US 3312974 A
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April 3, 1967 a. LEWIS 3,312,974
FRESNEL ZONE CORRECTING ANTENNA HAVING A PLURALITY OF CONCENTRIC SPACED CONICAL DIELECTRIC SECTIONS Filed July 17, 1964 IIIIIII III/ll UUAvEPRom GROUND pLANE INVENTOR BERNRRD L. LELLHS ATTORNEYS Patented Apr. 4, 1967 3,312,974 FRESNEL ZDNE CORRECTING ANTENNA HAV- ING A PLURALITY F CONCENTRIC SPACE!) CONICAL DIELECTRIC SECTIUNS Bernard L. Lewis, Satellite Beach, Fla, assignor to Radiation Incorporated, Melbourne, Fla, a corporation of Florida Filed July 17, 1964, Ser. No. 383,344 Claims. (Cl. 343-755) The present invention relates generally to antenna systems and more particularly to high frequency antenna systems employing multiple Fresnel zone correctors.
Various antenna systems have previously been utilized in attempts to correct differing zones of wave or field components in propagated radio waves. As is well known, the wave propagation characteristics of an ideal isotropic radiator are theoretically such that essentially spherical electromagnetic waves are transmitted therefrom; that is, concentric spheres of radiant energy are emanated traveling outwardly into space from the source. At points remote from the radiator or source the waves appear to be substantially uniform plane waves, the electric and magnetic fields of the waves being perpendicular both to each other and to the direction of propagation, the well known transverse electromagnetic wave (TEM wave). The concentric spheres emanating from the source may be visualized as representing the locus of the in-phase wave or field components at successive intervals of time. In addition, each point on the wavefront may be considered an independent source from which is emitted semi-spherical components, or wavelets, in the direction of propagation of the wavefront. Thus, alternate zones of in-phase and out-of-phase wave components occur along the wavefront of the plane wave, with reinforcement of the radiant energy thereof occurring at intersections of the in-phase components of the wavelets and cancellation occurring at intersections of the out-of-phase components. This phenomenon is similar to the theory of interference bands in the field of optics. Prior art attempts to correct these alternately-phased or Fresnel zones in the wavefront at transmitting or receiving antennas have resulted in rather complex and expensive antenna systems, generally extremely frequency sensitive and thus of relatively narrow band characteristics.
In accordance with an embodiment of the present invention, wave refraction and diffraction concepts are combined in an antenna system comprising a plurality of interspaced conical concentric dielectric media separated by free space. The dielectric media or elements are arranged to correspond or register with out-of-phase zones in the wavefront of the electromagnetic wave of interest, for example micro-waves, to produce a reinforcement or agreement of the phasing of the wave components at the antenna, while additionally performing as wave guides to funnel energy in the wave to or from the antenna and antenna feed according to whether the system is used for receiving or transmitting, respectively.
It is accordingly a broad object of the present invention to provide an improved Fresnel zone correcting antenna system.
It is a more specific object of the present invention to provide a Fresnel zone correcting antenna system employing concepts of electromagnetic wave refraction and diffraction.
It is another object of the present invention to provide an antenna system which simultaneously provides phase shifting of the radio wave components for reinforcement of the radiant energy and highly directive waveguiding for radiating the energy in a desired direction.
It is a further object of the present invention to provide an antenna system wherein a configuration of dielectric media produces phase correction of radio Wave components with consequent improved antenna gain and efiiciency.
Other objects, features, and attendant advantages of the present invention will become apparent from a consideration of the following detailed description of a specific embodiment thereof, taken in conjunction with the accompanying drawings in which:
FIGURE 1 is an end view of a Fresnel zone correcting antenna system in accordance with an embodiment of the present invention;
FIGURE 2 is a cross-sectional side view taken along the line 2-2 of the embodiment of FIGURE 1;
FIGURE 3 is an enlarged broken side view of a portion of the zone correcting antenna and an electromagnetic wavefront incident thereon;
FIGURE 4 is a side view of the antenna associated with a ground plane.
Referring noW to the drawings, wherein like reference numerals refer to like components in the several views, FIGURES 1 and 2 illustrate 'a specific embodiment of a refracting-diffracting antenna in accordance with the present invention. In the ensuing description it is to be understood that while reference will be made to a particular form of the antenna system, the invention is not limited to such form, and that the particular configuration is by way of illustration of a preferred embodiment only. Further, each view is exaggerated for simplicity and clarity. An antenna system, illustrated generally at 10, is comprised of a plurality of substantially lossless dielectric elements as 12, 14, 16. These dielectric elements are preferably in the form of coaxial or concentric hollow comes, with the antenna feed 20 placed at the apex of the conical structure. As shown in FIGURE 2, the dielectric elements are more aptly described as conical frusta or sections, the antenna feed being coupled at the smaller diameter base of the sections. The particular antenna feed employed will depend upon the characteristics of the wave desired to be transmitted or received, and, for example, may comprise a dipole, a horn, a Yagi, a log periodic array, a tracking feed or other conventional arrangements.
