Abstract:
A beam-forming antenna for transmission and/or reception of an electromagnetic signal having a given wavelength in a surrounding medium includes a transmission line electromagnetically coupled to an array of individually controllable antenna elements, each of which is oscillated by the signal with a controllable amplitude. The antenna elements are arranged in a linear array and are spaced from each other by a distance that does not exceed one-third the signal&#39;s wavelength in the surrounding medium. The oscillation amplitude of each of the individual antenna elements is controlled by an amplitude controlling device, such as a switch, a gain-controlled amplifier, or a gain-controlled attenuator. The amplitude controlling devices, in turn, are controlled by a computer that receives as its input the desired beamshape, and that is programmed to operate the amplitude controlling devices in accordance with a set of stored amplitude values derived empirically for a set of desired beamshapes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 11/201,680, filed Aug. 11, 2005, now U.S. Pat. No. 7,456,787 entitled BEAM-FORMING ANTENNA WITH AMPLITUDE-CONTROLLED ANTENNA ELEMENTS, the disclosure of which is hereby incorporated by reference as if set forth in full herein. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to the field of directional antennas for transmitting and/or receiving electromagnetic radiation, particularly (but not exclusively) microwave and millimeter wavelength radiation. More specifically, the invention relates to a composite beam-forming antenna comprising an array of antenna elements, wherein the shape of the transmitted or received beam is determined by controllably varying the effective oscillation amplitude of individual antenna elements. In the context of this invention, the term “beam shape” encompasses the beam direction, which is defined as the angular location of the power peak of the transmitted/received beam with respect to at least one given axis, the beamwidth of the power peak, and the side lobe distribution of the beam power curve. 
     Beam-forming antennas that allow for the transmission and/or reception of a highly directional electromagnetic signal are well-known in the art, as exemplified by U.S. Pat. No. 6,750,827; U.S. Pat. No. 6,211,836; U.S. Pat. No. 5,815,124; and U.S. Pat. No. 5,959,589. These exemplary prior art antennas operate by the evanescent coupling of electromagnetic waves out of an elongate (typically rod-like) dielectric waveguide to a rotating cylinder or drum, and then radiating the coupled electromagnetic energy in directions determined by surface features of the drum. By defining rows of features, wherein the features of each row have a different period, and by rotating the drum around an axis that is parallel to that of the waveguide, the radiation can be directed in a plane over an angular range determined by the different periods. This type of antenna requires a motor and a transmission and control mechanism to rotate the drum in a controllable manner, thereby adding to the weight, size, cost and complexity of the antenna system. 
     Other approaches to the problem of directing electromagnetic radiation in selected directions include gimbal-mounted parabolic reflectors, which are relatively massive and slow, and phased array antennas, which are very expensive, as they require a plurality of individual antenna elements, each equipped with a costly phase shifter. 
     There has therefore been a need for a directional beam antenna that can provide effective and precise directional transmission as well as reception, and that is relatively simple and inexpensive to manufacture. 
     SUMMARY OF THE INVENTION 
     Broadly, the present invention is a reconfigurable, directional antenna, operable for both transmission and reception of electromagnetic radiation (particularly microwave and millimeter wavelength radiation), that comprises a transmission line that is electromagnetically coupled to an array of individually controllable antenna elements, each of which is oscillated by the transmitted or received signal with a controllable amplitude. 
     More specifically, for each beam-forming axis, the antenna elements are arranged in a linear array and are spaced from each other by a distance that is no greater than one-third the wavelength, in the surrounding medium, of the transmitted or received radiation. The oscillation amplitude of each of the individual antenna elements is controlled by an amplitude controlling device that may be a switch, a gain-controlled amplifier, a gain-controlled attenuator, or any functionally equivalent device known in the art. The amplitude controlling devices, in turn, are controlled by a computer that receives as its input the desired beamshape, and that is programmed to operate the amplitude controlling devices in accordance with a set of stored amplitude values derived empirically, by numerical simulations, for a set of desired beamshapes. 
