US2517951A - Wide-band directive antenna - Google Patents

Description

8, 1950 H. WHEELER 2,517,951

WIDE BAND DIRECTIVE ANTENNA Filed June 20. 1947 WAVE-S e NA'L O TRANSMITTE l2 9. 12 2 2 1 T, T T3 T4 w I2 24 2' I2 25 u 12' B- D s FlG.l

WAVE-SIGNAL WAVE-SIGNAL TRANSMITTER RECEIVER INVENTOR. HAROLD A.WHEELER ATTORNEY Patented Aug. 8, 1950 UNlTED STATES: PATENT OFFICE vvmasnnn mneo'rrvs ANTENNA Harold A. t l1eeler,-.Great Neck, N. Y., assignor to:

Hazeltine Research, Inc., Chicago, Ill., a:corporation of Illinois Application June 20, 1947, Serial No. 755,981

In prior exploration systems, an ordinary di- While the antenna'of the present in-- po e antenna, is installedon the ground with the in the form of 13111563- prop-e na elements parallel to the ground surfaceexci'ed by high-frequency'signais usually Due to the dielectricies of th ground as contrasted with those air,- the antenna radiates: more'energyinto:

the ground than into the space above it, although such an antenna, in free space is nonclii ctive in a plane normal to theantenn elemerits; Reflections of the signals thus introduced the-earth are recordedand observedto ascertain thenature of the exploredarea. While found that the dipole antenna is essentially a narrow band radiator and does not exhibit the degree directivity nor-the operating band width most often desired for such applications, especially for modulation in short pulses to obtain echoes.

" ngements of this sort have been-employed,

There is'anotherantennaistructure known to the art whichhears a superficial similarity to that of the present invention:

tinned above a counterpoise resting on the ground. Conductors connect a signal source tmthe radiator and to its counterpoise to permit excitation of the structure at several positions along its length. Loading elements, such asrinductors, are included in the -feed connections so thattthe structure is excited-in phase at each of-the severa positions.

It comprises a: horizontally arranged conductive-radiator: Desi- It'isafurther objectofthe'invention to pro vide a Wide-band; directive antenna which is of simplifiedstructure' easily and cheaply fabricated;

It is aspecific object of' the: invention to provide a newandzimproved directiveantenna suitable: for operation over a wide bandof short wave lengths and especially useful for emcientlytransmittingwave signals into the-earth, as in:

aageophysical exploration system.

In accordance with the present "invention, an antenna for, operation over-a; wideband. of short Wave lengthscomprises a1 radiating conductivestructure in the form of an elongated"flat strip having an effectively continuous. length which is substantially greater than one-half of the mean operatingwave length and having an-efe fective width equal toat least asubstantial:

fraction of:'one-quarter of thefmean wave length.

Theantenna has an energy-distribution:system including a plurality of-transmission:lines of'sub stantially the same electrical lengths'for making connectionswfrom a multiplicity of points distrihutedalong'a longitudinal edge of the radiating' structure to signal-translating apparatus so tha-tnwave signal energy,- delivered by that sys--- tem from the translating apparatus energizes" the-radiating structure inthe same phase at: each' ofs-the multiplicity of points toefiect translation ofienergy by the structure in a transverse-electric;mode;

For a better understanding of the present in-- vention, together with other and. further objects thereof, reference is had'to the following description' taken in connection with the accormnanying drawing, and its scope: will becpoi-nt'ed out in the appended claims.

However, that arrangement contemplates peration at relatively long waves and for that reason cannot reasonably approzuzhav half wave length-in physical dimensions. The conductive structure thusdescribed is intended to achieve a low antenna-resistance andthe antenna is a narrow bandonegadaptedior single ircouency operation, andisrnon-direct'rve;

It is an object of the present invention,- therefore, to provide a wide-band, directive antenna;

. ich avoids theaforementioned.limitations-=01 v(or arrangements.