While three dielectric sections, 12, 14, 16, are shown, it will be understood that any number of such elements may be employed, antenna gain and efliciency increasing with increasing number of elements used. The dielectric elements are separated, one from another, by appropriate regions or zones of air or other suitable media desig nated generally at 13, 15. In the embodiment shown the central dielectric element 12 is solid, the remaining elements being hollow to accept other such elements therewithin. An axis of symmetry for the antenna configuration thus is present at the longitudinal axis of element 12.
The dielectric employed in elements 12, 14, 16 will have a dielectric constant based on the wavelength of the radio waves involved and, for example, may be in the form of solid, gas in inflatable envelopes having the above-described configuration, or synthesized media as short wires in inflatable structures. Suitable solid dielectrics are polystyrene, quartz, or the like, having the desired dielectric constant for wavelengths of interest.
The length L of the zone corrector dielectric sections is selected, in accordance with the dielectric material used and the wavelength x of the electromagnetic waves under observation, to introduce a half wavelength (M2) delay into the wave components impinging upon each dielectric element. That is, the wave components trapped by elements 12, 14, 16, for example, are delayed with respect to the components propagating through regions 13, 15, an equivalent length of air or other suitable media, such that all of the wave components are reinforced, i.e. are in phase, at the antenna feed 20, the entire antenna YFW (1) where X has a maximum value of L as indicated in FIG- URE 2. Similarly, element 14 is a hollow conical element having an inner radius, Y varying as and an outer radius varying as The next outer dielectric element, 16, with respect to the axis of symmetry of the configuration, fills the zone between Ya=v if (4) with each subsequent element or member having dimensions governed by equations having the same progression. Thus, considering each successive zone of the antenna as a separate region of predetermined dimensions, i.e. alternate zones of suitable dielectric and air, the multiple zone correcting antenna of the present invention comprises an electromagnetic wave transducer having alternate sections for introducing a half wavelength delay in wave components intercepted thereby to place such components in phase agreement with adjacent wave components traveling through an equivalent length of free space. Each successive zone has an outer radius, from a center at the axis of symmetry 25 and in a plane normal thereto, governed by and varying in accordance with where n is an integer and the other terms are as previously defined. Thus, for example, the fourth region from the axis of symmetry of the structure of the embodiment of FIGURES 1 and 2 is region or zone 15, of air, having an outer radius Y VIXT 7 while the next interior region (zone 3) is a dielectric member having an outer radius Y EYX (8) Thus zone 4, of air, is confined within a space between these two radii, Y and Y varying with the distance X from the phase center of the feed.
Referring now to FIGURE 3, there is illustrated a wavefront 40 incident upon the multiple Fresnel zone correcting antenna 10 employed, with feed 20, as a receiving antenna. Wavefront 40 comprises a series of wavelets or wave components as 41, 42, 43, and so forth, which are alternately in phase with each other. That is, adjacent wave components, as 41, 42, are out-of-phase. It is to be noted that without any zone correction these Wavelets would have an interference pattern of zones in which portions of the energy would be dissipated through cancellation. The zone corrector antenna, however, combines diffraction and refraction of the wave components to produce a reinforcement of the in-phase and out-ofphase wave components such that all wave components are substantially in phase or phase corrected, at the feed (by diffraction), and to produce a funneling of the total energy of the wave, each zone or region acting as a waveguide, into the feed (by refraction). Dilfraction of the wave is provided by introducing the half wavelength delay into wave components traversing the dielectric zones,
' while refraction is accomplished, bending or directing ated with the ground plane as shown.
the wave as desired, in accordance with concepts of Snells law. The multiple zone corrector provides simultaneous refraction and diffraction of the wave by virtue of the dielectric regions separated by free space regions. As previously noted, the dielectric constant of the dielectric zones will be chosen in accordance with the wavelength of the wave energy involved and with the desired dimensions of the correcting antenna.
When used as a transmitting antenna, the feed element 20 is located, as before, at the primary aperture of the conical structure. The radiation trapped by the dielectric waveguides is directed within the various zones of the structure toward the secondary aperture and is phase corrected in the process such that there is radiated into space a plane wave having a directivity proportional to the dimensions of the zone corrector and to the wavelength of the energy radiated. The gain G of the multiple zone correcting refracting-diffractirrg antenna of the present invention is equivalent to a conventional antenna having an effective area equal to the number of zones corrected plus one. Thus, if N is the number of the last zone or region corrected, the gain of the antenna of the preferred embodiment will be rays with high efficiency and gain. The zone correcting antenna is more efiicient than conventional antennas since its effective area is much greater than its actual area, and thus gain is essentially unlimited. Gain, as noted, will increase with the number of zones corrected. Additional advantages of antennas constructed in accordance with the present invention are extremely low side lobes (high directivity), ease of construction, light weight, "and relatively low cost of fabrication.
