Abstract:
Plural panelized phased arrays, possibly including electronic tilt, are controlled in physical orientation to present a reduced physical profile. Each panel may include a non-linear shaped aperture which physically mates with other shaped apertures to maintain a composite tapered aperture for reduced side lobes. Long delay compensation to equalize RF radiator element signal propagation times improves bandwidth.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from Israeli application IL 171,450 filed Oct. 16, 2005 and is related to U.S. patent application Ser. No. 10/546,264, filed Aug. 18, 2005, which is a national phase of PCT application PCT/IL2004/000149, filed Feb. 18, 2004 and published as WO 2004/075339, the dislosures of which are hereby incorporated by reference. This application is also related to copending divisional application 11/477,600 filed Jun. 30, 2006 for the purpose of provoking interference with U.S. Pat. No. 6,999,036 and published application 2005/0259021 A1. This application is also related to copending application Ser. No. 11/440,054 directed to exemplary individual radiator elements of a type may be used on the antenna panels described herein. 
     TECHNICAL FIELD 
     This application relates to antennas and particularly to low profile phased array RF antennas having plural phased sub-arrays of RF radiator elements, the sub-arrays being physically moveable to change the pointing direction of a radiation pattern lobe (which pointing direction may also be subject to electronic tilting). 
     BACKGROUND 
     One method of providing broadband communication services onboard moving vehicles (e.g., airplanes, trains, cars, buses, trucks, ships, etc.) is by communicating with a base station through RF transceivers on one or more earth satellites. For example, an antenna on the vehicle directed at the satellite may receive signals from the satellite. However, antennas externally mounted on vehicles moving in an ambient fluid (e.g., air) preferably have a low profile to minimize drag forces which slow vehicle motion and/or require extra motive power. 
     One approach (e.g., see earlier related application Ser. No. 10/546,264 referenced above) to achieving a low profile antenna is to use a plurality of arrayed antennas (including separately positioned sub-array components), each antenna being smaller (i.e., lower in profile) than a single antenna (or sub-array) with equivalent gain. A similar approach is described in U.S. Pat. No. 6,999,036 to Stoyanov et al. (the disclosure of which is hereby incorporated by reference) including the possibility of using electronic beam steering to supplement mechanical steering. 
     U.S. Pat. No. 5,678,171 to Toyama et al., the disclosure of which is hereby incorporated by reference, also describes use of a plurality of antenna arrays on an airplane. Using a plurality of antenna arrays rather than a single antenna, reduces the profile of the total antenna structure extending externally of the airplane for a given antenna gain. A similar approach is described in U.S. Pat. No. 4,679,051 to Yabu et al., the disclosure of which is hereby incorporated by reference. 
     U.S. Pat. No. 5,309,162 to Uematsu et al., the disclosure of which is hereby incorporated by reference, also describes use of two parallel antenna panels fixed with respect to each other but controllably rotatable together about azimuth and elevation axes. U.S. Pat. No. 6,657,589 to Wang et al., the disclosure of which is hereby incorporated by reference, also describes a low profile satellite antenna, which includes a pair of antenna assemblies. 
     Another approach used in the past to reduce antenna profile is to make a phased array antenna with an RF radiation pattern principal lobe beam direction not perpendicular (i.e., “tilted” at an acute angle) to the surface of the antenna array aperture. See, for example, the embodiments of  FIGS. 6A-C  in U.S. Pat. No. 6,999,036 to Stoyanov et al. noted above where electronic tilt is applied to each of plural antenna sub-arrays. 
     U.S. Pat. No. 6,259,415 to Kumpfbeck et al., the disclosure of which is hereby incorporated herein by reference, suggests a different approach, in which a single flat antenna panel (of arrayed elemental RF radiators) is used. In the Kumpfbeck antenna, the antenna beam is electronically fixed at an acute angle (e.g., 45°) relative to the antenna panel radiating surface. Thus, instead of requiring a 70° physical tilt of the antenna array panel (e.g., downward in elevation from a vertical orientation) in order to communicate with a satellite at a 20° elevation angle, a physical downward tilt of only 25° is sufficient. 
     U.S. Pat. No. 6,191,734 to Park et al., the disclosure of which is hereby incorporated by reference, describes an array of flat sub-array antenna panels, which have an electronic beam tilt control, such that instead of mechanically changing the elevation view direction of the panels, their beam direction is adjusted (i.e., tilted) electronically. 
     U.S. Pat. No. 6,864,837 to Runyon et al., the disclosure of which is incorporated by reference, describes a vertical antenna for base stations that implements electrical down tilt. Here the electrical tilt is used for purposes different than reducing antenna profile. 
     U.S. Pat. No. 6,873,301 to Lopez, the disclosure of which is hereby incorporated by reference, describes a flat antenna utilizing an array of sub-arrays contiguously positioned in a diamond-type pattern. This layout is claimed to achieve lower side lobes. 
