Patent Publication Number: US-11394114-B2

Title: Dual-polarized substrate-integrated 360° beam steering antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application contains subject matter related to U.S. application Ser. No. 16/294,404, entitled “DUAL-POLARIZED SUBSTRATE-INTEGRATED BEAM STEERING ANTENNA” filed on Mar. 6, 2019, published Sep. 10, 2020 under publication number 2020/0287297, and issued Dec. 1, 2020 (U.S. Pat. No. 10,854,996). 
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of wireless communications and, in particular, to antenna systems configured to transmit and receive a wireless signal to and from different directions. 
     BACKGROUND 
     Antenna systems having wide steering angles and high directivity are sought after in wireless communications applications. Planar phased array antennas do provide the capability of wide steering angles, but the directivity of such antennas has a tendency to decrease with increases in the steering angle of the directed beam. Planar phased array antennas may also have blind angular regions and are expensive due to fabrication processes and the costs associated with phase shifters. 
     SUMMARY 
     An object of the present disclosure is to provide a dual-polarized substrate-integrated 360° beam steering antenna for transmission and reception of a radio-frequency (RF) wave. The antenna is configured to transmit and receive a wireless signal in and from different directions. 
     In accordance with this objective, an aspect of the present disclosure provides an antenna for transmission of a radio-frequency (RF) wave, the antenna comprising a stack-up structure. The structure has a first control layer, a second control layer that is approximately parallel to the first control layer, a first parallel-plate waveguide and a second parallel-plate waveguide located between the first control layer and the second control layer, with the first parallel-plate waveguide and the second parallel-plate waveguide being approximately parallel to each other and to the first control layer and the second control layer. The structure further comprises a plurality of through vias operatively connecting the first control layer and the second control layer to center RF and direct current (DC) ground planes, one or a plurality of hollow portions through the stack-up structure; and a RF connector being proximate to a hollow portion, and configured to deliver a RF signal to a first central port located on the first control layer and a second central port located on the second control layer. The first central port is configured to radiate the RF wave into the first parallel-plate waveguide, and the second central port is configured to radiate the RF wave into the second parallel-plate waveguide. The structure further comprises vertical-polarization peripheral ports integrated with the first control layer and configured to radiate the RF wave in vertical polarization from the first parallel-plate waveguide, and horizontal-polarization peripheral ports integrated with the second control layer and configured to radiate the RF wave in horizontal polarization from the second parallel-plate waveguide, each one of the vertical-polarization peripheral ports being collocated with one of the horizontal-polarization peripheral ports such that they cross each other, and that a RF wave radiation beam may be steered at an angle of 0 to 360 degrees in the plane of the stack-up structure, around the first and second central port. 
     In at least one embodiment, the stack-up structure has an approximately circular shape. 
     In at least another embodiment, the stack-up structure has an approximately elliptical shape. 
     The antenna may further comprise a pair of frequency selective structures having frequency selective elements, each frequency selective structure being located partly on a corresponding one of the first control layer or the second control layer, each frequency selective element being configured: to allow propagation of the RF wave in one of the first parallel-plate waveguide or the second parallel-plate waveguide when the frequency selective element is in one operational mode and to forbid propagation of the RF wave in one of the first parallel-plate waveguide or the second parallel-plate waveguide when the frequency selective element is in another operational mode 
     In at least one embodiment, the antenna further comprises a pair of bent line structures having bent lines, with each bent line structure being located partly on a corresponding one of the first control layer or the second control layer. Each bent line is configured to bypass the one or the plurality of hollow portions of the stack-up structure. Each bent line located on the first control layer is configured to couple the first parallel-plate waveguide to one or a plurality of vertical-polarization peripheral ports, and each bent line located on the second control layer is configured to couple the second parallel-plate waveguide to one or a plurality of horizontal-polarization peripheral ports. 
     In at least one embodiment, all bent lines in each bent line structure have approximately the same electrical length. 
     Each frequency selective element may comprise a radial stub configured to choke high frequencies while passing low frequencies, and a switchable element operatively connected to the radial stub and one of the first parallel-plate waveguide or the second parallel-plate waveguide by one or two of the plurality of through vias, with the switchable element being configured to selectively control operational mode of the frequency selective element. 
     In at least one embodiment, the antenna may be configured to steer the RF wave radiation beam by selectively switching between one and the other operational mode of the frequency selective elements and by selectively switching on a first plurality of frequency selective elements and switching off a second plurality of frequency selective elements. 
     The frequency selective elements of at least one frequency-selective structure of the pair of frequency-selective structures may be arranged in rows, each frequency selective element in each row being located at approximately equal distance from the central port located on the same surface as the at least one frequency-selective structure of the pair of frequency selective structures. 
     Each switchable element may further comprise a connector stub, the connector stub being configured to operatively connect the switchable element to the one or two of the plurality of through vias, and at least certain of the frequency selective elements have a connector stub being shorter than connector stubs of the other frequency selective elements. 
     In at least one embodiment, the frequency selective elements of at least one frequency-selective structure of the pair of frequency-selective structures may be arranged in three rows approximately concentric around the central port located on the same surface as the at least one frequency-selective structure of the pair of frequency selective structures. 
