Patent Publication Number: US-11387557-B2

Title: Antenna for multi-broadband and multi-polarization communication

Description:
This application claims the benefit of U.S. provisional application Ser. No. 62/872,266, filed Jul. 10, 2019, the subject matter of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an antenna for multi-broadband and multi-polarization communication, more particularly, to a dipole antenna achieving dual-broadband by innovatively configured radiators and parasitic elements, wherein each radiator may include a folded arm and a ground wall with a meandering portion, and each parasitic element may partially surround an associated one of the radiators. 
     BACKGROUND OF THE INVENTION 
     Antenna is essential for modern electronic device which requires radio-frequency functionality, such as smart phone, tablet computer and notebook computer, etc. As communication standards evolve to provide faster data transfer rate and higher throughput, antenna needs to satisfy more challenging demands. For example, to meet requirements of fifth-generation (5G) mobile telecommunication at FR2 bands with MIMO (multi-input multi-output) of dual-polarization diversity, an antenna needs to support bandwidths broader than 19.5% and 16.1% respectively at two nonoverlapping bands starting from 24.25 to 29.5 GHz and from 37.0 to 43.5 GHz, and also needs to transmit and/or receive independent signals of different polarizations (e.g., two signals carrying two different data streams respectively by a horizontal polarization and a vertical polarization) with a high signal isolation between these different polarizations, so as to provide a high cross-polarization discrimination (XPD). 
     Besides, antenna desires to be compact in size since modern electronic device desires to be slim in form factor and therefore only has limited space left for antenna. Accordingly, antenna needs to have a high bandwidth-to-volume ratio representing bandwidth per unit volume (measured in, e.g., Hz/(mm{circumflex over ( )}3)). 
     In conventional art, a stacked patch antenna is utilized to support two bands by stacking two patches, but fails to satisfy bandwidth requirements of 5G mobile telecommunication. The stacked patch antenna also suffers a relatively low bandwidth-to-volume ratio. 
     SUMMARY OF THE INVENTION 
     An objectivity of the invention is providing an antenna (e.g.,  100  in  FIGS. 1 a  to 1 f   ) for multi-broadband (e.g., dual-broadband) and multi-polarization (e.g., dual-polarization) communication. The antenna may include a plurality of mutually separated radiators (e.g., r[ 1 ] to r[ 4 ] in  FIGS. 1 a  to 1 f  and 2 a  to 2 c   ) connected to a ground plane (e.g., G 0  in  FIG. 1 a   ). The plurality of radiators may be configured to jointly function as one or more (e.g., two) dipoles, and each said radiator may be configured to contribute to resonances at two or more nonoverlapping bands (e.g.,  810  and  820  in  FIG. 8 ). 
     Each said radiator (e.g., r[n] for n=1 to 4) may include a conductive arm (e.g., a[n] in  FIGS. 2 b  and 2 c   ) and a conductive ground wall (e.g., g[n] in  FIGS. 2 b  and 2 c   ) connecting the arm to the ground plane. Each arm may include a conductive arm plate (e.g., b[n] in  FIGS. 2 b  and 2 c   ) and a conductive folded arm (e.g., h[n 1 ] or h[n 2 ] in  FIG. 2 c   ). The ground wall may extend outward (e.g., downward along negative z-direction,  FIGS. 2 b  and 2 c   ) from a bottom surface (e.g., bb[n] in  FIG. 2 c   ) of the arm plate to the ground plane. The folded arm may extend outward (e.g., downward,  FIGS. 2 b  and 2 c   ) from the bottom surface of the arm plate or from a top surface of the arm plate opposite to the bottom surface of the arm plate, and the folded arm may be separated from the ground wall and the ground plane (e.g.,  FIG. 2 d   ). 
     In an embodiment (e.g.,  FIG. 2 d   ), the ground wall may extend outward from a first site (e.g., gs[n 1 ] or gs[n 2 ]) of the bottom surface of the arm plate, and the folded arm may extend outward from a second site (e.g., hs[n 1 ] or hs[n 2 ]) of the top or bottom surface of the arm plate; on a geometric reference surface (e.g., xy-plane) parallel to the bottom surface of the arm plate, a projection of the first site may be disposed in an inner geometric region (e.g., bc[n] in  FIG. 2 d   ) inside a projection of the arm plate, and a projection of the second site may be disposed in a peripheral geometric region (e.g., bd[n],  FIG. 2 d   ) between a boundary of the inner geometric region and a boundary of the projection of the arm plate, wherein the boundary of the inner geometric region and the boundary of the projection of the arm plate may be arranged not to intersect. 
     In an embodiment (e.g.,  FIG. 2 f    or  2   g ), each folded arm may include an extension plate (e.g., hd[n 1 ] or hd[n 2 ]) and a first extension wall (e.g., hc[n 1 ] or hc[n 2 ]). The extension plate may be parallel to the arm plate, and may be separated from the arm plate. The first extension wall may connect the arm plate and the extension plate. In an embodiment (e.g.,  FIG. 2 g   ), each folded arm may further include a second extension wall (e.g., hf[n 1 ] or hf[n 2 ]) which may extend outward from a top or bottom surface of the extension plate, and may be separated from the arm plate and the first extension wall. 
     In an embodiment, the antenna may further include a plurality of conductive parasitic elements (e.g., p[ 1 ] to p[ 4 ] in  FIGS. 1 a  to 1 f  and 4 a   ). The plurality of parasitic elements may be mutually insulated, and each said parasitic element may be insulated from the plurality of radiators and the ground plane. On a geometric reference surface (e.g., xy-plane in  FIG. 4 a   ), a projection of each said parasitic element (e.g., p[n] for n=1 to 4) may extend between two gaps (e.g., gp[ 1 ] and gp[ 2 ] in  FIG. 4 a   ) which clamp a projection of an associated one (e.g., r[n]) of the plurality of radiators, and may be arranged not to entirely enclose a geometric origin (e.g., p 0  in  FIG. 4 a   ) which may be a geometric center of the projections of the plurality of radiators. 
     In an embodiment (e.g.,  FIG. 4 d   ), on the geometric reference surface, the projection of each said parasitic element (e.g., p[n]) may partially overlap the projection of said associated one (e.g., r[n]) of the plurality of radiators. In an embodiment (e.g.,  FIG. 4 e   ), on the geometric reference surface, the projection of each said parasitic element may be inside the projection of said associated one of the plurality of radiators. In an embodiment (e.g.,  FIG. 4 f   ), on the geometric reference surface, the projection of each said parasitic element may be configured not to overlap the projection of said associated one of the plurality of radiators. 
     In an embodiment (e.g.,  FIGS. 1 a  to 1 f  and 5 a   ), the antenna may further include one or more conductive coupling elements (e.g., c[ 1 ] to c[ 4 ]). Each said coupling element may be insulated from the plurality of radiators, the plurality of parasitic elements and the ground plane. On the geometric reference surface, a projection of each said coupling element (e.g., c[ 1 ] or c[ 4 ] in  FIG. 5 a   ) may have two portions (e.g.,  511  and  512  or  514  and  515  in  FIG. 5 a   ) respectively inside the projections of two (e.g., p[ 1 ] and p[ 2 ] or p[ 4 ] and p[ 1 ]) of the plurality of parasitic elements. 
