Patent Publication Number: US-11050151-B2

Title: Multi-band antenna

Description:
TECHNICAL FIELD 
     The present invention relates to a multi-band antenna, and particularly, although not exclusively, to a multi-band antenna operating with wide axial ratio beamwidths. 
     BACKGROUND 
     In a radio signal communication system, information is transformed to radio signal for transmitting in form of an electromagnetic wave or radiation. These electromagnetic signals are further transmitted and/or received by suitable antennas. 
     Some wireless applications may require simultaneous communication of radio signals in more than one frequency bands to improve the performance of these applications, which therefore may require a deployment of multiple units of antennas with different designs in a single system or apparatus. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, there is provided a multi-band antenna comprising: a plurality of dipole antenna each arranged to operate in a frequency band different from each other; a back cavity structure mounted to the plurality of dipole antennas, wherein the plurality of dipole antennas are at least partially accommodated within a back cavity defined by the back cavity structure; and a feed network provided on the back cavity structure and coupled to the plurality of dipole antennas. 
     In an embodiment of the first aspect, the plurality of dipole antennas includes a plurality of cross-dipole antennas. 
     In an embodiment of the first aspect, the plurality of dipole antennas are arranged communicate electromagnetic signals with circular polarization. 
     In an embodiment of the first aspect, the plurality of cross-dipole antennas comprises a plurality of dipole arms each having a dimension different from each other. 
     In an embodiment of the first aspect, each of the plurality of dipole arms includes a curved structure, wherein the plurality of dipole arms are defined with different subtended angles so as to operate in different frequency bands. 
     In an embodiment of the first aspect, the plurality of cross-dipole antennas are provided on at least one antenna substrate mounted to the back cavity structure. 
     In an embodiment of the first aspect, each of the at least one antenna substrate is provided with the plurality of dipole arms defined on a first side of the respective antenna substrate. 
     In an embodiment of the first aspect, the plurality of dipole arms couple to a slot feeder defined on the respective antenna substrate. 
     In an embodiment of the first aspect, the antenna comprises two antenna substrates intersecting with each other. 
     In an embodiment of the first aspect, the two antenna substrates and a base of the back cavity structure are orthogonally arranged. 
     In an embodiment of the first aspect, each of the at least one antenna substrate is provided with a joining structure arranged to cooperate with another joining structure in another antenna substrate. 
     In an embodiment of the first aspect, the joining structure includes a slit formed on the each of the at least one antenna substrate. 
     In an embodiment of the first aspect, each of the at least one antenna substrate is provided with a ground plane on the first side of the substrate. 
     In an embodiment of the first aspect, each of the at least one antenna substrate is further provided with a microstrip feedline on a second side of the substrate, wherein the second side opposites to the first side. 
     In an embodiment of the first aspect, the plurality of cross-dipole antennas includes multiple sets of the plurality of dipole arms. 
     In an embodiment of the first aspect, the back cavity structure defines a corrugated back cavity. 
     In an embodiment of the first aspect, the back cavity structure comprises a side wall in a corrugated shape. 
     In an embodiment of the first aspect, the feed network includes a two-stage cascaded hybrid coupler. 
     In an embodiment of the first aspect, the feed network is defied with a first set of ports coupled to the plurality of dipole antennas and a second set of ports coupled to external connectors mounted on the back cavity structure. 
     In an embodiment of the first aspect, the first set of ports are defined on a base of the back cavity structure proximate to a center position of the base, and the second set of ports are defined proximate to an edge position of the base. 
