US 3697999 A
A unidirectional broadband horizontally polarized HF bi-planar rotatable log-periodic antenna with the radiating element to boom structure of each of the planar antenna half structures substantially the same and flipped 180 DEG one from the other. The bi-planar antenna is series fed through the lower boom acting as an infinite balun with the center conductor connected across to the forward end of the upper boom. The two half structures are relatively closely spaced with a dielectric insulator providing mutual structural support between the upper and lower booms of the half structures, and a vertical conductive material mast joins the structural booms both electrically and mechanically. The radiating elements are relatively fat truncated triangular teeth in a foreshortened log-periodic antenna employing a relatively large alpha angle of approximately 75 DEG , a tau ratio of approximately 0.5, and an array angle of PSI of less than approximately 10 DEG .
Description (OCR text may contain errors)
United States Patent Cory et al.
1 51 Oct. 10,1972
 ROTATABLE BI-PLANAR SERIES-FED LOG-PERIODIC HF ANTENNA  Inventors: Terry S. Cory; Roger A. Markley,
both of Richardson, Tex.
 Assignee: Collins Radio Company, Dallas,
 Filed: June 14, 1971 [211 App]. No.: 152,767
521 u.s.c| ..343/763,343/792.5 51 Int. Cl. ..l-l0lq 11/10  Field of Search....343/763, 766, 792.5, 884, 90s
 References Cited UNITED STATES PATENTS 2,977,597 3/1961 Du Hamel et al ..343/792.5
Primary ExaminerEli Lieberman Attorney-Warren H. Kintzinger et al.
 ABSTRACT A unidirectional broadband horizontally polarized HF bi-planar rotatable log-periodic antenna with the radiating element to boom structure of each of the planar antenna half structures substantially the same and flipped 180 one from the other. The bi-planar antenna is series fed through the lower boom acting as an infinite balun with the center conductor connected across to the forward end of the upper boom. The two half structures are relatively closely spaced with a dielectric insulator providing mutual structural support between the upper and lower booms of the half structures, and a vertical conductive material mast joins the structural booms both electrically and mechanically. The radiating elements are relatively fat truncated triangular teeth in a foreshortened logperiodic antenna employing a relatively large 0: angle of approximately 75, a 1- ratio of approximately 0.5, and an array angle of I of less than approximately 10.
9 Claims, 15 Drawing Figures PATENTEDncnoasrz v 3.697.999
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INVENTORS TERRY s ROGER A. MARK ATTORN Y PATENTEDnm 10 I972 SHEET 6 0F 6 INVENTORS TERRY s. com ROGER A. MA KLEY F Wu l 1. I 6&1 I? ,3 9 0 9 93 iv a x? 04 0 g a ROTATABLE BI-PLANAR SERIES-FED LOG- PERIODIC HF ANTENNA This invention relates in general to antenna systems and, in particular, to rotatable bi-planar series-fed log periodic, unidirectional HF antennas of minimal turning radius size for a broadband range of operation (8-25 MHz for example).
While there have been many rotatable log periodic antennas designed particularly for land-based use, there have been very few especially designed for ships. Some antennas that have been designed for shipboard use employ insulated dipole elements that are susceptible to vibration damage obviously an undesired state. Further, spatial limitations are such with many ships and some other installation environments that attempts have been made to reduce the size of what were originally land-based designs. One approach to antenna size reduction has been to make use of lumped inductive loading techniques with these, however, reducing antenna efficiency and having a susceptibility to failure.
Projected shipboard usage dictates a conservative rugged design approach with particular emphasis directed to effects of wind, ice, ships pitch and roll, vibration, shock and corrosion. Ships do encounter severe storms from time to time that antennas must be able to survive and through which they must be capable of providing reliable service. All structural connections in the antenna structure must be exceptionally clean so that contamination-collecting pockets are eliminated. Dissimilar metal connections should be held to a minimum and potted toexclude moisture particularly with the salt entrained humid air encountered at sea to minimize or prevent corrosion. Further, it is important that the antennas be structurally tight clean designs with predominately metal to metal interconnect in an electrically all-grounded antenna assembly that may be painted with a tightly-adhering epoxy-polyamide primer and glossy white acrylic top coat or their protective equivalents.
It is, therefore, a principal object of this invention to provide a unidirectional broadband horizontally polarized HF bi-planar rotatable log-periodic antenna of foreshortened minimum size for an antenna operational through approximately a frequency band of from 8 MHz to 25 MHz.
Another object is to provide such antennas of reduced size having minimal turning radius requirements without making use of lumped inductive loading techniques.
A further object is to provide such antennas with a structurally tight clean design with predominately metal-to-metal interconnect in an electrically allgrounded" antenna assembly.