     In an embodiment (e.g.,  FIG. 4 a    or  4   e ), on the geometric reference surface, the projections of any two of the plurality of parasitic elements may be arranged not to overlap. 
     In an embodiment (e.g.,  FIG. 4 g    or  5   b ), on the geometric reference surface, the projections of two (e.g., p[ 1 ] and p[ 2 ]) of the plurality of parasitic elements may partially overlap. 
     In an embodiment (e.g.,  FIG. 4 c   ), each said parasitic element may include at least two serially connected sections (e.g., s[n 1 ] to s[nQ] in  FIG. 4 c   ), and every two adjacent ones (e.g., s[n 1 ] and s[n 2 ]) of said sections may extend along two nonparallel directions (e.g., v[n 1 ] and v[n 2 ]). 
     In an embodiment, the ground wall of each radiator may include a meandering portion (e.g., gb[n] in  FIGS. 2 d , 3 a  and 3 c  to 3 e   , or gb[n 1 ], gb[n 2 ] in  FIG. 3 b   ) which may cause a distance (e.g., d 1  in  FIG. 2 d   ) between the arm and the ground plane to be shorter than a length of a current conduction path (e.g.,  200 ) along the ground wall between the arm and the ground plane. 
     In an embodiment (e.g., one of  FIGS. 3 a  to 3 e   ), the ground wall may further include a first support wall (e.g., ga[n 1 ] or ga[n 2 ]) and a second support wall (e.g., gc[n 1 ] or gc[n 2 ]); the first support wall may connect the arm and the meandering portion, and the second support wall may connect the meandering portion and the ground plane. 
     In an embodiment (e.g.,  FIG. 3 a   ), the meandering portion (e.g., gb[n]) may include: a first step plate (e.g., gp_a[n]) connected to the first support wall, a second step plate (e.g., gp_b[n]) connected to the second support wall, and a connection wall (e.g., gw[n]) connecting the first step plate and the second step plate. On a geometric reference surface (e.g., xy-plane) parallel to the ground plane, a projection (e.g., xyb[n]) of the connection wall may be arranged not to overlap projections (e.g., xya[n 1 ], xya[n 2 ], xyc[n 1 ] and xyc[n 2 ]) of the first support wall and the second support wall. 
     In an embodiment (e.g.,  FIG. 3 a   ), on the geometric reference surface, the projections (e.g., xya[n 1 ], xya[n 2 ], xyc[n 1 ] and xyc[n 2 ]) of the first support wall and the second support wall may be arranged not to overlap. 
     In an embodiment (e.g.,  FIGS. 6 a , 7 a  and 7 d   ), the antenna may also include two feed terminals (e.g., Pt 1  and Pt 2 ) for two multi-band signals (e.g., M 1  and M 2  in  FIG. 6 a   ) of two different polarizations. 
     In an embodiment (e.g.,  FIGS. 6 b , 7 b  and 7 c   ), the antenna may also include four feed terminals (e.g., Pt 1   a , Pt 2   a , Pt 1   b  and Pt 2   b ) for two low-band signals (e.g., LB 1  and LB 2  in  FIG. 6 b   ) of two different polarizations and two high-band signals (e.g., HB 1  and HB 2  in  FIG. 6 b   ) of the two different polarizations. In an embodiment (e.g.,  FIGS. 6 c  and 7 b   ), the four feed terminals may be arranged for a first pair of multi-band differential signals (e.g., M 1 + and M 1 − in  FIG. 6 c   ) of a first polarizations and a second pair of multi-band differential signals (e.g., M 2 + and M 2 − in  FIG. 6 c   ) of a second polarization different from the first polarization. 
     An objective of the invention is providing an antenna for multi-broadband and multi-polarization communication. The antenna may include a plurality of mutually separated radiators and four feed terminals (e.g., Pt 1   a , Pt 1   b , Pt 2   a  and Pt 2   b  in  FIG. 6 b    or  6   c ). The plurality of radiators may be conductively connected to a ground plane, and may jointly function as one or more dipoles. Two (e.g., Pt 1   a  and Pt 1   b  in  FIG. 6 b    or  6   c ) of said four feed terminals may be arranged for a first low-band signal (e.g., LB 1  in  FIG. 6 b   ) and a first high-band signal (e.g., HB 1  in  FIG. 6 b   ) of a first polarization, or for a first pair of multi-band differential signals (e.g., M 1 + and M 1 − in  FIG. 6 c   ) of the first polarization. The other two (e.g., Pt 2   a  and Pt 2   b  in  FIG. 6 b    or  6   c ) of said four feed terminals may be arranged for a second low-band signal (e.g., LB 2  in  FIG. 6 b   ) and a second high-band signal (e.g., HB 2  in  FIG. 6 b   ) of a second polarization, or for a second pair of multi-band differential signals (e.g., M 2 + and M 2 − in  FIG. 6 c   ) of the second polarization 
     Numerous objects, features and advantages of the present invention will be readily apparent upon a reading of the following detailed description of embodiments of the present invention when taken in conjunction with the accompanying drawings. However, the drawings employed herein are for the purpose of descriptions and should not be regarded as limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1 a    depicts a three-dimensional (3D) view of an antenna according to an embodiment of the invention; 
         FIG. 1 b    depicts portions of the antenna, which may include radiators, parasitic elements and optional coupling elements; 
         FIG. 1 c    demonstrates some features of the antenna; 
         FIG. 1 d    depicts another 3D view of the antenna; 
         FIGS. 1 e  and 1 f    depict a top view and a bottom view of the antenna; 
         FIG. 2 a    depicts a top view of the radiators of the antenna; 
         FIGS. 2 b  and 2 c    depict two 3D views of portions of the radiators which may include arm plates, folded arms and ground walls. 
         FIG. 2 d    depicts the folded arms and the ground wall of each radiator; 
         FIGS. 2 e  to 2 h    depict the folded arms according to different embodiments of the invention; 
         FIG. 3 a    depicts portions of each ground wall; 
         FIGS. 3 b  to 3 e    depict the ground wall according to different embodiments of the invention; 
         FIGS. 4 a  and 4 b    depict different views of the parasitic elements; 
         FIG. 4 c    depicts a top view of each parasitic element; 
         FIGS. 4 d  to 4 g    depict the parasitic elements according to different embodiments of the invention; 
         FIG. 5 a    depicts the coupling elements; 
         FIG. 5 b    depicts an arrangement of the coupling elements and the parasitic elements according to an embodiment of the invention; 
         FIGS. 6 a , 6 b  and 6 c    depict feeding configurations according to different embodiments of the invention; 
         FIGS. 7 a  to 7 d    depict feeding elements of the antenna according to different embodiments of the invention; and 
         FIG. 8  depicts reflection coefficient according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1 a    depicts a 3D view of an antenna  100  according to an embodiment of the invention, and  FIG. 1 b    depicts an exploded view of the antenna  100 . The antenna  100  may satisfy demands of advanced multi-broadband and multi-polarization communication standards, such as 5G mobile telecommunication at two separated FR2 bands with MIMO of dual-polarization diversity. Besides, the antenna  100  may also be compact in size to provide a high bandwidth-to-volume ratio. 