     The frequency selective elements of at least one frequency-selective structure of the pair of frequency-selective structures may be arranged in at least two rows approximately concentric around the central port located on the same surface as the at least one frequency-selective structure of the pair of frequency selective structures, and each switchable element in at least one of the at least two rows may further comprise a connector stub, the connector stub being configured to operatively connect the switchable element to one of the plurality of through vias, and each switchable element in at least another one of the at least two rows may further comprise a connector stub, the connector stub configured to operatively connect the switchable element to two of the plurality of through vias. 
     In at least one embodiment, at least two of the frequency selective elements are operatively connected to one DC circuit and are operated simultaneously. 
     In another embodiment, the antenna is one of a plurality of antennas, and frequency selective elements of each one of the plurality of antennas are configured to be selectively switched ON and OFF, such that the frequency selective elements of each one of the plurality of antennas may operate synchronously or asynchronously with the frequency selective elements of the other ones of the plurality of antennas. 
     The antenna, when one of a plurality of antennas, may be further configured to steer the RF wave radiation beam, the steering being provided by selectively switching on a first plurality of frequency selective elements of the antenna and switching off a second plurality of frequency selective elements of the antenna. 
     Protective layers may be located between neighboring antennas. 
     A RF power divider may be configured to be inserted through one of the one or the plurality of hollow portions, and to electrically and mechanically attach to the RF connector of each one of the plurality of antennas. 
     Another aspect of the present disclosure provides an antenna for transmission of a radio-frequency (RF) wave, with the antenna comprising a stack-up structure having: a first control layer; a second control layer being approximately parallel to the first control layer; a first parallel-plate waveguide and a second parallel-plate waveguide located between the first control layer and the second control layer, the first parallel-plate waveguide and the second parallel-plate waveguide being approximately parallel to each other and to the first control layer and the second control layer; a plurality of through vias operatively connecting the first control layer and the second control layer to center RF and direct current (DC) ground planes; and a RF connector configured to deliver a RF signal to a first central port located on the first control layer and a second central port located on the second control layer. The first central port may be configured to radiate the RF wave into the first parallel-plate waveguide, and the second central port may be configured to radiate the RF wave into the second parallel-plate waveguide. The structure may further comprise vertical-polarization peripheral ports integrated with the first control layer and configured to radiate the RF wave in vertical polarization from the first parallel-plate waveguide, and horizontal-polarization peripheral ports integrated with the second control layer and configured to radiate the RF wave in horizontal polarization from the second parallel-plate waveguide, each one of the vertical-polarization peripheral ports being collocated with one of the horizontal-polarization peripheral ports such that they cross each other. The antenna may further comprise a pair of bent line structures having bent lines, with each bent line structure being located partly on a corresponding one of the first control layer or the second control layer. Each bent line located on the first control layer may be configured to couple the first parallel-plate waveguide to one or a plurality of vertical-polarization peripheral ports. Each bent line located on the second control layer may be configured to couple the second parallel-plate waveguide to one or a plurality of horizontal-polarization peripheral ports. 
     In at least one embodiment, each bent line may be made of microstrip lines with a width optimized to ensure impedance matching of the antenna including transition of one of the first parallel-plate waveguide or the second parallel-plate waveguide to the bent line. 
     In at least another embodiment, all bent lines have the same electrical length. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
         FIG. 1A  depicts a top perspective view of a beam steering antenna, in an embodiment of the present technology; 
         FIG. 1B  provides an enlarged view of the center of the top perspective view of  FIG. 1A ; 
         FIG. 2A  depicts an underside perspective view of the antenna of  FIG. 1A ; 
         FIG. 2B  depicts an enlarged partial cross section view of the stack-up structure of the antenna of  FIG. 1A , in an embodiment of the present technology; 
         FIG. 3A  illustrates the total gain of the antenna of  FIG. 1A ; 
         FIG. 3B  illustrates the reflection coefficient (i.e., S 11 -parameter) of the antenna of  FIG. 1A ; 
         FIG. 3C  illustrates the radiation patterns of the antenna of  FIG. 1A ; 
         FIG. 4  provides an enlarged top view of bent lines, in an embodiment of the present technology; 
         FIG. 5A  illustrates the S parameters of the bent lines of  FIG. 4 ; 
         FIG. 5B  illustrates the isolation between the bent lines of  FIG. 4 ; 
         FIG. 5C  illustrates the phase of the bent lines of  FIG. 4 , and the phase difference; 
         FIG. 6A  depicts a top view of a Frequency Selective Element (FSE) in a portion of the antenna of  FIG. 1A , in an embodiment of the present technology; 
         FIG. 6B  illustrates an elevation side view of a FSE and a surrounding portion of the antenna of  FIG. 1A , in an embodiment of the present technology; 
         FIG. 7  illustrates a method of steering electromagnetic beam transmitted by the antenna of  FIG. 1A , in an embodiment of the present technology; 
         FIG. 8  depicts a stacked antenna, in an embodiment of the present technology; and 
         FIG. 9  depicts a RF power divider and its insertion through hollow portions of the structure of the stacked antenna. 
     
    
    
     It is to be understood that throughout the appended drawings and corresponding descriptions, like features are identified by like reference characters. Furthermore, it is also to be understood that the drawings and ensuing descriptions are intended for illustrative purposes only and that such disclosures are not intended to limit the scope of the claims. 
