US2508648A

US2508648A - Aerial system

Info

Publication number: US2508648A
Application number: US106577A
Authority: US
Inventors: William J O'brien; Toller-Bond Dudley Hales
Original assignee: Decca Record Co Ltd
Current assignee: Decca Record Co Ltd
Priority date: 1946-11-07
Filing date: 1949-07-12
Publication date: 1950-05-23
Anticipated expiration: 1967-05-23

Description

May 23, 1950 W. J. OBRIEN ET As. 2,508,648

AERIAL SYSTEM Original Filed Nov. '7, 1946 N VEN TOR. ML mM J Ogg/EN Y um fr /rzfs 5am-150Mo Patented May 23, 1950 UNITED STATES PATENT; OFF-ICE AERIAL SYSTEM wniiamY J. orien ana Dudley vnalesrollers Bond, London, England, assignors to Th''Dcca- Record Company, Limited, London,"Egland,' acorporation of'Great Britainv Original application November .7, 1946, SefiaINo..r

708,284. Divided and this application July/12, .1949, Serial No. 106,577 y v' 2 Claims.

Thisfinventionfrelates to Aaerial systems 'and has particularv reference to-A aerial or antenna constructions which' nd particular utility when employed as radiators of radio frequency energy Vof relatively Tong wawelengtli.

This application s-vaf-div-ision of a copending application i'iled by William J. OBrien and Dudley Hales Toller-Bond, Seria] No. '708;284, llled November :7, 1946-,` and entitled Aeralsysterns In the kradio transnilistingv art', greatfdiiiiculty has been experienced inthe past vin obtaining a reasonably high radiation eiciency. This is for the reason that withv antenna-constructions employed priorto this invention, it 'was di'ilcult, if not impossible, to h'tain Va'- relativel'y'hi'g'h radiation resistance.- Asis well known7 ltheradiation efficiency is equal tothe ratoof the radiation resistance to the rsum of thee-'radiation resistance, ground resistance 'Yandcircuit resistance. Since the radiation resistance is proportional to the square ofthe eifective'height'of the antennaein wavelengths,v and since at low frequencies it is impossible to erect "amast for tower which is comparable to a quarter wavelength in height, it becomes impossible withconventional constructions to erect an antennain whicrrtlie radiation resistance bears la favourable lratio tothe ground'rea sistance. Accordinglyyat best, the radiation einciency of conventional installations is much lower than is desired.

Furthermore; since atl lowl frequencies Ythe height of conventional installations is low as com; pared with 1the'wavelerigths of `the signals transmitted; the inductance :and capacity of the 4radiator are too low'forresonance and a series loading coil must be included `inthe circuit.v This adds additional `resistanceto the noneradiatingY parts of vthecircuit and further reduoes'the radiation ellciency;

Many prior attempts' have fbeenf made to improve the'radiation eiliciency at low frequencies and these attempts have-generally taken the form of flat topantennae .Where a considerable length of radiator is disposed parallel to the surface of the ground.' Thecost of such constructions is considerably increased, due Ito vthe necessity for erecting two supporting towers' instead of one. Furthermore, the two towers, notiorrning part vof the radiating structure, absorb energy radiated from the antenna and tend to odset the gains' in efficiency. to hev expected kfrom they iiat top construction.. Also, wherethe radiations are to be used for navigational ond-irection nding purv poses, furtherI disadvantagesV of the at top con- (Cl. Z50-33) struction are 'found in. .the non-circular radiation 55 pattern produced,y and infth'e horizontal polarizai. tion of the radiationv which 'tendsitoincrease'the sky wave diiiiculties, particularly at Fnight.

It is, therefore; an'obi'ectofthisinvention' to provide an antenna? or radiator for-use at relatively low frequenciesWhichoverconies the `above noted disadvantages fbyprov'dng 5a higher radiation resistance and `lower ground'reslstance rthan is foundin simple vertical radiatorso'f thesame height.