Features of the invention useful in accomplishing the above objects include, in a unidirectional broadband horizontally polarized HF bi-planar rotatable logperiodic antenna, a frequency band of from 8 MHz to approximately 25 MHz in an antenna with a maximum turning radius of approximately 28 feet. It is a foreshortened antenna with a good front-to-back ratio of at least 10 db down from the peak of the main beam throughout the frequency range of operation. The antenna is a continuously rotatable antenna having a coaxial feed system that extends through the mast and the interior of the lower boom to the front of the antenna as a series feed with the lower boom acting as an infinite balun and the center conductor connected across to the forward end of the upper boom. The antenna structure and mast assembly are substantially an allmetal all-grounded structure with only a dielectric insulator providing mutual structural support between the forward ends of the upper and lower booms of relatively closely spaced half structures of the antenna. The antenna half structures are substantially identical planar log-periodic radiating element structures flipped 180 one from the other. The radiating elements in each half structure are relatively flat truncated triangular teeth in a foreshortened log-periodic antenna employing a relatively large at angle of 75 for each half structure, a 1' ratio of 0.5 and a half structure array 1' angle of 7.
A specific embodiment representing what is presently regarded as the best mode of carrying out the invention is illustrated in the accompanying drawings.
- rotatable bi-planar log-periodic I-IF antennas;
FIG. 2, a horizontal plan view of the bi-planar antenna of FIG. 1;
FIG. 3, a side elevation view of the antenna of FIG. 1;
FIG. 4, a perspective view of another rotatable antenna embodiment similar in many respects to the antenna of FIG. 1;
FIG. 5, a horizontal plan view of the bi-planar antenna of FIG. 4;
FIG. 6, a side elevation view of the antenna of FIG. 4;
FIG. 7, a partial enlarged rotatable antenna mast and feed detail;
FIG. 8, a partial upper and lower boom front end dielectric structure and feed interconnect detail;
FIG. 9, a VSWR to frequency in MHz diagram for both antennas; I
FIG. 10, 11 and 12, II-plane patterns for the antennas at 8 MHz, 15 MHz, and 24 MHz respectively; and
FIGS. 13, 14 and 15, azimuth E-plane voltage patterns for the antenna at 8 MHz, l5 MHz and 24 MHz respectively.
Referring to the drawings:
The rotatable unidirectional broadband horizontallypolarized HF bi-planar log-periodic antenna 20 of FIGS. 1, 2 and 3 is shown to have planar upper and lower half structures 21 and 22 respectively that are substantially the same but flipped one from the other. These two half structures 21 and 22 are stacked vertically and arrayed with respect to common apex at a 1' angle of approximately 7 in the bi-planar antenna structure that is rotatable about the vertical center line of rotatable antenna mounting shaft 23. The longitudinally extended upper and lower boom structures 24U and 24L, respectively, may be in the form of stepped tubular fabricated construction, as shown, or tapered tubes, not shown, with the larger portions thereof at the large rear lower frequency end of the antenna to the smaller high frequency apex end of the antenna. The upper and lower booms or longerons 24U and 24L are structurally interconnected by a vertical conductive material mast such as metal tube 25 that may be in line with rotatable antenna mast 23, as shown, or longitudinally displaced therefrom if desired. A dielectric insulator 26 provides mutual structural support between the forward ends of the upper and lower booms 24U and 24L. Antenna rotatable mounting detail and boom forward end dielectric insulator and antenna feed detail is shown in greater detail in FIGS. 7 and 8, hereinafter described in more detail, not only for the embodiment of FIGS. 1, 2 and 3 but also for the embodiments of FIGS. 4, 5 and 6. In any event, the bi-planar antenna is series-fed through the lower boom acting as an infinite balun with the center conductor 27 connected across the forward end of insulator spacer 26 to the forward end of upper boom 24U.
The upper boom 24U mounts first a single monopole type conductive metal extension 28U extended at a forward angle from one side of the forward portion of boom 28U. An inline extension is continued on the other side thereof as a forward structural tubular or rod extension 29U of a truncated triangular tooth relatively fat radiating element 30U with the ends of both radiating structural elements 28U and 29U and the rear extension 31U of the tooth 30U terminated at a relatively large a angle of 75. Conductive structural element 29U in axial alignment with the element 28U of the other side are slanted relative to boom 24U so that with tooth 30U rear radiating element conductive metal tube or rod extension MD is slanted approximately the same amount, in the opposite direction, relative to the boom 24U, a triangular truncated tooth is formed. The outer ends of radiating element structural rods 29U and 31U are interconnected by rod 32U, or conductive cable in place thereof, to form a relatively fat triangular truncated tooth radiating element 30U.