     As shown in  FIGS. 1 a  and 1 b   , the antenna  100  may include a plurality of mutually separated radiators, such as r[ 1 ] to r[ 4 ], which may jointly function as a plurality of dipoles. The antenna  100  may further include a plurality of conductive parasitic elements, such as p[ 1 ] to p[ 4 ]. Optionally, the antenna  100  may also include one or more conductive coupling elements, such as c[ 1 ] to c[ 4 ]. 
     Each radiators r[n] (for n=1 to 4) may be conductive, and be conductively connected to a conductive ground plane G 0  which may be a planar conductor parallel to xy-plane (note that the ground plane G 0  depicted is just to demonstrate how the antenna  100  is disposed on the ground plane G 0 , not to limit the ground plane G 0  to the depicted size and shape; parallel to xy-plane, the ground plane G 0  may in fact extend wider beyond the depicted size). The parasitic elements p[ 1 ] to p[ 4 ] may be mutually separated (without mechanical interference and contact) and insulated, and each parasitic element p[n] (for n=1 to 4) may be separated and insulated from the radiators r[ 1 ] to r[ 4 ] and the ground plane G 0 . Each coupling element c[n] (for n=1 to 4), if included in the antenna  100 , may be separated and insulated from the radiators r[ 1 ] to r[ 4 ], the parasitic elements p[ 1 ] to p[ 4 ] and the ground plane G 0 . Spaces separating the radiators r[ 1 ] to r[ 4 ], the parasitic elements p[ 1 ] to p[ 4 ] and the coupling elements c[ 1 ] to c[ 4 ] may be filled by dielectric material(s), e.g., air and/or nonconductive filler(s). 
     By a cross-section view of the antenna  100 ,  FIG. 1 c    demonstrates some features of the antenna  100 , such as folded arm, meandering grounding and the parasitic element p[n] partially surround each radiator r[n]; these features will be detailed later. As  FIG. 1 a    depicts a high angle (above xy-plane) 3D view of the antenna  100 ,  FIG. 1 d    depicts a low angle (below xy-plane) 3D view of the antenna  100 , with the ground plane G 0  hidden.  FIGS. 1 e  and 1 f    respectively depict a top view and a bottom view of the antenna  100 . 
     To demonstrate the radiators r[ 1 ] to r[ 4 ],  FIG. 2 a    depicts a top view of the antenna  100  with the parasitic elements p[ 1 ] to p[ 4 ], the coupling elements c[ 1 ] to c[ 4 ] and the ground plane G 0  hidden;  FIGS. 2 b  and 2 c    depict portions of the radiators r[ 1 ] to r[ 4 ] respectively by a high angle 3D view and a low angle 3D view. As shown in  FIG. 2 a   , on xy-plane, projections of the radiators r[ 1 ] to r[ 4 ] may surround a geometric origin p 0  and may face toward four different directions vd[ 1 ] to vd[ 4 ]; for example, the directions vd[ 1 ] to vd[ 4 ] may respectively be 45, 135, 225 and 315 degrees rotated from x-direction. The radiators r[ 1 ] to r[ 4 ] may be separated by gaps gp[ 1 ] and gp[ 2 ] respectively extending along geometric lines gpL[ 1 ] and gpL[ 2 ]. For example, the radiators r[ 1 ] and r[ 2 ] may be at two opposite sides of the gap gp[ 2 ], the radiators r[ 2 ] and r[ 3 ] may be at two opposite sides of the gap gp[ 1 ], etc. Geometry (shapes, structure and sizes) of the radiators r[ 1 ] to r[ 4 ] may substantially be the same, though may have minor differences (e.g., for feeding, routing and/or mechanical design consideration, etc.) and/or variations (e.g., due to limited precision and accuracy of manufacture, etc.). 
     As shown in  FIG. 2 b   , each radiator r[n] (for n=1 to 4) may include a conductive arm a[n] and a conductive ground wall g[n] connecting the conductive arm a[n] and the ground plane G 0 . As shown in  FIG. 2 c   , each arm a[n] may include a conductive arm plate b[n] and one or more conductive folded arms, such as h[n 1 ] and h[n 2 ]. In an embodiment, the arm plate b[n] of each arm a[n] may be a planar conductor extending parallel to xy-plane; for example, in an embodiment, the antenna  100  may be implemented by a printed circuit board (PCB), and the arm plates b[ 1 ] to b[ 4 ] may be formed by a same metal layer. In an embodiment, each folded arm h[nk] (for k=1 to 2) of the arm a[n] may be a conductive wall extending outward (e.g., downward along negative z-direction) from a bottom surface bb[n] ( FIG. 2 c   ) of the arm plate b[n]. Each arm a[n] may therefore be “folded” because each folded arm h[nk] may be regarded as a downward folded extension of the arm plate b[n]. The folded structure of the arms a[ 1 ] to a[ 4 ] may help to enhance performances of the antenna  100 ; e.g., to expand bandwidth, to improve impedance matching, to reduce undesired tilt of radiation directivity and/or to increase XPD, etc. 
     As shown in  FIGS. 2 b  and 2 c   , while the folded arms h[n 1 ] and h[n 2 ] may extend downward from the bottom surface bb[n] ( FIG. 2 c   ) of the arm plate b[n], the ground wall g[n] of each radiator r[n] may also extend outward (e.g., downward along negative z-direction) from the bottom surface bb[n] of the arm plate b[n] to connect the ground plane G 0  ( FIG. 2 b   ), but the folded arms h[n] and h[n 2 ] may be kept separated from the ground wall g[n].  FIG. 2 d    depicts arrangement of the folded arms h[n 1 ], h[n 2 ] and the ground wall g[n] by a high-angle 3D view, a cross-section view and a top view. As shown in the cross-section view of  FIG. 2 d   , the ground wall g[n] may meander from the bottom surface bb[n] to the ground plane G 0 , and each folded arm h[nk] may be configured to be separated from the meandering ground wall g[n] and the ground plane G 0 . 
     As shown in the top view of  FIG. 2 d   , the ground wall g[n] may extend downward from sites gs[n 1 ] and gs[n 2 ] of the bottom surface bb[n], and the folded arms h[n 1 ] and h[n 2 ] may extend downward from sites hs[n 1 ] and hs[n 2 ] of the bottom surface bb[r 1 ]. In an embodiment, on xy-plane, a projection of each of the sites gs[n 1 ] and gs[n 2 ] and a projection of each of the sites hs[n 1 ] and hs[n 2 ] may be arranged not to overlap. 