     As will be more readily appreciated from the detailed description that follows, the present invention provides an antenna that can transmit and/or receive electromagnetic radiation in a beam having a shape and, in particular, a direction that can be controllably selected and varied. Thus, the present invention provides the beam-shaping control of a phased array antenna, but does so by using amplitude controlling devices that are inherently less costly and more stable than the phase shifters employed in phased array antennas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a beam-forming antenna in accordance with the present invention, in which the antenna is configured for transmission; 
         FIG. 2  is a schematic view of a beam-forming antenna in accordance with the present invention, in which the antenna is configured for reception; 
         FIG. 3  is a schematic view of a beam-forming antenna in accordance with the present invention, in which the antenna is configured for both transmission and reception; 
         FIG. 4  is a schematic diagram of a beam-forming antenna in accordance with the present invention, in which the spacing distances between adjacent antenna elements are unequal; 
         FIG. 5  is a schematic diagram of a plurality of beam-forming antennas in accordance with the present invention, wherein the antennas are arranged in a single plane, in parallel rows, to provide beam-shaping in three dimensions; 
         FIG. 6   a  is a first exemplary far-field beam shape produced by a beam-forming antenna in accordance with the present invention, wherein α denotes the azimuth angle; and  FIG. 6   b  is a graph of the RF power distribution for the array of antenna elements that results in the beam shape of  FIG. 6   a;    
         FIG. 7   a  is a second exemplary far-field beam shape produced by a beam-forming antenna in accordance with the present invention, wherein a denotes the azimuth angle; and  FIG. 7   b  is a graph of the RF power distribution for the array antenna elements that results in the beam shape of  FIG. 7   a;    
         FIG. 8   a  is a third exemplary far-field beam shape produced by a beam-forming antenna in accordance with the present invention, wherein α denotes the azimuth angle; and  FIG. 8   b  is a graph of the RF power distribution for the array of antenna elements that results in the beam shape of  FIG. 8   a;    
         FIG. 9   a  is a fourth exemplary far-field beam shape produced by a beam-forming antenna in accordance with the present invention, wherein a denotes the azimuth angle; and  FIG. 9   b  is a graph of the RF power distribution for the array of antenna elements that results in the beam shape of  FIG. 9   a;    
         FIG. 10   a  is a fifth exemplary far-field beam shape produced by a beam-forming antenna in accordance with the present invention, wherein α denotes the azimuth angle; and  FIG. 10   b  is a graph of the RF power distribution for the array of antenna elements that results in the beam shape of  FIG. 10   a;    
         FIG. 11   a  is a sixth exemplary far-field beam shape produced by a beam-forming antenna in accordance with the present invention, wherein α denotes the azimuth angle; and  FIG. 11   b  is a graph of the RF power distribution for the array of antenna elements that results in the beam shape of  FIG. 11   a ; and 
         FIGS. 12-14  are graphs of exemplary far-field power distributions produced in three dimensions by a 2-dimensional beam-forming antenna in accordance with the present invention, wherein α represents azimuth and β represents elevation, and wherein the power contours on the graph are measured in dB. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 ,  2 , and  3  respectively illustrate three configurations of a beam-forming antenna in accordance with a broad concept of the present invention. As will be described in more detail below, the beam-forming antenna in accordance with the present invention comprises at least one linear array of individual antenna elements, each of which is electromagnetically coupled to a transmission line through an amplitude controlling device, wherein the antenna elements are spaced from each other by a spacing distance that is less than or equal to one-third the wavelength, in the surrounding medium, of the electromagnetic radiation transmitted and/or received by the antenna. As shown in  FIGS. 1 ,  2 , and  3 , the spacing distances between each adjacent pair of antenna elements may advantageously be equal, but as discussed below with respect to  FIG. 4 , these spacing distances need not be equal. 
     More specifically,  FIG. 1  illustrates a beam-forming antenna  100  configured for transmitting a shaped beam of electromagnetic radiation in one direction (i.e., along one linear axis). The antenna  100  comprises a linear array of individual antenna elements  102 , each of which is coupled (by means such as a wire, a cable, or a waveguide, or by evanescent coupling) to a transmission line  104 , of any suitable type known in the art, that receives an electromagnetic signal from a signal source  106 . The phase velocity of the electromagnetic signal in the transmission line  104  is less than the phase velocity in the medium (e.g., atmospheric air) in which the antenna  100  is located. Each of the antenna elements  102  is coupled to the transmission line  104  through an amplitude controlling device  108 , so that the signal from the transmission line  104  is coupled to each of the antenna elements  102  through an amplitude controlling device  108  operatively associated with that antenna element  102 . 
