US2944258A - Dual-ridge antenna - Google Patents

Description

July 5, 1960 D. K. YEAROUT ET AL DUAL-RIDGE ANTENNA Filed July 25, 1958 IN VEN TORS Dean K. Yearouf Han e L. Jer ins BY g WWW n ce

' 2,944,258 DUAL-RIDGE ANTENNA Dean K. Yearout, Sandia Park, and Harvey L. Jergins,

7 guide and coaxial line.

7 been employed as a matching transformer between a high Albuquerque, N. Mex., assignors, by mesne assignments, to the United States of America as represented U by the United States Atomic Energy Commiss on Filed July 25, 1958, Ser. No. 751,101

4 Claims. (Cl. 3'43--767) The present invention relates to antennas and more particularly to a miniature dual-ridge transmitting and receiving radar antenna. 1

A principal object of the present invention is to provide a miniature antenna capable of transmitting and receiving radar signals.

A further object of this invention is to provide a miniature antenna having low voltage standing wave ratio operating in the microwave region.

A still further object of this invention is to provide a miniature antenna having broad bandwidth.

' Another object of this invention is to provide a miniature antenna having an impedance equal to a conventional transmission line.

A further object of this invention is to provide minia-' ture antenna capable of transmitting and receiving a broad radiation pattern.

Other and further objectsjwillbe hereinafter discussed 77 for specifiewavelengths'. In such antennas, if the .fre-

quency issp'ecified, the wavelength of eacl 1 element must be of a definite .length. Certain elements maybe a -qnarter of the Wavelength andmaintain good efliciency.

This establishesa. lower limit on antenna elements,

. It is well known that an antenna of the correct length Ja'cts like a resonant circuit and [presents pure resistance tothe excitation circuits An antenna having other than the correct length displays both resistance and reactance to the. excitation circuit. Thus, if anantenna is made smaller thanits resonant length, thefinputimped ance becomes reactive, To correct for capacitive reactancein the input impedance, we add inductance in series with the antenna to bring it back into resonance, or, inother words, toiincrease,the lengths of the antenna elements.

This means that the above-mentioned antennas cannot be employed efiiciently in broadbandfradar' system'slon missiles or airplanes where space, requiircmentfisat a premium. 1 I,

'It can beseen from the'foregoing'that the development of miniature antennas havin'gfall the characteristics of the" larger prior art antennas is an na eaantncior in "present and fu'rtherradar systems, By emplo ing a' i- *ous microwave techniques, wehave proj/ided a minia.

turized antennahavingall the characteristics required for h ii se'ipr n e 90 1 8 an a articleiby l svn "-13". published in the Proceedings of thelRE .for

z tugust i947, page 783. In this article, Mr. Cohn points I seen that there isa definite advantage in using miniatuge A Patented July 5, 1960 out that by employing ridges in a Waveguide, one can obtain broader bandwidths, and proper impedance match between'waveg'uide and ordinary coaxial cable. Mr.

Cohn further points out thatridge waveguide has been usedjfo'r elements'in'wideband junctions between wave- Also the ridge waveguide has impedance waveguide and an ordinary coaxial cable.

This information provides a background for the design ot a miniature antenna having broad bandwidth and proper irfnpedance match. 1 It is obvious that an 'openfend ridge waveguide is not an eflicient radiator.

' With the change in conventional configuration of the ridges and the eliminationand addition of various elenrents to be described in detail, the antenna of the pres,- ent invention complies with all of the requirements necessary-for a broadband radar system to be employed on missiles and airplanes.

- In its principal aspects, the present invention is a miniature antenna comprising a ground plane with a pair of oppositely disposed or matching directional elements herein referred to as ridgesr These ridges extend perpendicularly from the ground plane and have facing inner curved surfaces which converge toward the ground plane and terminate at a predetermined distance from the ground plane and from each other. An exciter 'is connected between the ridges adjacenttheirpoint of maximum convergence or minim-um separation. A suitable transmission line is connectedto the exciter. An-

other conductor' is connected across the two ridges at their point of maximum separation, in order to provide broader radiation and proper impedance.

