US3922683A

US3922683A - Three frequency band antenna

Info

Publication number: US3922683A
Application number: US482813A
Authority: US
Inventors: Richard J Kumpebeck
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1974-06-24
Filing date: 1974-06-24
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25

Abstract

Disclosed is an antenna for radiating wave energy signals in three frequency bands. Signals having frequencies in the first and third bands are radiated by a first radiator. Signals having frequencies in the second, intermediate frequency band are radiated by a second radiator. The impedance characteristics of the radiators are used to selectively couple signals from the input to the appropriate radiator.

Description

United States Patent Kumpebeck Nov. 25, 1975 [5 THREE FREQUENCY BAND ANTENNA 2,238,438 4/1941 Alford 343/858 2,318,237 5 i943 L' d bl d. 343 797 75 Inventor: Richard J. Kumpebeck, Hicksville, 2 600,949 1, y p y 4 v 343;? 2,631,238 3/1953 Hills 343/8l6 [73] Assignee: Hazeltine Corporation, Greenlawn,

N.Y. Primary E.ram1'nerEli Lieberman [22] Filed: June 24, 1974 57 ABSTRACT [2]] Appl. No.: 482,813 1 Disclosed is an antenna for radiating wave energy signals in three frequency bands. Signals having frequen- [52] 343/797; 343/816; 343/822 cies in the first and third bands are radiated by a first [51] Int. Cl. HOIQ 2l/26 radiator Signals having frequencies in the second. in- [58] held of Search 343/722 termediate frequency band are radiated by a second 343/822 radiator. The impedance characteristics of the radiators are used to selectively couple signals from the [56] References Cited UNITED STATES PATENTS Carter 343/858 input to the appropriate radiator.

6 Claims, 8 Drawing Figures US. Patent Nov. 25, 1975 Sheet 1 of4 3,922,683

FIG. IB

FIG.

FIG. IA

US. Patent Nov. 25, 1975 Sheet20f4 3,922,683

US. Patent Nov. 25, 1975 Sheet30f4 3,922,683

IMPEDANCE FIG. 3

US. Patent Nov. 25, 1975 Sheet40f4 3,922,683

FIG. 5

FIG. 6

THREE FREQUENCY BAND ANTENNA BACKGROUND OF THE INVENTION This invention relates to antennas, and more particularly to antennas designed to radiate over more than one frequency band.

In modern radio systems it is often necessary for a particular installation to be equipped to transmit and receive signals in many frequency bands. To achieve economy in constructing such an installation it is desirable to use the same antenna for transmission or reception over more than one frequency band. More important. however. is the factor that in installations such as ships or aircraft there are a limited number of desirable antenna locations and it is necessary to have a single antenna operate over different frequency bands so that radio systems can share the most desirable antenna location.

Economy in cable networks is also realized when a multi-band antenna has only a single input port. thereby enabling signals in various frequency bands to share both antenna and cable.

In some applications it is necessary that signals in one frequency band be radiated in a different antenna mode than signals in another band. When such signals are to share the same antenna and cable. it is not possible to use a simple broad-band antenna. Instead, an antenna must be designed to respond to signals in each frequency band in the desired radiation mode.

In a particular instance, for example, it is desirable for an antenna to operate in a vertically polarized mode in a first and third frequency band and in a horizontally polarized mode in an intermediate second frequency band.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an antenna for radiating wave energy signals in three frequency bands.

It is a further object of the present invention to provide such an antenna wherein signals in a first and third frequency band are radiated by a first radiator and signals in a second, intermediate frequency band are radiated by a second radiator.

It is a still further object of the present invention to provide such an antenna having a single input port, whereby signals in said first. second and third frequency band may be supplied using a common transmission line.

