summarizes dimensions and values with respect to the reflection area for the antenna with respect to four different operationalfrequencies.

unidirectional broadband HF antenna 20 has VSWR to frequency in MHz characteristics from a 50 ohm unbalanced coaxial cable input line through the balun to 235 ohm balanced transmission such as shown in FIG. 10 and not exceeding approximately 2.0 to 1 VSWR at any place over the frequency range of operation. The elevation H plane patterns are advantageously quite good with the elevation angle for the main lobe being at substantially 15 through the frequency range of operation such as illustrated by the elevation l-l plane patterns for the antenna at H MHz, 16 MHz, and 20.5 MHz by the FIGS. l1, l2, and 13, respectively. Furthermore, the E plane pattern remains much the same through the frequency range of operation of the antenna with the E plane azimuth plane radiation patterns optimal for unidirectional electromagnetic signal propagation such as shown for 8 MHz, 13 MHz, and 22.5 MHz in FIGS. 14, 15, and 16, respectively.

Whereas this invention is herein illustrated and described with respect to a single specific embodiment thereof, it should be realized that various changes may be made without departing from the essential contributions to the art made by the teachings hereof.

We claim:

1. In a unidirectional broadband horizontally polarized HF antenna operational through a substantial portion of an 8 MHz to 24 MHz frequency range: an upper log-periodic curtain bay array; a lower logperiodic curtain bay array; antenna mounting means mounting said upper and lower log-periodic curtain above a ground plane in vertically stacked relation and arrayed with respect to a common projected apex approximately at the ground plane; said lower and upper bays having higher frequency smaller ends toward said common projected apex and having lower frequency larger ends; said antenna mounting means including rear tower means connected to and mounting the larger low frequency ends of said lower and upper bays with the upper bay slanted at a materially steeper angle relative to the ground plane than the lower bay; balanced transmission line feed means located at the apex end of said lower and upper bays feed connected to said lower and upper bays; and with the log-periodic aangle of the lower bay being materially greater than the logperiodic or angle of the upper bay so that the low frequency large ends of said lower and upper bays are substantially in vertical alignment.

2. The unidirectional broadband horizontally polarized HF antenna of claim 1, wherein both said upper and lower bay arrays employ substantially the same log-periodic 1' ratio.

3. The unidirectional broadband horizontally polarized HF antenna of claim 2, wherein both said upper and lower bay arrays are truncated at the apex ends; and an antenna feed system including an unbalanced coaxial line feed connected to a balun having balanced output connections through said balanced transmission line feed means to said upper and lower bay arrays.

4. The unidirectional broadband horizontally polarized HF antenna of claim 3, wherein said balanced transmission line feed means includes two three-wire transmission line sections one connected, respectively, to each of said upper and lower bay arrays.

5. The unidirectional broadband horizontally polarized HF antenna of claim 4, wherein each of said three-wire transmission line sections includes outer side wires substantially in line with and extending along the at angle sides of the respective bay arrays to feed connection at the apex end of the antenna array.

6. The unidirectional broadband horizontally polarized HF antenna of claim 5, wherein each of said three-wire transmission line sections includes a center wire extending the length of the the respective bay array and electrically feed connected to all radiating elements of the array.

7. The unidirectional broadband horizontally polarized HF antenna of claim 6, wherein each of said upper and lower bays is an array of triangular tooth radiating elements.

8. The unidirectional polarized HF antenna of claim 7, wherein some teeth of each array include tooth end to feed center wire connective wires.

9. The unidirectional broadband horizontally polarized HF antenna of claim 5, wherein the lower bay array and the upper bay array are inclined over the ground plane at approximately 32 and 48, respectively.

10. The unidirectional broadband horizontally polarized HF antenna of claim 9, wherein the a angles of the lower bay array and the upper bay array are substantially 23 and 17, respectively.

11. The unidirectional broadband horizontally polarized HF antenna of claim 10, wherein said rear tower means includes two towers; each of said upper and lower bay arrays include opposite side catenaries connected to said towers at the rear of the antenna and to ground anchor pads at the apex end of the antenna structure.

12. The unidirectional broadband horizontally polarized HF antenna of claim 11, wherein the upper bay array is connected to the two towers at approximately 150 feet above the ground plane; and the lower bay array is connected to the two towers at approximately feet above the ground plane.

13. The unidirectional broadband horizontally polarized HF antenna of claim 12, including balun mounting means supporting the balun with the balun balanced output connections approximately 9 feet above the ground plane.

14. The unidirectional broadband horizontally polarized HF antenna of claim 13, wherein said catenaries are conductive metal cables broken with insulators along their lengths to prevent distortion of antenna radiation pattern.

broadband horizontally

Claims

1. In a unidirectional broadband horizontally polarized HF antenna operational through a substantial portion of an 8 MHz to 24 MHz frequency range: an upper log-periodic curtain bay array; a lower log-periodic curtain bay array; antenna mounting means mounting said upper and lower log-periodic curtain above a ground plane in vertically stacked relation and arrayed with respect to a common projected apex approximately at the ground plane; said lower and upper bays having higher frequency smaller ends toward said common projected apex and having lower frequency larger ends; said antenna mounting means including rear tower means connected to and mounting the larger low frequency ends of said lower and upper bays with the upper bay slanted at a materially steeper angle relative to the ground plane than the lower bay; balanced transmission line feed means located at the apex end of said lower and upper bays feed connected to said lower and upper bays; and with the log-periodic Alpha angle of the lower bay being materially greater than the log-periodic Alpha angle of the upper bay so that the low frequency large ends of said lower and upper bays are substantially in vertical alignment.

2. The unidirectional broadband horizontally polarized HF antenna of claim 1, wherein both said upper and lower bay arrays employ substantially the same log-periodic Tau ratio.

5. The unidirectional broadband horizontally polarized HF antenna of claim 4, wherein each of said three-wire transmission line sections includes outer side wires substantially in line with and extending along the Alpha angle sides of the respective bay arrays to feed connection at the apex end of the antenna array.

8. The unidirectional broadband horizontally polarized HF antenna of claim 7, wherein some teeth of each array include tooth end to feed center wire connective wires.

9. The unidirectional broadband horizontally polarized HF antenna of claim 5, wherein the lower bay array and the upper bay array are inclined over the ground plane at approximately 32* and 48* , respectively.

10. The unidirectional broadband horizontally polarized HF antenna of claim 9, wherein the Alpha angles of the lower bay array and the upper bay array are substantially 23* and 17*, respectively.

12. The unidirectional broadband horizontally polarized HF antenna of claim 11, wherein the upper bay array is connected to the two towers at approximately 150 feet above the ground plane; and the lower bay array is connected to the two towers at approximately 90 feet above the ground plane.