     In an embodiment of the first aspect, the feed network is defined with a folded side length between a proximate pair of ports in one of the first set of ports and one of the second set of ports. 
     In an embodiment of the first aspect, the feed network is provided on a bottom surface of a base of the back cavity structure, the feed network is coupled to the plurality of dipole antennas provided on an opposite surface of the base through a plurality of via structures. 
     In an embodiment of the first aspect, the electromagnetic signal includes a radiation pattern substantially covering the upper hemisphere in both xoz-plane and yoz-plane. 
     In an embodiment of the first aspect, the electromagnetic signals include 3-dB axial ratio beamwidth broader than 200°. 
     In accordance with a second aspect of the present invention, there is provided an antenna assembly comprising a plurality of multi-band antenna in accordance with the first aspect arranged in an array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a multi-band antenna in accordance with one embodiment of the present invention; 
         FIG. 2  is an illustration of an antenna substrate of the multi-band antenna of  FIG. 1 ; 
         FIG. 3A  is an illustration of a feed network for use in an antenna; 
         FIG. 3B  is an illustration of a feed network with a folded structure modified based on the feed network of  FIG. 3A ; 
         FIGS. 4A and 4B  are photographic images showing top and bottom perspective view of the antenna of  FIG. 1 ; 
         FIGS. 4C to 4F  are top and bottom view of the two antenna substrates of the antenna of  FIG. 4A ; 
         FIG. 5  is a plot showing measured and simulated VSWRs of the multi-band CP antenna; 
         FIGS. 6A to 6D  are color plots showing simulated current distribution of the multi-band CP antenna in L2 band (1.227 GHz) at t=0; in L2 band at t=T/4; in L1 band (1.575 GHz) at t=0; and in L1 band at t=T/4, respectively; 
         FIG. 7  is a plot showing measured and simulated ARs of the multi-band CP antenna in boresight direction (0=) 0°; 
         FIGS. 8A and 8B  are plots showing measured and simulated radiation patterns of the multi-band CP antenna in xoz (ϕ=0°) and yoz planes (ϕ=90°) in L2 band (1.227 GHz) and in L1 band (1.575 GHz), respectively; 
         FIGS. 9A and 9B  are plots showing measured and simulated AR beamwidths of the multi-band CP antenna in xoz (ϕ=0°) and yoz (ϕ=90°) planes in L2 band (1.227 GHz) and in L1 band (1.575 GHz), respectively; 
         FIG. 10  is a plot showing simulated AR beamwidths of the cavity-backed multi-band CP antennas with and without the corrugation at 1.227 GHz and 1.575 GHz in xoz (ϕ=0°) plane; 
         FIG. 11  is a plot showing measured and simulated antenna gains of the multi-band CP antenna in boresight direction (0=0°); and 
         FIG. 12  is a plot showing measured antenna efficiency of the multi-band CP antenna. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The inventors have, through their own research, trials and experiments, devised that global positioning system (GPS) may be deployed in different applications, such as military, commercial, and civilian applications. Circular polarization (CP) may be used in GPS because CP-based system may suppress multipath fading problem. Preferably, as compared with the linearly polarized antenna, CP antennas may be less sensitive to the angle between the transmitting and receiving antennas. 
     For GPS systems, antennas are necessary to facilitate wireless communication of electromagnetic signals between devices. To obtain higher precision, it may be preferable for antennas to have broad AR beamwidths that can cover the upper hemisphere to effectively receive low-elevation satellite signals. In some example embodiments, different frequency bands may be used in various GPS applications. For example, L1 (1.575 GHz) and L2 bands (1.227 GHz), may be used by satellites and it is therefore desirable to include them in GPS antenna designs. 
     In one example embodiment, quadrifilar helix antennas (QHA) with cardioid-shaped radiation patterns and broad gain beamwidths may be used for GPS applications. However, it is inconvenient to fabricate their curl arms and the fabrication tolerance may affect the antenna performance significantly. Furthermore, more than one QHA are needed for a multi-band design, which may increase the complexity of the antenna structure. 
