Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
2001-10-10
2002-10-22
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S081000, C342S441000
Reexamination Certificate
active
06469666
ABSTRACT:
CROSS-REFERENCE TO OTHER PATENT APPLICATIONS
Not applicable.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to antennas and, more particularly, to a digital goniometer especially suitable for controlling a steerable antenna pattern from two orthogonal antennas over the VLF/LF communications band.
(2) Description of the Prior Art
Submarine antenna systems may frequently utilize the VLF/LF communications band (8 kHz-200 kHz) by means of two magnetic loop antennas which may be referred to as a multifunction antenna. The two magnetic loop antennas are preferably identical and aligned perpendicular to each other in one housing. One loop is referred to as the Fore and Aft (F/A) antenna. The other loop is referred to as the Athwartships (ATH) antenna. The multifunction antenna does not rotate, and there are null spots where the antenna gain is near zero. Orienting this null spot toward a source of interference is desirable to reduce the received interference. Likewise, orienting the highest gain region of the antenna toward the desired signal is also desirable. Currently, an analog mechanical device is used to combine the F/A signal with the ATH signal in order to obtain the desired orientation. The mechanical device contains a stator for each loop and a rotor that can be rotated to adjust the proportional contribution of each loop. The device employs Faraday's Law of Induction for its operation. The mechanical device presently utilized is an electromechanical resolver often known as a goniometer. While goniometers may be utilized to achieve other effects and functions, a goniometer may also be utilized for steering a figure-eight antenna pattern with two identical orthogonal antennas by mechanical means.
It would be desirable to provide a more accurate, lightweight, compact, antenna goniometer that does not require elaborate external drive circuitry and has no moving parts.
Patents that show attempts to solve the above and other related problems are as follows:
U.S. Pat. No. 5,402,132, issued Mar. 28, 1995, to Hall et al., discloses a direction finding system utilizing a single monopole/crossed slot antenna in combination with associated electronic circuitry. Each of the four ports of the antenna are connected to amplitude varying elements whose outputs are combined by a power combiner. A microcontroller stores the signal. The microcontroller also generates the signals which control the amplitude variation supplied by each of the amplitude varying elements. Two configurations of the amplitude varying elements are provided by predetermined settings within the microcontroller. The two settings are selected to configure the antenna on two distinct reception patterns, each with a predetermined angular offset from a reference direction. In operation the antenna will be configured for a first reception pattern. The signals received will be detected, quantified, and stored by the microcontroller which subsequently reconfigures the antenna for a second reception pattern. A second signal is received by the antenna in the second configuration and again is detected, quantified, and stored by the microcontroller. The microcontroller determines the difference between the two signals and, based upon a predetermined calibration curve relating differences in the stored signals to the angle of arrival of the signals from the reference direction, determines the angle from which the signal arrived.
U.S. Pat. No. 6,160,519, issued Dec. 12, 2000, to Christian O. Hemmi, discloses a two-dimensionally steered antenna system including a planar lensing system operable to focus signals received from a plurality of ground-based cells. A first steering system is operable to steer a beam for each ground-based cell in a first direction by weighing signals associated with the ground-based cell based on a position of the antenna system relative to the ground-based cell in the first direction. A second steering system is operable to steer the beam for each ground-based cell in a second direction by weighing signals associated with the ground-based cell based on a position of the antenna system relative to the ground-based cell in the second direction.
U.S. Pat. No. 4,150,382, issued Apr. 17, 1979, to Ray J. King, discloses an invention which provides a guided wave antenna having a radiation pattern which can be controlled electronically, by control signals derived from a computer or any other suitable source. In this way, the directional characteristics of the antenna can be adjusted and/or scanned rapidly, without any mechanical manipulation of the antenna. In one embodiment, a guided radio wave is launched along an antenna surface having an array of elements which provide variable non-uniform surface impedance adapted to be controlled by electronic signals. For example, each variable impedance element may comprise a wave guide section having one end leading from the antenna surface. Each wave guide section may include a solid-state electronic reflection amplifier having characteristics which can be varied by supplying control signals to the amplifier, to vary the magnitude and phase angle of the wave reflected from the reflection amplifier. By changing the control signals supplied to any particular reflection amplifier, it is possible to cause attenuation or amplification and phase shift of the guided wave as it passes across the particular wave guide section. A wide variety of solid-state electronic control elements may be provided along one or more surfaces of the antenna. In another embodiment, a wave traveling in a closed subsurface wave guide is coupled into the guided wave open surface structure, using an array of wave guide elements containing electronically controllable amplifiers and phase shifters.
U.S. Pat. No. 5,714,961, issued Feb. 3, 1998, to Kot et al., discloses a directional planar antenna. The antenna has an array of coaxial ring-slot radiating elements formed through a conductive layer on a dielectric substrate. A number of probes, coupled to the ring-slot elements, selectively excite a separate resonant mode on each ring-slot element. The resonant mode supported by a ring-slot element depends upon the geometry of that ring-slot element. The resonant modes combine in the far field to form a radiation pattern directional in azimuth and elevation. By adjustment of the relative phase difference or relative amplitude between the excited modes, the radiation pattern can be steered.
The above-cited prior art does not show a suitable lightweight, compact antenna goniometer with non-moving components utilizing two orthogonal antennas that is operable for steering a figure-eight antenna pattern. Those skilled in the art will appreciate the present invention that addresses the above and other problems.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved antenna goniometer.
It is another object of the present invention to provide an antenna goniometer operable with two orthogonal antennas for steering a figure-eight antenna pattern.
An advantage of a system in accord with the present invention is an antenna goniometer that can be operated in a fully automated manner that can be controlled from software.
In accordance with the present invention, a VLF/LF communications antenna goniometer for a first antenna loop and a second antenna loop is provided that is operable for controlling an angular orientation of a figure-eight antenna reception pattern for the first antenna loop and the second antenna loop. The preferred embodiment shows first and second antennas which are orthogonal with respect to each other; however, the teachings of this invention can be applied by one of ordinary skill in the art to other antenna configurations. The goniometer comprises one or more elements such as, for instance, a first variable gain amplifier for a first signal produced utilizing the first antenna wherein the first variable gain amplifier has a first output, a first data register for storing a digital value related to a first gai
Kasischke James M.
McGowan Michael J.
Oglo Michael F.
Phan Dao
The United States of America as represented by the Secretary of
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