Abstract:
A wideband antenna apparatus including a harmonically suppressed low band antenna is provided. The low band antenna is configured as a folded monopole antenna with patch coupling for resonance in a first frequency band. A patch portion of the low band antenna is widely separated from a folded feed portion of the low band antenna to avoid slot resonances above the first frequency band. The patch portion is relatively large to avoid folding of the patch portion that could introduce resonances above the first frequency band. The wideband antenna apparatus may also include a high band antenna proximate with the low band antenna. The high band antenna may be a folded monopole patch coupled antenna configured for resonating in a second frequency band. The high band antenna may optionally be configured like the low band antenna to suppress resonances of the high band antenna above the second frequency band.

Description:
BACKGROUND 
     The increasing use of wireless communication links between a large variety of devices has led to numerous advancements in antenna design. Mobile devices such as mobile phones communicate wirelessly in a number of different frequency bands that are specified in various industry standards. Various antenna designs are incorporated in wireless devices such as mobile phones to facilitate communication on one or more appropriate frequency bands, in accordance with the standards. Mobile devices may include multiband antenna configurations that facilitate communication on more than one frequency band. However, it has been challenging to design multiband antennas that may provide acceptable performance in space constrained applications such as mobile phones and other mobile communication devices. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a more complete understanding of the present disclosure, reference is now made to the following description taken in conjunction with the accompanying drawings. 
         FIG. 1A  is a pictorial diagram showing a multiband antenna apparatus according to one aspect of the disclosure. 
         FIG. 1B  is a pictorial diagram showing physical dimensions in an example of an antenna apparatus according to one aspect of the disclosure. 
         FIG. 2  is a flow diagram illustrating an exemplary routine for configuring a multiband antenna apparatus to aspects of the present disclosure. 
         FIG. 3A  is a graph that shows an example of return loss in previously known multiband antenna structures. 
         FIG. 3B  is graph that plots the return loss of a multiband antenna apparatus according to aspects of the present disclosure. 
         FIG. 4  is graph that plots efficiencies of a low band portion and high band portion of a multiband antenna structure according to aspects of the present disclosure. 
         FIG. 5  is a pictorial diagram showing a harmonic suppressed low band antenna apparatus according to one aspect of the disclosure. 
         FIG. 6  is a pictorial diagram showing a multiband antenna apparatus according to one aspect of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The close proximity between a high band antenna and a low band antenna in a multiband antenna structure can cause mutual electromagnetic coupling between the low band antenna and the high band antenna. Low band antennas which are designed to operate in a predetermined low frequency band can also resonate at harmonic frequencies above the low frequency band. The harmonic resonation of the low band antenna in the operating band of the nearby high band antenna detrimentally affects performance of both the high band antenna and the low band antenna and can substantially reduce efficiency of the multiband antenna structure. 
     Aspects of the present disclosure include a multiband antenna structure including a low band antenna configured with a high band antenna. The low band antenna and the high band antenna are both configured as wide band antennas. The low band antenna is configured to reduce resonances in the band of the high band antenna. The high band antenna is configured to reduce resonances in the band of the low band antenna. Thus harmonic interference between the antennas may be reduced. 
     In one aspect of the disclosure, the low band antenna is a harmonic suppressed patch coupled folded monopole antenna. The high band antenna may also be a harmonic suppressed patch coupled folded monopole antenna. However, in certain aspects of the present disclosure the high band antenna may naturally avoid creating resonances in the band of the low band antenna, so particular configurations of the high band antenna for harmonic suppression may be optional. 
     A multiband antenna structure  100  according to aspects of the present disclosure is described with reference to  FIG. 1A . The multiband antenna structure  100  includes a low band antenna  102  and a high band antenna  104 . The low band antenna  102  includes a folded feed portion  106  and a patch portion  108  and is configured to operate in the low frequency band between about 700 MHz and about 960 MHz. The patch portion  108  includes a tab  109  and is electromagnetically coupled to the folded feed portion  106  via patch gap  110  and edge coupled to an energy source via a ground strip  112 . The folded feed portion  106  includes a first arm  114  and a second arm  116  parallel to the first arm  114 . The ground strip  112  includes a ground arm portion  118  spaced away from the first arm  114  by a separation distance  120 . 