     BRIEF SUMMARY 
     1. Panel Array with Electronic Tilt 
     In some exemplary embodiments, a controller controls the panels to present an apparently continuous surface over a range of beam direction angles (including use of electronic tilt), which includes angles in which the beam directions of the panels and a perpendicular to the panels are in different quadrants (i.e., separated by more than 90°). In such a configuration, the beam may actually be pointed towards a satellite viewed at a low elevation angle (e.g., 5, 10 or 15 degrees) while the panel appears to be directed almost vertically (i.e., presenting a very low profile). 
     In some embodiments, for some beam directions of the antenna (e.g., low orbit beam directions), some overlap of the panels in the beam direction is allowed, for example, by limiting the maximal allowed variable distance between adjacent panels. 
     Preferably, the panels maintain an apparently continuous surface (as viewed from the beam pointing direction) by adjusting the horizontal distance between edges of adjacent panels. However, in some embodiments, for at least some beam direction angles, the horizontal distance between adjacent panels is negative, i.e., the panels partially overlap from a vertical perspective. The term vertical overlap refers herein to a situation in which a straight line perpendicular to a nominally horizontal antenna base intersects two panels. 
     The electronic tilt of the antenna panels is in some embodiments fixed by the panel configuration of radiators and feedline (phase-shift) network on the panel or associated with the panel. In other embodiments, the electronic tilt of the panels can be controllably configurable, for example, according to the satellites with which the antenna is to communicate and/or the bandwidths of the communicated signals. In still other embodiments, the electronic “analog” tilt (i.e., electronically adjustable even if achieved in digitized increments) of the panels can be dynamically adjusted by the controller (e.g., by adjusting the relative feedline phasing of RF signals to/from RF radiator elements in each sub-array panel). 
     2. Panel Assembly with Fixed Physically Built-in “Digital” Tilt 
     An aspect of some exemplary embodiments relates to an antenna panel assembly including at least a pair of assemblies, each assembly having at least two sub-panels in different planes, which sub-panels are physically fixed relative to each other such that they move (e.g., rotate) together. The aforementioned U.S. Pat. No. 5,309,162 to Uematsu uses a single similar assembly structure. This may be referred to as a “digital” tilt to signify its fixed non-adjustable nature. The sub-panels of such assemblies also may have an electronic tilt such that their respective beam directions are not perpendicular to the associated sub-panel. 
     The sub-panels of each assembly may be optionally fixed together such that the sub-panels, when viewed from their common beam direction angle (possibly including electronic tilt), preferably present an apparently continuous surface without overlap or gaps. A plurality of sub-panel assemblies, each with digital tilt, are preferably controlled (i.e., by a programmed controller) to move relative to each other over a range of beam directions, such that all panels and/or sub-panels present an apparently continuous surface when viewed from the radiation pattern beam pointing direction. Using such an arrangement of plural sub-panel assemblies provides a choice of the fixed relationship (i.e., digital tilt) between the panels of a given sub-panel assembly so as to optimize operation over a given range of beam directions. 
     3. Panels of Different Heights and/or Thicknesses 
     An aspect of some embodiments relates to a multi-panel antenna, in which the beam direction of the panels may be mechanically controlled by a controller such that the beam pointing directions are substantially always parallel even though the upper surfaces of the antenna panels may be placed at different heights (e.g., vertically above a base mount), such that a lower panel does not block a higher panel. 
     In some embodiments, such panels may have the same thickness. A higher positioned panel may allow placement of some antenna control apparatus beneath that panel. Alternatively, the panels may have different thicknesses, for example, a panel with a higher upper surface may be thicker. 
     4. Elliptical/Oval Shaped Panel Array(s) 
     An aspect of some embodiments relates to an array of flat antenna panels which are shaped to border each other along non-straight (i.e., non-linear) border lines. The use of non-straight borders between the panels was found to reduce side lobes in the array radiation pattern for signals transmitted and/or received via the antenna. 
     In some embodiments, such antenna panels may be moveable relative to each other, but controlled so that over a range of beam pointing direction angles they appear to form a continuous surface, without gaps or overlay, when viewed from the beam pointing direction. In other embodiments, at least some antenna panels may be fixed relative to each other. 
     In some embodiments, the antenna panels may comprise a first panel having a generally elliptical or oval shape and at least one second panel (e.g., of a generally banana or crescent-shape) which completes, with the first panel (and possibly other similarly shaped second panels), a larger generally elliptical or oval shape. 
