Inventors:
Tellier, Jacob (Dallas, TX)
Burnett, Henry G. (Dallas, TX)
Lewis, Thomas S. (Charlottesville, VA)
Application Number:
04/497571
Publication Date:
12/31/1974
Assignee:
The United States of America as represented by the Secretary of the (Washington, DC)
International Classes:
H01P1/10; H01Q3/18; H01Q25/00; H01Q3/00; H04B7/00
Field of Search:
343/100.3,100.5,100,175,176,180,756,763,761,776,781,783,839,840,843,858,864 333/1.1,24.3
US Patent References:
| 2942260 | Circularly polarized wave apparatus | June 1960 | Carter | |
| 2991473 | Scanning antenna system for horizontally and vertically polarized waves | January 1961 | Van Staaden | |
| 3013266 | Beam steering apparatus employing ferrites | December 1961 | Wheeler | |
| 3231892 | Antenna feed system simultaneously operable at two frequencies utilizing polarization independent frequency selective intermediate reflector | January 1966 | Matson | |
Primary Examiner:
Farley, Richard A.
Assistant Examiner:
Blum T. M.
Attorney, Agent or Firm:
Herbert Jr., Harry Killoren Richard A. J.
Claims:
We claim
1. In an antenna, for providing lobing on receive on track only for a radio-frequency signal with a predetermined polarization, having a reflector; a center feed; means for supporting said center feed in front of said reflector; a transmit splash plate on the end of said center feed; a serrated receive ring surrounding said transmit splash plate; a trislot TR tube mounted on said center feed in energy receiving relation to said receiving ring; said trislot transmit-receive tube having a circular window on the side thereof remote from said transmitter splash plate; means adjacent said circular window of said trislot transmit-receive tube, adapted to be switched between two predetermined angular positions, for presenting a short at the trislot tube input to said radio-frequency signal in one position and for presenting an open circuit at the trislot tube input, to said radio-frequency signal to effect modulation of the receive signal by said trislot transmit-receive tube in the other position and means for selectively switching said last named means between said two predetermined positions.
2. In an antenna, for providing lobing on receive on track only for a radio-frequency signal with a predetermined polarization, having a reflector; a center feed; means for supporting said center feed in front of said reflector; a transmit splash plate on the end of said center feed; a serrated receive ring surrounding said transmit splash plate; a trislot transmit-receive tube mounted on said center feed in energy receiving relation to said receiving ring; said trislot transmit-receive tube having a circular window on the side thereof remote from said transmitter splash plate; a circular waveguide stub having an open end adjacent said circular window of said trislot transmit-receive tube and a closed end spaced a predetermined distance from said trislot tube to present an open circuit at the trislot tube input, to said radio-frequency signal, to effect modulation of the receive signal by said trislot transmit-receive tube; a grid, having a plurality of parallel wires, within said waveguide stub and spaced from said trislot tube by a predetermined distance; means for rotating said stub and said grid between two predetermined angular positions, to present a short at the trislot tube input in one position of said grid and an open circuit at the trislot tube input to said radio frequency signal in the other position of said grid; and an attenuation means within said waveguide stub for attenuating undesired received signals.
3. In an antenna, for providing lobing on receive on track only for a radio-frequency signal with a predetermined polarization, having a reflector; a center feed; means for supporting said center feed in front of said reflector; a transmit splash plate on the end of said center feed; a serrated receive ring surrounding said transmit splash plate; a trislot transmit-receive tube mounted on said center feed in energy receiving relation to said receiving ring; said trislot transmit-receive tube having a circular window on the side thereof remote from said transmitter splash plate; a circular waveguide stub having an open end adjacent said circular window of said trislot transmit-receive tube and a closed end spaced a predetermined distance from said trislot tube to present an open circuit at the trislot tube input to said radio-frequency signal to effect modulation of the receive signal by said trislot transmit-receive tube; a grid, having a plurality of parallel wires, within said waveguide stub and spaced from said trislot tube by a predetermined distance; means including a push-pull solenoid drive for rotating said stub and said grid between two predetermined angular positions, to present a short at the trislot tube input in one position of said grid and an open circuit at the trislot tube input to said radio-frequency signal in the other position of said grid; an attenuation means within said waveguide stub for attenuating undesired received signals; and means for supporting said attenuation means in a fixed angular position, as said waveguide stub is rotated.