     DETAILED DESCRIPTION 
     The instant disclosure is directed to addressing the deficiencies of current phased array antennas implementations. The instant disclosure describes a 360° beam steering antenna (also referred to herein as “antenna”), having two parallel-plate waveguides and integrated frequency selective structures (FSSs). The antenna is configured to provide increased ranges of steering angles for both vertical and horizontal polarizations while also providing high directivity (of about 13 dB to 16 dB) with low variation (about 10%) for various steering angle ranges. 
     The technology described herein may be embodied in a variety of different electronic devices (EDs) including base stations (BSs), user equipment (UE), etc. 
     It will be appreciated that the electromagnetic wave that is one of propagated by and received by the disclosed antenna configuration may be within a radio frequency (RF) range (RF wave). In some embodiments, the RF wave may be a millimeter wave range and below (e.g., operating frequencies of about 10 GHz to about 300 GHz). In other embodiments, the RF wave may be in a microwave range (e.g., about 1 GHz to about 10 GHz). 
     The antenna structure as described herein may be configured to operate in a millimeter wave range and below (i.e., between 10 GHz and about 300 GHz). It should be understood, however, that the presented antenna structure may also operate at other RF range frequencies. Moreover, the antenna structure, as described herein may, in various embodiments, be formed from appropriate features of a multilayer printed circuit board (PCB). The features of the antenna structure may be formed by etching of conductive layers and manufacturing of vias along with other such conventional PCB manufacturing techniques. Such a PCB implementation may be suitably compact for inclusion in electronic devices such as BS and UEs. Mature manufacturing techniques known in the PCB field may be used to provide suitable cost-effective volume production. 
     As used herein, the term “about” or “approximately” refers to a +/−10% variation from the nominal value. It is to be understood that such a variation is always included in a given value provided herein, whether or not it is specifically referred to. 
     As referred to herein, the term “guided wavelength” refers to a wavelength of propagation of an RF wave to provide propagation of a transverse electromagnetic mode (TEM) inside a corresponding waveguide. In addition, as referred to herein, the term “via” refers to an electrical connection providing electrical connectivity between the physical layers of an electronic circuit. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the described embodiments appertain to. 
     In accordance with the contemplated embodiments of the instant disclosure, the antenna structure, as described herein, may be configured to steer the angle of RF beam transmission and reception by actuating a plurality of Frequency Selective Elements (FSEs) integrated with two parallel-plate waveguides. In particular, the antenna structure may be configured to switch and operate to an “ON” state based on a first plurality of FSEs and operate to switch to an “OFF” state based on a second plurality of FSEs. 
     Compared to conventional planar phased array antennas, the embodiments of the instantly disclosed antenna structure, may provide any or all of a wider steering angle range (e.g., at least 180 degrees and up to 360 degrees), while exhibiting lower losses and a lower power consumption. Furthermore, the disclosed antenna structure may be integrated with a substrate of a stacked-up arrangement that may be configured to operate in vertical and horizontal polarizations as well as radiate and receive multiple RF beams. In addition, as compared to the conventional planar phased array antennas, the disclosed antenna structure may be less expensive to manufacture in view of the implementation of switchable elements instead of phase shifters to steer the beam angle, and the use of a multilayer PCB process when fabricating the antenna. 
     Referring now to drawings,  FIG. 1A  depicts a perspective top view of the structure of antenna  100 , in an embodiment of the present technology, and  FIG. 2A  depicts an underside (i.e., bottom) perspective view of antenna  100  of  FIG. 1A , in an embodiment of the present technology. 
     As shown, antenna  100  comprises a stack-up structure  110  having two control layers: a first control layer  101  (referred to herein as “first control circuit layer”) and a second control layer  202  (referred to herein as “second control circuit layer”). Antenna  100  further comprises central port  105  disposed on the top, central port  206  disposed on the underside, and two FSS  191 ,  292 . 
       FIGS. 1A and 2A  indicate that stack-up structure  110  has an approximately circular shape having a circumferential edge  104 . It is contemplated that stack-up structure  110  may encompass other shapes that may be suitably used for radiation of the RF wave therefrom, with a beam that may be steered at an angle of 0 to 360 degrees in the plane of the stack-up structure. For example, and without limitation, the shape may be approximately elliptical. The disclosed shape of antenna  100  provides an exemplary structure of an effective configuration, but is not intended to be limiting, as other antenna shapes may be applied in accordance with the inventive concepts disclosed heretofore. 
       FIGS. 1A and 2A  further indicate that stack-up structure  110  has one or several hollow portions  121 , and one or several holes  122 . When stack-up structures  110  are stacked-up (as shown  FIG. 8 ), and these holes are aligned, this alignment allows respectively to electrically feed RF connector  120  and DC connector  181 , and to mechanically maintain (fixing and/or positioning) the stack-up structures  110  together. 
     The first control layer  101  of antenna  100  includes vertical-polarization peripheral ports  151  that are configured to receive and transmit RF waves in a vertical polarization. The vertical-polarization peripheral ports  151  are also referred to herein as vertical-polarization peripheral radiating elements  151 , and are radiating elements, having vertical polarization, located as illustrated in  FIG. 1A , on the periphery of the first control layer  101 , distributed radially around the circumference of the first control layer  101 , and proximate to circumferential edge  104  of antenna  100 . 