     Alternatively, some systems may employ planar cross-dipole antennas for wideband and dual-/multi-band CP applications. By taking advantage of the inherent phase difference between the signal line and ground plane, the sequential rotation feed network can be simplified considerably. Also, the artificial magnetic conductor or high impedance surface can be incorporated into the antenna structures to reduce the antenna profile or enhance the front-to-back ratio. However, the AR beamwidths of planar cross-dipole antennas may be insufficient to fully cover the upper hemisphere. 
     In one preferable embodiment, a multi-band CP cross-dipole antenna with wide AR beamwidth that fully cover the upper hemisphere is provided. The antenna has unequal dipole-arm lengths to obtain two operating bands. A very wide CP beamwidth of more than 200° may be achieved by using curved dipole arms and a corrugated cavity. 
     With reference to  FIG. 1 , there is shown an example embodiment of a multi-band antenna  100 , comprising: a plurality of dipole antenna  102  each arranged to operate in a frequency band different from each other; a back cavity structure  104  mounted to the plurality of dipole antennas  102 , wherein the plurality of dipole antennas  102  are at least partially accommodated within a back cavity defined by the back cavity structure  104 ; and a feed network  106  provided on the back cavity structure  104  and coupled to the plurality of dipole antennas  102 . 
     In this embodiment, the antenna  100  comprises a number of parts includes two antenna substrates  108  mounted and connected to a base  104 B of the back cavity structure  104 . The back cavity structure  104  is preferably formed by a circular base  104 B and a cylindrical sidewall  104 S which combine to define a back cavity of the antenna  100 . 
     Preferably, the side wall  104 S has a corrugated shape or profile, thereby defining a corrugated back cavity when combined with the base  104 B. Referring to  FIG. 1 , the side wall  104 S includes different heights at different positions around the circular base  104 B. For example, the circular cavity may include a radius of R defined by the base  104 B, height of h c , and thickness of the side wall  104 S may be t c . The heights in other positions of the side wall  104 S may be further defined by h c -h c1  or h c -h c2  with a width of w c1  and w c2  respectively. Based on these parameters, a non-uniform corrugation is introduced to the cavity side wall  104 S to broaden the beamwidth. The performance enhancement of such corrugated back cavity will be further discussed later in the disclosure. 
     The multi-band antenna has a plurality of dipole antennas  102 , preferably includes at least one dipole antenna  102  operating in a first frequency band and at least one dipole antenna  102  operating in a second frequency band different from the first band, such that the antenna  100  may be used in an at least dual-band application. For example, the L1 band and the L2 band include a 1.575 Ghz wireless communication band and a 1.227 Ghz wireless communication band respectively, therefore is suitable for GPS applications as discussed earlier. Alternatively, other communication bands may be selected for other multi-band or multi-band applications. 
     In this example, the dipole antennas  102  are cross-dipole antennas  102  which include dipole arms provided on two antenna substrates  108  being mounted to the back cavity structure  104 . Referring to  FIG. 1 , the two antenna substrates  108  intersects with each other and is substantially perpendicular to each other. The substrates  108  are further mounted on the base  104 B of the back cavity structure  104 , such that the two antenna substrates  108  and the base  104 B of the back cavity structure  104  are orthogonally arranged. In addition, the substrates  108 , as well as the dipole antennas  102  thereon, are at least partially accommodated within the corrugated back cavity defined by the back cavity structure  104 . 