It is another oh ect'of the invention to proride new in proveddirective antenna strzucture for operation over a wideband of short, Wave, lengths,

In the drawing, Fig. 1 is a plan view of drama};- ing= conductive structure embodied'in an antenin accordance withthe invention; Fig: 2 is" a schematic representation ofan energy-distri-- bution system associated; with theradiating structure; and Fig. 3-represents schematically ageophysical exploration systemiutilizing the pres-' invention. Referring now more particularly-tothe drawing; it ishelpful to anwunderstanding-of the in vention initially to describethe-radiating struc ture and itsenergy-distributlonsystem-before discussing their application to the exploration system:

of Fig. 3. The radiatingrconductive structure of Fig; 1 includes a pair of similar conductivemetal lic strips i F3 and l i which may be flat areas of-metal plates, screen or wire mesh. These strips are coplanar and are in space-opposedrelation which is intendedto define a mirrorr-image relationship obtamed-by coplanar positioning ofthe strips about an axis of symmetry in the manner represented in the drawing. Each strip has an effectively continuous length S which is substantially greater than one-half of the mean operating wave length contemplated for the antenna system. Preferably, the length is approximately equal to n times one-half of the mean wave length, where n is any integer greater than unity. Each strip has an eifective width equal to at least a substantial fraction of one-quarter of the mean wave length, the width usually being within the range of one-twentieth to three-quarters of the wave length, Preferably, the strips Ill and II are so dimensioned and spaced that the Width W of the over-all structure is Withir thev range fromone-half to one wave length. This dimension is not critical although most efficient operation-results by utilizing the preferred dimensions indicated. 3 The strips may be of thin, sheet-like conductive material having a thickness which is small compared with their individual widths.

The band width of the antenna structure as well as its directivity result from the manner in which strips I9 and II are excited with signal energy. In particular, for broadside directivity the strips are to be excited substantially in phase at a multiplicity of points distributed along their lengths. This is accomplished through the use of a multiplicity of feed conductors of approximately the'same lengths. As shown, groups or sets of conductors [2, I2 are associated with the first metallic strip ID and similar groups or sets of conductors I2, I 2' are associated with the other strip II. 'One end of each conductor included in the groups I2, I2 is connected at a particular one of a series or multiplicity of feed points distributed along one edge of strip ID, as shown in Fig. 1. while one end of each of the conductors included in the groups I2, I2 is connected with a corresponding arrangement of feed points distributed along strip II. .The opposite or free ends of the conductors of each group are connected together to provide feed point terminals along the radiating structure. The preferred method of grouping, represented in the drawing, is one wherein the conductors connected with succeeding half wave-length sections of conductive strips I and II are grouped to provide feed point terminals with a separation of approximately one-half of the mean wave length. I

To understand more fully the optimum grouping arrangement, it is convenient to visualize the radiating structure as comprising a series of contiguous half wave-length sections designated l3-I6, inclusive, in Fig. 1 where the antenna length is equal to twice the mean wave length. Five feed conductors of the first group I2 are equally distributed along the first half wavelength section I3 of conductor I0 and the conductor arrangement for radiator I I is essentially the same. The f'eed'point ends of these two groups of conductors are connected together to constitute a first'terminal pair T1, centrally located within the section I 3. A generally similar conductor arrangement provides additional terminal pairs T2. T3. and Trim the sections I4, I5, and I B, respectively. I

An energy-distribution system is associated with the radiating structure for making connections through the conductors I2 and I2 to the multiplicity of distributed feed points. This distribution system is represented schematically in Fig. 2, being connected at one end to a wavesignal transmitter 20. The signal-translating apparatus which is connected through the distribution system to the radiating structure will, of course, vary with the particular installation. Since such apparatus forms no portion of the resent invention, unit 20 is shown in block diagram and may have any conventional design and construction. Its output terminals are con- 7 nected with one end of a transmission line 2| which branches at its opposite end .0, 0 into parallel feed lines 22 and 23 having equal lengths. These in turn connect as points a, a and b, b to the center points of additional transmission lines 24, 25 also having equal lengths. For the embodiment under consideration, line 24 extends between terminal pairs T1 and T2 while line 25 extends between the remaining terminal pairs T3 and T The lines 22-25, inclusive, due to the physical configuration of the radiating structure, preferably provide the same physical and electrical length of line from the end of line 2i to each of the terminal pairs Tl-T, inclusive. As a result, the distribution system includes a plurality of transmission lines of the same physical and electrical lengths and, where open-wire lines are employed, they are nonradiating and have no material effect on the directive pattern of the radiating structure.