     The second control layer  202  of antenna  100  has horizontal-polarization peripheral ports  252 , configured to receive and transmit RF waves in a horizontal polarization. The horizontal-polarization peripheral ports  252  are also referred to herein as horizontal-polarization peripheral radiating elements  252 , and are radiating elements, having horizontal polarization, located as illustrated in  FIG. 1B , on the periphery of the second control layer  202 , distributed radially around the circumference of the second control layer  202 , and proximate to circumferential edge  104  of antenna  100 . 
     Referring now to  FIG. 2B , stack-up structure  110  has a first parallel-plate waveguide  131  and a second parallel-plate waveguide  132 , two ground layers  103 ,  204  and two metal plates  133 ,  134 , as well as first control layer  101  and second control layer  202 . The metal plates  133 ,  134  along with a first ground layer  103  and a second ground layer  204  form two parallel-plate waveguides  131 ,  132 . In at least one embodiment, parallel-plate waveguides  131 ,  132  are filled with a waveguide dielectric material, such as, for example, a dielectric composite material. In some portions of stack-up structure  110 , a layer of dielectric material may cover the metal plates  133 ,  134  on the sides of first control layer  101  and second control layer  202 , respectively. 
     The first ground layer  103  and the second ground layer  204  are located between the first control layer  101  and second control layer  202 . The ground layers  103 ,  204  are connected to an electrical ground. 
     In illustrated embodiments, the distance between first control layer  101  and second control layer  202  is about a quarter of the wavelength. The first ground layer  103  and the second ground layer  204  may be separated by a spacer. In some embodiments, there is a spacing  135  between the first ground layer  103  and the second ground layer  204 . The spacing width  136  is such that the total distance between first control layer  101  and second control layer  202  is about a quarter of the wavelength. Such spacing width  136  may be preferable for integration and operation of vertical-polarization peripheral ports  151 . 
     The first control layer  101  and second control layer  202  are connected to each other by through vias  130  located in various places of stack-up structure  110 . The through vias  130  (also referred to herein as “vias”) go all the way through stack-up structure  110  and various elements located on first control layer  101  and second control layer  202  of antenna  100  may be connected to vias  130 . The vias  130  are operatively connected to ground layers  103 ,  204 . As illustrated in  FIG. 2B , via  130  may be approximately perpendicular to first control layer  101  and second control layer  202 . It should be noted that first control layer  101  and second control layer  202  are electrically isolated from each other because vias  130  are connected to electrical grounds. 
     The stack-up structure  110  may be made of a PCB. The dielectric materials used in the stack-up structure  110  may be those known in the art of the PCB technology. Alternatively, the stack-up structure  110  may be made with metallic plates which may be assembled with a circuit board, or using LTCC or liquid crystal polymer (LCP) technology. 
     Referring again to  FIGS. 1A and 2A , two central ports  105 ,  206  may be located at or near a center of stack-up structure  110 , one on first control layer  101  and the other on second control layer  202 , respectively. The center of stack-up structure  110  is defined herein to be located at approximately equal distances from any point of circumferential edge  104  of antenna  100 . It should be understood that central ports  105 ,  206  may be located at any other part of stack-up structure  110 . The central ports  105 ,  206  may be operatively connected to one common via  130 . 
     The central ports  105 ,  206  may be designed for example as described in the cross-referenced application, using feeds and shoulder portions made for example of microstrip lines, as well as vias, and are configured to be sources of radiation of an RF wave. The RF wave may radiate radially from central ports  105 ,  206  into parallel-plate waveguides  131  and  132 . The central ports  105 ,  206  are also configured to receive radiation from parallel-plate waveguides  131  and  132 . Each central port  105 ,  206  is operatively connected to a corresponding RF connector  120  through respectively RF feeds (for example microstrip lines)  119 A and  119 B (also visible on  FIG. 1B ), which, in its turn, is operatively connected to an RF signal source operated by an RF controller (not shown). The RF connector  120  may be located proximate to a hollow portion  121 . In some embodiments, there are two RF feeds  119 A and  119 B as represented, but a different number of RF feeds may be had between the central ports  105 ,  206  and the RF connector  120 . In operation, RF signal is delivered from the RF connector  120  (as depicted in  FIGS. 1A and 2A ) through RF feeds  119 A and  119 B to a center point of respectively the central ports  105 ,  206 . Leads deliver RF signal to vias positioned radially from the center point. Three portions of the vias, located inside stack-up structure  110 , radiate RF wave into parallel-plate waveguides  131  and  132  (also visible on  FIG. 2B ). Complete description of central ports that may be used herein as central ports  105 ,  206 , may be found in the cross-referenced application. 
     In order to be able to radiate efficiently at various steering angles  8 , central ports  105 ,  206  may be optimized to provide similar gain for RF radiation in all of, or in most of, the directions, or in a broad radiating angle range. In some embodiments, central ports  105 ,  206  provide similar gain in a desired frequency range of antenna  100 . 
     In operation, RF signal is delivered from RF connector  120  (as depicted in  FIGS. 1A and 2A ) through feeds  119 A and  119 B to respectively the central ports  105  and  206 . It should be understood that although central ports  105 ,  206  may be different from each other, they may have similar configuration. A configuration may for example be as described in the cross-referenced application, and is not shown in the present disclosure. 
       FIG. 3A  illustrates the total gain of the antenna  100  versus frequency. It further illustrates the realized gain, as the total gain minus the return loss. The gain is more than 13 dB between 27 GHz to 29 GHz, providing evidence that antenna  100  in the disclosed embodiment offers high gain in a broad frequency band. 
