Патент USA US2502156код для вставки
Patented Mar. 28, 1950 . UNITED . 2,502,155 STATES PATENT OFFICE 2,502,155 ' LOW-‘ANGLE n-AmAT'ioN ANTENNA Charles L‘. jefi‘ers, San Antonio, Tex. Application March 2, 1948, Serial No. 12,592 G'Clainls.‘ (Cl. 250—33‘); . . , v2 1 This invention. relates to a radio antenna sys with each individual station; and a de?nite ver tem especially useful as a broadcasting antenna‘, although it is: not limited to thisuse. tical radiation characteristic is required to achieve the ideal in each case. p An object of the invention is to devise an‘ an tenna system which radiates very little energy done towards improving the vertical radiation over a rather wide high-angle range and- at the same time provides a substantial gain in signal strength over the usual sing-1e vertical antenna. Still‘ another object. of the invention» is to de vise an antenna system in which the angle of minimum radiated energy can be varied electri~ cally from. 40 to 60° with. respect to' the hori~ zontal, thus permitting adjustment of the fad characteristics of broadcast antennas, and today a tower of uniform‘ cross-section and approxi mately 0.53 wavelength high is generally used to‘ secure the maximum nonfading range‘. This antenna is still far from ideal since the distor tion. zone usually‘ limits the primary service area at night.- This undesirable limitation is caused by the radiation of considerable power at the ing wall for maximum primary service. The above objects and others are attained by forming the antenna system of- two vertically aligned. sections which are excited by in-phase currents of- predetermined relative magnitudes, and the dimensions of the two antenna sections are chosen. to reduce the high-angle radiation and increase the low-angle radiation. My invention will be described in. connection with the accompanying drawing‘in which higher vertical angles. Figure I‘ is a diagrammatic representation of In recent years, considerable work has been 7 My improved antenna system radiates practi cally all energy at angles below 50 degrees of the horizontal and extremely little energy above this elevation. Further, this angle ‘can be varied from 40 to 60 degrees by a simple electrical adjust ment with, but a small increase in‘ higher angle radiation. ’ These‘ ‘limits are equivalent to dis tances of 80 to 160 miles for the ?rst re?ection skywave signal, ?xing the location of the center of the fading zone at approximately 100 to 200 miles from‘ the transmitter. My antenna system broadly‘ consists of two ver ferent components of the antenna system; tical elements, one directly above the other as Figure 4 is a diagrammatic showing of one shown in Fig. 1. It‘ is apparent that this is a speci?c form of antenna system according to my invention: ‘ 30 combination- of an antenna I at ground‘ eleva tion and an antennaZ‘ elevated above the earth. Figure 5 is‘ a diagrammatic showing of a sec The vertical radiation characteristics of each of ond form of the antenna system; and these antenna types are‘ well known. It is the Figure 8: shows three radiation curves for di'fé unique combination of these two antennas into fe'rent current ratios in the‘ two sections of the a single radiator that reduces the high angle antenna. the‘ antenna system; Figures 2 and 3 are radiation curves- for the dif > The primary service area of a broadcast sta radiation. tion is important from a service and a commer cial point of‘ view. The ideal antenna for a high In Fig‘. I, the section" I at ground elevation has a length- A; and the‘ elevated section 2 has a powered broadcast station, providing both a groundwave and a" skywave service, should‘ have‘ av vertical radiation characteristic such that they skywave signal does not interfere with the desir able groundwave service. The nightt'me primary service area would‘ then be practically as large as the daytime area, since the fading or distor tion wall would not be) the limiting factor. It is. length B‘- with the center of this. section at a height H above ground. The dimensions A, B and may‘ be expressed in degrees of the wave length‘x in free space'as follows: further desirable that the skywave signal strength rise rapidly- in order to limit the intense fading area to a narrow band?‘ around the‘ station. The power, frequency, and the ground conduc- ' tivity around the individual station, determine the signal strength at‘ a given location, while the general noise level ?xes the minimum signal‘ in; tensity required to‘ provide a satisfactory service. Thus,v the limit of satisfactory service“ is" unique 55 ', A=360> (ct/X) degrees. ‘5:360’ (b/x) degrees H=360 (iii/M degrees where a, 5 and h are the corresponding distances expressed in the same unit. of length as A. The antenna sections are excited or driven so that the loop currents in elements I and 2 are‘ inlvphase. If the magnitude of the loop current inv I is considered as unity, the currentra'tio can‘ be expressed-as. ‘ 2,502,155 3 4 the vertical radiation characteristic for the lower section I is KAJ‘(0) =[cos (A sin 6) —cos Al/cos 0 (2) where 0 is the angle above the horizontal. For the upper section 2, which for simplicity in cal culations is considered a half-Wave element, the vertical characteristic is KBf<6> =2m cos (so sin 0) cos (H sin 0) /cos a (3) and for both sections, adding’ (2) and (3), we have Kof(9) =[cos (a sin 0) —cos Al/cos 0+ 2m cos (90 sin 0) cos (H sin 0) /cos 0 (4) The form factor, Kc, referred to the current loop is 1-cos A+2ml and the vertical radiation characteristic for the antenna is (9) = , cos (A sin 6) — cos A+2m cos (90 sin 6) cos (Hsin 0) (l—~cos A+2m) cos 0 (5) ‘ Since the vertical characteristic of a half wave element in space (cos (90 sin 0)/cos 0), is prac tically equal to cos 6, Equation 4.