Considering the combined radiating structure of Fig. 1 and the electrical system of Fig. 2, the signal paths aiforded between the transmitter 20 and the multiplicity of feed points along the radiating conductors I0 and. II have the same physical and electrical lengths so that signal energy delivered by the transmitter energizes each conductive metal strip of the structure in the same phase at each of its several feeding points. In view of the fact that the same potential conditions are established by the feeding system at closely spaced points along the strips II], II the current flow in the radiator strips is substantially transverse thereof, there being little tendency for longitudinal current flow. Therefore, the applied signal energy is radiated in what may be described as a transverse electric mode. The radiating structure is then analogous to a broadside array of dipoles, where the dipole elements are considered to be provided by corresponding transverse sections of the strips I0 and II. The antenna exhibits a directive pattern similar to that of a broadside array of dipoles known to the art and is suitable for operation over an exceedingly wide band of short wave lengths.

The groups of feed conductors I2 and I2 may also contribute components of radiation which arereadily controlled by orienting the conductor groups relative to the metal strips ID and II. Locating the conductor grou s in the same plane as the metal strips has the effect of increasing the width of strips I0 and II and, therefore, the antenna structure has been described with reference to its effective width.- The radiating strips II] and II have further been described as being of an effectively continuous length because the in-phase method of feeding produces the effect of a continuous length even though there may be a condenser or break between any two succeeding ones of the multiplicity of feed points.

The schematic arrangement of Fig. 3 indicates a geophysical exploration system wherein a transmitter 30 is connected with a first transmitting antenna structure .3I through a distribution system 32. The antenna 3| rests upon the earth and is positioned close to a receiving antenna 33 B. Wave-signal energy supplied from transmitter 30 is-radiatedinto the" earth from the transmittingantenna 3i and; assuming the exploredarea=to have an upper stratum P1 and a-lower= stratum P2 which reflectsthe transmitted signal,- energ-yds intercepted by the'receiving antenna-33 and. recorded in the receiver35. The=reflection maybe-utilized in well-know-n-manner to indi= catethe-nature of the explored area. This system, utilizing antenna structures in accordance withthe" present invention, is highly efficient because the antenna presentsrnaximum area on the'ground surface andhas minimum frequency selectivity. It is found that very nearly 100 percent; of the applied energy is transmitted into the-earth due tothe-directiveproperties of the antenna structure andthe difference iii-dielectric constants of' the ether and the earth. While the antennas-3| and 33 have been described as resting onthe ground, the'system may be-operated with these antennas placed slightly above theearth-although the energy-distribution system in=either case should be above the radiating conductors land I l of any antenna.

While" the invention has been described as utilizing a pair of. conductivestrips v:H'i and H in:

the radiating structure; it will be appreciated that-this is by way of illustration only.v The pair of strips permits a'result similar to thatlobtained by'a broadside array of dipole antennas as already indicated;.but one strip associated with a ground planeinormal'thereto likewise has high utility as va broad-band antenna.

Where the dimensions ofthe antenna have been recitedin terms of wave length, it is to. be

understood that the reference is to the wave.

length with. the antenna in operating position. This is. an important design factor where the antenna isplaced upon the earthslsurface for.

the reason that the wavelength in the earth is.,difierent from thatin free space so that the close proximity of the ground may cause the effective antenna width to. be substantially.

greater than would. be the case were .the antenna to. be. suspended in .free space.-

Thatransmitting and receiving'antennas 3|.

and-33 maybe. placed in-longitudinal alignment,

close toone another, without danger of appreciable direct transmission therebetween; That is, the radiations from the several excited areasof conductors: [Band I Paddin phase ina broadside direction'but are of such phase asto cancel one another in their end directions; The antennas are, therefore, highly directive in the broadside sense and exhibit little end radiation; making it possible to operate satisfactorily with the antennas. in close. longitudinal alignment as mentioned.