     5. Delay Correction for Antenna 
     An aspect of some embodiments relates to an antenna formed of one or more phased array multi-element panels, in which a time delay can be electronically added to the RF signal(s) associated with each element of the array, such that the arrival time of signals from (or to) a remote source, together with the added delays, are substantially the same for all elements. Adding entire delay compensation values rather than compensating only for desired relative element phasing helps reduce signal error, (e.g., to achieve wider frequency bandwidth as required in TV reception), although slightly adding to the delay of signals passing via the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Particular non-limiting exemplary embodiments will be described in conjunction with the accompanying Figures. Identical structures, elements or parts which appear in more than one Figure are preferably labeled with a same or similar number in all the Figures in which they appear, in which: 
         FIG. 1  is a schematic side view of an antenna, in accordance with one exemplary embodiment; 
         FIG. 2  is a schematic side view of the antenna of  FIG. 1 , with a pointing angle tilted away from 90° with respect to an antenna base structure; 
         FIG. 3  is a schematic illustration of an antenna with antenna sub-assemblies, in accordance with another exemplary embodiment; 
         FIG. 4  is a schematic perspective view of an antenna, in accordance with another exemplary embodiment; 
         FIG. 5  is a schematic illustration of the antenna of  FIG. 4 , as from the beam pointing direction of the antenna array; 
         FIG. 6  is a schematic illustration of another antenna as viewed from the beam direction of the antenna, in accordance with another exemplary embodiment; 
         FIG. 7  is a schematic illustration of an antenna as viewed from the beam pointing direction of the antenna, in accordance with still another exemplary embodiment; 
         FIG. 8  is a schematic illustration of signal paths between antenna elements and a controller of the antenna, in accordance with an exemplary embodiment; and 
         FIGS. 9-11  are schematic illustrations illustrating the splitting of the antenna into plural panels, controlling the plural panels in a positive displement mode and in a negative displacement mode respectively. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is a schematic side view of an antenna  100 , in accordance with an exemplary embodiment. Antenna  100  includes a plurality of flat panels  102 , each including respective phased arrays of individual antenna RF radiator element. Panels  102  are optionally mounted on a rotatable base  104 , which is used to rotate panels  102  about axis  105  in azimuth toward a satellite  120  (e.g., using suitable electromechanical transducers, feedback control systems and the like as will be apparent to those in the art). Panels  102  are optionally mounted on base  104  via respective arms  106  pivoted at  110 . 
     In some embodiments, panels  102  have a beam pointing direction  116  which is not perpendicular to the panel, but rather is at a tilt angle α from a line  118  that is perpendicular to the panel (direction  118  being the nominal beam pointing angle without electronic tilt). The tilt angle α is optionally achieved by providing feedlines to antenna elements at different locations on panels  102  with different respective relative signal phases and/or time delays (e.g., to achieve a broadband frequency response) as is known in the art. Alternatively or additionally, any other methods of achieving a tilt angle may be used. Using a beam pointing direction  116  with a tilt relative to the perpendicular axis or broadside direction  118  of the panel, allows directing the panel toward satellite  120  at lower elevational angles, while maintaining panels  102  at a lower vertical profile or height relative to a moving vehicle on which the panels are mounted. 
     Panels  102  are optionally movable relative to each other, under control of a controller  112 . In some embodiments, panels  102  are rotatably mounted on arms  106 , such that panels  102  may be controllably rotated around at least one axis at respective pivot points  108  and/or  110 , to adjust their respective elevation angles φ and/or horizontal/vertical separations. It will be understood that elevation angle φ is typically measured from a horizontal (or vertical)—which may or may not coincide with the orientation of base  104  (or a perpendicular thereto). As already noted, arms  106  may be rotatably mounted on base  104 , such that the arms can also controllably rotate around at least one axis at respective pivot points  110 . If the arms  106  are separately rotatable about their respective axes  110 , then controller  112  adjusts the respective angles of arms  106  in order to adjust horizontal (and vertical) distances between panels  102  (e.g., so as to maintain a substantially continuous apparently contiguous projection of the panels with respect to each other when viewed from the beam pointing direction). Suitable conventional electromechanical transducers and associated mechanical linkage (and servo-controlled feedback systems) may be used to achieve such controllable rotational motions as will be appreciated by those in the art. 
     Alternatively or additionally to arms  106  and pivots  108  and  110 , any other controllably adjustable mechanical mounting of panels  102  may be used to allow controlled relative movements of the panels. 