     In an embodiment, on xy-plane, the projection of the site hs[nk] (for k=1 to 2) may be placed closer to a boundary of a projection of the bottom surface bb[ 4 ], comparing to the projection of the site gs[nk]. That is, on xy-plane, the projection of each site gs[nk] (for k=1 to 2) may be placed in an inner geometric region bc[n] which may be inside a projection of the arm plate b[n] (i.e., the projection of the bottom surface bb[n]), and the projection of each site hs[nk] may be in a peripheral geometric region bd[n] between a boundary of the inner geometric region bc[n] and a boundary of the projection of the arm plate b[n], wherein the boundary of the inner geometric region bc[n] and the boundary of the projection of the arm plate b[n] may be arranged not to intersect. 
     In an embodiment, on xy-plane, the projection of the site hs[nk] may be arranged close to a nearby gap gp[m] with m=((n+k) mod 2))+1 (for n=1 to 4 and k=1 to 2); e.g., the projection of the site hs[nk] may be arranged between the projection of the site gs[nk] and the gap gp[m]. For example, the projection of the site hs[ 11 ] may be arranged between the projection of the site gs[ 11 ] and the gap gp[ 1 ], and the projection of the site hs[ 12 ] may be arranged between the projection of the site gs[ 12 ] and the gap gp[ 2 ]. 
     In an embodiment, on xy-plane, the projection of the site hs[nk] may be arranged near the geometric origin p 0 ; e.g., the projection of the site hs[nk] may be arranged closer to a near point p_near[n] comparing to a far point p_far[n], wherein the origin p 0  may also be a geometric center of the projections of the arm plates b[ 1 ] to b[ 4 ] (i.e., the projections of the bottom surfaces bb[ 1 ] to bb[ 4 ]), and the points p_near[n] and p_far[n] may be two geometric points, on the boundary of the projection of the bottom surface bb[n], which are respectively closest to and farthest from the origin p 0 . For example, in an embodiment, the site hs[nk] may be configured such that, on the boundary of the projection of the site h[nk], there may exist (at least) one geometric point ph[n] (not shown) which may cause a distance between said geometric point ph[n] and the near point p_near[n] to be shorter than a distance between said geometric point ph[n] and the far point p_far[n]. 
     In the embodiment depicted in  FIGS. 2 b  to 2 d   , the folded arm h[nk] of each arm a[n] may simply be a conductive wall; however, the invention is not so limited.  FIGS. 2 e  to 2 g    demonstrate more embodiments of the folded arms h[n 1 ] and h[n 2 ] of each arm a[n]. As shown in  FIG. 2 e   , in an embodiment, each folded arm h[nk] (for k=1 to 2) may include two (or more) separated walls, such as ha[nk] and hb[nk]. As shown in  FIG. 2 f   , in an embodiment, each folded arm h[nk] (for k=1 to 2) may include an extension plate hd[nk] and an extension wall hc[nk] connecting the bottom surface bb[n] of the arm plate b[n] and the extension plate hd[nk], wherein the extension plate hd[nk] may be a planar conductor parallel to the arm plate b[n] ( FIGS. 2 a  to 2 c   ) but be separated from the arm plate b[n], and the extension wall hc[nk] may be conductive. As shown in  FIG. 2 g   , in an embodiment, besides the extension wall hc[nk] and the extension plate hd[nk], each folded arm h[nk] may further include another conductive extension wall hf[nk] which may extend outward (e.g., upward or downward) from a top or bottom surface of the extension plate hd[nk], and may be separated from the bottom surface bb[n] of the arm plate b[n] and the extension wall hc[nk]. 
     As the antenna  100  may be implemented by a PCB, each folded arm h[nk] may be formed by serially interlacing one or more layers of conductive vias and one or more conductive plates respectively formed by one or more metal layers. For example, as shown in  FIG. 2 h    which depicts an embodiment of the folded arms h[n 1 ] and h[n 2 ], each folded arm h[nk] (for k=1 to 2) may be formed by stacking a first layer of vias vb[nk], a first plate pa[nk], a second layer of vias vb[nk] and a second plate pb[nk]. Similarly, each of the walls ha[nk], hb[nk] ( FIG. 2 e   ), hc[nk] ( FIGS. 2 f    and  2 G) and hf[nk] ( FIG. 2G ) may be formed by interlacing layer(s) of conductive vias and conductive plate(s). In the embodiments depicted in  FIGS. 2 a  to 2 h   , the folded arm h[nk] may extend downward (along negative z-direction) from the bottom surface bb[n] of the arm plate b[n]; however, in other embodiments (not shown), each folded arm h[nk] may extend upward (along positive z-direction) from a top surface, which is opposite to the bottom surface bb[n], of each arm plate b[n]. 
     As shown in the cross-section view of  FIG. 2 d   , the ground wall g[n] of each radiator r[n] may include a meandering portion gb[n], and the meandering portion gb[n] may cause a distance d 1 , which is measured between the bottom surface bb[n] of the arm b[n] and a top surface of the ground plane G 0 , to be shorter than a length of a (e.g., shortest) current conduction path  200  which routes along the ground wall g[n] from the bottom surface bb[n] of the arm plate b[n] to the top surface of the ground plane G 0 . The meandering portion gb[n] may help to improve performances of the antenna  100 , e.g., to reduce sizes of the antenna  100  and to increase bandwidth-to-volume ratio, etc. Because antenna design may desire the conduction path  200  to have a preferred length L 0  (not shown), if the ground wall g[n] extends downward from the bottom surface bb[n] of the arm plate b[n] to the ground plane G 0  alone a straight line without meandering, the distance d 1  would have to equal the preferred length L 0  and would therefore cause the antenna to occupy a larger volume. However, by arranging the ground wall g[n] to meander as shown in  FIG. 2 d   , the distance d 1  may be shortened to be much shorter than the preferred length L 0 , and the overall volume of the antenna  100  may therefore be decreased. 
     Along with  FIG. 2 d   ,  FIG. 3 a    depicts portions of each ground wall g[n] by a high angle 3D view and a top view. Besides the meandering portion gb[n], the ground wall g[n] may further include first support walls ga[n 1 ] and ga[n 2 ], as well as second support walls gc[n 1 ] and gc[n 2 ]. The walls ga[n 1 ] and ga[n 2 ] may be conductive, and may connect the bottom surface bb[n] of the arm plate b[n] and a top surface of the meandering portion gb[r 1 ]. The walls gc[n 1 ] and gc[n 2 ] may conductive, and may connect a bottom surface of the meandering portion gb[n] and the top surface of the ground plane G 0 . 
     As shown in  FIG. 3 a   , in an embodiment, the meandering portion gb[n] may include a first step plate gp_a[n], a second step plate gp_b[n] and a connection wall gw[n]. The plate gp_a[n] may be a planar conductor parallel to xy-plane, and may be connected to the walls ga[n 1 ] and ga[n 2 ] respectively at sites ua[n 1 ] and ua[n 2 ] of a top surface of the plate gp_a[n]. The plate gp_b[n] may a planar conductor parallel to xy-plane, and may be connected to the walls gc[n 1 ] and gc[n 2 ] at sites uc[n 1 ] and uc[n 2 ] of a bottom surface of the plate gp_b[n]. The wall gw[n] may be conductive, and may connect a bottom surface of the plate gp_a[n] and a site ub[n] of a top surface of the plate gp_b[n]. 