       FIG. 2  illustrates a beam-forming antenna  200  configured for receiving electromagnetic radiation preferentially from one direction. The antenna  200  comprises a linear array of individual antenna elements  202 , each of which is coupled to a transmission line  204  that feeds the electromagnetic signal to a signal receiver  206 . Each of the antenna elements  202  is coupled to the transmission line  204  through an amplitude controlling device  208 , so that the signal from each of the antenna elements  202  is coupled to the transmission line  204  through an amplitude controlling device  208  operatively associated with that antenna element  202 . The antenna  200  is, in all other respects, similar to the antenna  100  of  FIG. 1 . 
       FIG. 3  illustrates a beam-forming antenna  300  configured for both receiving a beam of electromagnetic radiation preferentially from one direction, and transmitting a shaped beam of electromagnetic radiation in a preferred direction. The antenna  300  comprises a linear array of individual antenna elements  302 , each of which is coupled to a transmission line  304  that, in turn, is coupled to a transceiver  306 . Each of the antenna elements  302  is coupled to the transmission line  304  through an amplitude controlling device  308 , so that signal coupling between each antenna element  302  and the transmission line  304  is through an amplitude controlling device  308  operatively associated with that antenna element  302 . The antenna  300  is, in all other respects, similar to the antennas  100  and  200  of  FIGS. 1 and 2 , respectively. 
     The amplitude controlling devices  108 ,  208 ,  308 , of the antennas  100 ,  200 ,  300 , respectively, may be switches, gain-controlled amplifiers, gain-controlled attenuators, or any suitable, functionally equivalent devices that may suggest themselves to those skilled in the pertinent arts. The electromagnetic signal transmitted and/or received by each antenna element  102 ,  202 ,  302  creates an oscillating signal within the antenna element, wherein the amplitude of the oscillating signal is controlled by the amplitude controlling device  108 ,  208 ,  308  operatively associated with that antenna element. The operation of the amplitude controlling devices, in turn, is controlled by a suitably programmed computer (not shown), as will be discussed below. 
       FIG. 4  illustrates a beam-forming antenna  400 , in accordance with the present invention, comprising a linear array of antenna elements  402  coupled to a transmission line  404  through an amplitude controlling device  408 , as described above. In this variant of the invention, however, each adjacent pair of antenna elements  402  is separated by a spacing distance a 1  . . . a N , wherein the spacing distances may be different from each other, as long as all are less than or equal to one-third the wavelength of the electromagnetic signal in the surrounding medium, as mentioned above. The spacing distances may, in fact, be arbitrarily distributed, as long as this maximum distance criterion is met. 
       FIG. 5  illustrates a two-dimensional beam-forming antenna  500  that provides beam-shaping in three dimensions, the beam&#39;s direction being typically described by an azimuth angle and an elevation angle. The antenna  500  comprises a plurality of linear arrays  510  of individual antenna elements  512 , wherein the arrays  510  are arranged in parallel and are coplanar. Each array  510  is coupled with a transmission line  514 , and the transmission lines  514  are connected in parallel to a master transmission line  516  so as to form a parallel transmission line network. Each antenna element  512  is coupled to its respective transmission line  514  through an amplitude controlling device  518 . The phase of the signal fed to each of the transmission lines  514  is determined by the location on the master transmission line  516  at which each transmission line is coupled to the master transmission line  516 . Thus, as shown in  FIG. 5 , in one specific example, a first phase value is provided by coupling the transmission lines  514  to the master transmission line  516  at a first set of coupling points  520 , while in a second specific example, a second phase value may be provided by coupling the transmission lines  514  to the master transmission line  516  at a second set of coupling points  520 ′ (shown at the ends of phantom lines). Each linear array  510  is constructed in accordance with one of the configurations described above with respect to  FIGS. 1-4 . As an additional structural criterion, in the two-dimensional configuration, the distance between adjacent arrays  510  is less than or equal to one-half the wavelength, in the surrounding medium, of the electromagnetic signal transmitted and/or received by the antenna  500 . 
       FIGS. 6   a ,  6   b  through  11   a ,  11   b  graphically illustrate exemplary beam shapes produced by an antenna constructed in accordance with the present invention. In general, as mentioned above, the amplitude controlling devices, be they switches, gain-controlled amplifiers, gain-controlled attenuators, or any functionally equivalent device, are controlled by a suitably-programmed computer (not shown). The computer operates each amplitude controlling device to provide a specific signal oscillation amplitude in each antenna element, whereby the oscillation amplitudes that are distributed across the element antenna array produce the desired beam shape (i.e., power peak direction, beam width, and side lobe distribution). 