     Controller  112  may include conventional electrical control circuitry (e.g., microprocessor controlled) to achieve controlled accurate adjustment of electromechanical actuators. For example, controller  112  may optionally control movement of panels  102  responsive to movements of the vehicle on which antenna  100  is mounted, such that a common beam pointing direction of panels  102  is constantly directed toward satellite  102  (e.g., using suitable beam tracking feedback control circuits driven by received RF signal strength), while forming an apparently substantially continuous antenna plane when viewed from the satellite, i.e., from beam pointing direction  116 . Thus, for low satellites requiring a close to horizontal beam direction  116 , panels  102  are distanced from each other by a relatively large distance (indicated by arrow  124 ), while for high orbit satellites, the horizontal distance between panels  102  is very small, is zero or is even negative, as discussed below. 
     Controller  112  may include suitable controls for substantially any type of driving actuator, such as a pneumatic actuator, electrical actuator or a linear or rotary motor with suitable mechanical transmission linkage. The driving actuator may be linear or non-linear. As will be appreciated, the mechanical actuators are mechanically linked to the antenna apparatus so as to control pivoting and/or other motions as required. 
     Panels  102  optionally all have the same electronic tilt angle α and are controlled by controller  112  to have the same elevation angle φ, in order to minimize side lobes and/or other signal degradation effects. 
     The tilt angle α may be “built in” (e.g., a fixed value) and may be optionally selected according to the range of possible beam directions (e.g., to satellites with which antenna  100  is to be used to communicate). In an exemplary embodiment, tilt angle α is selected in the middle, or close to the middle, of the range of desired possible beam direction angles from antenna  100  to the satellite. For example, for a desired range of 10°-80°, a built-in panel tilt of a α=45° may be used. Thus, perpendicular line  118  need only have a range of physical movement between 55°-135°. For this example, panels of length L, rather than requiring a maximum height above base  104  of H=L*cos(10°)=0.98L, a maximal height of only H′=L*cos(45°)=0.707L is required. 
     Alternatively, instead of defining the inherent or built-in fixed tilt α according to the range of possible beam directions, the tilt angle α may be selected according to probabilities of the angles, in a manner which reduces or minimizes height of panels  102  above base  104  a large portion of time. 
     In some embodiments, for simplicity, the tilt angle α is selected such that a maximum movement angle for perpendicular line  118  does not exceed 90° (i.e., a vertical direction as measured from the horizon), at which 90° position the distance  124  between panels  102  is zero. Alternatively, as is described with reference to  FIG. 2 , the range of elevational angles of perpendicular line  118  may be allowed to exceed 90°. 
       FIG. 2  is a schematic side view of an antenna  100  where a panel perpendicular  118  has a maximum angle of elevation greater than 90°. When antenna  100  is directed at satellite  120  with a close to vertical tilted beam pointing direction  116 , perpendicular  118  is in a different quadrant than tilted beam direction  116 . In order that panels  102  will form an apparently continuous surface as viewed from beam pointing direction  116 , panels  102  may need to overlap in a vertical plane (e.g., perpendicular to a horizontal base  104 ), such that the horizontal distance between the edges of adjacent panels  102  can be considered “negative”. 
     In some embodiments, at substantially any pointing angle, panels  102  are positioned at the same height above base  104  (e.g., their lowest points are at a same height above base  104 ). Alternatively, in at least some angles of tilted beam direction  116 , different panels  102  may be at different heights above base  104 . In some embodiments, in accordance with this alternative, when panels  102  are in a negative displacement state, i.e., the panels partially overlap in a vertical plane, the panels are at different heights above base  104 , to allow overlap. In other embodiments, at low angles of beam pointing direction  116 , panels  102  may be at different heights to reduce horizontal distance  124  ( FIG. 1 ) between the panels  102  and hence the total area (volume) occupied by antenna  100 . In still other embodiments, panels  102  are at different heights at substantially all pointing angles, for example in order to allow positioning of controller  112  beneath one or more panels. 
     In some embodiments, antenna  100  has a wide range of possible beam pointing angles, covering at least 50°, at least 65° or even at least 75°. Preferably, controller  112  adjusts panel orientations and locations, such that when viewed from the beam pointing direction, the panels appear to form a continuous surface without overlap or gaps, over the entire range of beam pointing directions of the antenna. Alternatively, at some beam pointing angles, panels may be allowed to partially overlap. In some embodiments, a maximum horizontal distance between adjacent panels is defined by structural limitations. At those angles where preventing overlap (when viewed from the beam direction) would require a larger distance than such maximum, overlap is allowed. Preferably, overlap is allowed in less than 20% of the range of beam direction angles, or even in less than 10% or less than 5% of the range of beam pointing direction angles. Alternatively or additionally, the maximum horizontal distance between panels is selected such that more than 5% or even 10% of the range of beam direction angles involves partial panel overlap. 
