Patent Publication Number: US-6211836-B1

Title: Scanning antenna including a dielectric waveguide and a rotatable cylinder coupled thereto

Description:
FIELD OF THE INVENTION 
     This invention relates to scanning antennas and more particularly to such antennas which steer electromagnetic radiation from a dielectric waveguide in directions determined by the geometry of a rotatable cylinder (or drum) coupled to it. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5,572,228 issued Nov. 5, 1996 and U.S. Pat. No. 5,815,124 issued Sep. 29, 1998 describe evanescent coupling antennas which employ rotatable cylinders placed in close proximity to a dielectric rod waveguide and operative to radiate the coupled energy in directions determined by the period of features on the surface of the cylinder. By defining rows of features where the features of each row have a different period, the radiation can be directed in a plane over a range determined by the different periods and by rotating the cylinder about an axis parallel to the axis of the waveguide. 
     The features on the cylinder surface, of each of the antennas disclosed in the above-noted patents, comprise conductor strips of like thickness and at a given and different spacing in each row about the cylinder. The operation of such an antenna as well as the advantages in such applications as vehicle collision avoidance systems for automobiles and aircraft and the like are described in the above-noted patents which are incorporated herein by reference. 
     BRIEF DESCRIPTION OF THE INVENTION 
     It has been discovered that by including features which vary in vertical dimension as well as in period from row to row, greater control over the transmitted (or received) waveform, arbitrary polarization, and increased gain are achieved. Accordingly, generic features of embodiments of this invention include a dielectric rod waveguide (DRW) with an electromagnetic wave launched therein and a rotatable cylinder including rows of generally circular recesses of different depths or generally circular stubs of different heights where the period in each row varies in a prescribed manner. The cylinder is rotated to scan that electromagnetic radiation over a lateral space determined by the varying feature periods and by the rotation of the cylinder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic representation of a beam steering antenna including a dielectric waveguide and a spinning drum in accordance with the principles of this invention; 
     FIGS. 2 and 3 are schematic representations of a dielectric rod waveguide and a coupled row of the drum of FIG. 1 including recesses and stubs in the drum surface respectively; 
     FIGS. 4 a ,  4   b ,  4   c ,  4   d ,  4   e ,  4   f ,  4   g ,  4   h ,  4   i ,  4   j  and  5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f ,  5   g  and  5   h  are charts of stub and recess profiles and of waveguide profiles for the drum and waveguide of FIG. 1, respectively; 
     FIGS. 6 a ,  6   b ,  6   c ,  6   d ,  6   e  and  6   f  are charts of feature configurations and gap variations for the drum of FIG. 1 in accordance with the principles of this invention; 
     FIGS. 7 a  and  7   b  are graphs of different wave patterns for different gap profiles between the waveguide and drum of FIG. 1; 
     FIG. 8 is a schematic representation of an antenna as in FIG. 1 also including a parabolic reflector; 
     FIG. 9 is a graph of the beam profile radiated by the antenna of FIG. 8; 
     FIGS. 10 and 12 are schematic representations of the antenna of FIG. 1 with a parabolic reflector and a moving planar reflector and of a duplex system using such reflectors in both a transmitting mode and a receiving mode; 
     FIG. 11 is a schematic representation of the antenna of FIG. 1 with an additional planar, leaky dielectric waveguide; and 
     FIG. 13 is a schematic representation of a beam steering antenna with a switching mechanism. 
    
    
     DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT OF THIS INVENTION 
     FIG. 1 shows a dielectric rod waveguide  11  placed in close proximity to a cylinder or drum  12 . Drum  12  includes rows of recesses or holes where the holes of each row have a different period. A periodic set of holes in a representative row is shown in the figure as PSH line  14 . It can be seen from the figure that the features have similar X and Y dimensions. 
     In operation, a signal is launched into waveguide  11  by signal generator  16  and drum  12  is rotated about an axis  17  by drum driver  18 . The drum is made of metallic material and is coupled to the evanescent field generated by the signals in the waveguide in a manner fully described in the above-noted patents. Signal generator  16  and driver  18  are controlled by controller  19  in a well understood manner. 
     The apparatus of FIG. 1 is operative to radiate signals in lateral directions dictated by the period of the features (recesses) in each row of drum  12  as that row comes into alignment with the waveguide. As the drum spins, the direction of the (beam) radiation changes. By choosing the periods of the features in the rows carefully and by spinning the drum, the lateral space over which the beam is broadcast is determined. The direction of the beam radiated as the waveguide is in alignment with each of the consecutive rows of features is determined by the equation: 
     Coupling angle (for both transmitting and receiving): 
     