In accordance with the present invention there is provided an antenna for radiating wave energy signals in first. second and third frequency bands, the second frequency band being intermediate to the first and third frequency bands. The antenna includes an input port and first means. responsive to wave energy signals supplied to the input port and presenting a substantially matched impedance at the input port for signals in the first and third frequency bands and presenting a substantially mismatched impedance at the input port for signals in the second frequency band, for radiating signals which lie within the first and third frequency bands. The antenna also includes second means. responsive to wave energy signals supplied to the input port and presenting a substantially matched impedance at the input port for signals in the second frequency band and presenting a substantially mismatched impedance at the input port for signals in the first and third 2 frequency bands. for radiating signals which lie within the second frequency band.

For a better understanding of the present invention together with other and further objectives thereof reference is had to the following description taken in conjunction with the accompanying drawings and its scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE FIGURES FIGS. 1, 1A and 13 are an antenna constructed in accordance with the present invention.

FIG. 2 is an equivalent circuit representation of the FIG. I antenna.

FIG. 3 is an impedance diagram illustrating the tuning of the first radiator of the FIG. 1 antenna.

FIG. 4 is an impedance diagram illustrating the tuning of the second radiator of FIG. I antenna.

FIG. 5 is an impedance diagram illustrating the impedance presented by the first radiator of the FIG. I antenna at the input port of that antenna.

FIG. 6 is an impedance diagram illustrating the impedance presented by the second radiator of the FIG. I antenna at the input port of that antenna.

DESCRIPTION AND OPERATION OF THE EMBODIMENT OF FIGURE I FIG. I shows an antenna constructed in accordance with the present invention. Shown in FIG. I is a conductive ground plane 10 and dipoles I2 and I4. Dipole I2 has a length L Which is usually selected to be approximately a half-wavelength at the operating frequency of dipole [2. The two arms of dipole I2 are mounted on ground plane I0 by supporting

members

16 and 18, which also form a first balanced transmission line. Likewise. the two arms of dipole 14 have a total length L and are mounted on ground plane 10 by supporting

members

20 and 22 which form a second balanced transmission line. Support members I6, 18, 20 and 22 are enclosed in conductive shield 23 in the FIG. 1 embodiment. Conductive shield 23 prevents undesired radiation by the support members and additionally may be used to control the impedance of the balanced transmission lines. The distance of dipoles I2 and I4 from ground plane 10 is selected in accordance with the desired radiation pattern and is usually approximately a quarterwavelength at the operating frequency of the dipole. Dipoles I2 and I4 comprise respectively first and second means for radiating applied wave energy signals.

FIG. 1A shows a cross-section of the antenna of FIG. I and details of the construction of dipole I2. Supporting member 16 of dipole I2 is a conductive cylinder. Mounted to support member 16 is a coaxial transmission line 24 which is used to provide electrical signals to be radiated by dipole I2. The outer conductor of transmission line 24 is electrically connected to supporting member 16 at point 28. The inner conductor of transmission line 24 is electrically connected to supporting member 18 at point 26. These connections cause wave energy signals on transmission line 24 to be supplied to dipole I2 and radiated into space.

Transmission line 24 is connected to supporting member 18 at a point 26 which is a selected distance L from dipole 12. Short circuit 38 is connected between supporting members 16 and I8 at a distance L from connection point 26. The short circuit 38 and distances L and L are related to the electrical tuning of dipole 12 as will be further explained.

Dipole 14 is constructed similar to dipole 12, but different values have been chosen for dipole length L and distances L and L for the connecting point 29 and short circuit 39 respectively. As a result dipole 14 has a substantially different frequency response characteristic than dipole 12.

Transmission line 24 has a first selected length L and connects dipole 14 to input port 32. Transmission line has a second selected length L and connects dipole 12 to input port 32. As will be further explained. the frequency responses of dipoles l2 and 14 and the lengths of

transmission lines

24 and 30 interact to cause signals supplied to input port 32 by input transmission line 34 to be radiated by dipole 12 in first and third frequency hands and by dipole I4 in a second intermediate frequency band.