     Optionally, the range of possible beam pointing directions for antenna  100  is predetermined at the time of production. Alternatively, the range of beam directions may be configurable. The range of beam directions is optionally selected according to the position of a remote transmitter/receiver with which antenna  100  is expected to communicate, the width of the antenna principle beam and/or the surface area of the antenna or other design parameters as will be appreciated. 
       FIG. 3  is a schematic illustration of an antenna  200 , in accordance with another exemplary embodiment. Antenna  200  includes a plurality of sub-units  206  (two in  FIG. 3 ), each of which is formed of a plurality (e.g.,  2 ) of panels  204  held together in a fixed orientation, for example by one or more rods  202 . As in antenna  100 , each sub-unit  206  is mounted on a controllable arm  106  (e.g., see controllable rotary joints  108 ,  110 ) and is controllably moved by controller  112  relative to the other sub-units  206  and base  104 . The use of panels  204  fixed relative to each other allows achieving some low profile benefits associated with a large number of panels, while avoiding the need to separately control movements of each of a large number of panels. 
     In some embodiments, panels  204  do not need to have a built-in tilt (e.g., because height reduction due to the use of a large number of panels  204  may be considered sufficient). In other embodiments, however, as illustrated by antenna  200 , panels  204  of sub-units  206  have built-in tilt to beam pointing angle  116 , to reduce antenna profile as much as possible. Relative orientation of panels  204  in a single sub-unit  206  is optionally selected such that, when viewed from beam pointing direction  116 , the panels  204  form an apparently continuous surface. That is, controller  112  optionally controls pointing movements (e.g., including electrical tilt  116 ) of sub-units  206  relative to each other such that all panels  204  appear to be on a continuous surface as viewed from beam direction  116 . 
     While only two panels  204  are shown in  FIG. 3  as being part of each sub-unit  206 , in some embodiments, one or more of sub-units  206  may include more than two panels  204  or even more than three or more than four panels  204 . In some embodiments, all sub-units  206  in a single composite antenna structure have the same number of panels  204 . Alternatively, different sub-units  206  may have different numbers of panels  204 . 
     Controller  112  is optionally located beside base  104 , as shown in  FIG. 4 . Alternatively, controller  112  may be located on base  104 , for example beneath one of panels  252  and  254 . 
     In some embodiments, all panels  204  or  102  may be of the same size and shape. Alternatively, for example, to help reduce side lobes, different ones of the panels may have different shapes, for example as described with reference to  FIG. 4 . 
       FIG. 4  is a schematic view of an antenna  250 , in accordance with an exemplary embodiment. Antenna  250  also includes rotatable base  104 —now carrying two panels  252  and  254  rotatably mounted at  108  on racks  256 . Racks  256  are slidably mounted (e.g., see arrows  258 ) on rails  260  fixed to base  204 . Controller  112  controls the elevational angles and horizontal locations of panels  252  and  254  such that the panels substantially constantly appear to form a continuous surface as viewed from the beam pointing direction (e.g., as viewed from a tracked earth orbiting satellite transceivers). 
       FIG. 5  is a schematic illustration of antenna  250  as viewed from the beam pointing direction, in accordance with an exemplary embodiment. As mentioned above, antenna  250  comprises panels  252  and  254  which appear to form a continuous surface when viewed from the beam pointing direction (as in  FIG. 5 ). Each of panels  252  and  254  is formed of a plurality of active antenna radiator elements  262  (depicted as elemental rectangular blocks in  FIG. 5 ). 
     Active elements  262  may include cavity backed dual polarization aperture transceivers radiator elements (e.g., as described in copending U.S. patent application Ser. No. 11/440,054 which is hereby incorporated by reference). Alternatively, any other types of elements may be used, such as microstrip patch antenna radiators and the like (as will be understood by those in the art). 
     In an exemplary embodiment, active elements  262  are of a size of about 12×14 millimeters, although other sizes may be used as long as grating lobes are avoided. Antenna  250  operationally includes at least 300 elements  262  or even at least 400 such elements. The number of elements  262  in antenna  250  can be selected to achieve a required antenna gain factor. 