     As shown in the top view of  FIG. 3 a   , in an embodiment, on xy-plane, a projection xyb[n] of the connection wall gw[n] (e.g., a projection of the site ub[n]) may be arranged not to overlap with projections xya[n 1 ], xya[n 2 ], xyc[n 1 ] and xyc[n 2 ] of the walls ga[n 1 ], ga[n 2 ], gc[n 1 ] and gc[n 2 ] (e.g., projections of the sites ua[n 1 ], ua[n 2 ], uc[n 1 ] and uc[n 2 ]). Also, in an embodiment, each of the projections xya[n 1 ] and xya[n 2 ] (e.g., each of the projections of the sites gs[n 1 ] and gs[n 2 ]) and anyone of the projections xyc[n 1 ] and xyc[n 2 ] may be arranged not to overlap. 
     In addition to the embodiment depicted in  FIGS. 2 d  and 3 a   ,  FIGS. 3 b  to 3 e    depict more embodiments of the ground wall g[n] according to the invention. As shown in  FIG. 3 b   , in an embodiment, the ground wall g[n] may include multiple mutually separated parts, such as gd[n 1 ] and gd[n 2 ]; each part gd[nk] (for k=1 to 2) may have a meandering portion gb[nk]. On the other hand, in an embodiment (not depicted), the separated walls ga[n 1 ] and ga[n 2 ] in  FIG. 3 a    may be combined to one joint wall, and/or the separated walls gc[n 1 ] and gc[n 2 ] may be combined to one joint wall. 
     By reconfiguring structure of the meandering portion gb[n] of each ground wall g[n], the conduction path  200  ( FIG. 2 d   ) of the ground wall g[n] may have fewer or more turns. For example, as shown in  FIG. 3 c   , in an embodiment, the meandering portion gb[n] of the ground wall g[n] may be simplified to have only one single plate gp_a[n] connected between the walls ga[nk] and gc[nk]. On the other hand, as shown in  FIG. 3 d   , in an embodiment, the meandering portion gb[n] of the ground wall g[n] may include more than two step plates, such as gp_a[n], gp_b[n] and gp_c[n], and more than one connection walls, such as gw_a[n] and gw_b[n], connecting every two adjacent step plates. 
     As shown in  FIGS. 2 d  and 3 a   , the meandering portion gb[n] of the ground wall g[n] may form a U-shaped turn with its opening directed toward each folded arm h[nk]; however, as shown in  FIG. 3 e   , in an embodiment, the meandering portion gb[n] of the ground wall g[n] may form a U-shaped turn with its opening directed away from each folded arm h[nk]. In an embodiment, the antenna  100  may be implemented by a PCB, and each of the walls ga[nk], gw[n] and gc[nk] ( FIG. 3 a   ) may be formed by interlacing layer(s) of conductive vias and conductive plate(s), similar to  FIG. 2   h.    
       FIG. 4 a    depicts an embodiment of the parasitic elements p[ 1 ] to p[ 4 ] by a top view of the antenna  100  (with the ground plane G 0  and the coupling elements c[ 1 ] to c[ 4 ] hidden). Each parasitic element p[n] may be a planar conductive path parallel to xy-plane. On xy-plane, as the projection of each radiator r[n] (e.g., the projection of the arm plate b[n]) may be clamped between the two gaps gp[ 1 ] and gp[ 2 ] similar to a sector (not shown) clamped between two radii, in an embodiment, a projection of the parasitic element p[n] may also extend between the two gaps gp[ 1 ] and gp[ 2 ] which clamp the radiator r[n], and may therefore partially surround the radiator r[n] (e.g., the ground wall g[n], shown by outline in  FIG. 4 a    for conciseness) by an boomerang-shaped middle segment pp[n] between two claw-like radial segments ps[n 1 ] and ps[n 2 ] pointing toward a center of the sector. As shown in  FIG. 4 a   , each parasitic element p[n] may be configured not to entirely enclose the geometric origin p 0 . The parasitic elements p[ 1 ] to p[ 4 ] may help to enhance performances of the antenna  100 ; e.g., to expand bandwidth, to improve impedance matching, to reduce undesired tilt of radiation directivity and/or to increase XPD, etc. 
       FIG. 4 b    depicts arrangement of the parasitic elements p[ 1 ] to p[ 4 ] in an embodiment of the antenna  100  by a side view (with the coupling elements c[ 1 ] to c[ 4 ] and the radiators r[ 1 ] to r[ 4 ] hidden except the arm plates b[ 1 ] and b[ 2 ]) As shown in  FIG. 4 b   , in an embodiment, the parasitic elements p[ 1 ] to p[ 4 ] may be positioned above the ground plane G 0  by a distance (height) d 2  (measured between a bottom surface of each parasitic element p[n] and the top surface of the ground plane G 0 ). While each arm plate b[n] may be positioned above the ground plane G 0  by the distance (height) d 1  (also shown in  FIG. 2 d   ), in an embodiment, the distances d 1  and d 2  may be different. For example, in an embodiment as shown in  FIG. 4 b   , the height d 1  may be higher than the height d 2 , i.e., each arm plate b[n] may be higher than each parasitic element p[n]. In another embodiment (not depicted), the height d 1  may be lower than the height d 2 , i.e., the parasitic element p[n] may be placed above the arm plate b[n]. In an embodiment, the antenna  100  may be implemented by PCB, and each parasitic element p[n] may be formed by a metal layer. 
     In an embodiment, such as the one shown in  FIG. 4 b   , all parasitic elements p[ 1 ] to p[ 4 ] may be placed at the same height d 2 . On the other hand, in other embodiments, different subsets of the parasitic elements pH to p[ 4 ] may be arranged at different heights; some of this kind of embodiments will be described later. 
       FIG. 4 c    depicts an embodiment of each parasitic element p[n] by a top view. Each parasitic element p[n] may include a plurality of serially connected sections s[n 1 ] to s[nQ]; each section s[nq] (for q=1 to Q) may extend along a direction v[nq] by a length L[nq] (a size along the direction v[nq]) and a width w[nq] (a size perpendicular to the direction v[nq]). In an embodiment, the directions v[nq] and v[n(q+1)] of every two adjacent sections s[nq] and s[n(q+1)] (for q=1 to (Q−1)) may be different, i.e., every two adjacent sections s[nq] and s[n(q+1)] may respectively extend along two nonparallel directions v[nq] and v[n(q+1)], and an angle between the directions v[nq] and v[n(q+1)] may be less than, equal to or greater than 90 degrees. In an embodiment, the xy-plane projection of each parasitic element p[n] may be configured not to be rectangular. The count Q of the sections s[n 1 ] to s[nQ], as well as the direction v[nq], the width w[nq] and the length L[nq] of each section s[nq] may be adjustable and configurable for flexibility, adaptability and/or performance tuning, etc. For example, in an embodiment, the width w[n 1 ] to w[nQ] of the sections s[n 1 ] to s[nQ] may be set substantially equal; in other embodiments, different subsets of the sections s[n 1 ] to s[nQ] may have different widths, e.g., w[n 1 ]=w[nQ]&gt;w[n 2 ]=w[n(Q−1)], etc. 