FIG. 2 is an equivalent circuit representation of the FIG. I antenna. In the FIG. 2 circuit dipoles l2 and 14 are approximated by series tuned circuits and 42, respectively. R and R represent. respectively. the radiation resistance of dipoles l2 and 14. Reactive ele ments C L C and L. are approximations of the reactance associated with dipoles I2 and I4 at the feed point. that is the point at which the arms of the dipoles meet the support members 16, I8, 20 and 22. Transmission lines of lengths L L L,-, and L in the FIG. 2 circuit are representative of the corresponding lengths of transmission line on the antenna formed by supporting members l6, 18, 20 and 22 and having lengths L L L,-, and L.,. Transmission lines of lengths L; and L are representative of

transmission lines

24 and 30 in the FIG. I antenna,

FIGS. 3, 4. 5 and 6 are Smith Chart impedance diagrams which will be used to explain the operation of the FIG. I antenna. with reference to the equivalent circuit of FIG. 2. The coordinates shown on the diagrams include the real axis 44 representing all points of pure resistance ranging from a short circuit (0) at the left to an open circuit on the right. The center of the chart represents a relative resistance of unity (matched impedance} and radial distance from the center is representative of the amount of impedance mismatch (usually designated VSWR). Circle 47 represents all points of unity relative resistance and arcs 45 and 46 represent lines of unity positive or negative reactance. respectively. Shown in dotted form is the unity conductance circle 48.

Curve 50 in FIG. 3 illustrates the impedance of series tuned circuit 40, at input terminal 51 in FIG. 2, over three frequency bands. designated X. y and Z. The arrowheads indicate the direction of increasing frequency. Curve 50 is an are along a resistance circle which intersects the real axis at R at a point on the curve corresponding to the resonant frequency of dipole I2. The location of R is determined by the radiation resistance of dipole I2 and the characteristic impedance of the transmission line formed by support mem bers l6 and 18. The characteristic impedance of this transmission line is controlled by the radius R of the support members. spacing I. of the support members and radius R of conductive shield 23, all indicated in FIG. 13. A lower characteristic impedance for these transmission lines may be realized by encapsulating support members 16, I8. 20 and 22 with dielectric material. which also improves the mechanical strength of the antenna. Curve 52 represents the same impedance displaced by a transmission line of length L and represeats the impedance at terminal 26 presented by dipole 12. The shape of the curve has become somewhat distorted since the transmission line has a different electrical length for signals in the lower X-frequency band than for signals in the higher Y- or Z-frequency bands. The transmission line with length L on the FIG. 1 antenna is a balanced transmission line formed by

support members

16 and 18. The length L of the transmission line and resonant frequency of dipole 12 have been selected so that frequencies in frequency bands X and Z on curve 52 are near the unity conductance circle 48. Attached to terminal 26 in FIG. 2 is a transmission line having a length L which is short circuited. This represents the section of the balanced transmission line. formed by support members 16 and I8 and short circuited by member 38, which has length L; illustrated in FIG. IA. The susceptance associated with this short circuited transmission line stub is represented by curve 54 in FIG. 3. Since this susceptance is connected in parallel with the impedance ofdipole I2 at terminal 26, the resulting impedance at point 26 is represented by curve 56. Curve 56 is a typical "double tuned impedance curve. It may be seen that frequencies in frequency bands X and Z are located near the center of the impedance chart and therefore represent a substantially matched impedance. Frequency band Y is substantially displaced from the center of the chart and is therefore representative of a substantially mismatched impedance. It should be noted that the location of frequency band Y on curve 56 is at a substantially lower impedance than frequency bands X or Z. Curve 56 is shown for the case where the characteristic impedance of transmission line 24 is substantially the same as the characteristic impedance of the transmission line formed by support members I6 and 18. Differences in characteristic impedance between these transmission lines would cause displacement of curve 56 along real axis 44 as is well known to those skilled in the art.