     Antenna  250  has an overall oval shape, to help improve side-lobes (e.g., because a tapered array radiation aperture is thereby defined). Preferably, at least one row of antenna  250  has more elements than a column with the most elements. Elements  262  may be rectangular, with their larger dimension parallel to a major axis (e.g., along the rows) of the antenna. In some embodiments, most columns of antenna  250  have elements from both panels  252  and  254 , while most rows of antenna  250  have elements from only a single panel  252  or  254 . In some embodiments, less than 40%, or even less than 25% or the rows of antenna  250  include elements in more than one panel. 
     Central columns  264  (six of which are schematically depicted in  FIG. 5 ) may have a maximum number of columnar elements  262  in all of antenna  250 . The number of elements in columns in some embodiments does not increase from the column(s) with the most elements  262  as one moves toward the outer lateral edge columns (e.g., with monotonically decreasing numbers of elements), such that the edge columns  268  have the fewest elements  262 . In some embodiments, one panel, namely panel  252  (shown with hashed elements in  FIG. 5 ), has an oval shape by itself. Panel  254  (shown with open rectangular elements in  FIG. 5 ) then preferably has a mating banana or crescent-like shape which, with panel  252 , forms a larger oval. Each of panels  252  and  254  may have a monotonic layout of elements as described above, such that the number of elements in each column is non-increasing from a centrally positioned column with the most elements as one moves outwardly. A column with the most elements may be within a central third of the panel (e.g., one or more central columns). 
     In some embodiments, panels  252  and  254  have a monotonically non-increasing layout of “horizontal” rows of elements, such that from a row having the most elements, the number of elements in the rows decreases monotonically as one moves toward each top and bottom side (as depicted in  FIG. 5 ). The row with the most elements may be the central row. Alternatively, as in banana-shaped panel  254 , a row with the most elements may be located slightly off from the center. Preferably, a row with the most elements may be within a central third of the rows (e.g., the seventh and eighth rows out of twelve). 
     Antenna panels  252  and  254  may have the same number of elements organized in the same number of rows. It is noted, however, that in some embodiments, the number of columns in panels  252  and  254  can be different, (e.g., banana-shaped panel  254  may have more columns than oval panel  252 ). 
     In some embodiments, the border between panels  252  and  254  is an approximately curved line (albeit pixelated due to the non-zero size of elements  262 ). Panels  252  and/or  254  may be, for example, oval, circular, and/or in other shapes, including a pseudo random shape to achieve desired side lobe or other antenna characteristics. 
     Antenna  250  is preferably symmetric around at least one axis. In some embodiments, antenna  250  may be symmetric around both of orthogonal axes (e.g., a horizontal axis and a vertical axis). Preferably, an axis of symmetry of antenna  250  does not coincide with the border between panels  252  and  254 . 
       FIG. 6  is a schematic illustration of an antenna  280  as viewed from the beam pointing direction of the antenna, in accordance with another exemplary embodiment. Antenna  280  includes a relatively oval panel  282  (shown in  FIG. 6  with hatched square elements) and a banana-shaped panel  284  (shown in  FIG. 6  without hatching), with a different layout from antenna  250 . In antenna  280 , the rows having the most elements are closer to the common edge of panels  282  and  284 , optionally within 40% or even 30% of from the common edge. The number of rows having elements in both panels is less than 20% of the rows, and even less than 15% of the rows. 
       FIG. 7  is a schematic illustration of an antenna  300  as viewed from the beam pointing direction of the antenna, in accordance with another exemplary embodiment. Antenna  300  includes four panels  302 ,  304 ,  306  and  308  (each shown with square elements distinguished from those of an adjacent panel by hatch marks in  FIG. 7 ). The panels may all be controlled in their respective positions separately, or may be combined into commonly controlled pairs of panels as discussed above with reference to  FIG. 3 . 
     Panel  304  is relatively oval in shape, while the other panels are suitably crescent-shaped to provide complete panel  304  as a larger oval shape. In some embodiments, all panels have the same number of rows. Alternatively, one or more of the panels may have a different number of rows (e.g., panel  302 ). 
     In some embodiments, all panels have the same number of elements. Alternatively, each of the panels may have a different number of radiator elements  262 . In some embodiments, each pair of panels  302 ,  304  and  306 ,  308  are fixed together (i.e., with respect to each other). 
       FIG. 8  is a schematic illustration of transmission line signal paths between antenna RF radiator elements  262  and controller  112  (or a directly connected receiver or transmitter) in an antenna system  400 , in accordance with an exemplary embodiment. As will be appreciated, a typical feed transmission line structure may include a corporate-organized microstrip transmission line structure leading from a common feed point to each individual radiator element. Each antenna radiator element  262  is optionally connected to controller  112  (or to a transceivers) through a delay unit  350 . Alternatively, one or more of elements  262  are base elements  262 A, which are defined to have zero relative delay and therefore do not have a delay unit  350  along their connection with controller  112 . 