       FIGS. 4 d  to 4 f    depict different embodiments of each parasitic element p[n] by top views. As shown in  FIG. 4 d   , in an embodiment, on xy-plane, the projection of each parasitic element p[n] may partially overlap the projection of the radiator r[n] (e.g., the projection of the arm plate b[n]). In other words, the projection of the parasitic element p[n] may have one or more portions, e.g.,  401  and  402 , inside the projection of the radiator r[n], and may also have other portion(s), e.g.,  403 , outside the projection of the radiator r[n]. As shown in  FIG. 4 e   , in a different embodiment, the projection of the parasitic element p[n] may be completely inside the projection of the radiator r[n]. As shown in  FIG. 4 f   , in another embodiment, the projection of the parasitic element p[n] may be configured not to overlap the projection of the radiator r[n]; i.e., the projection of the parasitic element p[n] may be entirely outside the projection of the radiator r[n]. In the embodiment shown in  FIG. 4 f   , the height d 2  of each parasitic element p[n] ( FIG. 4 b   ) may also be set substantially equal to the height d 1  of the arm plate b[n] besides setting the heights d 2 &gt;d 1  or d 1 &gt;d 2 . 
     In an embodiment, such as the one shown in  FIG. 4 a    or  4   e , on xy-plane, the projections of any two parasitic elements p[n] and p[n′] (with n and n′ unequal) may be configured not to overlap. On the other hand, in a different embodiment, such as the one shown in  FIG. 4 g    described below, the projection of one parasitic element p[n] may be configured to partially overlap the projection of another parasitic element p[n′] (with n and n′ unequal), i.e., the projection of the parasitic element p[n] may have a portion inside the projection of another parasitic elements p[n″]. 
       FIG. 4 g    depicts an embodiment of the parasitic elements p[ 1 ] to p[ 4 ] by a top view of the antenna  100  (with the ground plane G 0  hidden). In this embodiment, the parasitic elements p[ 1 ] and p[ 3 ] may be arranged at the height d 2  (not shown) above the ground plane G 0  (not shown), while the parasitic elements p[ 2 ] and p[ 4 ] may be arranged at a different height d 2 ′ (not shown) above the ground plane G 0 . In addition, two adjacent parasitic elements of two different heights may be configured to have partially overlapping xy-plane projections. For example, as shown in  FIG. 4 g   , the parasitic elements p[ 1 ] and p[ 2 ] of two different heights may have partially overlapping xy-plane projections; because of the height difference, the parasitic elements p[ 1 ] and p[ 2 ] may remain insulated even though their xy-plane projections partially overlap. Similarly, the xy-plane projections of the parasitic elements p[ 2 ] and p[ 3 ] of different heights, p[ 3 ] and p[ 4 ] of different heights, as well as p[ 4 ] and p[ 1 ] of different heights may also partially overlap. Arranging different parasitic elements to have partially overlapping xy-plane projections may help to enhance electromagnetic mutual coupling between the parasitic elements. In this embodiment, the antenna  100  may not need to include the optional coupling elements c[ 1 ] to c[ 4 ]. 
       FIG. 5 a    depicts arrangement of the parasitic elements p[ 1 ] to p[ 4 ] and the coupling elements c[ 1 ] to c[ 4 ] in an embodiment of the antenna  100  by a top view, a side view and a zoomed view detailing a portion of the top view. Each coupling element c[n] may be a planar conductor parallel to xy-plane; as shown in the side view of  FIG. 5 a   , each coupling element c[n] may be positioned above the ground plane G 0  by a distance (height) d 3  (between a bottom surface of the coupling element c[n] and the top surface of the ground plane G 0 ). While each arm plate b[n] and each parasitic element p[n] may respectively be at the heights d 1  and d 2  above the ground plane G 0 , in an embodiment, the height d 3  may be set different from the heights d 1  and d 2 ; for example, in an embodiment ( FIG. 5 a   ), the height d 1  may be higher than the height d 3 , and the height d 3  may be higher than the height d 2 ; i.e., each arm plate b[n] may be higher than each coupling element c[n], and each coupling element c[n] may be higher than each parasitic element p[n], However, the antenna  100  may also have other embodiments (not depicted) with different d 1 -d 2 -d 3  arrangements, including but not limited to; an embodiment with d 1 &gt;d 2 &gt;d 3 , an embodiment with d 1 =d 3 &gt;d 2 , an embodiment with d 3 &gt;d 2 &gt;d 1  an embodiment with d 2 &gt;d 3 &gt;d 1  an embodiment with d 2 &gt;d 3 =d 1  and an embodiment with d 2 &gt;d 1 &gt;d 3 , etc. It is noted that the coupling elements c[ 1 ] to c[ 4 ] are optional; in some embodiments, the antenna may only need a subset (e.g., none, one, fewer than all or all) of the coupling elements c[ 1 ] to c[ 4 ]. In an embodiment, the antenna  100  may be implemented by PCB, and each coupling element c[n] may be formed by a metal layer. 
     In an embodiment, on xy-plane, a projection of each coupling element c[n] may have two portions respectively inside the projections of two associated parasitic elements p[n] and p[(n mod 4)+1], and one portion outside the projections of the parasitic elements p[ 1 ] to p[ 4 ]. For example, as shown in the zoomed view of  FIG. 5 a   , the projection of the coupling element c[ 1 ] may have two portions  511  and  512  respectively inside the projections of the parasitic elements p[ 1 ] and p[ 2 ], as well as a portion  513  outside the projections of the parasitic elements p[ 1 ] to p[ 4 ]; similarly, the projection of the coupling element c[ 4 ] may have two portions  514  and  515  respectively inside the projections of the parasitic elements p[ 4 ] and p[ 1 ], along with a portion  516  outside the projections of the parasitic elements p[ 1 ] to p[ 4 ]. Because the projection of each coupling element c[n] may be arranged to partially overlap the projections of the two associated parasitic elements p[n] and p[n mod 4)+1], each coupling element c[n] may provide a capacitive coupling to enhance electromagnetic coupling between said two associated parasitic elements. 
     By a 3D view,  FIG. 5 b    depicts another embodiment of arranging the parasitic elements and the coupling elements. In this embodiment, the parasitic elements p[ 1 ] and p[ 4 ], along with the coupling element c[ 2 ], may be placed at a height d 2 , while the parasitic elements p[ 2 ] and p[ 3 ], along with the coupling element c[ 4 ], may be placed at another height d 2 ′ different from the height d 2 . The coupling elements c[ 1 ] and c[ 3 ] may not be included in this embodiment. The parasitic elements p[ 1 ] and p[ 2 ] of different heights may have partially overlapping xy-plane projections; the parasitic elements p[ 3 ] and p[ 4 ] may also have partially overlapping xy-plane projections. On the other hand, the parasitic elements p[ 2 ] and p[ 3 ] of the same height may not have partially overlapping xy-plane projections, and the parasitic elements p[ 1 ] and p[ 4 ] of the same height may not have partially overlapping xy-plane projections. Furthermore, the coupling element c[ 2 ] of the height d 2  and each of the parasitic elements p[ 2 ] and p[ 3 ] of the height d 2 ′ may have partially overlapping xy-plane projections, and the coupling element c[ 4 ] of the height d 2 ′ and each of the parasitic elements p[ 1 ] and p[ 4 ] of the height d 2  may have partially overlapping xy-plane projections. 