       
         φ=arcsin ( C/V   ph   −λ/A ) 
       
     
     where C is the velocity of light, V ph  is the phase velocity of the electromagnetic wave in the waveguide. λ is the wavelength of the electromagnetic wave in free space and Λ is the period of the features in the row. The direction of the radiated beam is indicated in FIG. 1 by the solid arrow  20  and the broken arrows φ 1  and φ 2  which indicate the plane of the beam. 
     FIG. 2 shows an illustrative section  21  of drum  12  of FIG. 1 with a row of holes aligned with waveguide  11 . The radiated beam is indicated by arrow  22  and the plane of radiation is indicated by curved arrow  23 . FIG. 3 shows an arrangement analogous to that shown in FIG. 2 except that the features of the illustrative section of the drum comprise stubs rather than holes. 
     The features of the various rows of the apparatus of FIG. 1 may comprise holes, recesses or stubs. FIG. 4 a  demonstrates a cross section through an illustrative feature as indicated by plane  25 . FIGS  4   b  through  4   j  illustrate nine alternative cross sections arranged in three rows. The top row as viewed shows illustrative stub profiles  27 ,  28 , and  29 . The middle row shows recesses  30 , 31 , and  32 . The bottom row shows holes  33 , 34 , and  35 . 
     Not only may the feature profile be different, the waveguide cross section also may be different. FIGS. 5 a  through  5   h  show illustrative cross sections for the waveguide. It is clear from the figures that the waveguide cross section may be disk-shaped ( 51 ), donut-shaped ( 52 ), square-shaped ( 53 ), diamond-shaped ( 55 ) (viz. square-shaped but rotated 90 degrees with respect to the coupled drum). The cross section also may be oval ( 56 ), T-shaped ( 57 ) or rectangular ( 58 ). The drum material may comprise quartz, Teflon™ polyethylene, polystyrene, sapphire, or microwave ceramic and may be embedded in foam or other material with a small dielectric constant and loss. 
     FIGS. 6 a  through  6   f  show an illustrative set of waveguide ( 11 ) and drum ( 12 ) variations. The gap between the drum and the waveguide may vary as shown at  60  and  61  in the FIGS. 6 a  and  6   b , the representation at  60  illustrating the apparatus with recesses  62 . The representation at  61  illustrates the apparatus with stubs  63 . Further, the recess depth may vary as shown at  65  or the stub height may vary as shown at  66  as shown in FIGS. 6 c  and  6   d . Also, the recess or stub diameter may vary as shown at  67  and  68 , respectively as shown in FIGS. 6 e  and  6   f . 
     FIG. 7 a  is a graph of gap δ in mm versus X, the position along the waveguide of FIG. 6 a  at  60 . FIG. 7 b  is a graph of power db versus the angle of the radiated beam. Curves in FIG. 7 b  correspond to the different gap arrangements of FIG. 7 a.  For a constant gap represented by horizontal line  70  in FIG. 7 a,  the power curve is as represented by curve  71  in FIG. 7 b.  For a straight line variation of about three millimeters at the end of the drum to about one millimeter at a six inch position as represented by line  74  in FIG. 7 a,  the power curve is as represented by curve  72  in FIG. 7 b.  A gap of from five millimeters at the end of the drum to one millimeter at the six inch position varying as represented by the curve  75  in FIG. 7 a,  produces a power curve represented by curve  73  in FIG. 7 b.    
     Parabolic reflectors are conveniently used with the scanning antenna of FIG. 1 in accordance with the principles of this invention for directing the beam from the antenna in elevation planes that are at angles to the azimuth X-Y plane. FIG. 8 shows one such apparatus with an oval-shaped waveguide  80  and a drum  81  with rows of recesses. The parabolic reflector is designated  82 . FIG. 9 is a graph of power (dB) versus azimuth in degrees showing the far-field beam pattern. The power is −49 at an azimuth at −35 degrees, −45 at −10 degrees, and zero at the reference X-Y plane. 