     Delay units  350  optionally add (to at least some of the signal paths) respective delays, which compensate for different distances between a given radiator element  262  and satellite  120 . It will be understood that suitable relative phasing between elements  262  and/or  262 A must also be provided to achieve desired phased array operation (e.g., tilt direction  116 ). Such relative phase control may be included in delay units  350  or provided separately as will be appreciated. After adding the delays provided by delay units  350 , the signal paths between satellite  120  and control  112  through substantially all of elements  262  may have the desired propagation time (e.g., equal). Optionally, at least one of delay units  350  adds a delay of at least three, at least five or even at least eight wavelength propagation time periods of the transmitted/received signals. Correcting for the entire multi-wavelength delay (e.g., not only for relative partial wavelength or phase differences) can achieve a more accurate correction, which is worth the slightly longer overall delay time. 
     It is noted that in those embodiments in which antenna panels are to have a built-in electrical tilt angle, the delay added by different delay units is optionally selected in a manner which includes relative phase controls to induce the desired electronic tilt. Those in the art will appreciate that conventional phased array beam steering effects can be included with the delay compensation—and that he delays can be dynamically controlled to change the tilt angle and/or delay compensation as the panels are physically moved with respect to base  104  and/or satellite  120 . 
     In some embodiments, antenna  400  may include a test signal generator  352 , which can be used in calibrating delay units  350 . Optionally, when calibration is required, generator  352  generates a known test signal which is coupled to antenna elements  262 ,  262 A. Controller  112  measures reception characteristics (e.g., relative propagation delays along each elemental channel) of the test signal and accordingly adjusts delay times of delay units  350  to achieve the desired antenna characteristic(s). For example, the test signal may be provided to transmission lines  356  that connect elements  262  to delay units  350 . 
     In some embodiments, the test signal is injected when antenna  400  is not used for signal reception and/or transmission. Optionally, calibration is performed at set-up and/or as part of long term maintenance procedures. Alternatively or additionally, payload data transmission and/or reception can be stopped periodically for a short period (preferably imperceptible to an average user), in order to perform calibration. Alternatively or additionally, the test signal can use one or more carrier frequencies not used for data transmissions (i.e., it can be frequency multiplexed with ongoing data traffic on other frequencies). In some embodiments, the calibration is performed at least once a day or even once an hour. Alternatively, the calibration is performed at a high rate, at least once every minute or even once every second. 
     All above described antenna configurations may be used for both half-duplex (e.g., only reception or only transmission) and full-duplex antennas (i.e., which service concurrent RF reception and transmission). The antennas described above may be used for substantially any type of communications, such as reception from a direct broadcast television satellite (DBS) located in a fixed orbital position (geostationary) satellite and/or for communication with a millimeter wave (MMW) geosynchronous satellite. Alternatively or additionally, the above described antennas are used for ground-based communications. The antennas may be used, for example, in multi-channel multi-point distribution systems (MMDS), in local multi-point distribution systems (LMDS), cellular phone systems and/or other wireless communication systems where low profile antennas are required or preferred. In some embodiments, the antennas are used in low energy communication systems. 
     In an exemplary embodiment, an antenna implementing one or more of the above described features operates in a “C-band” system, using carrier frequencies between about 3.7-4.2 GHz. Alternatively or additionally, the above described antennas operate in the millimeter wave range, at wavelengths shorter than the MMW range, such as sub-millimeter waves and/or terra-beam waves, and/or at wavelengths longer than the MMW range, such as microwave wavelengths. In an exemplary embodiment, the above described antennas operate at about 24 mm wavelength range, i.e., 10-15 GHz. 
     The above described antennas may be used for substantially all types of signals, including audio, video, data and multimedia. 
     The following table provides an illustration (based on simulated antenna operation using an oval multi-panel antenna as in  FIGS. 5-7 ) of substantial improvements in sidelobes (and even minor improvements in gain) that can be achieved by adding time delay compensation at each of various antenna elevation pointing angles. The last three lines of this table represent low elevational angles where there was simulated “overlap” of panels in the vertical direction. 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Before correction 
                 After correction 
               