       FIG. 3B  illustrates the return loss (or reflection coefficient) of antenna  100  versus frequency. The return loss is about −10 dB in the frequency band between 27 GHz-29 GHz, providing evidence that antenna  100  in the disclosed embodiment is well matched in a broad frequency band. 
       FIG. 3C  illustrates the radiations patterns of antenna  100  for different frequencies in the band between 26.5 GHz-29.5 GHz, providing evidence that antenna  100  in the disclosed embodiment delivers a high directivity of about 15 dB in a broad frequency band. 
     Referring again to  FIGS. 1A and 2A , first control layer  101  has an array of vertical-polarization peripheral ports  151  and second control layer  202  has an array of horizontal-polarization peripheral ports  252 . Polarization peripheral ports  151  and  252  may for example be designed as described in the cross-referenced application, and are not detailed in the present disclosure. The vertical-polarization peripheral ports  151  and horizontal-polarization peripheral ports  252  are collocated such that both structures may be complementary to each other. 
     How the coupling may be performed of the RF wave from parallel-plate waveguides  131  and  132  to respectively vertical-polarization peripheral ports  151  and horizontal-polarization peripheral port  252 , and vice versa, may be found as described in the cross-referenced application. In addition, bent lines as described below, also form part of such coupling. 
     The number of vertical-polarization peripheral ports  151  and horizontal-polarization peripheral ports  252  may be determined from the radius of the stack-up structure  110  and a distance between neighboring peripheral ports, either between neighboring vertical-polarization peripheral ports  151  on first control layer  101  or between neighboring horizontal-polarization peripheral ports  252  on second control layer  202 . In some embodiments, the distance between vertical-polarization peripheral ports  151  is approximately half of the wavelength. The radius of the stack-up structure  110  is determined by the desired gain and directivity of the antenna  100 . For example, and without limitation, the radius of the stack-up structure  110  may be about 70 mm, and the distance between vertical-polarization peripheral ports  151  or between horizontal-polarization peripheral ports  252  may be about 6.87 mm allowing for 64 such peripheral ports. 
     Referring again to  FIG. 1A ,  FIG. 1B ,  FIG. 2A , and  FIG. 2B , two FSS  191 ,  292  are located on first control layer  101  and second control layer  202 , respectively. Both FSS  191 ,  292  are integrated with stack-up structure  110  and comprise a plurality of FSEs  600 A- 600 B operatively connected to through vias  130  of stack-up structure  110 . As described in more details below, FSEs  600 A- 600 B are arranged in rows  115 ,  116  and  118  that may be concentric as shown in  FIG. 1B , with the FSEs  600 A- 600 B in FSS  191  controlling propagation of the RF wave inside parallel-plate waveguides  131 ,  132 , which are coupled to vertical-polarization peripheral ports  151  through vias and bent lines  123 . The same may be implemented with respect to FSEs  600 A- 600 B in FSS  292  and horizontal-polarization peripheral ports  252 . 
     Not only are FSS  191 ,  292  integrated with stack-up structure  110 , they are also integrated with each other because they are both operatively connected to through vias  130  of stack-up structure  110 . It should be noted that, in at least one embodiment, vias  130  of antenna  100  are through vias, which is generally cheaper to fabricate than other types of vias. 
       FIG. 4  provides an enlarged top view of bent lines  123 . As indicated, they couple parallel-plate waveguides  131 ,  132  to vertical-polarization peripheral ports  151  (and horizontal-polarization peripheral ports  252  in FSS  292 ). As seen in the embodiment depicted  FIG. 4 , each bent line  123  in FSS  191  corresponds to two vertical-polarization peripheral ports  151  (and each bent line  123  in FSS  292  corresponds to two horizontal-polarization peripheral ports  252 ). However each bent line  123  could correspond to a different number of polarization peripheral ports. Bent lines  123  are designed so as to both bypass hollow portions  121 , and to offer a high symmetry in transmission coefficients between bent lines, as well as a low coupling between them, in particular adjacent ones. It will be apparent that groupings of more than two bent lines  123  may be had around hollow portions, to the extent still achieving the same objectives of high symmetry and low coupling. In an embodiment of the present technology, bent lines  123  are designed so as to attain the characteristics as shown below in relation to  FIGS. 5A-5C . Such characteristics are calculated in relation to four reference points  400   a/b/c/d  at the extremities of two bent lines  123 , as shown  FIG. 4 , the other bent lines  123  featuring identical characteristics owing to the symmetry of shape of the bent lines. 
     Bent lines  123  may be made of microstrip lines with a width optimized to ensure impedance matching of the full antenna  100  which includes transitions from parallel-plate waveguides  131  and  132  to bent lines  123 . As shown  FIG. 4 , bent lines  123  do not all have the same physical length or shape, but they are shaped so as to provide the same electrical length, at the same time allowing space for integrating DC and RF connectors and features for mechanical assembling. Bent lines  123  may for example be straight microstrip lines, or microstrip lines with a crenellated shape as seen in  FIG. 4 . It should be noted that bent lines  123  may be advantageously used regardless of whether hollow portions  121  need be bypassed, as they reduce the number of required switchable elements  620  in FSEs  600 A- 600 B. 
