Turnstile Antenna

Abstract

A multimode turnstile antenna providing simultaneously, without interference, right and left hand circularly polarized omnidirectional patterns and a vertically polarized omnidirectional pattern. Four coaxial cables are disposed vertically and parallel to each other. A frusto-conical member has its smaller diameter end disposed adjacent the upper ends of the coaxial cables to electrically and physically interconnect the outer conductors of all the coaxial cables. This arrangement, when the two pairs of diagonally disposed coaxial cables are excited in a balanced relationship and the pairs are excited orthogonally by first energy, provides simultaneously both right and left hand circularly polarized omnidirectional patterns. When four members are disposed adjacent the upper half of the coaxial line with each of these members being coupled to the center conductor of a different one of the coaxial lines and extending outwardly at an angle (preferably 90.degree.) with respect to the associated one of the coaxial lines with the members orthogonally related with respect to each other, the antenna, in addition, simultaneously provides, when each of the four coaxial lines are excited inphase by second energy, a vertically polarized omnidirectional pattern. An embodiment of a feed arrangement is disclosed enabling the four coaxial lines to be excited inphase by the second energy and simultaneously to enable each of the four coaxial lines to be excited by the different orthogonally related first energy.

Description

BACKGROUND OF THE INVENTION

This invention relates to antennas and more particularly to turnstile antennas.

Because of existant space limitations and a need for greater numbers of antennas to provide radiating means for a multiplicity of services, the trend in antenna design is toward compact multipurpose radiators which provide more than one function. For example, in mobile applications, requirements exist for providing radio communications and navigation functions simultaneously in either different frequency bands, or in the same frequency band. The antenna radiation characteristics with respect to pattern coverage and polarization are not necessarily identical. The advent of communications and navigation systems which utilize satellites have greatly complicated the design of common multipurpose antennas because of requirements of pattern coverage and polarization which differs from those for line-of-sight (LOS) ground-to-ground and ground-to-air links. The satellite systems require circular polarization and overhead coverage from ground base antenna, necessitating different modes of excitation in the antenna from those used in conventional systems.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a multimode antenna suitable for utilization in satellite systems.

Another object of the present invention is to provide a multimode turnstile antenna capable of having simultaneously a vertically polarized omnidirectional pattern, a right hand circularly polarized omnidirectional pattern and a left hand circularly polarized omnidirectional pattern.

Still another object of the present invention is to provide a multimode turnstile antenna capable of utilization with satellite systems, LOS communication systems and/or navigation systems.

A feature of the present invention is the provision of a multimode turnstile antenna capable of having simultaneously a vertically polarized omnidirectional pattern, a right hand circularly polarized omnidirectional pattern and a left hand circularly polarized omnidirectional pattern comprising four coaxial transmission lines disposed in a vertical, parallel relationship, each of the coaxial lines including an inner conductor and an outer conductor; and a frusto-conical member having its smaller diameter end disposed adjacent the upper end of the coaxial lines to electrically and physically interconnect the outer conductors of all the coaxial lines.

Another feature of the present invention is the provision of four members disposed adjacent the upper end of the coaxial lines, each of the members being coupled to the center conductor of a different one of the coaxial lines and extending outwardly at an angle with respect to the associated one of the coaxial lines.

A further feature of the present invention is the provision of a multimode turnstile antenna as described above wherein each of the four coaxial lines are excited by inphase energy and simultaneously each of the coaxial lines are excited by different orthogonally related energy.

BRIEF DESCRIPTION OF THE DRAWING

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a multimode turnstile antenna and its feed arrangement in accordance with the principles of the present invention;

FIG. 2 is a top view of FIG. 1;

FIG. 3 is the elevational pattern for left hand circular polarization resulting from the antenna of FIG. 1;

FIG. 4 is the elevational pattern for right hand circular polarization resulting from the antenna of FIG. 1; and

FIG. 5 illustrates the figure 8 elevational pattern for vertical polarization resulting from the antenna of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For purposes of explanation, let us consider a UHF (ultra-high frequency) line-of-sight (LOS) ground-to-ground communication, UHF satellite communications and L-band DME (distance measuring equipment)/Tacan or RSB (Radar Safety Beacon)/IFF (Identification Friend or Foe) applications wherein the following requirements would exist for an antenna at a user terminal.