     Two-dimensional beam steering can be achieved with the apparatus of FIG. 1 by employing a parabolic reflector which is in a fixed position and a planar reflector which moves. FIG. 10 illustrates such an arrangement. Specifically, FIG. 10 illustrates apparatus comprising a waveguide  90  having an illustrative oval cross section. The apparatus also includes a (spinning) drum  91  and a parabolic reflector  92 . A planar reflector  93  rotates back and forth from a position in the plane of the axis of the drum as shown through an angle O to a position parallel to that axis. The directions of the beam are dictated by the positions of reflector  93 . The solid arrows  94 ,  95 , and  96  indicated the beam path from waveguide  90  to reflector  92  to reflector  93  in one position of reflector  93 ; the broken arrows  97 ,  98 , and  99  indicate the beam path for a second position of reflector  93 . 
     FIG. 11 illustrates a waveguide  100  and an adjacent spinning drum  101  with rows of recesses. The apparatus also includes a planar, “leaky”, dielectric waveguide  102  which has a printed circuit dipole grating formed on it. The grating is represented by dashed lines  103 ,  104 ,  105 , and  106 . Waveguide  102  is positioned in the path of the beam radiated from drum  101  as shown. The plane in which radiation is directed from waveguide  102  is represented at  107 . This embodiment of the invention is particularly attractive when space is limited. 
     The apparatus represented in FIG. 1 is described in terms of a transmitting antenna. The apparatus also is useful as a receiving antenna. FIG. 12 illustrates one transmitting and receiving embodiment, both the transmitting antenna and the receiving antenna employing parabolic reflectors and a moving planar reflector. Specifically, the transmitting antenna of FIG. 12 includes a waveguide  11  and a spinning drum  112  with rows of recesses as shown. Antenna  112  also includes a parabolic reflector  113  and a moving planar reflector  114 . The receiving antenna includes a waveguide  116 , a spinning antenna  117 , a parabolic reflector  118 , and a moving planar reflector  119 . An electromagnetic wave launched into waveguide  111  as indicated by arrow  120  is directed as indicated by the arrows  121  and  122  and received by the receiving antenna as indicated by solid arrows  126  and  127  to generate an electromagnetic wave as indicated by arrow  128 . 
     Duplex beam steering can also be achieved without the two moving planar reflectors  114  and  119  of FIG. 12 with a shared spinning drum using two dielectric waveguides each with an associated parabolic mirror instead. 
     A problem might appear when an antenna in accordance with the principles of the invention is designed to operate at relatively large scanning angles. The problem is overcome by using a switch to feed the antenna from opposite ends of the dielectric rod waveguides (DRW). Such an arrangement is illustrated in FIG. 13 where a switch  130  is operative to feed signals alternatively to end  131  and end  132  of the waveguide  133  as illustrated in the figure. 
     The number of beam positions in a lateral plane is determined by the number of rows of features on a drum. The number of rows on a drum determines the resolution. Antennas in accordance with the invention have a drum length of four to twenty inches with the spacing between rows of one wavelength. A drum may have twenty to eighty rows of features with the spacing between features of two to five millimeters. The drum typically is rotated at from one revolution per minute to twenty revolutions per second. 
     The use of stubs, recesses, or holes on the drum provides for increased efficiency per unit length, arbitrary polarization and for an increased coupling efficiency. Specifically, it has been found that when both, the waveguide and features have cross-section with rotating symmetry of 4 th  order (square, round, octagonal etc.) the antenna can operate with arbitrary polarization, i.e. the main lobe of the antenna pattern for each fixed drum position is the same for any polarization. This includes such fundamental polarizations as horizontal and vertical polarizations, and right-hand and left-hand circular polarizations.