     According to one aspect of the present disclosure, the patch portion  108  is non-folded. For example, in one aspect, the patch portion  108  does not include a second arm portion extending back in the direction of the ground arm portion  118 . 
     The high band antenna  104  includes a folded feed portion  122  and a patch portion  124  and is configured to operate in the high frequency band between about 1.7 GHz and 2.2 GHz. The patch portion  124  is electromagnetically coupled to the folded feed portion  122  via a patch gap  126  and edge coupled to a ground feed via a ground strip  128 . The folded feed portion  122  includes a first arm  130  and a second arm  132  parallel to the first arm  130 . 
     According to aspects of the present disclosure, high band resonances of the low band antenna  102  are suppressed by parasitic coupling of the grounded patch portion  108 . The patch portion  108  also provides lower resonance mode matching for the low band antenna  102 . According to further aspects of the present disclosure, the patch portion  108  is configured with a large area at the end of the parasitic ground strip  112 . The large area suppresses high band resonances by allowing the patch portion to be constructed without a folding arm, which would create one or more high band resonances. 
     Other sources of harmonic resonances that can be suppressed according to the aspects of the present disclosure include slot mode resonances. Slot mode resonances can occur when an antenna element includes a narrow slot in an element or between two elements. The slot may resonate electromagnetic waves in the manner of a di-pole antenna, for example. According to an aspect of the present disclosure, the ground arm portion  118  is configured as a thin strip with a comparatively wide separation  120  from the first arm  114 . The separation  102  may be sufficiently large to avoid creating a narrow slot between the folded feed portion  106  and the patch portion  108  that could create slot mode high frequency resonances, for example. Thus slot mode resonances may be reduced. 
     The patch portion  124  of the high band antenna  104  provides high frequency resonance mode matching for the high band antenna  104 . The high band antenna  104  may be configured using the same harmonic suppression techniques described above with regard to the low band antenna  102  in structures where it could be desirable to suppress harmonics above the range of the high band antenna  104 . However, persons having ordinary skill in the art should appreciate that the described harmonic suppression structure including wide separation between the folded feed portion  122  and the patch portion  124  is optional in the high band antenna  104  as it may not affect lower frequency harmonics in the band of the low band antenna  102 , for example. 
     Referring to  FIG. 1B , certain primary dimensions are shown in an example of a suppressed harmonic multiband antenna structure  100  according to aspects of the present disclosure. In this example, a length  134  of the low band antenna  102  is 41 mm and a length  136  of the low band antenna  104  is 13 mm. A length  138  of the patch portion  108  is 19 mm and a height  140  of the tab  109  is 5 mm. The patch portion  108  overlaps the folded feed portion  106  along a length  142  of 10 mm. A length  144  of the second arm  116  is 12 mm. A height  146  of the low band antenna  102  is 11 mm and a width  148  of the low band antenna  102  is 5 mm. In this example, the separation distance  120  is about 8 mm to 9 mm. 
     A method for configuring a multiband antenna structure according to one aspect of the present disclosure is described with reference to the process flow diagram  200  shown in  FIG. 2 . At block  202 , the method includes configuring a first folded monopole antenna element. At block  204 , the method includes configuring a non-folded first patch element for electromagnetic coupling with the first folded monopole antenna to generate a primary resonance with the first folded monopole antenna element in a predetermined low band. According to aspects of the present disclosure The non-folded first patch element is configured to be large enough to resonate with the first folded monopole antenna element in the low band without including a folded patch portion. At block  206 , the method includes configuring a feed of the first folded monopole antenna element at a predetermined distance from a feed of the patch portion. The predetermined distance may be large enough to reduce slot mode resonances. 
     At block  208 , the method includes configuring a second folded monopole antenna element proximate with the first folded monopole antenna element. At block  210 , the method includes configuring a second patch element for electromagnetic coupling with the second folded monopole antenna element to generate a primary resonance with the second folded monopole antenna element in a high band. 