In the detailed discussion ofFigs: l and 2 it has been convenient to refer particularly to wave.- signaltransmission. However, it is welllunderstood that the functions of reception and transmission withany suchantenna are unavoidably associated by the reciprocity; theorem. There'- fore; such terms. as a radiating conductive structure and the like are used in the text and in the appended claims in a generic-sense to define an antenna structure-in accordance with the invention; whether;- that antenna; has utilized'lforr signal.itransmission oii'receptioni.

While; there: has: been; described;v what is at 1 present: considered: to be the preferred; embodi ment:orthissinvention; .it: willzbe obvious tonthose skillediin the: art thativarious'changes andmodifications may be made thereimwithoutdeparting;- fromitlie invention, audit is; therefore, aimedto; coveralll such. changes' and; modifications; as: fallwithin: the. true; spirit and scope. of. then invention:

What is claimed-is:-

1; Anuantenna; for "OQeI'BJfiOIIiOVBlI a wide; band of short: wave: lengths. comprising: a radiating; conductive structure; ini-the form of .anwxelongated flat :strip havingarreiliectively. continuous length substantially greater. than-one-.ha1f 0151131365 mean; wavelength of:said1..band and having ranleffective width: equalto: at? least-a substantial fraction ofr'oner-quarter ofgsaidrlmean wave length; and :an: energy distribution system including -:a plurality; of. transmissionlines of substantially, the-same: electrical lengths forrmaking. connections from multiplicity of points distributed 2 along a longia tuciinal edgeof said-structure lie-Signal-translat ing apparatus so thatzwave-signal renerg-y deliv ered .bysaid systemirom.saidtapparatus energizes said structure, in the same phase. at. each 1 of said points to effect translation QfsaidenergYS by sa-id1structureiin aitransverse-electric modem 2: Anuantenna for operation over 'a. wide bandi of short wave lengths comprising; a radiating. conductive structure-fin the form of an..elongated fiat .strip-havingan .eiiectively continuousslength approximately equaltontimes one-half of i the 1 mean wave. length Ofsaidiband; where'nis any integer greater than unitypand-having an eiiec--- tiVeJWidth-at leastiequal to. a substantial fraction of-one-quarter of said mean wave length; andyan energy-distributionsystem including a -plura1ity of tIdl'lSIl'liSSiOILliIlBSf of substantially the same. electrical lengths .for makingconnections from a multiplicity of points-distributed along a'longie tudinaledge" of said structure tovsig-nal-translating apparatusv so; thatv wave-signal energysubstantiallygreater'than one-half orthe-mean":

wave length of. said band'and havingan effective width within the range ofone-twentieth to threesquarters' of i said mean wave length; and an energydistribution system includinga plus rality' of transmission lines of: substantially the same: electrical lengths for making'connections from amultiplicity of points distributed along: a longitudinaledge of said structure .to signal translating apparatus so that wave-signal energy" delivered by said" systemfrom said apparatus: energizes said structure in the same phase att each of-said points to efiect translation of said" energy by said structurein a=transverse electric mode;

4. An antenna for operation over a wide band of short' wave' lengths comprising: a radiating structure including a thin substantially flat me--- tallic strip having an effectively continuous length substantially greater than one-half 0f-th'emean 1 wavelength ofsaid band'and having an efi'ective a arm-95 1 width equal-teat least a substantial iraction: of

tudinal edge of said strip to signal-translating apparatus so that wave-signal energy delivered by said system from said apparatus energizes said structure in the same phase at each of said points to effect translation of said energy by said structure in a transverse electric mode.

5. An antenna for operation over a wide band of short wave lengths comprising: a radiating structure including a pair of similar, coplanar, thin metallic strips in space-opposed relation individually having an effectively continuous length substantially greater than one-half of the mean wave length of said band and having an effective width equal to at least a substantial fraction of one-quarter of said mean wave length; and an energy-distribution system including a plurality of transmission lines of substantially the same electrical lengths for making connections from a multiplicity of corresponding points distributed along the adjacent longitudinal edges of said strips ft'o'signal-translating apparatus so that wave-signal energy delivered by said system from said apparatus energizes said structure in the same phase at each of said points to eflect translation of said energy by said structure in a transverse electric mode.