The opposite side rod extension 33U in axial alignment with rod 31U is the forward slanted member of truncated triangular tooth 34U- having a rear element extension 35U that is slanted in the opposite direction of extension SSH and the outer ends of extensions 33U and 35U are interconnected by conductive interconnect member 36U. It is of interest to note that the successively larger truncated tooth extension members starting with rod extension 35U are formed with en- 7 larged inner portions such as tubular portion 37U and that all of the successively larger lower frequency radiating element extensions are equipped with such structural strengthening sections. The upper half section is in like manner equipped with the successively larger fat radiating element truncated triangular teeth 38U, 39U and 40U in alternate side-to-side relationship with the final triangular largest low frequency triangular truncatedtooth 40U having a rear extension 41U axially in line with a monopole type extension 42U to the opposite side that is provided with a formed over tip and 43U a little within the limits of the 75 a angle. The tip end 43U lets the radiating element effective length be effective at the lowest designed operational frequency while in cooperation with formed over tip end 43U permitting a relatively small antenna turning radius of 28.3 feet for a foreshortened antenna having an operational frequencyrange of 8 MHz to 25 MHz.
The lower antenna half structure 22 is in effect the flip mirror image of the upper antenna half structure 21 with the effectively fat radiating element truncated triangular teeth thereof in line with the tooth gaps of the upper half structure and the teeth of the upper half structure in line with the gaps of the lower half structure. This is with the triangular truncated tooth outer end truncated conductive members lying along the respective at angle sides with the teeth in each half structure being progressively larger in log-periodic relation in accord with a 1' ratio of 0.5 and in this structure with a half structure 1' angle of 7. The upper and lower half structures of the antenna are relatively closely spaced so as to effectively electrically be quasi coplanar and the 1' angle could actually fall in a range of from approximately 10 down to approaching 0 with the half structures oriented toward an infinitely spaced forward apex without adversely effecting or varying the performance of the antenna structure. The rotatable mast 23 of the'embodiment of FIGS. 1, 2 and 3 and for that matter of the embodiment of FIGS. 4, 5 and 6 is mounted on a stub support mast 44. Nonconductive dielectric rope tension members 45U, 46U, 47U, 480 and 49U in the upper half structure and 45L, 46L, 47L, 48L and 49L in the lower half structure advantageously enhance structural integrity of the antenna unit particularly in dampening radiating element vibrations.
Referring now to the rotatable log-periodic antenna embodiment of FIGS. 4, 5 and 6, the smaller radiating element and teeth are the same as with the embodiment of FIGS. 1, 2 and 3, except that dielectric tension members such as those employed with the embodiment of FIGS. 1, 2 and 3 are not used. Teeth and radiating elements otherwise duplicating those of the FIG. 1, 2 and 3 embodiment carrying the same numbers and portions similar carrying primed numbers as the case may be. The major difference of this embodiment resides in the lowest frequency larger rear radiating elements being much shorter rear end radiating element members in order that an antenna having the same operational frequency range of 8 MHz to 25 MHz as with the embodiment of FIG. 1 be attained in a minimum size antenna with a turning radius as small as 23.7 feet. This antenna provides substantially the same advantageous operational capabilities as those attained with the embodiment of FIGS. 1, 2 and 3 and has the same at angle, 1' ratio of 0.5 and upper and lower half structure array I angle of 7. While the largest rear element transverse length in the embodiment of FIG. 1 is slightly less than a half wavelength at the lowest frequency of 8 MHz by virtue of the formed over conductive ends 43U and 43L, the FIGS. 4, 5 and 6 embodiment is considerably further foreshortened in the transverse dimension at the expense of slightly greater cost in order to ensure mechanical ruggedness of the folded back rear elements. With this approach rearward most triangular truncated teeth 40U and 40L are formed with a bent over inwardly extended ends 50U and 50L, respectively, extending from forward turned corner 51U and 51L lying on the at angle limit lines and also on the inscribed turning radius circle of 23.7 feet. End members 50U and 50L extend as cords of a circle to tip ends 52U and 52L that contact the inscribed tuming radius circle at a material distance to the rear of connective junction with the transverse rear tooth projection rod structures 41U and 41J. The opposite side rear projections in axial alignment projections 42U' and 42L in longitudinal alignment with the projections 40U and 41L extend to comers 53U and 53L respectively at the turning radius inscribed circle to extend forwardly therefrom in radiating element ends 43U' and 43L that are materially longer than their counterparts 43U and 43L of the embodiment of FIG. 1.