     One specific way of providing computer-controlled operation of the amplitude controlling devices is to derive empirically, by numerical simulation, sets of amplitude values for the antenna element array that correspond to the values of the beam shape parameters for each desired beam shape. A look-up table with these sets of amplitude values and beam shape parameter values is then created and stored in the memory of the computer. The computer is programmed to receive an input corresponding to the desired beam shape parameter values, and then to generate input signals that represent these values. The computer then looks up the corresponding set of amplitude values. An output signal (or set of output signals) representing the amplitude values is then fed to the amplitude controlling devices to produce an amplitude distribution along the array that produces the desired beam shape. 
     A first exemplary beam shape is shown in  FIG. 6   a , having a peak P 1  at about −50° in the azimuth, with a moderate beam width and a side lobe distribution having a relatively gradual drop-off. The empirically-derived oscillation amplitude distribution (expressed as the RF power for each antenna element i) that produces the beam shape of  FIG. 6   a  is shown in  FIG. 6   b.    
     A second exemplary beam shape is shown in  FIG. 7   a , having a peak P 2  at about −20° in the azimuth, with a narrow beam width and a side lobe distribution having a relatively steep drop-off. The empirically-derived oscillation amplitude distribution that produces the beam shape of  FIG. 7   a  is shown in  FIG. 7   b.    
     A third exemplary beam shape is shown in  FIG. 8   a , having a peak P 3  at about 0° in the azimuth, with a narrow beam width and a side lobe distribution having a relatively steep drop-off. The empirically-derived oscillation amplitude distribution that produces the beam shape of  FIG. 8   a  is shown in  FIG. 8   b.    
     A fourth exemplary beam shape is shown in  FIG. 9   a , having a peak P 4  at about +10° in the azimuth, with a moderate beam width and a side lobe distribution having a relatively steep drop-off. The empirically-derived oscillation amplitude distribution that produces the beam shape of  FIG. 9   a  is shown in  FIG. 9   b.    
     A fifth exemplary beam shape is shown in  FIG. 10   a , having a peak P 5  at about +30° in the azimuth, with a moderate beam width and a side lobe distribution having a relatively steep drop-off. The empirically-derived oscillation amplitude distribution that produces the beam shape of  FIG. 10   a  is shown in  FIG. 10   b.    
     A sixth exemplary beam shape is shown in  FIG. 11   a , having a peak P 6  at about +50° in the azimuth, with a relatively broad beam width and a side lobe distribution having a moderate drop-off. The empirically-derived oscillation amplitude distribution that produces the beam shape of  FIG. 11   a  is shown in  FIG. 11   b.    
       FIGS. 12-17  graphically illustrate exemplary far field power distributions produced by a two-dimensional beam-forming antenna, such as the antenna  500  described above and shown schematically in  FIG. 5 . In these graphs, the azimuth is labeled α, and the elevation is labeled β. The power contours are measured in dB. 
     From the foregoing description and examples, it will be appreciated that the present invention provides a beam-forming antenna that offers highly-controllable beam-shaping capabilities, wherein all beam shape parameters (angular location of the beam&#39;s power peak, the beamwidth of the power peak, and side lobe distribution) can be controlled with essentially the same precision as in phased array antennas, but at significantly reduced manufacturing cost, and with significantly enhanced operational stability. 
     While exemplary embodiments of the invention have been described herein, including those embodiments encompassed within what is currently contemplated as the best mode of practicing the invention, it will be apparent to those skilled in the pertinent arts that a number of variations and modifications of the disclosed embodiments may suggest themselves to such skilled practitioners. For example, as noted above, amplitude controlling devices that are functionally equivalent to those specifically described herein may be found to be suitable for practicing the present invention. Furthermore, even within the specifically-enumerated categories of devices, there will be a wide variety of specific types of components that will be suitable. For example, in the category of switches, there is a wide variety of semiconductor switches, optical switches, solid state switches, etc. that may be employed. In addition, a wide variety of transmission lines (e.g., waveguides) and antenna elements (e.g., dipoles) may be employed in the present invention. These and other variations and modifications that may suggest themselves are considered to be within the spirit and scope of the invention, as defined in that claims that follow.