       FIG. 5A  illustrates the S parameters of the bent lines  123  in  FIG. 4 . Reflection coefficients S 11 , S 22 , S 33  and S 44 , as measured using the four reference points  400   a/b/c/d  on  FIG. 4  as respectively ports  1 / 2 / 3 / 4  for the S parameters, are below −15 dB in the band 26 GHz-30 GHz, providing evidence that the bent lines  123  are well matched in a broad frequency band. Coefficients S 21  and S 43  are higher than −1.4 dB in the frequency band 26 GHz-30 GHz, providing evidence that bent lines  123  have low insertion losses and good transmission coefficients. 
       FIG. 5B  illustrates the isolation between the bent lines  123  of  FIG. 4 , as measured using the four reference points  400   a/b/c/d  on  FIG. 4 . It further illustrates the transmission coefficients for uncoupled ports of the bent lines  123 , providing evidence that the coupling coefficients are below −29 dB in a broad frequency band (26 GHz-30 GHz). 
       FIG. 5C  illustrates the phase of the bent lines  123  of  FIG. 4 , and the phase difference, as measured using the four reference points  400   a/b/c/d  on  FIG. 4 . It further illustrates the phases of the transmission coefficients versus frequency for coupled ports of the bent lines  123  of  FIG. 4 , and the differences of these two phases versus frequency. It shows that the bent lines  123  have the same phase in a broad frequency band (26 GHz-30 GHz). This ensures that the complete antenna  100  will present symmetrical radiation pattern and no scan loss when the RF beam is steered. 
     The structure of FSE  600 B may be as found in the cross-referenced application, and is not detailed further in the present disclosure. 
     The structure of FSE  600 A will now be described in further detail.  FIG. 6A  depicts a top view of a configuration of FSE  600 A in a portion of antenna  100 , in accordance with an embodiment of the present disclosure. 
     The FSE  600 A is operably connected to a double via  630 A- 630 B and has a switchable element  620 , a radial stub  622 , and a direct current (DC) circuit  624 . FSE  600 A also has a connector stub  629  that operatively connects double via  630 A- 630 B to switchable element  620 . Double via  630 A- 630 B passes through two apertures  631 A- 631 B formed in first control layer  101  and metal plates  133 ,  134 , as also more clearly seen on  FIG. 6B . 
     The radial stub  622  is illustrated as an open-ended radial stub. The length of the radial stub is determined by ¼ of the microstrip line guided wavelength (λ g ). The radial stub  622  may be implemented as any of a microstrip, a substrate integrated waveguide, a stripline, a coplanar waveguide, or the like. The radial stub  622  is configured to choke high frequencies while passing low frequencies. The open-ended radial stub  622  provides a ground to RF signal, while not grounding the DC signal. 
     The switchable element  620  may be a PIN diode, such as a beam lead PIN diode. In at least one another embodiment, switchable element  620  may be a microelectromechanical systems (MEMS) element. 
     The switchable element  620  of the FSE  600 A is operatively connected to radial stub  622  and to double via  630 A- 630 B. The switchable element  620  may also be connected through DC circuit  624  and DC line  670  to a controller  680 . 
     The controller  680  may be, for example, a DC voltage controller. The DC circuit  624  has a resistor  675 , which allows controlling the current of the switchable element  620 . The resistor  675  may be a millimeter wave thin film resistor or a regular thick film resistor. 
     The controller  680  may operate the switchable element  620  that is configured to actuate voltage/current supplied to radial stub  622  and control the operation of switchable element  620  by switching it to ON or OFF operation mode. 
     When switchable element  620  is in ON operation mode, the switchable element  620  acts as a resistance, equivalent to serial resistance of switchable element  620  (for example, to the serial resistance of the PIN diode). When switchable element  620  is in OFF operation mode, the switchable element  620  acts as a capacitor. When switchable element  620  is in OFF mode, the RF wave continues its propagation in first parallel-plate waveguide  131  or second parallel-plate waveguide  132 . 
     By increasing or decreasing the length of connector stub  629  by a quarter wavelength, one may invert the ON and OFF effect of FSE. That is, when the switchable element  620  is OFF, FSE  600 A does not permit (e.g. it prevents) propagation of the RF wave. When switchable element  620  is ON, FSE  600 A permits (allows) propagation of the RF wave. 
     Double via  630 A- 630 B, as opposed to a single via for FSE  600 B as shown in the cross-referenced application, increases the reflectivity of FSE  600 A when it is in ON operation mode. This in turn improves the ability to control propagation of the RF wave inside the first parallel-plate waveguide  131  or second parallel-plate waveguide  132 . The length of connector stub  629  may be adapted (compared for example to a connector stub for FSE  600 B as seen in the cross-referenced application) so that FSE  600 A may be optimized for the frequency of the RF wave. 
     Referring to  FIG. 6B , stack-up structure  110  has a first parallel-plate waveguide  131  and a second parallel-plate waveguide  132 , ground layers  103 ,  204 , first control layer  101  and second control layer  202 , as well as first metal plate  133  and second metal plate  134 , as discussed above. 
     One FSE  600 A or  600 B is located on first control layer  101  and connected to a double via  630 A- 630 B (or a single via, as shown in the cross-referenced application). Another FSE  600 A or  600 B is located on an opposite side of stack-up structure  110 , i.e. on second control layer  202 . 