     With reference also to  FIG. 2 , each of the antenna substrates  108  is defined with a plurality of dipole antennas  102  which may be cross-dipole antennas  102  in this preferable embodiment. Preferably, the antenna substrate  108  may be of a dielectric material as appreciated by a skilled person in the art, and the cross-dipole antennas  102  may be patters of metal layer, such as copper, defined on one or both surfaces of the substrate. 
     In this example, the substrate  108  is provided with a ground plane  110  in electrical connection with two sets of dipole arms  112  on a first side of the substrate  108 . Preferably, each set of dipole arms  112  including at least one first dipole arm  112 A and at least one second dipole arm  112 B each having a different dimension. For example, each of the dipole arms  112  includes a curved structure defined with different subtended angles so as to operate in the different bands, i.e. L1 and L2 band for GPS applications. 
     Referring to  FIG. 2 , the cross-dipole has unequal curved arms  112 , and each arm has a uniform width of w 1 . For the smaller curved dipole arm  112 A, its radius and subtended angle are denoted by r 1  and θ 1 , respectively, whereas the corresponding parameters of the larger dipole  112 B are r 2  and θ 2 . The dipole arms  112  in each adjacent pair are separated by a uniform distance of d 1  along the curvature. 
     It will be appreciated by a skilled person that the cross-dipole may further include additional arms which have dimensions different from the dipole arms  112 A or  112 B, such that the antenna may operate in frequency bands other than L1 and L2 bands as discussed above. 
     Preferably, the plurality of dipole arms  112  couple to a slot feeder defined on the antenna substrate  108 . In this example, an elongated slot  114  is defined between two sets of dipoles  112  with a width of d 2 . A microstrip feedline  116  is further arranged on a second side, being opposite to the first side, of the substrate  108 , such that the dipole  112  on the first side may receive excitations via the microstrip feedline  116  and the slot feeder. For example, a 50-Ω microstrip feedline may be obtained by including a short conductive tape  118  stuck across the slot  114  and connected to a printed conductive line  116  on the back side of the substrate. Preferably, in response to the excitations, the dipole antennas  102  communicate an electromagnetic signal with circular polarization. 
     In addition, the at least one antenna substrate  108  is provided with a joining structure, such as a slit  120  with a length of h 4  and a width of d 3 , arranged to cooperate with another joining structure in another antenna substrate. Referring to  FIG. 2 , one of the substrate has a slit  120  formed adjacent to the elongated slot structure  114  and the other one (as shown in the inset) has the same slit  120  formed at the bottom edge of the substrate  108 , such that when two substrates intersects with each other in a substantially perpendicular configuration, and mutually locking each other in such configuration when the substrates  108  are further mounted on the back cavity structure  104 . 
     In one preferred embodiment, each substrate  108  has a size of h 0 ×w 0 , dielectric constant of ε r , thickness of t, and a slit  120  for the perpendicular insertion of the other substrate. After the mutual insertion of the two substrates  108 , a short adhesive conducting tape  118  of length l 1  is stuck across the slot  114 , connecting the microstrip feedline  116  to the dipole ground  110  through a via, which then forms a merchant balun to obtain a differential feed for the dipole. 
     The inset shows the other substrate. Basically, the layout is the substantially the same as that of the first substrate, but the narrow slit  120  is fabricated at the bottom. Also, the horizontal conducting strip  118  may be slightly shifted upwards (or downwards) to avoid shorting that of the first substrate. 
     With reference to  FIGS. 3A and 3B , the feed network  106  includes a two-stage cascaded hybrid coupler. In GPS applications, L1 band (1.227 GHz) is nearby L2 band (1.575 GHz). Since the frequency ratio of these two bands is small, it may only require very narrow coupled lines for a dual-band hybrid coupler. Preferably, the feed network  106  may include a two-stage cascaded hybrid coupler. 