- and likewise 5 will hold as an approximation if the upper ele ment is made less than one half wave long. The form factor, K0, is a constant for a par ticular combination of element length, A, and current ratio, m, and cos 0 affects both elements similarly; therefore it is convenient to omit the eifect of the denominator of Equation 5 in de- 1' veloping the optimum design of an antenna to give a particular radiation characteristic. This is done by evaluating separately the ?rst part of the numerator of (5) for 40 (6) K0 cos 0f(0)A=cos (A sin 0)-—cos A and the second part of the numerator for From Figure 6 it will be seen that the angle of zero radiation may be shifted from 40 to 60 de grees simply by changing the current ratio in the two antenna sections, and this involves only an electrical adjustment. It is of interest to note from Figure 6 that for the design of zero radiation at 50 degrees, the maximum high-angle radiation occurs at 56 de grees where it is less than 0.02 of that in the hori zontal plane. The theoretical ?eld gain of my antenna, for an m ratio of 0.69, is 14.5% compared to a 0.53 wavelength antenna, or 41.5% referred to a quar ter wavelength antenna. These ?eld gains are equivalent to power gains of 32 and 100 per cent respectively. The advantage of my antenna system may be shown by comparing its performance with that of a 0.53 wavelength antenna. Both antennas are assumed to radiate a ?eld of 1770 millivolts per meter at one mile on a frequency of 1000 kilo cycles over earth with a conductivity of 10-13 E. M. U. The skywave signal values are for 50% of the time. For the 0.53 antenna, the center of the fading zone is at 127 miles where the ground wave signal has an intensity of 0.6 mv./m. My antenna has the same distortion point at 164 miles and at a signal intensity of 0.29 mv./m. The width of the tWo-to-one signal ratio skywave and groundwave fading zone has been reduced from 36 miles to 24. miles because of the differ ence in the angle of the skywave signal rise. In other words, the distortion zone of bad fading has been moved from a point of good rural pri mary service to a point where the groundwave signal strength is hardly adequate for year round noise-free reception. If a current ratio, m, of 0.9 is used, the point of maximum fading would be moved to a distance of 185 miles for a signal level of 0.2 mv./m. Two physical embodiments of my improved antenna system are diagrammatically illustrated in Figures 4 and 5. K0 cos 0,f(0)B/m=2 cos (90 sin 0) cos (H sin 0) (7) In Figure 4 the lower antenna section I is Fig. 2 is a plot of Equation 6, K0 cos 0 times the A ' formed of a vertical metallic tube I2 in which is positioned a coaxial cable l3 containing a center vertical radiation characteristics of the lower sec conductor 14 and being grounded at its lower end. tion I for various lengths A, while Fig. 3 is a The upper end of tube [2 is connected to cable similar plot of Equation '7 for the upper section l3 at II, and the tube [2 is also connected to the 2 for certain center heights II. cable H3 at the point l8 located one-quarter In Fig. 2 curves 6, l and 8 show the character wavelength above the lower end of tube l2 which istics for three different lengths of lower sec is insulated from the cable it by insulator 9. tion I, that is, for A values of 140°, 120° and 100°, respectively. On Fig. 3 curves 3, 4 and 5 show the The upper antenna section is formed of two aligned tubular sections l0 and H positioned characteristics for three different heights of the above the lower section I. Tubular section H] section 2, that is, for H values of 190°, 210° and ' 230°, respectively. is supported on section II by an insulator 9a, and the lower end of this section is connected An examination of Fig. 3 shows, for the values to the center conductor of the coaxial cable 13 of H considered, that the field from the elevated element goes through a phase reversal around 25 at l5. The upper end of middle tubular section degrees, and above this point will be 180 degrees II is connected to the outer conductor of cable out of phase with the high angle ?eld from the l3 as shown at 56, and the lower end of this lower element. If the parameters A and H are section is supported on the cable l3 by the in sulator 9b. correctly selected and if the loop current in the elevated element is made less than the current The two sections of the antenna are excited in the lower element by the proper amount, the with energy from a transmission line 22 through ?elds of the two elements can be made nearly a suitable phasing and power dividing network equal and will cancel for angles deviating con 2|, the lower section I being excited through siderably from the vertical. connection 19 to the lower end of tube l2, and Figure 6 shows the radiation characteristic of the upper section being excited by connection the combined radiation from both vertical sec- A 20 to the lower end of the center conductor M tions of the antenna system, for three diiferent of the coaxial cable 1 3, current ratios. For curve 40, the current ratio In the arrangement shown in Figure 5 the lower m is 0.9, for curve 50 the ratio is 0.69, and for section l of the antenna is formed of a vertical curve 60 the ratio is 0.6. These curves are for tubular portion 24 which is insulated from the dimensions of A=120°, B=1y80° and