Referring now to FIGURE 4, a multiple zone correcting antenna 10 in accordance with the previously described concepts is employed in conjunction with a refleeting sheet or ground plane 5% such that radiation from the feed passes through the ,zone corrector twice before being propagated into space. The characteristics of an antenna in the vicinity of a ground plane are well known and need not be extensively discussed. Basically, the ground plane provides an image equivalent of the antenna to efiectively produce a double element array. In this case, the zone correcting antenna may be visualized as a half lens which forms a complete lens when associ- Radiation from the feed is guided by the dielectric elements toward the secondary aperture from which it is partially reflected and reguided to be radiated into space. The full lens zone corrector has a wider band width than the half lens corrector, and additional support is obtained for the overall structure.
While a preferred embodiment of the invention has been described, various changes and modifications may occur to those skilled in the art Without departing from the true spirit and scope of the present invention. Therefore, it is desired that this invention be limited only by the appended claims. I
1. An antenna for correcting the phase of components of a radio wave incident thereon such that said wave components arrive at the antenna feed in an in-phase condition, said antenna comprising a plurality of spaced dielectric elements radiating geometrically from said feed about a common axis through the phase center of said feed, said elements arranged and adapted to intercept alternate Fresnel zones occurring in a plane a distance X from the phase center of said feed, said elements having a preselected dielectric constant for introducing a phase delay of half wavelength of said radio wave traveling therethrough with respect to those portions of said radio wave passing through an equivalent length of the space between said elements.
2. The combination according to claim 1 wherein said elements form a plurality of Waveguides for directing said radio wave toward said antenna feed.
3. An electromagnetic wave transducer comprising a plurality of dielectric elements, a plurality of dielectric regions separating said dielectric elements, said elements and said regions being aligned to intercept adjacent Fresnel zones in a Wavefront of an electromagnetic wave to be translated by said transducer, said elements comprising concentric hollow cones for guiding energy of said wave therethrough and having a dielectric constant different from the dielectric constant of said regions, said dielectric constants being preselected to introduce a half wavelength delay in the passage therethrough of Wave components in zones intercepted by said elements relative to passage of wave components in zones intercepted by said regions, an antenna feed, and means coupling said elements and said regions to said feed.
4. An electromagnetic wave transducer comprising a plurality of dielectric elements, a plurality of dielectric regions separating said dielectric elements, said elements and said regions being aligned to intercept adjacent Fresnel zones in a wavefront of an electromagnetic wave to be translated by said transducer, said elements having a dielectric constant different from the dielectric constant of said regions, said dielectric constants being preselected to introduce a half wavelength delay in the passage therethrough of wave components in zones intercepted by said elements relative to passage of wave components in zones intercepted by said regions, an antenna feed, and means coupling said elements and said regions to the feed, said elements comprising concentric hollow conical frusta defining a configuration having a pair of parallel bases, one of said bases having a diameter greater than the other, said antenna feed being coupled at said other base.
5. The combination according to claim 4 wherein said elements extend outwardly about the axis of symmetry of said concentric configuration, each of said elements having a diameter varying as a function of distance along said axis from the phase center of said antenna feed and as a function of the wavelength of said electromagnetic wave.
6 6. The combination according to claim 5 wherein each of said elements and said regions therebetween has an outer diameter, with respect to said axis, defined by where n is an integer representing the number of the zone of each element and each region consecutively numbered outwardly from said axis, X is said distance along said axis, and A is said wavelength.
7. The combination according to claim 5 wherein the distances from said greater diameter base to said phase center of said antenna feed has a maximum value determined by said dielectric constant of said elements to introduce said halt wavelength delay.
8. The combination according to claim 7 including a ground plane superposed on said greater diameter base.
9. A Fresnel zone correcting antenna for electroma netic waves having a mean wavelength A, said antenna comprising an antenna feed, said feed having a phase center; a plurality of concentric spaced conical dielectric sections coupled to and emanating from said feed; said sections and the spaces therebetween forming zones about the common axis of said concentric sections; each of said zones having an outer radius measured from a center along said axis, and in a plane perpendicular thereto, which varies according to where n is an integer representing the number of each zone in a count beginning from said axis and extending outwardly therefrom, and X is the distance from said plane to said phase center measured along said axis; the dielectric constant of said sections being preselected to introduce a half wavelength phase delay, at said mean wavelength A, in said electromagnetic waves passing the length thereof, with respect to the phase of said electromagnetic waves passing through an equivalent length of said space therebetween.
10. The combination according to claim 9 wherein said length of said conical sections is a function of said dielectric constant and wherein a wave reflecting plane is positioned at the end of said elements opposite said antenna feed from which they emanate.
References Cited by the Examiner UNITED STATES PATENTS 2,412,202 12/1946 Bruce 343910 X 3,189,907 6/1965 Van Buskirk 343-910 X HERMAN KARL SAALBACH, Primary Examiner.
ELI LIEBERMAN, Examiner.
P. L. GENSLER, Assistant Examiner,