Function Polarization Frequency Band Pattern Coverage UHF LOS Vertical 225-400 MHZ Figure 8 in Communications elevation, omnidirectiona l UHF Satellite Dual Circular 225-400 MHZ Hemispherical Communication DME/Tacan Vertical 960-1215 MHZ Figure 8 in RSB/IFF elevation, omnidirectiona l

The term "dual circular" as presented in the above table refers to right and left hand circularly polarized radiation. The term "hemispherical" present in the above table has reference to a right and left hand circularly polarized omnidirectional pattern.

Referring to FIGS. 1 and 2, there is illustrated therein a multimode turnstile antenna in accordance with the principles of the present invention including four coaxial transmission lines 1-4, each of which includes an outer conductor 5 and an inner conductor 6. The outer conductor 5 of coaxial lines 1-4 are interconnected electrically and physically by frust-conical member 7 which has its smaller diameter end 8 physically and electrically interconnecting the outer conductors of coaxial transmission lines 1-4. The length of the side of member 7 is greater than one quarter wavelength at the operating frequency. To inner conductors 6 at the upper end thereof are connected members 9, 10, 11 and 12 to form a turnstile antenna. Members 9-12 are disposed at an angle, preferably 90.degree., with respect to coaxial transmission lines 1-4 and extend outwardly from the center conductors 6 thereof in such a manner as to dispose elements 9-12 in an orthogonal relationship with respect to each other.

The structure including members 9-12 and frust-conical member 7 (member 7 acting as a reflecting element) provides a hemispherical antenna pattern when each of the pairs of coaxial lines 1 and 4 and coaxial lines 2 and 3 are excited in a balanced relationship and these pairs of coaxial lines are orthogonally excited by a given energy for transmission from the antenna structure, or when hemispherically radiated energy is received by member 7 in conjunction with members 9-12. The frusto-conical member 7 and members 9-12 due to their hemispherical antenna pattern provides the multifunction of providing both right and left hand circular polarization with an omnidirectional pattern. This arrangement would be suitable for UHF satellite communication as indicated in the above table.

To provide vertical polarization for UHF LOS communications or DME/Tacan, RSB/IFF applications, members 9-12 together with member 7 (member 7 acting as a radiating element) are employed. Each of members 9-12 having a length equal to approximately 0.35D at the operating frequency of the antenna, where D is equal to the diameter of the base of the frusto-conical member 7 as shown in FIG. 2. The length of the side and the diameter D of the base of member 7 and the length of members 9-12 controls the radiation patterns generated by the antenna of this invention. To provide the desired transmission of vertically polarized omnidirectional energy, coaxial lines 1-4 must be energized by the desired energy inphase or upon reception of vertically omnidirectional energy, coaxial lines 1-4 will be excited inphase by the received energy.

FIG. 3 illustrates the elevational hemispherical pattern produced by the left hand circularly polarized excitation of members 9-12 and member 7, FIG. 4 illustrates the hemispherical elevation pattern provided by right hand polarization excitation of members 9-12 and member 7 and FIG. 5 illustrates the figure 8 elevational pattern produced by the vertically polarized excitation of members 9-12 and member 7.

The feed arrangement for the antenna structure of this invention as shown in FIG. 1 is used for both transmission and reception and includes two balanced hybrids 13 and 14, a quadrature hybrid 15 and a power divider or power adder 16 depending upon whether energy is being radiated or received.

For transmission the feed arrangement operates as follows. The energy to be transmitted with vertical polarization is applied to port 17 and fed through power divider 16 to the inphase ports of balanced hybrids 13 and 14. This results in an inphase excitation of coaxial lines 1-4 as indicated by the (+) symbol applied to the ports of hybrids 13 and 14 connected to the center conductors of coaxial lines 1-4. This inphase excitation of the coaxial lines 1-4 will result in the figure 8 elevational antenna pattern shown in FIG. 5 due to members 9-12 and member 7.