FIG. 5 shows the impedance curve 58 of dipole 12 as it appears at input port 32. Curve 58 is the result of tra'nsposing the impedance of curve 56 by the length L; of transmission line 24, which is approximately a quarter-wavelength in length. As a result dipole 12 retains a substantially matched input impedance for signals in frequency bands X and Z, but has a substantially higher input impedance for signals in frequency band Y as seen from input port 32.

Curve 60 in FIG. 4 illustrates the impedance of series tuned circuit 42 in FIG. 2, at input terminal 61 over three frequency bands, designated X. Y and 2. Curve 60 is similar to curve 50 of FIG. 3 except that because dipole 14 is much shorter than dipole I2, curve 60 does not cross the real axis within any of the desired frequency bands. The impedance of dipole 12 at terminal 29 after transposing the impedance of curve 60 by a transmission line of length L,-,, is represented by curve 62 in FIG. 4. The transmission line of length L is formed by supporting

members

20 and 22. The effect of transposing curve 60 through the transmission line is different for dipole 14 because of the tuning of the dipole. In the case of dipole I4, curve 62 tends to be extended. Length L of the transmission line is chosen so that a frequency within frequency band Y lies on the unity conductance circle in curve 62. The stub formed by the transmission line comprising supporting

members

20 and 22 and short circuiting member 39 associated with dipole 14 is much shorter than the stub associated with dipole 12. The resulting susceptance of the stub is shown by curve 64 in FIG. 4. The combined effect of the impedance of dipole 14 at terminal 29 and the short circuited stub of length L,, is represented by curve 66. Unlike curve 56 of FIG. 3, curve 66 is single tuned over the frequency bands of interest and is impedance matched at only one frequency, within frequency band Y, and substantially mismatched at frequencies within frequency bands X and Z. Terminal 29 is connected to input port 32 by transmission line 30 which has length L Length L is chosen to be slightly shorter than the length L; of transmission line 24 because of the orientation of curve 66.

The resulting impedance of dipole 14 at input terminal 32 is shown by curve 68 in FIG. 6. As may be seen by examination of curve 68, dipole 14 presents a substantially matched impedance at input terminal 32 to frequencies within frequency band Y and a substantially higher impedance for frequencies within frequency bands X and Z.

Dipoles 12 and 14 are connected in parallel to input terminal 32. As a result of the impedance presented by

dipoles

12 and 14 at input terminal 32 signals supplied to terminal 32 in frequency bands X and Z will be mostly radiated by dipole 12, while signals within frequency band Y will be mostly radiated by dipole 14. This frequency selection may easily be seen by considering the dipoles as resistors in parallel at terminal 32. When resistors are connected in parallel most of the energy applied to the terminal is supplied to the resistor having the lowest resistance or impedance. Likewise, most of the energy in frequency band X applied to input terminal 32 will be supplied to dipole 12 which has a substantially matched impedance, rather than dipole 14 which has at that frequency a substantially higher impedance.

Those skilled in the art will recognize that a similar effect is possible if dipoles l2 and 14 are series connected at input port 32. in such an embodiment it would be appropriate to tune dipole 12 to present a matched impedance at input port 32 in frequency bands X and Z and a substantially lower, mismatched impedance in frequency band Y. Similarly dipole 14 would be tuned to have a substantially matched impedance in frequency band Y and a substantially lower. mismatched impedance in frequency bands X and Z. Since, in the case of series connected circuits, most of the incident energy is delivered to the circuit having the highest resistance, energy within frequency bands X and Z would be primarily supplied to dipole 12, while energy in frequency band Y would be primarily supplied to dipole 14.