     Referring to  FIG. 3A , there is shown an example two-stage hybrid coupler, with all the four ports defined near the edges of the feed network  106 . It may be more preferable that two of the ports are placed near the center of the feed network  106 , such that the feed network  106  may be provided on the base  104 B of the back cavity structure  104 . 
     Referring to  FIG. 3B , there is shown an example embodiment of a “folded” version of the two-stage hybrid coupler. The feed network  106  is defied with a first set of ports (ports 2 and 3) coupled to the plurality of dipole antennas  102  and a second set of ports (ports 1 and 4) coupled to external connectors mounted on the back cavity structure  104 . Preferably, ports 2 and 3 may be defined on a base  104 B of the back cavity structure  104  proximate to a center position of the base  104 B, and ports  1  and  4  are defined proximate to an edge position of the base  104 B. 
     The base  104 B of the back cavity structure  104  may be a feed substrate which has a dielectric constant of ε r1  and thickness of t 1 . Its radius is substantially the same as that of the back cavity or the cylindrical side wall  104 S. The feed network  106  is provided on a bottom surface of a base  104 B of the back cavity structure  104 . Preferably, the feed network  106  is defined with a folded side length between a proximate pair of ports in one of the first set of ports and one of the second set of ports. For example, the length L 1  between ports 1 and 2 (or ports 4 and 3) is substantially “folded”, with ports 2 and 3 placed near the center of the base  104 B. The ports 2 and 3 may be further connected to the microstrip feedline  116  on the dipole antennas  102  mounted on top of the base  104 B. 
     In addition, the feed network  106  is coupled to the plurality of dipole antennas  102  provided on an opposite (top) surface of the base  104 B through a plurality of via structures. For example, the vias may allow electrical connectors such as wires or metal leads to pass through such that features on both sides of the feed substrate or the base  104 B may be electrically connected. 
     In some example embodiments, the antenna  100  may include a different number of antenna substrates  108  and/or dipole arms formed on the substrates  108 . Alternatively, the antenna  100  may be included in an antenna assembly which comprising a plurality of multi-band antenna  100  arranged in an array. 
     With reference to  FIGS. 4A to 4F , there is shown an antenna fabricated in accordance with an embodiment of the present invention. In this embodiment, the multi-band CP antenna that consists of a cross-dipole  112  printed on two perpendicular substrates  108 , a circular aluminum back cavity  104 , and a feed network  106  with a cascaded hybrid coupler. The cross dipoles  112  are placed (partially) inside the cavity, and beneath the cavity  104  is the feed network  106 . A via passing through the cavity  104  is used to connect the cross-dipole  112  to the feed network  106 . 
     In addition, two connectors  122  (e.g. SMA connectors) are mounted at an edge of the base  104 B and connect to ports 1 and 4 of the feed network  106 , with ports 2 and 3 connecting to the antennas on the other side of the base  104 B through the vias by soldering. 
     In this embodiment, the multi-band antenna  100  has the following parameters: R=53.75 mm, h c =45 mm, h c1 =14.5 mm, h c2 =19.5 mm, w c1 =7.5 mm, w c2 =7.5 mm, t c =1.5 mm, ε r =6.15, ε r1 =2.94, t=0.635 mm, t 1 =0.76 mm, h 0 =70 mm, h 1 =17.14 mm, h 2 =17.38 mm, h 3 =33.48 mm, h 4 =10 mm, d 1 =2.42 mm, d 2 =2 mm, d 3 =0.635 mm, d 4 =3 mm, r 1 =12.4 mm, r 2 =16.3 mm, θ l =158 deg, θ 2 =152 deg, w 0 =50 mm, w 1 =1.8 mm, W 1 =4.62 mm, W 2 =0.45 mm, W 3 =5.25 mm, l 1 =6.94 mm, L 1 =70 mm, L 2 =31.88 mm, L 3 =2 mm, W f =1.92 mm, and W f 1 =0.92 mm. The performance of the fabricated antenna has been measured as well as evaluated using ANSYS HFSS simulation, in particular in the L1 and L2 bands. It was observed that there is reasonable agreement between the measured and simulated results. 
     To begin with, the wideband cascaded hybrid coupler was designed to cover the two bands. Table I lists its simulated phase difference and amplitude imbalance between the two output ports, along with the S-parameters of the four ports. The overlapping bandwidth is 44.0% (1.10-1.72 GHz), which is sufficient for GPS L1 and L2 bands. The antenna was fabricated and measured to verify the simulations. 
     