       FIGS. 6 a , 6 b  and 6 c    depict feeding configurations of the antenna  100  according to different embodiments of the invention. As shown in  FIG. 6 a   , the antenna  100  may be configured to have two feed terminals Pt 1  and Pt 2  respectively for two multi-band (e.g., dual-band) signals M 1  and M 2  of a first and a second polarizations, such as a horizontal and a vertical polarizations. The terminals Pt 1  and Pt 2  may be respectively connected to two signal circuits  601  and  602 , each of the signal circuits  601  and  602  may be a switch or a diplexer. When transmitting, a transceiver  600  may provide multiple single-band signals, such as two low-band signals LB 1 , LB 2  and two high-band signals HB 1  and HB 2 ; the signal circuit  601  may form the multi-band signal M 1  at the terminal Pt 1  according to the signals LB 1  and HB 1 , the signal circuit  602  may form the multi-band signal M 2  at the terminal Pt 2  according to the signals LB 2  and HB 2 , and the antenna  100  may therefore transmit the signals M 1  and M 2  respectively by electromagnetic waves of the first polarization and the second polarization. When the antenna  100  receives electromagnetic waves of the first polarization and/or the second polarization, the antenna  100  may provide the signals M 1  and/or M 2  at the terminals Pt 1  and/or Pt 2 ; the signal circuit  601  may form the signals LB 1  and HB 1  from the signal M 1 , and/or the signal circuit  602  may form the signals LB 2  and HB 2  from the signal M 2 , so the transceiver  600  may receive the signals LB 1 , HB 1  and/or LB 2 , HB 2 . 
     As shown in  FIG. 6 b   , the antenna  100  may also be configured to have four feed terminals Pt 1   a , Pt 2   a , Pt 1   b  and Pt 2   b  connected to the transceiver  600 , for the two low-band signals LB 1 , LB 2  and the two high-band signals HB 1 , HB 2 . When transmitting, the transceiver  600  may provide the low-band signals LB 1 , LB 2  and the high-band signals HB 1 , HB 2  respectively at the terminals Pt 1   a , Pt 2   a , Pt 1   b  and Pt 2   b , so the antenna  100  may transmit the signals LB 1  and HB 1  by electromagnetic waves of the first polarization, and may transmit the signals LB 2  and HB 2  by electromagnetic waves of the second polarization. When the antenna  100  receives electromagnetic waves of the first polarization and/or the second polarization, the antenna  100  may form the signals LB 1 , HB 1  and/or LB 2  and HB 2  respectively at the terminals Pt 1   a , Pt 1   b  and/or Pt 2   a , Pt 2   b  to be received by the transceiver  600 . 
     As shown in  FIG. 6 c   , the antenna  100  may also be configured to have four feed terminals Pt 1   a , Pt 1   b , Pt 2   a  and Pt 2   b  respectively for a first pair of differential signals M 1 + and M 1 − and a second pair of differential signals M 2 + and M 2 −. For example, the differential signals M 1 + and M 1 − may be a pair of multi-band (dual-band) differential signals; similarly, the differential signals M 2 + and M 2 − may be another pair of multi-band (dual-band) differential signals. In an embodiment, the terminals Pt 1   a  and Pt 1   b  may be connected to a signal circuit  611 , and the terminals Pt 2   a  and Pt 2   b  may be connected to a signal circuit  612 ; each of the signal circuits  611  and  612  may be a differential switch or a differential diplexer. When transmitting, a transceiver  600  may provide multiple pairs of single-band differential signals, such as two pairs of low-band differential signals LB 1 + and LB 1 −, LB 2 + and LB 2 −, as well as two pairs of high-band differential signals HB 1 + and HB 1 −, HB 2 + and HB 2 −. The signal circuit  611  may form the multi-band differential signals M 1 + and M 1 − at the terminal Pt 1   a  and Pt 1   b  according to the signals LB 1 +, LB 1 −, HB 1 + and HB 1 −, and the signal circuit  612  may form the multi-band differential signal M 2 + and M 2 − at the terminal Pt 2   a  and Pt 2   b  according to the signals LB 2 +, LB 2 −, HB 2 + and HB 2 −, and the antenna  100  may therefore transmit the signals M 1 + and M 1 − by electromagnetic waves of the first polarization, and transmit the signals M 2 + and M 2 − by electromagnetic waves of the second polarization. When the antenna  100  receives electromagnetic waves of the first polarization and/or the second polarization, the antenna  100  may provide the signals M 1 + and M 1 − and/or M 2 + and M 2 − at the terminals Pt 1   a , Pt 1   b  and/or Pt 2   a  and Pt 2   b , the signal circuit  611  may form the signals LB 1 +, LB 1 −, HB 1 + and HB 1 − from the signals M 1 + and M 1 −, and/or the signal circuit  612  may form the signals LB 2 +, LB 2 −, HB 2 + and HB 2 − from the signals M 2 + and M 2 −, so the transceiver  600  may receive the signals LB 1 +, LB 1 −, HB 1 + and HB 1 − and/or LB 2 +, LB 2 −, HB 2 + and HB 2 −. 
       FIG. 7 a    depicts an embodiment of a feeding arrangement of the antenna  100  by a high angle 3D view and a top view of the antenna  100  (with the ground plane G 0 , the parasitic elements p[ 1 ] to p[ 4 ], the optional coupling elements c[ 1 ] to c[ 4 ] and the radiators r[ 1 ] to r[ 4 ] hidden except r[ 3 ]). As shown in  FIG. 7 a   , the antenna  100  may further include multiple conductive feeding elements, such as two feeding elements  701  and  702 . Each of the feeding elements  701  and  702  may be separated and insulated from the ground plane G 0 , the optional coupling elements c[ 1 ] to c[ 4 ], the parasitic elements p[ 1 ] to p[ 4 ] and the radiators r[ 1 ] to r[ 4 ]. The feeding elements  701  and  702  may also be separated and insulated from each other. As shown in  FIG. 7 a   , in an embodiment, the feeding element  701  may extend across the gap gp[ 2 ] along the gap gp[ 1 ], and one end of the feeding element  701  may connect a conducive via and a conductive outbound trace to function as the terminal Pt 1  for the feeding configuration in  FIG. 6 a   ; on the other hand, the feeding element  702  may extend across the gap gp[ 1 ] along the gap gp[ 2 ], and one end of the feeding element  702  may connect a via and an outbound trace to function as the terminal Pt 2  for the feeding configuration in  FIG. 6 a   . By the feeding element  701  shown in  FIG. 7 a   , the radiators r[ 1 ] and r[ 4 ] may jointly function as one pole of a first dipole for a polarization along x-direction, while the radiators r[ 2 ] and r[ 3 ] may jointly function as an opposite pole of the first dipole. By the feeding element  702  shown in  FIG. 7 a   , the radiators r[ 1 ] and r[ 2 ] may jointly function as one pole of a second dipole for a polarization along y-direction, while the radiators r[ 3 ] and r[ 4 ] may jointly function as an opposite pole of the second dipole. 