As an example of the embodiment of the invention shown in FIG. 1, an antenna designed to operate over the following frequency bands would have the below listed dimensions:

X l3lU to l36U MHZ Y l-HU to i520 MHZ Z 2060 to Ilt'lU MHz Frequency Bands Antenna Dimensions:

-contmued Transmission lines 24 and EU ha\e dielectric of k 2.05 Support members [6. 18. 2t) and 22 en- 4 1 capsulated in dielectric of k It will be evident to those skilled in the art that curves similar to curve 58 in FIG. 5 may result from known tuning techniques different than those described in connection with the specific embodiment of FIG. 1. The essential feature of the present invention is that the first radiator have a substantially matched impedance for signals in frequency bands X and Z and a substantially mismatched impedance for signals in frequency band Y and conversely that the second radiator have a substantially matched impedance for signals in frequency band Y and a substantially mismatched impedance for signals in frequency bands X and Z. These impedance characteristics may be achieved using a variety of known tuning techniques. It will also be evident that the teachings and principles of the present invention may be applied to other types of antennas which may be tuned in a manner similar to that which has been described for the dipole antenna of FIG. 1.

One antenna type which easily lends itself to the par ticular technique is the cavity-backed slot antenna. As the magnetic analog of the electric dipole. the slot has substantially the same type of impedance characteris tics and therefore is easily adapted to the same types of tuning techniques.

As may be'seen from the illustration of FIG. 1, dipoles l2 and 14 are oriented perpendicular to each other and therefore will radiate different polarization modes. It will be evident, however. to those skilled in the art that antennas tuned in a similar manner to the tuning of dipoles l2 and 1-1 may be arranged in alternative physical configurations wherein the different modes radiating between differently tuned antennas are other than cross polarized modes or both radiators operate in the same mode. For example, dipole 12 could be located on the opposite face of conductive ground plane 10 to dipole l4 and therefore radiate in a different direction rather than in a different polarization. In such a configuration dipole 14 may be used to feed a focusing reflector and therefore provide a narrow beam mode while dipole 12 radiates away from the focusing reflector and consequently radiates a broad beam mode.

Another possibility is that substantially the same structure could be used to radiate in two antenna modes. A specific embodiment of this nature is a square or rectangular cavity antenna which is capable of radiating in two cross-polarized modes. The single cavity would then comprise both first and second means for radiating since it operates in two different modes which may be independently tuned.

While the operation of the invention has been described with respect to transmitting antennas it will be evident to those skilled in the art that such antennas are reciprocal and may be also used as receiving antennas. it is intended that such antennas be within the scope of the present invention.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is. therefore, aimed to cover all such changes and modifi- 7 cations as fall within the true spirit and scope of the invention.

What is claimed is;

1. An antenna for radiating wave energy signals in first. second and third frequency bands. said second frequency band being intermediate to said first and third frequency bands. comprising:

an input port;

first means, responsive to wave energy signals supplied to said input port for radiating substantially only those signals which lie within said first and third frequency bands. said first means including a first combination of a double-tuned radiator and a first transmission line coupling said radiator to said input port, said combination presenting a substantially matched impedance at said input port for signals in said first and third frequency bands and presenting a substantially mismatched impedance at said input port for signals in said second frequency band.

and second means. responsive to wave energy signals supplied to said input port for radiating substantially only those signals which lie within said second frequency band. said second means including a single-tuned radiator and second transmission line coupling said single-tuned radiator to said input port, said combination presenting a substantially matched impedance at said input port for signals in said second frequency band and presenting a substantially mismatched impedance at said input port for signals in said first and third frequency bands for radiating signals which lie within said second frequency band.

2. An antenna system as specified in claim 1 wherein:

said first combination presents a substantially higher impedance at said input port for signals in said second frequency band than in said first and third frequency bands;

said second combination presents a substantially higher impedance at said input port for signals in said first and third frequency bands than in said second frequency band;

and said first and second means for radiating signals are connected across said input port in parallel.