       
         
           
               
             
               
                 TABLE I 
               
               
                   
               
               
                 SIMULATED PERFORMANCE OF 
               
               
                 WIDEBAND FEED NETWORK 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 10-dB Impedance bandwidth 
                 1.08-1.82 GHZ (51.0%) 
               
               
                   
                 90° ± 5° Phase difference 
                 1.00-1.86 GHZ (60.1%) 
               
               
                   
                 1.5-dB amplitude imbalance 
                 1.10-1.72 GHZ (44.0%) 
               
               
                   
                 Overlapping bandwidth 
                 1.10-1.72 GHZ (44.0%) 
               
               
                   
               
            
           
         
       
     
     In the measurement experiments for evaluating the performance of the antenna, the voltage standing wave ratio (VSWR) was measured with the Keysight VNA 8361A, whereas the AR, radiation pattern, realized antenna gain, and total antenna efficiency were measured with a Satimo StarLab System. Since the antenna in this example was designed for GPS applications, only the results of the right-handed CP (RHCP) port (Port 1) are presented here. 
     With reference to  FIG. 5 , there is shown the measured and simulated VSWRs of the antenna, with reasonable agreement between them. With reference to the plot, the measured and simulated impedance bandwidths (VSWR  2 ) are 46.3% (1.13-1.81 GHz) and 47.8% (1.10-1.79 GHz), respectively. The plot also shows the simulated VSWR without the feed network. With reference to the figure, two frequency bands corresponding to L1 and L2 bands are found, showing that the wideband matching of the full structure is due to the feed network. 
     With reference to  FIGS. 6A to 6D , there is shown the simulated current of the cross-dipole. The currents mainly flow along the outer and inner dipole arms at 1.227 GHz (L2 band) and 1.575 GHz (L1 band), respectively, which can be expected. 
     With reference to  FIG. 6A , the dipole currents at t=0 mainly flow along the +y direction in the yoz-plane, radiating the +y-directed E-field. In this case, the currents on all the other dipole arms are very weak. At t=T/4 as shown in  FIG. 6B , the currents mainly flow on the other pair of the outer arms in the □x direction (xoz-plane). Therefore, the □x-directed E-field is radiated. As a result, RHCP fields can be generated at 1.227 GHz. Similar current variations at 1.575 GHz (L1 band) can also be observed referring to  FIGS. 6C and 6D  respectively. 
     With reference to  FIG. 7 , there is shown the measured and simulated ARs in the boresight direction (6=) 0°. The measured and simulated 3-dB AR bandwidths of L2 band are 13.0% (1.15-1.31 GHz) and 20.4% (1.10-1.35 GHz), respectively. For L1 band, the measured and simulated AR bandwidths are given by 30.2% (1.35-1.83 GHz) and 23.2% (1.41-1.78 GHz), respectively. Both the measured and simulated VSWR and AR bandwidths entirely cover L1 and L2 bands. 
     With reference to  FIG. 8 , there is shown the measured and simulated radiation patterns of the multi-band CP antenna. For the entire upper hemisphere, the measured L2- and L1-band cross-polar fields are about 30 dB and 20 dB weaker than their co-polar counterparts, respectively, leading to very wide 3-dB AR beamwidths. The measured xoz- and yoz-plane half-power beamwidths (HPBWs) of L2 band are as wide as 111° and 114°, respectively. For the L1 band, the xoz- and yoz-plane HPBWs are 103° and 109°, respectively. 
     With reference to  FIGS. 9A and 9B , there is shown the measured and simulated AR beamwidths of the antenna, with acceptable agreement between the measurement and simulation. With reference to  FIG. 9A , very wide measured L2-band 3-dB AR beamwidths of 211° and 228° are obtained in the xoz- and yoz-planes, respectively. For the L1 band as shown in  FIG. 9B , the measured 3-dB AR beamwidths in the xoz- and yoz-planes are 202° and 213°, respectively. Both the measured and simulated results can fully cover the upper hemisphere. 
     To study the effect of the corrugation, the AR beamwidths of two cavity-backed multi-band CP antennas with and without the corrugation were simulated. With reference to  FIG. 10 , there is shown the simulated AR beamwidths of two cavity-backed multi-band CP antennas with and without the corrugation. For brevity, the plots only shows the results in the xoz-(0=0°) plane only. AS shown in the Figure, when there are no corrugations, the AR beamwidths of the antenna are 171° and 151° at 1.227 GHz and 1.575 GHz, respectively. By inserting the corrugation, they are broadened to the respective values of 228° and 225°, fully covering the upper hemisphere. 
     It may be observed that for a given corrugation depth, the AR beamwidth is affected over a narrow frequency range only. To broaden the AR beamwidth for both frequency bands, a non-uniform corrugation with different depths is therefore deployed in a preferred embodiment. 
     With reference to  FIG. 11 , there is shown the measured and simulated realized antenna gains (mismatch included) in the boresight direction (0=0°). Again, the measured and simulated results are in reasonable agreement. With reference to the figure, both the measured and simulated results show two peaks at around 1.227 GHz (L2 band) and 1.575 GHz (L1 band). At 1.227 GHz, the measured and simulated peak values are 4.39 dBic and 5.88 dBic, respectively. The discrepancy may be because of imperfections in the experiment. Similar measured and simulated gains of 5.06 dBic and 5.45 dBic are obtained at 1.575 GHz (L1 band). 
     With reference to  FIG. 12 , there is shown the measured total antenna efficiency (mismatch included). As can be observed from the figure, the efficiency also exhibits two peaks in L1 and L2 bands, as expected. Its peak values are 82.6% and 89.3% at 1.220 and 1.550 GHz, respectively, which are very close to the L2- and L1-band frequencies. 
     Table II below illustrates a summary of the performance of the multi-band CP antennas in accordance with embodiment of the present invention. Advantageously, the antenna is found to be having wide AR beamwidths that can cover the upper hemisphere for both frequency bands. Therefore, the antenna may be used in GPS ground terminals, vehicles, and ships. 
     