     Based on the embodiment shown in  FIG. 7 a    which may implement the feeding configuration in  FIG. 6 a   ,  FIG. 7 b    depicts another embodiment of the feeding arrangement which may implement the feeding configuration in  FIG. 6 b    or  6   c . As shown in  FIG. 7 b   , two opposite ends of the feeding element  701  may respectively connect two vias and two outbound traces to function as the terminals Pt 1   a  and Pt 1   b  for the feeding configuration in  FIG. 6 b    or  6   c , while two opposite ends of the feeding element  702  may respectively connect two vias and two outbound traces to function as the terminals Pt 2   a  and Pt 2   b  for the feeding configuration in  FIG. 6 b    or  6   c.    
     Based on the embodiment shown in  FIG. 7 b   ,  FIG. 7 c    depicts one more embodiment of the feeding arrangement. In  FIG. 7 c   , two opposite ends of the feeding element  701  may respectively connect two vias, a low-pass filter LPF 1  and a high-pass filter HPF 1 , as well as two outbound traces to function as the terminals Pt 1   a  and Pt 1   b  for the feeding configuration in  FIG. 6 b   ; similarly, two opposite ends of the feeding element  702  may respectively connect two vias, a low-pass filter LPF 2  and a high-pass filter HPF 2 , as well as two outbound traces to function as the terminals Pt 2   a  and Pt 2   b  for the feeding configuration in  FIG. 6 b   . The filters LPF 1  and HPF 1  of the feeding elements  701  may suppress mutual interference between the low-band signal LB 1  and the high-band signal HB 1  ( FIG. 6 b   ) to enhance signal isolation between the signals LB 1  and HB 1 ; similarly, the filters LPF 2  and HPF 2  of the feeding elements  702  may suppress interference between the low-band signal LB 2  and the high-band signal HB 2  ( FIG. 6 b   ) to enhance signal isolation between the signals LB 2  and HB 2 . It is noted that the filter(s) LPF 1 , LPF 2 , HPF 1  and/or HPF 2  may be optional; whether to include said filter(s) in the antenna  100  may depend on consideration(s) such as isolation requirements. In other embodiment(s) (not depicted), the filter(s) LPF 1 , LPF 2 , HPF 1  and/or HPF 2  may be replaced by SPST (single pole single throw) switch(es) and/or impedance tuner(s). Again, it is emphasized that said filter(s), switch(es) and/or impedance tuner(s) may be optional, and whether to include said filter(s), switch(es) and/or impedance tuner(s) in the antenna  100  may depend on factor(s) such as isolation requirements. 
       FIG. 7 d    depicts another embodiment of the feeding arrangement of the antenna  100  by a high angle 3D view and a top view of the antenna  100  (with the ground plane G 0 , the parasitic elements p[ 1 ] to p[ 4 ], the optional coupling elements c[ 1 ] to c[ 4 ] and the radiators r[ 1 ] to r[ 4 ] hidden except r[ 3 ]). As shown in  FIG. 7 d   , in an embodiment, the feeding elements  701  and  702  may be fitted in an intersection of the gaps gp[ 1 ] and gp[ 2 ]. The feeding element  701  may extend parallel to a direction v 701 , and one end of the feeding element  701  may connect a conducive via and a conductive outbound trace to function as the terminal Pt 1  for the feeding configuration in  FIG. 6 a   . The feeding element  702  may extend parallel to a direction v 702 , and one end of the feeding element  702  may connect a via and an outbound trace to function as the terminal Pt 2  for the feeding configuration in  FIG. 6 a   . For example, in an embodiment, the direction v 701  may substantially be 45 degrees rotated from x-direction, and the direction v 702  may substantially be 45 degrees rotated from y-direction. By the feeding element  701  shown in  FIG. 7 d   , the radiators r[ 1 ] and r[ 3 ] may respectively function as two opposite poles of a first dipole for a polarization along the direction v 701 , and the radiators r[ 2 ] and r[ 4 ] may respectively function as two opposite poles of a second dipole for the polarization along the direction v 701 . By the feeding element  702  shown in  FIG. 7 d   , the radiators r[ 2 ] and r[ 4 ] may respectively function as two opposite poles of a third dipole for a polarization along the direction v 702 , and the radiators r[ 1 ] and r[ 3 ] may respectively function as two opposite poles of a fourth dipole for the polarization along the direction v 702 . Similar to  FIGS. 7 b  and 7 c   , by utilizing both ends of each of the feeding elements  701  and  702 , the embodiment having two feed terminals Pt 1  and Pt 2  in  FIG. 7 d    may be modified to other embodiments (not depicted) having four feed terminals Pt 1   a , Pt 1   b , Pt 2   a  and Pt 2   b  for the feeding configuration in  FIG. 6 b    or  6   c . Besides the embodiments shown in  FIGS. 7 a  to 7 d   , the antenna  100  may also adopt other feeding arrangements, such as direct feeding or slot feeding, etc. 
       FIG. 8  depicts reflection coefficient of the antenna  100  according to an embodiment of the invention. By the radiators r[ 1 ] to r[ 4 ] and the parasitic elements p[ 1 ] to p[ 4 ] (as well as the optional coupling elements c[ 1 ] to c[ 4 ]) of the invention, in an embodiment, the antenna  100  may form four notches  801 ,  802 ,  803  and  804  to cover a low-band  810  and a high-band  820 , and may therefore satisfy challenging demands of dual-broadband communication. For example, in an embodiment, the radiators r[ 1 ] to r[ 4 ] may provide two resonance modes respectively at the low-band  810  and the high-band  820 , and the parasitic elements p[ 1 ] to p[ 4 ] may provide another two resonance modes respectively at the low-band  810  and the high-band  820 . In other words, each radiator r[n] may contribute to resonances at the two bands  810  and  820 . Different from the antenna  100  of the invention, conventional dipole antenna can only support a single band. 
     To sum up, by folded arms (e.g., h[ 11 ] to h[ 41 ] and h[ 12 ] to h[ 42 ]), meandering grounding (e.g., gb[ 1 ] to gb[ 4 ]) and partially surrounding parasitic elements (e.g., p[ 1 ] to p[ 4 ]), the antenna  100  according to the invention may achieve multi-broadband and multi-polarization. Comparing to conventional antenna such as stacked patch antenna, the antenna  100  according to the invention may provide much broader bandwidths at multiple bands, higher bandwidth-to-volume ratio, less undesired tilt in radiation directivity, better XPD and superior signal isolation between different polarizations for MIMO. The antenna  100  according to the invention may therefore satisfy demanding needs of modern communication, such as 5G mobile telecommunication with MIMO. 
     While the invention has been described in terms of what is presently, considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.