It is also 'ani'ohject lof this invention 'to provide an antennaf'of theecharacter described'in'thepreceding paragraphfin *which 4an .array yof radiators is so arrangedwtha't the cross-section area of th array' increasesfaway rromfthe transmitter.

It is `another*object ior this invention to provide' an antennafof thecharacterreferred 'to in the precedingfparagraphs .which comprises' a group of radiating'"cc'mductorsV s'odisposed as to define a conical' shape 'positioned with the apex thereof nearesttheaigroundr l It is 'a stilldiirther-` 'obj ect'o'f this invention to provide an aerial 'systemfof rthe character here inbefore referred *tofwhich has fa largel radiating surfaceV to thereby uprovide an yantenna v'having high capacity. l

It is also an object of this invention to provide an antenna constructionvof the character hereirrbefore referred' to'fwhich includes ar single sup*- porting mast:

It is a stil-1 Yfurther"objectfoftlfiis invention to provide an antennarconst'ruction of the character set forth in the precedingfparagraphs which is symmetrical in horizontal cross-section'to 'provide a circular radiation pattern. I

It is another object ofthis invention to provide an antenna ofthe lcharacter hereinbefore-described in 'which @the currentfis fed to the radiators in suchv mannerV as 'to Jprovide an effective height' greatly exceeding .one-half -of the actual height.

Other objects-and advantages of this inven- 'tionwill be apparent from -a studyfof the following specications, readiny conjunctionu with the 'accompanying drawings, wherelnr f The vsingle ngure is a'perspective view showing :the preferred embodiment of this invention.

' ReferringI yto *thev drawings; thereC is illustrated in the drawing an antenna constructed in accordance with the'principles of this invention. The Ysupporting stru'ctnrefor the .antenna comprises a tower 5u whichl may beof conventional tower construction vand which may be insulated from ground as by'fmeans- .of tower leg insulators 5I Near thel top ofthe tower' 50 thereareprovided four outwardly extending horizontal booms, l

ends of the booms but pulled inwardly towardsthe tower by means of upper radiating conductors 59 and 60 which are'connected at spaced points along the length of the conductors 58 andextended to the extreme tip of the tower. The conductors B and 60 are also extended downwardly as indicated at 6i and 62 into connection vwith one of the tower legs near the base insulator 5i. Similar conductors $3 may be extended from the extreme tip of each of the booms into connection with the bottom of the corresponding leg of the tower.

The antenna is preferably fed from a tuning house 64 which is placed within the area dened by the base of the tower and from which a single vertical lead 65 extends. This lead may b e di-` vided as shown in the drawing and extended into connection with each of the four legs of the tower at a point a short distance above the ground.

It will be noted that the invention described herein embodies the principle of providing an array of radiating conductors which are so disposed as to denne a conical or semi-conical shape in which the apex of the cone `is located nearest the ground.` As will be understood. a single vertical wire antenna which is short compared to the wavelength of the signal to be radiated therefrom has neither sufilcient capacity nor inductance to resonate at the frequency desired to be resonated. Such an antenna may be tuned by the addition of a series loading coll. but this reduces the radiation efdciency. Each of the antennae described herein substitutes additional capacity for the series loading inductors, the additional capacity being achieved through the use of a large number of radiating conductors so as to provide a larger surface area. Preferably to increase the surface area and to reduce the resistance due to skin effect, each of the radiating conductors is formed of multi-strand cable or similar high eniciency radio frequency conductor. Additional capacity is included by employing the supporting structure as part of the radiating array. Furthermore, by concentrating a great part of the vsurface area of the radiating array in that area which is located high above the ground, the effective height of the antenna is increased so as to increase the radiation resistance.

It has been found that -with antennae constructed as described herein, wherein a. `large number of paths are provided for the flow of radio frequency current from the lead 65 to the high capacity elements of the structure, the current concentration in each of the conductors is such 'as to place the effective height of the' antenna well above the mid-point of the1 actua.l height. Furthermore the distribution of ,theglines of force about the structure as a whole appears to be such as to reduce the ground resistance to a value materially lower than that associated with a simple vertical conductor of the same'` height. The ground resistance is further reduced by using a network of ground conductors which are buried a convenient distance below the surface of the ground and extended radially away from the base of the antenna a distance which is comparable to the height of the structure.

