US3422436A - Omnidirectional retrodirective antenna - Google Patents

Description

Jan. 14, 1969 A. E. MARSTON 3,422,436

OMNIDIRECTIONAL RETRODIRECTIVE ANTENNA Filed Jan. 17, 1966 mpmsms PLANE PHASE FRONT"' \J CIRGULATOR INVENTOR ARTHUR E. MARSTON BY M ATTORNEY 3,422,436 OMNIDIRECTIONAL RETRODIRECTIVE ANTENNA Arthur E. Marston, Alexandria, Va., assignor to the United States of America as represented by the Secretary of the Navy Filed Jan. 17, 1966, Ser. No. 521,220 [1.5. Cl. 343-754 Int. Cl. H01q 19/06; H01q 13/00; H0111 3/26 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates generally to improvements in retrodirective antennas and the like and more particularly to new and improved retrodirective antennas whereby a signal can be received from any direction and re-radiated back in that direction to the exclusion of all other directions.

In the field of retrodirective antennas and reflectors it has been the general practice to employ devices which are passive, such as Luneberg lenses or corner reflectors, to reradiate received signals back in the direction from which they came. Where it has been desired to amplify the reradiated signal, to shift its frequency, or to impress some intelligence on it, the device has generally taken the form of an antenna having wide-angle scanning properties. Although such devices have served the purpose they have not proved entirely satisfactory under all conditions of service for the reasons that such devices do not operate over all 360 in azimuth, and are not capable of receiving a signal from any direction and reradiating that signal back toward the direction from which the signal originated, to the exclusion of all other directions.

The general purpose of this invention is to provide a retrodirective antenna which embraces all of the advantages of similarly employed prior art devices and possesses none of the aforedescribed disadvantages. To attain this the present invention contemplates a unique arrangement of three-port circulators, electromagnetic energy refraction devices, such as Luneberg lenses, and a circular focusing antenna array, whereby a signal can be received from any direction in azimuth and reradiated back exclusively in the direction from which it came, and whereby the signal can be received and reradiated with a receiving and transmitting gain comparable to the gain of a focusing antenna of similar physical dimensions. The present invention also provides for a true antenna as opposed to a passive reflector, thus allowing the impression of intelligence on the reradiated signal.

An object of the present invention is the provision of a retrodirective antenna capable of receiving signals from all 360 in azimuth.

Another object is to provide such a device that will reradiate a signal received from any direction in azimuth back in that direction only.

A further object of the invention is the provision of an omnidirectional retrodirective antenna which will nited States Patent F 3,422,436 Registered Jan. 14, 1969 ice receive and transmit with a gain comparable to the gain of a focusing antenna of similar physical dimensions.

Still another object is to provide a retrodirective antenna which is capable of receiving signals from any direction in azimuth and which will reradiate the signal back exclusively in the direction from which the signal originated while beng able to impress intelligence on the reradated signal.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following description of a preferred embodiment of the invention as illustrated in the accompanying sheet of drawing in which:

The figure shOWs a perspective view of one embodiment of the invention with some electrical connections not shown for the purpose of clarity.

Referring now to the drawing there is shown in the figure a complete circular ring 4 of receiving and radiating focusing elements, such as wave-guide horns, some of which elements are designated as 5-9 and 15-19. Each of the elements in the ring 4 is electrically connected to one port of a three-port circulator, as exemplified in the figure by the connections between elements 5-9 and circulators 21-25, and between elements 15-19 and circulators 27-31, respectively.

Each of the circulators, in turn, is electrically connected, by means of its remaining two ports, to two stacked Lune- berg lenses 35 and 36, each of which has a diameter equal to the diameter of the ring 4.

As exemplified in the figure, circulators 21-25 and 27-31 are electrically connected to Luneberg lens 35 by means of ports 5'-9' and by means of ports 15'-19', respectively, and circulators 21-25 and 27-31 are electrically connected to Luneberg lens 36 by means of ports 5"-9" and 15-19", respectively. The electrical lengths of the connections between each of the receiving and radiating focusing elements and their respective circulators must be uniform with respect to each other, as must be the electrical lengths between each circulator and each Luneberg lens.

In the operation of the retrodirective antenna, an electromagnetic wave is received, for example, by the receiving and radiating elements 15-19, and the energy from this incident wave is routed from each focusing element 15-19 through equal-length electrical connections, to circulators 27-31, respectively. The energy is then directed, by circulators 27-31, through another set of equal-length electrical connections to the lower Luneberg lens 36. A Luneberg lens, e.g., lens 36, has the property that when energy from a plane wave is incident and is received by the ports 1 5"-19", the energy is focused down to a port 7" on the opposite side of the lens 36. The energy then exits from port 7" and is routed by circulator 23 upwards to the upper lens 35 and to port 7', where the energy is reformed by the action of lens 35 into a wave which exits the lens 35 at ports 15'-19'. The energy of this wave is then routed through equal-length electrical connections to circulators 27-31, which in turn, direct the energy through equallength electrical connections to radiating elements 15-19, respectively. The energy then leaves the antenna, as a plane wave, aimed back exclusively in the direction of incidence. It is obvious, from the circular symmetry of the antenna, that this will work for all angles of arrival, and it is also apparent that because the received signal is transmitted through transmission lines it is possible to impress a piece of intelligence upon that signal if it so desired.

It can, therefore, be seen that the invention very efiectively provides an omnidirectional retrodirective antenna which can receive a signal from any direction in azimuth and which can reradiate that signal, or a modified form of that signal, back exclusively in the direction from which the signal originated. This can be accomplished while providing a power gain comparable to that achieved by a focusing antenna of similar physical dimensions.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. In an omnidirectional, retrodirective antenna, the combination comprising:

receiving and radiating elements,

first and second signal delay means each having a plurality of ports connected thereto and being equal in number to the number of receiving and radiating elements,

a plurality of nonreciprocal switches,

each of said receiving and radiating elements being connected to a respective port on each delay means by a separate nonreciprocal switch to direct received signals sequentially through both delay means and then back to the same elements at which the signals were received for reradiation.

2. The combination of claim 1 wherein said receiving and radiating elements comprise wave-guide horns.

3. The combination of claim 1 wherein said receiving and radiating elements are oriented in a complete circular ring.

4. The combination of claim 3 wherein said first and second delay means each comprise a circular Luneberg lens.

5. The combination of claim 4 wherein the diameter of each of said Luneberg lenses is equal to the diameter of said circular ring.

6. The combination of claim 1 wherein said nonreciprocal switches are three-port circulators.

7. The combination of claim 6 wherein each of said receiving and radiating elements is connected to its respective circulator by equal-length electrical connections 8. The combination of claim 7 wherein each of said circulators is connected to said refraction means by equal-length electrical connections.

References Cited UNITED STATES PATENTS 3,170,158 2/1965 Rotman 343753 3,230,536 1/1966 Cheston -a 343-754 3,259,902 7/1966 Malech 343753 3,354,461 11/1967 Kelleher 343-854 ELI LIEBERMAN, Primary Examiner.

US. Cl. X.R. 343-777, 854

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