H=210°. ground and is excited by a connection 25 from 2,502,155 5 the phasing network 2'! connected to transmis ial cable arranged within said tubular sections and having its lower end grounded, a connection from the center conductor of said cable to the lower end of the upper section, connections from the outer conductor of said cable to the upper sion line 28. The upper section 2 of the antenna system is formed of a linear conductor 23, which may be in the form of a conducting tube or a tower, supported on insulator 9d and extending upwardly through the tube 24 and beyond the upper end of this tube to the distance B. The ends of the middle and lower tubular sections, a connection between the outer conductor of said tube 24 is supported on the antenna part 23 by cable and the lower tubular section at a point one-quarter wavelength above ground, and ex insulators 9 and 9c. Antenna section 2 is ex cited by a connection 26 to the lower end of 10 citing connections to the lower end of said lower part 23 from the phasing network 21. section and to thelower end of the center con It will be understood that by suitable adjust duct-or of said cable. ment of the phasing networks 2| and 21, the loop 5. An antenna system comprising a vertical currents in the two antenna sections are ad conductor supported in insulated relation with justed to in-phase relation, and the amplitudes respect to ground and having a length of sub of the currents are also adjusted to the desired stantially 3000 ‘of the operating wavelength, a values as explained above. tubular conductor surrounding the lower section It will be further understood that top loading of said ?rst conductor for a ‘distance of sub of the top part of the elevated section 2 would ‘stantially 120° of the operating wavelength and still preserve the required electrical length yet 20 being insulated therefrom, and exciting connec reduce the physical length substantially. tions to the lower ends of said conductors for I claim: I exciting in-phase currents in the tubular con 1. An antenna system comprising a vertical ductor and in the upper section of the ?rst con antenna section extending above ground a dis ductor. tance of substantially 120 degrees of the operat~ 26 6. A two-part vertical antenna comprising a ing wavelength, a second vertical antenna sec lower radiating section insulated from ground tion arranged immediately above said ?rst section and extending from ground to a point above and in alignment therewith, said second section ground a distance of substantially 129 degrees having a radiating length of not more than one— of the operating Wavelength, an upper radiat half wavelength, and the center of the radiat 30 ing section arranged immediately above said low ing part of said second section being positioned or section and in alignment therewith, said up above ground a distance of substantially 210 de per section extending above said lower section a grees of the operating wavelength, and means for distance of not more than one-halal? wavelength, exciting said sections by in-phase currents, the and the center of the radiating part of said up loop current in the upper section having an am per section being positioned above ground a dis- plitude of substantially 0.7 of the amplitude of the loop current in the lower section. tance of substantially 210 degrees of the operat ing wavelength, and feed connections to the lower ends of said radiating sections for exciting 2. An antenna system comprising a vertical antenna section extending above ground a dis in-phase currents therein, the loop current in tance of between 100 to 140 degrees of the op .40 the upper section having an amplitude of sub erating wavelength, a second vertical antenna stantially 0.7 of the amplitude of the loop cur section arranged immediately above said ?rst section and in alignment therewith, said second rent in the lower section. I ' ‘CHARLES L. JEFFERS. ‘ section having a length of not more than one half wavelength, and the center of said section lik ill REFERENCES CITED The following references are of record in the tween 190 to 230 degrees of the operating wave ?le of this patent: length, and means for exciting said sections by UNITED STATES PATENTS in-phase currents. 3. An antenna system according to claim 2 50 Number Name Date wherein the ratio of the loop current in the upper 2,066,874 Bohm _____________ __ Jan. 5, 1937 section to the loop current in the lower section 2,113,136 Hansel] ___________ 1. Apr. 5, 1938 is within the range of 0.5 to 0.9. 2,118,429 ‘ Duttera __________ __ May 24, 1938 4. An antenna system comprising three verti 2,171,256 Moullin _________ __ Aug. '29, 1939 ‘ being positioned above ground a distance of be cally aligned tubular sections supported in in sulated relation, the lower section having a length of substantially 120° of the operating wave length, and the two upper sections having lengths of substantially one-quarter wavelength, a coax 55 2,196,187 2,201,857 2,234,234 2,321,454 Blair ______________ __ Apr. 9, 1940 Dome ___________ __ May 21, 1940 Cork ____________ __. Mar. 11, 1941 Brown __________ __ June 8, 1943 v . Certi?cate of Correction Patent No. 2,502,155 March 28, 1950 CHARLES L. JEFFERS _ It is hereby certi?ed that error appears in the‘printed speci?cation of the above numbered patent requiringcorreotion as follows: Column 3, line 22, for “(6):” readf(6)=; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Of?ce. Signed and sealed this 8th day of August, A. D. 1950. [SEAL] THOMAS F. MURPHY, Assistant Commissioner of Patents.