6. An antenna for operation over'a wide band of shortwave lengths comprising: a radiating conductive structure in the form of an elongated flat'strip having an effectively continuous length substantially greater than one-half of the mean wave length of said band and having an effective width equal 'to at least a substantial fraction of one-quarter of said mean Wave length; and an energy-distribution system including a plurality of transmission lines of substantially the same physical-and electrical lengths for making connections from a multiplicity of points distributed along a longitudinal edge of said structure to signal-translating apparatus so that wave-signal energy delivered by said system from said apparatus energizes said structure in the same phase at each of said points to effect translation of said energy by said structure in a transverse electric mode 7. An antenna for operation'over a wide band of short wave lengths comprising: a radiating conductive structure in the form of an elongated flat strip having an efiectively continuous length substantially greater than one-half of the mean wave length of said band and having an effective Width equal to at least a substantial fraction of one quarter of said mean wave length; and an energy distribution system including a plurality of 'nonradiating transmission lines of substantiallythe same electrical lengths for making connections from amultiplicity of points distributed along a longitudinal edge of said structure to signal-translating apparatus so that wave-signal energy delivered by said system fromlsaid apparatus energizes said structure in the same phase at each of said points to effect translation of said energy by said structure in a transverse electric mode.

8." An antenna for operation over awideband of short wavelengths comprising: aradiating conductive'structure in the form Of an elongated flat strip having an effectively continuous length substantially ,%raterthanone'-ha1f of the mean wave length of said'band ands-having: an effective :1 width equal to at least a substantial fraction'of one-quarter of i said mean Wave-length; a -multi--' plicity of conductors of approximately the same length each connected at one end to oneof several points distributed, along a longitudinal edge of said structure; and an energy-distribution SYS": tem including a plurality of transmission, lines of substantially equal electricallengths for making connections from the opposite end of each of said conductors to signal-translating apparatus so that wave-signal energy delivered by said system from said apparatus energizes said structure in the same phase at each of said-pointsto effect translation ofsaid energy by said structure in'a transverse electric mode. 1 l 9. An antenna for operation over. a wide band of short wavelengths comprising: a radiatingconductive structure in the form of an elongated; flat strip having an effectively .continuouslength I substantially greater than one-half-of the mean Wave length of saidib and and having an effective width equal to at least a substantial fraction of one-quarter of said mean Wavelength; a multiplicity of conductors of approximately the same length each connected at one'end to one of several points distributed along alongitudi nal edge of said structure, the free ends of succeeding groups of said conductors being joined together to provide feed point terminals along said structure; and an energy-distribution system including a plurality of transmissionlines of substantially equal electrical lengths for making connections from said terminals to: signaletranslating apparatus so that wave-signal energy delive. ered by said system from said apparatus energizes said structure in the same phase at each of said points to effect translation of said energy by said structure in a transverse electric mode.

10. An antenna for operation over a wide band i of shortwave lengths comprising: a radiating conductive structure in the form of an elongated flat strip having an effectively continuous length substantiallyflgreater than one-half of the mean Wave length of said band andv having an effective width equal to at leasta substantial fraction of one-quarter of said mean Wave length; a multiplicity of conductors of approximatelyl the same length each connected at one end to one of sev-' eral points distributed along a longitudinal edge of said structure, the free ends of succeeding groups of said conductors being joined together to provide feedpoint terminals along saidstructure with a separation between succeeding terminals of approximately one-half of said wave length; and an energy-distribution system in cluding a plurality of" transmission line'sof substantially equal electrical lengths for making connections from said terminals to signal-translating apparatus so that Wave-signal energy delivered by saidsystem from said apparatus ener-i gizes said structure in the samephase at each of said points to effect translation of saidenergyby said structure in. a transverse electric mode. HAROLD A. WHEELER.

REFERENCES CITED The following referencesare ofrecord in the file of this patent:

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