       
         
           
               
             
               
                 TABLE II 
               
               
                   
               
               
                 MEASURED PERFORMANCE OF THE MULTI-BAND CP ANTENNA 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Measured results 
                 L2 Band (1.227 GHz) 
                 L1 Band (1.575 GHz) 
               
            
           
           
               
               
            
               
                 Impedance 
                 (46.3%) 1.13-1.81 GHz 
               
               
                 bandwidth 
                   
               
            
           
           
               
               
               
            
               
                 3-dB AR bandwidth 
                 13.0% (1.15-1.31 GHz) 
                 30.2% (1.35-1.83 GHz) 
               
               
                 Peak antenna gain 
                 4.39 dBic @1.22 GHz 
                 5.06 dBic @1.55 GHz 
               
            
           
           
               
               
               
               
            
               
                 HPBW 
                 xoz 
                 111° 
                 103° 
               
               
                   
                 yoz 
                 114° 
                 109° 
               
               
                 3-dB AR 
                 xoz 
                 211° (−91°, 120°)  
                 202° (−105°, 97°)  
               
               
                 beamwidth 
                 yoz 
                 228° (−111°, 117°)  
                 213° (−105°, 108°)  
               
            
           
           
               
               
               
            
               
                 Antenna 
                     82.6% 
                     89.3% 
               
               
                 efficiency 
               
               
                   
               
            
           
         
       
     
     These embodiments may be advantageous in that, the impedance and AR passbands of the multi-band antenna are sufficient for the two bands. It has been also found that the L1- and L2-band AR beamwidths are both over 200° in the two principal radiation planes, covering the entire upper hemisphere. Thus, the multi-band CP cross-dipole antenna is suitable for GPS L1- and L2-band applications. 
     Advantageously, the two sets of curved dipoles have been designed to obtain the multi-band operation. Such design with the shorter and longer arms may facilitate the communication of signals in for L1 and L2 bands, respectively. Apart from using curve dipole arms, a non-uniform corrugated cavity has been deployed to broaden the beamwidth. 
     In addition, the antenna of the present invention outperforms when comparing with some example antennas. For example, with reference to Table 3 below, although the HPBW in example 1 antenna is wider than that of the present invention, its peak gain (&lt;1 dBic) and AR beamwidth)(−100° of example 1 are much smaller than those of the present invention (peak gain &gt;4 dBic; AR beamwidth &gt;200°) for both frequency bands. Example 1 antenna also has a higher profile despite its footprint is smaller. Also, it vertically puts two individual quadrifilar helix antennas together to obtain the two frequency bands, requiring two feeding ports. On the other hand, for the design in Example 2 antenna, a very low profile and relatively higher peak gains can be obtained, but both its HPBW and AR beamwidth are much narrower than those of the present invention. 
     
       
         
           
               
             
               
                 TABLE III 
               
               
                   
               
               
                 Performances of other example multi-band CP antennas 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Antenna 
                 Example 1 
                 Example 2 
               
               
                 Structure 
                 Combine two quadrifilar 
                 Single planar cross dipole 
               
               
                   
                 helix antennas together 
                 on AMC surface 
               
               
                 Overall size (λ 0 ) 
                 0.140λ 0  × 0.140λ 0  × 0.387λ 0   
                 0.576λ 0  × 0.576λ 0  × 0.088λ 0   
               
               
                   
                 @1.615 GHz 
                 @2.4 GHz 
               
            
           
           
               
               
               
               
               
            
               
                 Operating frequencies 
                 1.615 
                 2.492 
                 2.4 
                 5.2 
               
               
                 (GHz) 
                   
                   
                   
                   
               
               
                 Impedance bandwidth 
                 28% 
                 39% 
                  16.7% 
                  11.5% 
               
               
                 AR bandwidth 
                 Not 
                 Not 
                     8.30% 
                     5.77% 
               
               
                   
                 available 
                 available 
                   
                   
               
               
                 Peak gain (dBic) 
                   &lt;1 
                   &lt;1 
                 5.1 
                 6.2 
               
               
                 HPBW (Degree) 
                 &gt;180° 
                 &gt;180° 
                 60 e   
                 82°  
               
               
                 AR beamwidth (Degree) 
                 ~100° 
                 ~100° 
                 &lt;120°   
                 &lt;60°   
               
               
                   
               
            
           
         
       
     
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 
     Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.