Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2000-06-26
2001-05-15
Hellner, Mark (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C343S778000
Reexamination Certificate
active
06232920
ABSTRACT:
GOVERNMENT RIGHTS
Not applicable.
1. Field of the Invention
This invention relates generally to radio frequency (RF) antennas and more particularly to RF array antennas.
2. Background of the Invention
As is known in the art, a phased array antenna is a directive antenna made up of a plurality of individual radiating antenna elements, which generate a radiation pattern or antenna beam having a shape and direction determined by the relative phases and amplitudes of the excitation signal associated with the individual antenna elements. By properly varying the relative phases of the respective excitation signals, it is possible to steer the direction of the antenna beam. The radiating antenna elements may be provided as dipole antenna elements, open-ended waveguides, slots cut in waveguides, printed circuit antenna elements or any type of antenna element.
The array antenna thus includes of a number of individual radiating antenna elements suitably spaced with respect to one another. The relative amplitude and phase of the signals applied to each of the antenna elements are controlled to obtain the desired radiation pattern from the combined action of all of the antenna elements. Two common geometrical forms of array antenna are the linear array and the planar array. A linear array antenna includes a plurality of antenna elements arranged in a straight line in one dimension. A planar array antenna is a two-dimensional configuration of antenna elements arranged to lie in a plane. The planar array antenna may thus be thought of a linear array of linear array antennas.
The linear array antenna generates a fan beam when the phase relationships are such that the direction of radiation is perpendicular to the array. When the radiation is at some angle other than perpendicular to the array, the linear array antenna generates an antenna beam having a conical shape.
A two-dimensional planar array antenna having a rectangular aperture can produce an antenna beam having a fan-shape. A square or a circular aperture can produce an antenna beam having a relatively narrow or pencil shape. The array can be made to simultaneously generate many search and/or tracking beams with the same aperture.
One particular type of phased array antenna in which the relative phase shift between antenna elements is controlled by electronic devices is referred to as an electronically controlled or electronically scanned phased array antenna. Electronically scanned phased array antennas are typically used in those applications where it is necessary to shift the antenna beam rapidly from one position in space to another or where it is required to obtain information about many targets at a flexible data rate. In an electronically scanned phased array, the antenna elements, the transmitters, the receivers, and the data processing portions of the radar are often designed as a unit.
In some applications, it is desirable to provide an antenna system capable of producing multiple, independent antenna beams. Such antenna systems are advantageous in a variety of different applications such as communication satellites, ECM, ESM radar and shared aperture antennas used to accomplish simultaneously a combination of these functions. In communication satellite applications, for example, the simultaneous objectives of relatively high EIRP (Equivalent Isotropically Radiated Power) and G/T (Gain over System Temperature), wide access footprints, channelized operation and a high spectral efficiency (i.e., frequency reuse) leads to the need for multiple, independent antenna beams. It is relatively difficult to provide an electronically scanned phased array antenna capable of producing multiple independent antenna beams due to the interaction between the signals of the multiple antenna beams and the complexity of the multiple beamformer circuitry necessary to produce such multiple independent antenna beams.
The requirement for the phase array designer is made even more difficult when the operating frequency is selected to have a relatively high operating frequency in the frequency range of 20 to 30 GHz, for example, due to the corresponding decrease in the spacing between the antenna elements required for operation at that frequency. The problem is further exacerbated when it is desirable to provide a compact antenna system operating at a relatively high frequency range since the relatively small spacing between antenna elements and the need to couple feed circuits to the antenna elements result in difficult packaging requirements.
One approach to provide an antenna system having a relatively high operating frequency and multiple independent antenna beams is to utilize a lens or dish antenna which includes a separate feed circuit for each separate antenna beam. However, such an approach is relatively inflexible and it is relatively difficult to change the directions of the individual antenna beams. Thus, there is a significant interest in phased array antennas and in particular in electronically scanned phased array antennas.
It would, therefore, be desirable to provide an antenna capable of producing multiple independently steered antenna beams and which is compact, relatively low loss, and which consumes a relatively small amount of power. It would also be desirable to provide an electronically scanned phased array antenna capable of steering multiple independent antenna beams.
It would further be desirable to provide an electronically scanned phased array antenna in which failure of one phase shifter only affects one antenna beam and the one antenna element associated with the antenna beam. It would also be desired to provide an antenna in which there is no cascading of the amplitude and phase errors of phase shifters included in the phased array antenna.
SUMMARY OF THE INVENTION
In accordance with the present invention, an array antenna system for forming multiple independently steered beams includes an array of antenna elements, a first plurality of series feed signal paths each of the first plurality of series feed signal paths coupled to one of the antenna elements, a plurality of phase shifters each of the plurality of phase shifters having a first phase shifter port coupled to first ones of a plurality of couplers and with each of the first ones of the plurality of couplers disposed to couple a signal from a corresponding one of the first plurality of series feed signal paths and having a second phase shifter port coupled to second ones of the plurality of couplers with each of the second ones of the plurality of couplers disposed to couple a signal from the second phase shifter ports to a corresponding one of a second plurality of series feed signal paths and a signal combiner for combining the signals to provide one or more antenna beams.
With this particular arrangement, an antenna capable of providing multiple independent antenna beams is provided. The antenna may be provided as an electronically controlled phased array antenna which includes an electronic device for controlling a relative phase shift between antenna elements such as electronically controlled phase shifters. By disposing the phase shifters such that they are not directly in the antenna element feed circuit signal paths, the phase shifter settings for the i
th
beam are independent of that from the j
th
beam. The failure of one phase shifter only effects a single beam as a failure of only one element. Furthermore, the phase shifter amplitude and phase errors as well as losses do not cascade. Moreover, the signal from one antenna element propagates through only one phase shifter to form the antenna beam before the signals for that antenna beam are summed. Hence, the antenna is provided as a relatively low loss antenna. Finally, by appropriately arranging phase shifters and couplers in the feed circuit, coupling between the multiple antenna beams is minimized. That is, the power from beam the i
th
does not couple to beam the j
th
as it does in prior art techniques. It should be noted that the technique may be used to provide both receive and transmit array
Brookner Eli
Mather John R.
O'Shea Richard L.
Payne William J.
Sarcione Michael G.
Daly, Crowley & Mofford LLP
Hellner Mark
Raytheon Company
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