Referring also to FIG. 7 the shipboard fixed stub support mast 44 includes an RF coaxial connection to radio equipment via line 55 that connects to rotary joint means in an azimuth rotator and coaxial RF rotary joint unit 56. Coaxial line 52 extends up rotary shaft 23 to the interior of lower boom 24L within which the grounded outer sheath coax line 57 extends to the forward end (see FIG. 8) with the forward center conductor 27 thereof being passed through a dielectric nonconductive .boom 24L end cap 58 to lie across the dielectric material member 26 to electrically connected connection with the end of boom 24U. The azimuth rotator and coaxial RF rotary joint unit 56 is driven by a drive motor 59 structurally mounted along with the unit 56 on the mast 44, that is also equipped with an access plate 60. The structural dielectric member 26 that interconnects the forward apex end of booms 24U and 24L is fixed in place in assembly with the forward end of the booms by strap and bolt assemblies 61. It should be noted that the internal mast and lower boom 24L coaxial line 57 internal feed to the forward end of the lower boom 24L acts as an infinite balun feed to the antenna structure and includes the inner coaxial line lead 27 cross connection to the forward end of the upper boom 24U forward end. This advantageously functions very well in a substantially all electrically grounded antenna structure with feed from the forward end of the structure being in effect inductively transmitted down the structure with the upper and lower half structures in the bi-planar log-periodic structure being quasi-planar operationally to and thereby enhance inductive feed the forward apex end to the resonant element area of the antenna throughout the frequency range of operation thereof. This is particularly enhanced with the optimized triangular truncated tooth shape with a combination between trapezoidal fatness near the element ends and tapering of the elements to provide some spacing between adjacent teeth as the half structures are brought close together. With this structure the feed exciting wave progresses toward the longer elements from the feed tip end is guided from element to element in this inductive action along the entire antenna longitudinal length. This is evidenced by the ability to place a short circuit along the booms in the vicinity of the geometric mean spacing between element tie-on points without the operation of the antennas.
The unidirectional broadband horizontally polarized HF bi-planar rotatable log-periodic antenna embodiments of FIGS. 1 and 4 have VSWR to frequency in MHz characteristics that vary to some degree only in the lower 8 MHz to 12 MHz region. The portion thereof indicated by dotted line, representing a somewhat higher VSWR through that range, is for the smaller turning radius embodiment of FIG. 4, and the VSWR to frequency characteristics for the larger tuming radius antenna embodiment of FIG. 1 is shown in solid through the 8 MHz to 12 MHz region. Both antennas have duplicate VSWR to frequency in MHz operational characteristics throughout the remainder of their operational frequency range from 12 MHz to 24 MHz. The elevation H-plane patterns for the antennas are advantageously quite good as shown for 8 MHz, 15 MHz and 24 MHz in FIGS. 10, 11 and 12, respectively. Furthermore, the E-plane patterns remain very much the same through the frequency range of operation in the antenna such as is the case with the patterns for 8 MHz, 15 MHz and 24 MHz as shown by FIGS. l3, l4 and 15, respectively.
Whereas this invention is herein illustrated and described with respect to a 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.
1. In a unidirectional broadband horizontally polarized HF bi-planar rotatable log-periodic antenna, operational through a substantive portion of an 8 MHz to 24 MHz frequency range; upper and lower antenna planar half structures substantially the same and flipped 180 one from the other; said half structures each having a relatively large 0: angle approximating in a foreshortened antenna structure with a 1' ratio of approximately 0.5 and with a I angle between half structuresin the array toward a common apex of less than approximately 10.
2. The unidirectional broadband rotatable logperiodic antenna of claim 1, wherein each of said upper and lower half structures includes a plurality of truncated triangular teeth alternating opposite sides; and with truncated triangular tooth outer edges lying substantially along respective a angle limit lines.
3. The unidirectional broadband rotatable logperiodic antenna of claim 2, wherein the antenna is provided with a coaxial line feed system; said upper and lower half structures each include a longitudinally front to rear extended center boom; and rotatable mounting of said antenna on a mast structure.
4. The unidirectional broadband rotatable logperiodic antenna of claim 3, wherein said mast structure includes a fixed mast portion; and a rotatable portion mounted on said fixed mast portion.
' 5. The unidirectional broadband rotatable logperiodic antenna of claim 4, wherein coaxial RF line feed means is extended through said fixed mast portions and said rotatable portion; and with a coaxial line feed section extended through said lower half section boom from said rotatable mast portion to the front end of the boom; and a coaxial line feed section center line electrical feed cross connection to the forward end of the upper half section boom.
6. The unidirectional broadband rotatable logperiodic antenna of claim 5, wherein the forward ends of the upper and lower half section booms are structurally interconnected by a dielectric material structural member; and with the booms interconnected by a conductive material structural member in the mast supporting area of the antenna structure.
7. The unidirectional broadband rotatable logperiodic antenna of claim 6, wherein rearward mast lowest frequency radiating elements of said half structures have bent over and inwardly angled electrically conductive end extensions.
8. The unidirectional broadband rotatable logperiodic antenna of claim 7, wherein said antenna inscribes a turning radius of approximately 28 feet.
9. The unidirectional Broadband rotatable logperiodic antenna of claim 7, wherein said antenna inscribes a turning radius of approximately 24 feet.
* l II