     A method for configuring a multiband antenna structure such as the method described above with reference to  FIG. 2  can be performed using known techniques in a manufacturing environment. For example, one or more portions of the multiband antenna structure may be formed in a printed circuit board manufacturing process in which conductive traces and patches are etched on a substrate. Multiple printed circuit boards may be coupled together to provide antenna elements in one or more planes, for example. Portions of the multiband antenna structure may also be formed as metal traces or patches on flexible substrates in a flexible circuit manufacturing environment or may be deposited on a base structure using various known metal deposition techniques such sputtering, for example. Metal stamping techniques may also be used to form portions of the multiband antenna structure, which can be formed without a corresponding substrate, for example. Metal stampings forming portions of the multiband antenna structure may be assembled to supportive structures such as thermoplastic housings of a device or may be incorporated therein using techniques such as insert molding, for example. Small scale multiband antenna structures according to aspects of the present disclosure may be formed on integrated circuit chips using known integrated circuit manufacturing processes, for example. 
       FIG. 3A  is a return loss graph illustrating an example of performance of a previously known wide band antenna structures in which harmonics of the low band antenna element are not suppressed and appear as resonances in the band of the high band antenna. This resonance of the low band antenna in the high band range is an example of mutual coupling, which can occur between closely spaced antenna elements. Undesirable effects of such mutual coupling include significant decrease in efficiency of the wideband antenna structure as well as altered impedances and radiation patterns of the wideband antenna structure. A low band antenna element resonance plot  302  shows a low band resonance of the low band antenna element at about 0.72 GHz and about −4 dB harmonics in the high frequency band above 1.8 GHz. A high band antenna element resonance plot  304  shows a high band resonance of the high band antenna element at about 1.87 GHz. The harmonics of the low band antenna above 1.8 GHz influence the high band antenna resonance and cause poor performance of the high band antenna element as above 1.9 GHz, for example. The low band antenna element resonance plot  302  also shows a large harmonic resonance at about 2.58 GHz. The high band antenna element resonance plot  304  shows a corresponding resonance at about 2.58 GHz due to the mutual coupling between the high band antenna element and the low band antenna element. Combining the low band antenna element resonance plot  302  and the high band antenna element resonance plot  304  provides an antenna isolation plot  308  of the previously known multiband antenna structure of this example. The antenna isolation plot  308  shows poor isolation in the high band between about 1.8 and GHz 2.3 GHz and around the 2.58 GHz harmonics. 
     Performance of a multiband antenna structure according to aspects of the present disclosure is described with reference to the multiband antenna structure  100  shown in  FIG. 1A  and the return loss graph  310  shown in  FIG. 3B . A low band antenna resonance plot  312  shows a low band resonance of the low band antenna  102  at about 0.8 GHz. A high band antenna resonance plot  314  shows a high band resonance of the high band antenna  104  at about 1.8 GHz. The various aspects of the present disclosure including the non-folded patch portion  108  and the wide separation  120  between the ground arm portion  118  and the first arm  114  of the folded feed portion  106  suppress harmonics of the low band antenna  102  in the band of the high band antenna  104 . The absence of higher frequency harmonics may be seen in the high band portion  316  of the low band antenna resonance plot  312 , between about 1.6 GHz and 2.5 GHz, for example. Combining the low band antenna resonance plot  312  and the high band antenna resonance plot  314  provides an antenna isolation plot  318  of the multiband antenna structure  100 . The antenna isolation plot  318  shows isolation between about −10 dB and −8 dB in the frequency range of the high band antenna resonances, between about 1.7 GHz and about 2.65 GHz. 
     Mutual coupling between multiband antenna elements may significantly reduce antenna efficiency. However, according to aspects of the present disclosure, isolation between the low band antenna  102  and the low band antenna  104  of the multiband antenna structure  100  prevents significant loss of efficiency. The efficiency of a multiband antenna structure according to aspects of the present disclosure is described with reference to the multiband antenna structure  100  shown in  FIG. 1A  and the efficiency graphs  402 ,  404  shown in  FIG. 4 . A low band antenna efficiency plot  406  shows good efficiency of about −4 dB in the frequency band of the low band antenna around 830 MHz, for example. A high band antenna efficiency plot  408  shows good efficiency of about −4 dB in the frequency band of the high band antenna  104  around 1800 MHz, for example. The efficiency plots shown in  FIG. 4  may be achieved with the antenna configuration shown in  FIG. 1A . 