The circular polarization pattern for transmission is simultaneously provided by excited port 18 of quadrature hybrid 15 with left hand circularly polarized signal and port 19 of quadrature hybrid 15 with right hand circularly polarized signal. This results in a 0.degree. phase shift for left hand circularly polarized signals (a 90.degree. phase shift for right hand circularly polarized signals) at port 20 of hybrid 15 which is coupled to the balanced port of hybrid 13. Hybrid 13 produces a 0.degree. phase shift for left hand circularly polarized signals (a +90.degree. phase shift for right hand circularly polarized signal) for excitation of transmission line 4 and a 180.degree. phase shift for left hand circularly polarized signal (a -90.degree. phase shift for right hand circularly polarized signal) for excitation of transmission line 1. Simultaneously, the energy applied to ports 18 and 19 is coupled from port 21 of hybrid 15 to the balanced port of hybrid 14 resulting in a +90.degree. phase shift for left hand circularly polarized signal (a 0.degree. phase shift for right hand circularly polarized signals) for excitation of transmission line 3 and a -90.degree. phase shift for left hand circularly polarized signal (a 180.degree. phase shift for right hand circularly polarized signal) for excitation of transmission line 2. The resultant excitation of coaxial lines 1-4 with different balanced and orthogonal energy results in a circularly polarized signal radiated from the antenna structure including members 9-12 and member 7.

When the antenna structure of FIG. 1 is employed for receiving left and right hand circularly polarized energy, members 9-12 and member 7 cause coaxial lines 1 and 4 and coaxial lines 2 and 3 to be excited in a balanced relation with these pairs of coaxial lines being excited in phase quadrature. This results in the ports of hybrids 13 and 14 being excited as follows: 0.degree. (+90.degree.) from line 4, 180.degree. (-90.degree.) from line 1, +90.degree. (0.degree.) from line 3 and -90.degree. (180.degree.) from line 2. There then will result at ports 18 and 19 output signals resulting from received left hand and right hand circularly polarized signals. When the antenna structure including members 9-12 and member 7 receive vertically polarized omnidirectional radiation, coaxial transmission lines 1-4 are excited by inphase received energy as indicated by the (+) symbol applied to the ports of hybrids 13 and 14. The output from the inphase ports of hybrids 13 and 14 are coupled to port 17 through power adder 16.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

Claims

I claim:

1. A multimode turnstile antenna capable of having simultaneously a vertically polarized omnidirectional pattern, a right hand circularly polarized omnidirectional pattern and a left hand circularly polarized omnidirectional pattern comprising:

four coaxial transmission lines disposed in a vertical parallel relationship, each of said coaxial lines including an inner conductor and an outer conductor;

a frusto-conical member having its smaller diameter end disposed adjacent the upper end of said coaxial lines to electrically and physically interconnect said outer conductors of all said coaxial lines; and

four members disposed adjacent said upper end of said coaxial lines, each of said members being coupled to said center conductor of a different one of said coaxial lines and extending outwardly at an angle with respect to the associated one of said coaxial lines.

2. An antenna according to claim 1, wherein

said members are orthogonally related with respect to each other.

3. An antenna according to claim 2, wherein

each of said coaxial lines are excited by inphase energy and simultaneously each of said coaxial lines are excited by different orthogonally related energy.

4. An antenna according to claim 2, wherein

each of said members have a length equal to approximately one quarter wavelength at the operating frequency of said antenna.

5. An antenna according to claim 2, wherein

the side of said frusto-conical member has a length greater than one quarter wavelength at the operating frequency of said antenna.

6. An antenna according to claim 2, further including

a first balanced hybrid having a first balanced port, a first inphase port, a first port coupled to said center conductor of a first of said coaxial lines and a second port coupled to said center conductor of a second of said coaxial lines diagonally disposed with respect to said first of said coaxial lines, said first port being responsive to first energy, said second port being responsive to said first energy having a 180.degree. phase relationship with said first energy at said first port and said first and second ports simultaneously being responsive to inphase second energy;

a second balanced hybrid having a second balanced port, a second inphase port, a third port coupled to said center conductor of a third of said coaxial lines and a fourth port coupled to said center conductor of a fourth of said coaxial lines diagonally disposed with respect to said third of said coaxial lines, said third port being responsive to said first energy having a -90.degree. phase relationship with said first energy at said first port, said fourth port being responsive to said first energy having a +90.degree. phase relationship with said first energy at said first port and said third and fourth ports simultaneously being responsive to said inphase second energy;

third means connected in common to said first and second inphase ports; and

a quadrature hybrid having a fifth port, a sixth port, a 0.degree. phase port coupled to said first balanced port and a 90.degree. phase port coupled to said second balanced port.

7. An antenna according to claim 6, wherein

said third means includes

a power divider.