     The double via  630 A- 630 B (or single via as shown in the cross-referenced application) is electrically connected to ground layer  103  and passes through two apertures  631 A- 631 B (or a single aperture, as shown in the cross-referenced application) formed in first control layer  101  and metal plates  133 ,  134  through two other apertures (not shown, or a single aperture, as shown in the cross-referenced application) in second control layer  202  to join FSE  600 A or  600 B located on the second control layer  202 . 
     On horizontal-polarization surface  202 , double via  630 A- 630 B (or single via as shown in the cross-referenced application) is operatively connected to another connector stub  629 , which is operatively connected to another switchable element  620 , operatively connected to radial stub  622 . The switchable element  620  may be also connected through DC circuit  624  to a controller  680 . 
     It should be noted that FSE  600 A or  600 B on second control layer  202  may be similar to FSE  600 A or  600 B on first control layer  101 , with similar structural elements and parameters. 
     Each FSE  600 A or  600 B, and in particular, each switchable element  620  may be operatively connected, through a separate DC connection line  670  to DC controller  480 . The controller  680  is configured to control switchable elements  620  by operating each of them between ON and OFF operation modes. 
     Referring now also to  FIG. 1A ,  FIG. 1B , the FSEs  600 A- 600 B of FSS  191 ,  292  may be operatively connected to the DC connector  181  (depicted in  FIG. 1A ), which are then operatively connected to the controller  680  (shown in  FIG. 6A ). The DC connector  181  may be located proximate to a hollow portion  121 . The controller  680  may control beam direction for vertical and horizontal polarizations separately by controlling operation of FSEs  600 A- 600 B and in particular, operation of the switchable elements of FSEs  600 A- 600 B. It should be noted that although each switchable element (such as switchable element  620  shown in  FIG. 6A ) is connected to the controller  680  with a DC line (such as DC line  670  shown in  FIG. 6A ), DC lines are not illustrated in  FIGS. 1A and 1B  to simplify the drawing. 
     It should be noted that there may be one controller  680  for vertical and horizontal polarizations, or there may be a separate controller  680  for each polarization. It should also be understood that each switchable element of, and therefore each, FSE  600 A- 600 B, may be controlled separately. Alternatively, switchable elements may be grouped as discussed below. 
     The FSEs  600 A- 600 B are configured to permit propagation of the RF wave when their switchable element is in OFF operation mode. When their switchable element is in ON operation mode, the RF wave is captured by radial stubs (such as radial stub  622  shown in  FIG. 6A ) and therefore FSEs  600 A- 600 B block the RF wave from further propagation towards the circumferential edge  104  of stack-up structure  110 . 
     In order to determine a configuration of FSE  600 A- 600 B, amplitudes of reflection and transmission coefficients of FSE  600 A- 600 B may be obtained using a rectangular waveguide as disclosed in the cross-referenced application. 
     Referring again to  FIGS. 1B and 2A , FSEs  600 A- 600 B are positioned radially on stack-up structure  110  and are arranged in FSE rows  115 ,  116  and  118  where each FSE  600 A- 600 B is located radially from central port  105 ,  206 . 
     Referring to  FIGS. 1B, 6A and 6B , connector stub  629  may be made shorter in some of FSEs  600 A- 600 B of FSS  191 . In at least one embodiment, one FSS row  115  may have FSEs  600 B with longer connector stub  629 , while the neighboring row  116  of the same FSS may have FSEs  600 A with shorter connector stub  629  compared to row  115 . For example, some FSE rows  115  may have one length of connector stubs  629 , and the other neighboring rows  116  may have shorter (or longer) length of connector stubs  629  in FSEs  600 A- 600 B. For example, every second FSE row  116  may have FSE  600 A- 600 B with shorter connector stub  629 . Such configuration of FSS  191  may result in smooth transmission characteristics over a broad frequency bandwidth of antenna  100 . In addition to their different length, the connector stub  629  can also have different microstrip line widths. While FSEs  600 B may be located in rows  115  and  118 , and FSEs  600 A in row  116 , other distributions of FSEs  600 A/ 600 B may be had among the different rows  115 ,  116  and  118 . For example, FSEs may all be of one type,  600 A or  600 B, FSEs  600 A may be located in rows  118 , etc. 
     Referring to  FIG. 1B , the number of FSE rows  115 ,  116 ,  118 , and distances  117 A and  117 B between perimeters of respectively rows  118  and  116 , and rows  116  and  115 , may be optimized for desired RF characteristics of antenna  100 , for example: the total gain of the antenna  100  versus frequency such as the one illustrated on  FIG. 3A , and antenna  100  radiation patterns such as the ones illustrated on  FIG. 3C . In the embodiment shown  FIG. 1B , FSS  191  comprises three rows  115 ,  116 , and  118 , but a different number of rows could form FSS  191 . In particular, if one increases the radius of stack-up structure  110 , the number of FSE rows  115 ,  116 ,  118  may be increased. In some embodiments, the distance  117  between FSE rows  118 ,  116  may vary and may be longer towards the center port  105 ,  206  and shorter towards peripheral ports  151 ,  252 . 