4. In combination with an antenna, for providing lobing on receive on track only for a radio-frequency signal with a predetermined polarization, having: a reflector; a center feed; means for supporting said center feed in front of said reflector; a transmit splash plate on the end of said center feed; a transmitreceive arm connected to said center feed; a serrated receive ring surrounding said transmit splash plate; a trislot transmit-receive tube mounted on said center feed in energy receiving relation to said receiving ring; said trislot transmit-receive tube having a circular window on the side thereof remote from said transmitter splash plate; a device for reacting on the beam being received through said center feed, comprising: a circular waveguide stub having an open end adjacent said circular window of said trislot transmit-receive tube and a closed end spaced a predetermined distance from said trislot tube to present an open circuit at the trislot tube input to said radio-frequency signal to effect modulation of the receive signal by said trislot transmit-receive tube; a grid, having a plurality of parallel wires, within said waveguide stub and spaced from said trislot tube by a predetermined distance to present a short at the trislot tube input; means for rotating said stub and said grid between two predetermined angular positions, to present a short at the trislot tube input in one position of said grid and an open circuit at the trislot tube input to said radio-frequency signal in the other position of said grid; an attenuation means within said waveguide stub for attenuating undesired received signals; and means for supporting said attenuation means in a fixed angular position, as said waveguide stub is rotated.
Description:
This invention relates to an improved Lobe-on-Receive-on-Track-Only antenna which will hereinafter be referred to as a LOROTO antenna.
One object of the invention is to provide a LOROTO antenna requiring fewer components than prior art structure.
Another object of the invention is to provide a LOROTO antenna which incorporates a method for defeating circularly polarized jammers.
These and other objects will be more fully understood from the following detailed description taken with the drawing, wherein:
FIG. 1 is a partially schematic plan view of a prior LOROTO antenna;
FIG. 2 is a partially schematic plan view of a LOROTO antenna according to this invention;
FIG. 3 is an enlarged view, partially in section, of the modified antenna feed system of the device of FIG. 2;
FIG. 4 is a top view of the feed system of FIG. 3;
FIG. 5A is a schematic cross-sectional view of the short line unit of the device of FIG. 3 in the search mode;
FIG. 5B is an end view of the short line unit of FIG. 5A;
FIG. 5C shows the quadrative components of circular polarization as related to the position of the tuning stub in FIGS. 5A and 5B;
FIG. 6A is a schematic cross-sectional view of the short line unit of the device of FIG. 3 in the track mode;
FIG. 6B is an end view of the short line unit of FIG. 6A; and,
FIG. 6C shows the quadrative components of circular polarization as related to the position of the tuning stub in FIGS. 6A and 6B.
One form of prior art LOROTO antenna to which this invention applies is shown in FIG. 1. In these systems lobing action takes place only during track operation and not during search operation and then only on receive-track. This antenna has a reflector 10, a center feed 12, transmit-receive-search arm 13, a receive track arm 14, and a plurality of feed support rods, one of which is shown at 15. The center feed terminates in a Teflon mushroom 16 and a serrated transmit splash plate 17, shown in greater detail in FIG. 3. A trislot pre-TR tube 18, is connected between the serrated receive ring 19, shown in greater detail in FIG. 3, and the receive track arm 14. The pre-TR tube 18 has three energy receiving windows 28, two of which are shown, and an energy exit window 29 shown in FIG. 3. The choke ring 20 provides a primary pattern shaping element. A feedome 21 is provided around the antenna center feed. Rotation of the center feed is provided by means of a spin motor 23.