A more thorough understanding of the invention'may be secured from astudy of the following description of severalspecific embodiments. r I

Inthedrawings: Figffil is a perspective view of the invention in pre- {erred form,a part being broken a-way to illhstratedetails fco'nstruction. 40 v Fig. 2 is a'plan side view to illustrate relative size with respect towavelength."

f Fig. 3 is an top view' to illustrate the width or the ridges with respect to wavelength.

" 'In' Fig. 1; the dual-ridge transmitting and receiving antennais shown comprising ridges 10 and 11 supported on base 12; Connector 13 is mounted 'onridge- 10 and extends through base 12. Connector '13'provides coupling between an external transmission line (not shown) andconduc'tor 14, whichis, in turn, connected to conductor 15. i The portion of conductor 15 s which lies between ridges 10 and 11 constitutes exciter 20.

Base '12 is not only a' support for ridges 10 and ll,

' but also provides a means for mounting the antenna in specific "radar -systems.i The 11a rii agamma qr vf afisa t le ap r matel One i h 'tsevq imep th mi hafli tsa aas r t e a e rad s ste S 1 a ground plane. In the description, base 12 will also be example of the relative sizeof the ground plane the ridges for good 'liemispherical radiation is a width ratio of.;th1'ee. a'nd'one halfito one. A relative change in ground: plane-pr directional elein'ent size will vary these values.

In some cases, it is desirable to employ two complete radar systems in which two-antennas are positioned in a single ground plane at right angles to each other. This prevents excessive coupling betweensystems. It can be antennas in such a case because it makes it possibleto keep the ground plane size to a minimum and yet maintain acceptable gain.

Conductive directional elements or ridges and 11 are located perpendicular with respect to ground plane 12. Each ridge 10 and 11 has a shape substantially defined'by two parallel right angular sector-like surfaces. Each of the surfaces is bounded by two radii and an included arc with a rectangular cutout section located adjacent ground plane 12. There are two mutually perpendicular rectangular surfaces individually joining like radii of the parallel sector-like surfaces. A curved surface 16 joins the arc of the sector-like surfaces. Curved surfaces 16 and 17 converge from what-may be called the mouth 18 of the antenna to a narrow section which may be referred to as the throat 19 of the antenna. There is no exact mathematical formula that can be applied to calculating curvatures 16 and 17. They must, however, be flared upwardly from the ground plane in accordance with an experimentally predetermined radius of curvature to obtain maximum bandwidth .for given radiation requirements. Also, in developing curvatures 16 and 17, the antenna impedance must be kept at the impedance of :aselected transmission line. With an appropriate ground plane, the bandwidth is, for example, 4 to l, and the radiation pattern is approximately 70 and the gain is approximately 7 db as compared to isotropic radiators. As shown in Fig. 1, each ridge 10 and 11 has a generally rectangular portion removed adjacent the ground plane. This creates a predetermined separation between the throat 19 and ground plane 12, which provides a high impedance at the throat 19. The antennas exciting ele ment 20 is that section of conductor connected be tween ridges 10 and 11 at the throat 19. The section of conductor 15 located in insulator 21 land in turn ridge 10 acts essentially as a transmission line and may be varied in diameter to serve as a quarter wave matching section. One end of conductor 15 is inserted in a triction tight cylinder of a threaded metallic plug 22. This arrangement-permits tuning the antenna by inserting a nonarnetallic screwdriver in cylinder 23 and adjusting plug 22 to slide over conductor 15. ,The antenna tuned for maximum efficiency at a predetermined center frequency. Then conductor '15 is solder-ed to plug 22. The other end of conductor 15 is threaded and is turned into a threaded bore of conductor 14. The threads of conductor 15 and the bore of conductor 14 are not shown.

Conductor 14 also provides the male terminal of connector 13 and is insulated from ridge 10- by insulator 24. Insulators 2'1 and 24 are of a size to provide for'proper transmission line impedance; Connector 13 is threaded into ridge 10 with an additional threaded portion extending below ground plane 12 for connecting a female connector of the transmission line from the radar system.

To obtain broader beam width and proper impedance, a conductor 25 is positioned across the mouth 18 of the antenna. Each end of conductor 25 is conveniently connected in the center of the width of ridges 10 and 11.