     In operation, antenna  100  may be steered by switching ON and OFF the switchable elements  620  of FSEs  600 A- 600 B. The switchable elements  620  are operated by controller  680 . The RF wave is transmitted when switchable elements  620  are in OFF operation mode and reflected when the switchable elements  620  are in ON operation mode. As disclosed in the cross-referenced application, FSEs  600 A- 600 B which are located inside a particular area (not shown in the present disclosure) may be operated simultaneously and switched ON and OFF by a controller (not shown), the particular area&#39;s characteristics being determined based on various parameters, such as, for example, a desired gain, a steering angle, and a desired beam width. Various combinations of grouping and selective switching of FSEs  600 A- 600 B of antenna  100  may permit steering the beam with a beam-steering step of as low as 3 degrees. As also disclosed in the cross-referenced application, antenna  100  may transmit RF wave to various directions simultaneously by switching OFF several particular areas, therefore becoming a multi-directional antenna. 
       FIG. 7  illustrates a method  700  of steering RF beam transmitted by antenna  100 , in an embodiment of the present technology. At task block  710 , a controller (for example, a RF controller, or a RF controller combined with a DC controller) may receive an externally provided steering angle and RF signal for transmission by antenna  100 . The controller then determines at task block  720  FSEs  600 A- 600 B that need to be ON and FSEs  600 A- 600 B that need to be OFF in order to transmit the RF signal at the provided steering angle. Polarization of radiated RF wave may also be determined by the controller at this task block  710 . 
     DC signal is then applied at task block  730  to FSEs  600 A- 600 B of antenna  100  such that some FSEs  600 A- 600 B are ON and the others are OFF, as determined previously by the controller. At the same time as the appropriate DC signal is applied to FSEs  600 A- 600 B, RF signal is applied to one central port  105  or  206 . As discussed above, the polarization of the transmitted RF wave may be controlled by supplying the RF signal to the central port, i.e. either to the central port located on first control circuit layer  101  or on second control circuit layer  202 . 
     In order to modify at task block  740  the steering angle, the controller needs to determine  720  again the appropriate number of FSEs  600 A- 600 B that need to be OFF, as well as their location. The other FSEs  600 A- 600 B may be turned ON by the controller. As discussed above, the polarization of radiated RF wave may be controlled by supplying RF signal to either one or another central port  105 ,  206 . 
     When implemented using a PCB, antenna  100  may be integrated on one substrate, that is stack-up structure  110 , using low-cost multilayer PCB manufacturing process. Several multilayer PCBs may be stacked together. This may aid in either or both of increasing total gain and improving the control of beam direction in elevation. 
       FIG. 8  depicts a stacked antenna  800 , in an embodiment of the present technology. In stacked antenna  800 , several antennas  100  are stacked together. Eight are shown on  FIG. 8  but a different number may be used. In particular, stacked antenna  800  may be built when stack-up structure  110  of antennas  100  is made of PCB. Due to integration of the elements of antennas  100  with stack-up structure  110 , such antenna  800  may remain compact. 
     Protective layers  810  may be provided between neighboring antennas  100  of stacked antenna  800 . The protective layers  810  may help to reduce energy coupling between the FSSs (not depicted in  FIG. 8 ) of the neighboring antennas  100 . The protective layer  810  may be made of a metal material, for example, aluminum. 
     When antennas  110  are stacked-up, hollow portions  121 , and holes  122  may be aligned, to allow mechanically maintaining (fixing and/or positioning) the stacked-up antennas  110 , such as for example through the use of screws  811  through holes  122 . 
     Alignment of hollow portions  121 , and holes  122  further allows to electrically feed RF connector  120  and DC connector  181 , from the inside of circumferential edge  104  of antennas  110 . DC connectors  181  of antennas  100  may be connected to a master controller (not shown), which may be configured to operate the FSSs  191 - 292  of antennas  100 , and in particular, their switchable elements. Operation of FSSs  191 - 292  and of FSEs  600 A- 600 B may or may not be independent or asynchronous from one stacked antenna  100  to the next. This allows to have a single steered RF beam with all stacked up antennas  100 , or up to as many independent steered RF beams as there are stacked up antennas  100 . For example between 1 and 8 different RF beams may be transmitted with the stacked up structure of  FIG. 8 , when multiple RF beams may not be had with a single antenna  100 , having an optimized impedance matching for a single RF beam. Grouping certain of antennas  100  in the stack to share the same synchronous operation of their FSSs  191 - 292  and FSEs  600 A- 600 B may provide a higher gain for a particular steered RF beam. 
     Conversely, as shown  FIG. 9 , RF connectors  120  of antennas  100  may be operatively connected to a RF power divider  900  that is configured to feed the central ports (not depicted in  FIG. 9 ) of antennas  100 . RF power divider  900  may be inserted through one of the hollow portions  121 , and electrically and mechanically attach to each one of the RF connectors (not shown) of antennas  100 . 
     It is to be understood that the operations and functionality of at least some components of the disclosed antenna may be achieved by hardware-based, software-based, firmware-based elements and/or combinations thereof. Such operational alternatives do not, in any way, limit the scope of the present disclosure. 
     It will also be understood that, although the inventive concepts and principles presented herein have been described with reference to specific features, structures, and embodiments, it is clear that various modifications and combinations may be made without departing from the such disclosures. The specification and drawings are, accordingly, to be regarded simply as an illustration of the inventive concepts and principles as defined by the appended claims, and are contemplated to cover any and all modifications, variations, combinations or equivalents that fall within the scope of the present disclosure.