The effectiveness of the antenna may be seen from the following actual operational data. A fiat top antenna of conventional construction strung between masts 325 ft. high and with a relatively elaborate network of buried ground conductors, was found to have a capacity of 0.0042 mid. When excited at kc.. an input power of three kilowatts produced an antenna current of 22 amperes. An antenna of the type shown in Fig. 3 having a tip height of 325 ft. and associated with a ground conductor network identical with that used in the flat top construction was found to have a capacity of 0.0040 mfd., substantially identical with the capacity of the flat top. The loading coil was therefore also substantially identical with that used on the flat top construction. When the antenna was excited at 85 kc., an input power of two kilowatts produced an antenna current of 44 amperes. Since, because of they sag in the fiat top antenna, the effective heights of the two constructions were substantially equal and their radiation resistances therefore the same, it is seen that the energy radiated was increased by a factor of four with two-thirds the input power. In other words, for the same input power, the antenna was radiating six times as much energy as the flat top construction.

It should be noted that the gain in efficiency is apparently obtained principally through a reduction in ground resistance which must result from the change in character of the radiated neld since both antennae were tested with identical ground conductor networks.

Thus, through an increase in the ratio of radiation resistance to ground resistance, an improvement in radiation efnciency by a factor of six or more is readily obtainable.

It should also be noted that the elimination (or the reduction in size) of the series loading coil required for a single vertical radiator materially reduces the circuit losses and also provides a lower ratio of antenna reactance to transmission resistance, thereby providing a relatively broad tuning antenna. A broadly tuned antenna will eiiiciently radiate a wider band of frequencies and will also produce smaller phase changes as the result of varying external conditions, an item of considerable importance when the antenna is used in radio navigation and beacon systems operating on the phase comparison principle.

From the foregoing it will be observed that this invention provides a new aerial system which is characterized by high capacity, high radiation resistance, low ground resistance, and low ratio of antenna reactance to radiation resistance. It will also be noted that the construction employed is such as to reduce to a minimum the amount of structure which must be erected, thus providing a definite advantage over the conventional flat top constructions which require a minimum of two supporting towers. It should also be noted that the structure disclosed herein is symmetrical about a vertical centre line and therefore operates to radiate a truly circular field strength pattern.

While there has been shown and described the preferred embodiment of the invention, the invention is not to be limited to any of the details shown or described herein except as deiined in the appended claims.

We claim:

l. In an antenna system, the combination of: a supporting tower extending upwardly from the ground surface; means insulating said tower from ground; a plurality of outwardly extending u booms secured and electrically connected to said tower near the upper end thereof; tension means connecting the outer ends of each of said booms with the top of said tower; girdle conductors electrically interconnecting the outer ends of adjacent booms; and a plurality of radiating conductors extending upwardly and outwardly from the lower end of said tower, the upper ends qf said conductors being spaced from each other and electrically connected to said girdle conductors, said radiating conductors being disposed outside of said tower for their entire length.

2. In an antenna system, the combination of: a supporting tower extending upwardly from the ground surface, said tower tapering inwardly and upwardly from a base defined by a plurality of legs; means at each of said legs insulating said tower from ground; a plurality of outwardly extending booms secured and electrically connected to said tower near the upper end thereof; tension means connecting the outer ends of each of said booms with the top of said tower; girdle conductors electrically interconnecting the outer ends of adjacent booms; and a group of radiating conductors for each of said legs, the conductors of each of said groups being connected at their lower ends to the associated one of said legs and extending upwardly and outwardly from the lower end of said tower, the upper ends of all of said conductors being spaced from each other and connected to said girdle conductors, said radiating conductors being disposed outside of said tower for their entire length.

WILLIAM J. OBRIEN.

DUDLEY HALES TOLLER-BOND.

No references cited.