Patent Application
20110215979
(Not Applicable)
(Not Applicable)
This invention relates to communication antennas and methods and, more specifically, to antennas and methods suitable for omnididrectional reception and transmission of circularly polarized signals.
Many forms of antennas capable of omnidirectional operation with circular polarization have previously been described. However, for applications such as battlefield discrimination between friendly and unfriendly vehicles and other platforms there is a need for small, economical and efficient antennas capable of reliably receiving and transmitting information suitable for platform identification purposes and additional communication purposes as may be appropriate.
Objects of the present invention are, therefore, to provide new and improved antennas and methods suitable for reception and transmission via onmidirectional circularly polarized antenna patterns.
In accordance with the invention, an embodiment of an antenna providing an omnidirectional antenna pattern includes a cylindrical structure, which may have the form of a closed-end coaxial line section, a center conductor, which may be the center conductor of the coaxial line section, and upper and lower disk members, which may form a radial waveguide radiator. The cylindrical structure may have a square-pipe cylindrical side portion including four slanted openings forming slot radiators, one in each side of the square-pipe configuration. The upper and lower disk members may extend in parallel relation outward from the coaxial line section forming the radial waveguide radiator which is arranged to receive excitation from the coaxial line section, via the four slot radiators. The radial waveguide radiator may be configured to provide an omnidirectional right-hand circularly polarized antenna pattern.
Also in accordance with the invention, a method, for providing an omnidirectional circularly polarized antenna pattern, may include the steps of:
(a) energizing a closed-end coaxial line section having a center conductor and an outer conductor;
(b) responsive to step (a), exciting a radiation pattern external to the coaxial line section via a plurality of slanted radiator slots in the outer conductor; and
(c) responsive to step (b) exciting a radial waveguide radiator, formed by upper and lower disks extending outward in parallel relation from the outer conductor respectively above and below the radiator slots, to provide an omnidirectonal circularly polarized antenna pattern.
In step (c) of the method, responsive to step (b) horizontal TE mode and vertical TEM mode components may be excited to arrive at the outer circumference of the upper and lower disks with a 90 degree phase differential to provide an omnidirectional right hand circularly polarized antenna pattern.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.
The antenna 10 of
The antenna also includes a center conductor 40 extending within cylindrical structure 20 along its center axis. Center conductor is supported within, but electrically isolated from, cylindrical structure 20. As represented in
The antenna, as illustrated, further includes upper and lower disk members 62 and 64 extending in parallel relation outward from side portion 22 of the cylindrical structure 20 respectively above and below the slanted openings 30. While disk members 62 and 64 are illustrated as having a twelve-sided perimeter, in production this perimeter may desirably be circular.
In use, the antenna may be coupled to a receiver/transmitter configuration, such as transponder or interrogator/transponder equipment of the type used for IFF (Identification Friend or Foe) operations. Thus, a given battlefield platform may merely provide a coded reply to an identification query or may also have the capability to interrogate other platforms for identification purposes. Other communication capabilities may also be provided utilizing the antenna.
Referring now to
When energized, cylindrical structure 20 excites a radiation pattern external to the coaxial line section (i.e., external to outer conductor 22) via the slanted openings 30, referred to alternatively as slot radiators 30. Thus, the slanted openings have the form of slot radiating elements (slot radiators) inclined at nominally 50 degrees relative to the center axis and are effective to excite a radiation pattern between the upper and lower disk members 62 and 64. In this configuration, the slot radiators 30 may have a length of nominally 0.4 wavelength at an operating frequency, with a width which is small relative to that length, as illustrated. For present purposes, the term “an operating frequency” is defined as a frequency within an operating bandwidth of the antenna.
The slot radiators 30 are effective to excite vertical and horizontal field components in the space between the disk members. The propagation constant for the vertical component (TEM mode) is near that of free space, while waveguide propagation (TE mode) is characteristic of the horizontal component. As a result, the horizontal component advances relative to the vertical component during propagation toward the outer edges of the disks. The configuration of the radial waveguide extending between the disks, and particularly the radius (determined by the disk diameter) of that waveguide, is specified so that the phase of the horizontal component leads that of the vertical component by 90 degrees at the outer circumference of the radial waveguide (i.e., at the disk perimeter edge). In this way, the radial waveguide is excited, in response to the radiation pattern of the slot radiators, to provide an omnidirectional circularly polarized antenna pattern and, more particularly, such a pattern of right-hand circular polarization. While signal transmission terminology may be used for convenience of description, it will be understood that antenna components operate reciprocally to provide excitation to enable received signals to be provided to the input/output port, as well as to enable transmission of signals provided to that port.
Consistent with the foregoing,
At 72, energizing a closed-end coaxial line section 20 having a center conductor 40 and an outer conductor 22 including a plurality of slot radiators 30.
At 74, responsive to energizing the coaxial line section 20, exciting a radiation pattern external thereto via the slot radiators 30.
At 76, responsive to the slot radiator radiation pattern, exciting a radial waveguide radiator, formed by upper and lower disks 62 and 64 extending outward in parallel relation from outer conductor 22, to provide an omnidirectional circularly polarized antenna pattern.
The antenna in this embodiment is double tuned. The coaxial cavity provided by coaxial line section 20 forms one tuned circuit. The Q of this coaxial cavity is controlled by the impedance level of the coaxial line. The radial waveguide (e.g., as shown in
Computed elevation and azimuth antenna patterns are shown in
By way of example, for a particular design of an antenna of the form shown in
antenna height: 0.30 inches
antenna width: 0.73 inches
slot length: 0.14 inches
slot angle 40 degrees to horizontal
Contained within a very small package, the antenna may additionally include a protective radome or cover of suitable transmissive properties, for weather and damage protection, and an antenna mounting arrangement, as may be provided by skilled persons employing known design techniques.
While there have been described currently preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made without departing from the invention and it is intended to claim all modifications and variations as fall within the scope of the invention.