3. An antenna for radiating wave energy signals in first second and third frequency bands. said second frequency band being intermediate to said first and third frequency bands. comprising:

an input port;

a double-tuned radiator presenting a substantially matched impedance at its input for signals in said first and third frequency bands and a substantially mismatched impedance for signals in said second frequency band. for radiating substantially only supplied signals which lie within said first and third frequency bands;

a single-tuned radiator presenting a substantially matched impedance at its input for signals in said second frequency band and a substantially mismatched impedance for signals in said first and third frequency bands. for radiating substantially only supplied signals which lie within said second frequency band;

means for coupling said double-tuned radiator to said input port such that the combination thereof presents a substantially higher impedance at said input port for supplied signals in said second frequency band than for supplied signals in said first and third frequency bands;

and means for coupling said single-tuned radiator to said input port such that the combination thereof presents a substantially higher impedance at said input port for supplied signals in said first and third frequency bands than for supplied signals in said second frequency band.

4. An antenna as specified in claim 3 wherein said means for coupling said radiator to said input port comprises a transmission line having a first selected length. and said means for coupling said single-tuned radiator to said input port comprises a transmission line having a second selected length.

5. Apparatus as specified in claim 4 wherein said double-tuned radiator comprises a first dipole and said single-tuned radiator comprises a second dipole. perpendicular to said first dipole.

6. Apparatus as specified in claim 5 wherein said first and second transmission lines comprise coaxial cables and said cables are connected at said input port in parallel.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent M 3,922,683 Dated November 25, 1975 Richard J. Kumpfbeck Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventor's name should read Richard J. Kumpfbeck Signed and Scaled this Arrest."

RUTH C. MASON C. MARSHALL DANN A resting Officer (ummissimwr uflalents and Tradcmurkx

Claims

1. An antenna for radiating wave energy signals in first, second and third frequency bands, said second frequency band being intermediate to said first and third frequency bands, comprising: an input port; first means, responsive to wave energy signals supplied to said input port for radiating substantially only those signals which lie within said first and third frequency bands, said first means including a first combination of a double-tuned radiator and a first transmission line coupling said radiator to said input port, said combination presenting a substantially matched impedance at said input port for signals in said first and third frequency bands and presenting a substantially mismatched impedance at said input port for signals in said second frequency band; and second means, responsive to wave energy signals supplied to said input port for radiating substantially only those signals which lie within said second frequency band, said second means including a single-tuned radiator and second transmission line coupling said single-tuned radiator to said input port, said combination presenting a substantially matched impedance at said input port for signals in said second frequency band and presenting a substantially mismatched impedance at said input port for signals in said first and third frequency bands for radiating signals which lie within said second frequency band.

2. An antenna system as specified in claim 1 wherein: said first combination presents a substantially higher impedance at said input port for signals in said second frequency band than in said first and third frequency bands; said second combination presents a substantially higher impedance at said input port for signals in said first and third frequency bands than in said second frequency band; and said first and second means for radiating signals are connected across said input port in parallel.

3. An antenna for radiating wave energy signals in first, second and third frEquency bands, said second frequency band being intermediate to said first and third frequency bands, comprising: an input port; a double-tuned radiator presenting a substantially matched impedance at its input for signals in said first and third frequency bands and a substantially mismatched impedance for signals in said second frequency band, for radiating substantially only supplied signals which lie within said first and third frequency bands; a single-tuned radiator presenting a substantially matched impedance at its input for signals in said second frequency band and a substantially mismatched impedance for signals in said first and third frequency bands, for radiating substantially only supplied signals which lie within said second frequency band; means for coupling said double-tuned radiator to said input port such that the combination thereof presents a substantially higher impedance at said input port for supplied signals in said second frequency band than for supplied signals in said first and third frequency bands; and means for coupling said single-tuned radiator to said input port such that the combination thereof presents a substantially higher impedance at said input port for supplied signals in said first and third frequency bands than for supplied signals in said second frequency band.

4. An antenna as specified in claim 3 wherein said means for coupling said radiator to said input port comprises a transmission line having a first selected length, and said means for coupling said single-tuned radiator to said input port comprises a transmission line having a second selected length.

5. Apparatus as specified in claim 4 wherein said double-tuned radiator comprises a first dipole and said single-tuned radiator comprises a second dipole, perpendicular to said first dipole.