             
          
           
               
                 Angle 
                   
                   
                 Side- 
                 Add. 
                   
                   
                   
               
               
                 Antenna 
                   
                   
                 lobe 
                 time 
               
               
                 Pointing 
                 Gain 
                 Squint 
                 Level, 
                 delay 
                 Gain 
                 Squint 
                 Sidelobe 
               
               
                 degrees 
                 dB 
                 degrees 
                 dB 
                 Δd 1 , ps 
                 dB 
                 degrees 
                 Level, dB 
               
               
                   
               
             
          
           
               
                 90 
                 37.9 
                 0 
                 −20 
                   
                   
                   
                   
               
               
                 80 
                 37.76 
                 0 
                 −17.8 
                 1.5 
                 37.79 
                 0 
                 −19 
               
               
                 70 
                 37.74 
                 0.5 
                 −15 
                 3.5 
                 37.79 
                 0 
                 −17.8 
               
               
                 60 
                 37.7 
                 0.5 
                 −14 
                 5.5 
                 37.75 
                 0 
                 −17.5 
               
               
                 50 
                 37.52 
                 0.5 
                 −12.5 
                 7 
                 37.7 
                 0 
                 −17 
               
               
                 40 
                 37.5 
                 −1 
                 −11 
                 11 
                 37.7 
                 0 
                 −16 
               
               
                 30 
                 37.23 
                 −1.5 
                 −9 
                 16 
                 37.7 
                 0 
                 −16.5 
               
               
                 20 
                 36.44 
                 −2 
                 −5 
                 24 
                 37.78 
                 0 
                 −16.2 
               
               
                 15 
                 34 
                 −2.5 
                 −1 
                 32 
                 36.6 
                 0 
                 −13.3 
               
               
                   
               
             
          
         
       
     
       FIG. 9  schematically depicts an embodiment wherein sub-array panels  102  are depicted at different (Δ H) heights above the mounting base  104 . As will be appreciated, only two panels have been depicted (and controlled movement mechanisms not shown) to simplify the depiction and to better teach salient movement parameters. A maximum height H max  permitted by the physical mechanical constraints of movement is also depicted. An “effective” pseudo panel position is also depicted as a pseudo panel  102 ′ constructed at a right angle to the beam pointing direction  116 . This is, in effect, the projection of panel  102  when viewed from the beam pointing angle direction. A similarly constrained (i.e., by finite dimensions and parameters of a particular physical embodiment) maximum horizontal dimension (e.g., D) will also be present as those in the art will appreciate. The elevation angle φ for the beam pointing direction  116  is also depicted. 
     Operation of the  FIG. 9  embodiment during a “positive” displacement mode is depicted in  FIG. 10 . Here the equations for controlled motion within the system constraints for given controllable parameters are shown. Similarly, operation of the  FIG. 9  embodiment during a “negative” displacement mode is depicted in  FIG. 11 . Here the equations for controlled motion within the system constraints for given controllable parameters are shown. 
     The above exemplary embodiments have been described using non-limiting detailed descriptions that are provided by way of example and are not intended to limit the scope of the appended claims. It should be understood that features and/or steps described with respect to one embodiment may be used with other embodiments and that not all embodiments have all of the features and/or steps shown in a particular figure or described with respect to one of the embodiments. Variations of embodiments described will occur to persons skilled in the art. It will be appreciated that the above described description of methods and apparatus is to be interpreted as including apparatus for carrying out the methods and methods of using the apparatus. 
     It is noted that some of the above described embodiments describe the best mode presently contemplated by the inventors and therefore include structure, acts or details of structures and acts that may not be essential to the invention and which are therefore only described as examples. Structure and acts describe herein are replaceable by equivalents which perform the same function, even if structure or acts are different, as known in the art.