Referring to Figs. 2 and 3, the dimensions of the antenna of this invention are expressed in fractional values of wavelength at any given frequency. These are typical figures which apply in the UHF or microwave region. An example is given below of the determination of actual antenna dimensions for a predetern'iinedfrequency applying these relative values, and assuming the transmission line between antenna and radar system is a conventional coaxial cable of 50 ohms impedance. The

wavelength is found by applying the equation:

ond and f is the selected center frequency. If the center frequency f is selected as 500 me, the wavelength will equal:

antenna according to this invention at a center frequency of 500 me.

The distance from the throat to themouth of the antenna is:

= 23.7 inches .223)\=(.233) (23.7) =5.52 inches 7 The distance from the highest vertical extent of one of the ridges to the ground plane is:

.32)\-=(.32)(23.7)=7.58 inches The distance across the mouth of the antenna is:

.388)\=(.388)(23.7)-=9.2O inches The vertical space between the throat and the ground plane is:

.0874 \=(.0874) (23.7) =2.07 inches The horizontal space between the throat and the ground plane is the same as between the throat and the mouth or 5.52 inches.

The width of each ridge as shown in Fig. 3 is: V .147A=(.147)(23.7)=3.39 inches The relative wavelength values given above were determined experimentally for maximum antenna efficiency and therefore no antenna theory accounts for them exactly. It is emphasized, however, that these dimensions are in no sense to be regarded as a limitation and are shown for purposes of illustration only. The basic invention resides in the general configuration as shown in Fig. 1. The exact dimensions of the ridges and the curvature of their inner surfaces are determinable by those skilled in the art for given bandwidth, radiation pattern and other requirements prescribed for a particular installation. V

What has been described is a miniature antenna having the necessary characteristic to operate efficiently with a radar system. This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is: 1. An antenna for transmitting and receiving radio waves of predetermined frequencies comprising a pair of similar oppositely disposed conductive ridges mounted perpendicular to a ground plane, a pair of curved surfaces on the facing inner ridge portions converging at a predetermined radius of curvature toward the ground plane and terminating a selected distance therefrom, thereby forming an antenna mouth and throat respectively, an exciter element parallel to the ground plane across the antenna throat, a conductor joining the ridges at the antenna month, an energy transferring connector mounted in one of said ridges, and a transmission line within said ridge joining said connector to the exciter element.

2. An antenna .for transmitting and receiving radio waves of predetermined frequencies comprising a pair of similar oppositely disposed conductive ridges mounted perpendicular to a ground plane, a pair of curved surfaces on the facing inner ridge portions converging at a -predetermined radius of curvature toward the ground antenna moutlnan energy transferring connector mounted in the first of said pair of ridges, a transmission line within first said ridge joining said connector for the exciter element, and tuning means located within the second ridge slidably connected to the exciter element;

3. An antenna for transmitting and receiving radio Waves of predetermined frequencies comprising a ground plane, a pair of oppositely disposed conductive ridges mounted perpendicular thereto, each ridge having a substantially sector-like longitudinal section with a generally rectangular cutout portion adjacent the ground plane, a pair of curved surfaces on the'facing inner ridge portions converging at a predetermined radius of curvature toward the ground plane and terminating a selected distance therefrom, thereby forming an antenna mouth and throat respectively, an exciter element parallel to the ground plane across the antenna throat, a conductor joining the ridges at the antenna mouth, an energy transferring connector mounted in one of said ridges, and a transmission line Within said ridge joining said connector to the exciter element.

4. An antenna for transmitting and receiving radio waves of predetermined frequencies comprising a ground 30 plane, a pair of oppositely disposed conductive ridges mounted perpendicular thereto, each ridge having a substantially sector-like longitudinal section with a generally I rectangular cutout portion adjacent the ground plane, a pair of curved surfaces on the facing inner ridge portions converging at a predetermined radius of curvature toward the ground plane and terminating a selected distance References Cited in the file of this patent UNITED STATES PATENTS 2,531,454 Marshall Nov. 28, 1950 2,691,731 Miller Oct. 12, 1954 2,825,060 Ruze Feb. 25, 1958 2,825,062 Lan Jen Chu et a1 Feb. 25, 1958

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