It is evident in FIGS. 1 and 2 that energy from space collimated by the reflector and received at the primary radiator structure will be split between the receive ring and the transmit splash plate in some proportion. The choke ring may be said to be a primary pattern shaping element. To effect efficient receive performance on the original lobing system, not shown, an ATR device was used in the transmit arm, as shown in FIG. 1, which was properly phased by a phase shift element 27 so as to present a short at the transmit splash plate entrance 17 so that essentially all the energy received from space would enter the receive ring, where it was modulated by the spinning trislot junction, and would pass back to the receiver through the receive track arm. On transmit, the high power would fire the pre-TR 18 so that the trislot junction would appear as a solid cylinder and no lobing would be effected. This basic scheme was revised in the prior art device shown in FIG. 1 accomplishing LOROTO by changing the ATR tube to an ATR-AATR device 22 and adding the shorting switch 25 and phase shifter 26. In this device on receive search, the shorting switch is closed, the ATR tube 22 is switched to AATR position and phase shifter 26 is used to present a short at the trislot input in the unfired state. This shorts out the receive ring so that the receive search energy passes through the transmit arm 12. For track operation, the ATR-AATR device and the shorting switch are switched and the system again works as described above. Some of the difficulties with this design are the long line lengths to the shorting devices which make tuning supersensitive, the aperture blocking the receive track arm, and the multiplicity of components required.
The trislot junction may be used either as a transmission or as a reactive device. In the prior art device, since the tracking energy is received through the trislot, the trislot may be said to be in transmission. An equally effective scheme can be devised by properly terminating the trislot output with a stub so that the action of the trislot reacts on the beam as being received through the on-center feed.
According to this invention, a mechanization of the reactive trislot concept is shown in FIG. 2. Two stub lengths are required: (1) to present a short at the trislot input for receive search operation; and, (2) to present an open circuit at the trislot input to effect modulation on receive track. The mechanism used to achieve the two stub lengths is a circular waveguide which is polarization insensitive. A polarization sensitive element is placed at a point to present a first short and the end of the circular stub is the second short plane. This polarization sensitive element is a grid of parallel wires. When the wires are parallel to the impinging E vector, a short circuit is presented. If the grid is rotated 90°, the wires act only as a septum and have no effect. Thus the track arm 14, shorting switch 25, ATR-AATR device 22, and the phase shifters 26 and 27 are made unnecessary.
As shown in greater detail in FIG. 3, the track arm is replaced by a short tuning stub 30 placed adjacent the circular window 29 of the trislot TR tube 18. The tuning stub 30 has a polarization sensitive grid 31, with a plurality of parallel wires 32, located therein. An attenuation card 33 is supported on a support plate 34, in any well-known manner such as with an adhesive. The stub 30 is supported for rotation in bearings 37 and 38. A stub driving lever 40 is driven by a rod 41 which passes through hollow support rod 42 which is operated by push-pull solenoid device 43, shown in block form in FIG. 2. The support plate 34 is secured to a support spider 44 by a rectangular bolt 45 and nut 46 to prevent rotation of the card as the stub is rotated. Other means to prevent rotation of the card with the stub could also be provided. The remainder of the structure, except for the parts eliminated, is the same as in the prior art device of FIG. 1.
In the operation of the device in the receive search mode of operation, the tuning stub 30 is located to position the wires 32 parallel to the impinging E vector and a short is presented so that the energy is not coupled to the trislot tube, resulting in a nonlobing mode of operation. On track the solenoid drive 43 is operated to rotate the grid 31, 90° to position the wires 32 perpendicular to the impinging E vector so that it is invisible to the properly polarized energy. The back wall 35 of the stub 30 is positioned to provide the proper coupling between the center feed and the trislot tube, resulting in a lobing mode on track. The position of the grid and back wall can be determined experimentally.
The polarization of a circularly polarized jammer may be thought of as two components displaced by 90° as shown in FIGS. 5C and 6C.
With the grid in the track position, component (b) will be rejected (not coupled to the trislot). Component (a) will be coupled to the trislot, but since it is not cross polarized in respect to the transmitted energy, it will not result in a phase error at the reference generator of the antenna.
With the grid in the search position, component (a) will be rejected from the trislot. By means of the RF attenuator card 33, component (b) can be absorbed without affecting the required polarization.
There is thus provided a LOROTO antenna requiring fewer components than prior art devices which thus simplifies some of the design difficulties.
Though a certain specific embodiment has been described, it is obvious that numerous changes may be made without departing from the general principle and scope of the invention.