     In some circumstances it may be useful to configure a low band antenna with suppressed harmonics to avoid mutual coupling with other or interference with other components in an environment. A suppressed harmonic low band antenna may be constructed as described in  FIG. 1A  without including the high band antenna  104 , for example. 
     According to an aspect of the present disclosure that is described with reference to  FIG. 5 , an antenna structure  500  includes a suppressed harmonic low band antenna  502 . The antenna structure  500  includes a low band antenna  502  configured with a folded feed portion  506  and a patch portion  508 . The patch portion  508  is electromagnetically coupled to the folded feed portion  506  via patch gap  510  and edge coupled to an energy source via a ground strip  512 . The folded feed portion  506  includes a first arm  514  and a second arm  516  parallel to the first arm  514 . The ground strip  512  includes a ground arm portion  518  spaced away from the first arm  514  by a separation distance  520 . 
     According to one aspect of the present disclosure, the patch portion  508  is non-folded. In other words, the patch portion  508  does not include a second arm portion extending back in the direction of the ground arm portion  518 . 
     In some circumstances it may be useful to configure the high band antenna in a multiband antenna structure to suppress harmonics from the high band antenna structure above the high band, for example. 
     A multiband antenna structure  600  that is configured to suppress harmonics both the low band antenna and the high band antenna according to aspects of the present disclosure is described with reference to  FIG. 6 . The multiband antenna structure  600  includes a low band antenna  602  and a high band antenna  604 . The low band antenna  602  includes a folded feed portion  606  and a patch portion  608 . The patch portion  608  is electromagnetically coupled to the folded feed portion  606  via patch gap  610  and edge coupled to an energy source via a ground strip  612 . The folded feed portion  606  includes a first arm  614  and a second arm  616  parallel to the first arm  614 . The ground strip  612  includes a ground arm portion  618  spaced away from the first arm  614  by a separation distance  620 . 
     According to one aspect of the present disclosure, the patch portion  608  is non-folded. In other words, the patch portion  608  does not include a second arm portion extending back in the direction of the ground arm portion  618 . 
     The high band antenna  604  includes a folded feed portion  622  and a patch portion  624 . The patch portion  624  is electromagnetically coupled to the folded feed portion  622  via a patch gap  626  and edge coupled to ground feed via a ground strip  628 . The folded feed portion  622  includes a first arm  630  and a second arm  632  parallel to the first arm  628 . 
     According to aspects of the present disclosure, high band resonances of the low band antenna  602  are suppressed by parasitic coupling of the grounded patch portion  608 . The patch portion  608  also provides lower resonance mode matching for the low band antenna  602 . According to further aspects of the present disclosure, the patch portion  608  is configured with a large area at the end of the parasitic ground strip  612 . The large area suppresses high band resonances by allowing the patch portion to be constructed without a folding arm, which would create one or more high band resonances. According to yet another aspect of the present disclosure, the ground arm portion  618  is configured as a thin strip with a comparatively wide separation  620  from the first arm  614 . The separation  602  is sufficiently large to avoid creating a narrow slot between the folded feed portion  606  and the patch portion  608  that could create slot mode high frequency resonances, for example. 
     According to aspects of the present disclosure, high band resonances of the high band antenna  604  are suppressed by parasitic coupling of the grounded patch portion  624 . The patch portion  624  of the high band antenna  604  also provides high frequency resonance mode matching for the high band antenna  604 . The high band antenna  604  is configured using the same harmonic suppression techniques described above with regard to the low band antenna  602 . According to further aspects of the present disclosure, the patch portion  624  is configured with a large area at the end of the ground strip  628 . The large area suppresses high band resonances by allowing the patch portion  624  to be constructed without a folding arm, which would create one or more high band resonances. According to yet another aspect of the present disclosure, the ground strip  628  is configured with a comparatively wide separation  634  from the folded feed portion  622 . The separation  634  may be sufficiently large to avoid creating a narrow slot between the folded feed portion  622  and the ground strip  628  that could create slot mode high frequency resonances, for example. 
     As discussed above, the various aspects of the present disclosure may be implemented in a wide variety of operating environments, which in some cases may include one or more mobile devices, user computers, computing devices, or processing devices which may be used to operate any of a number of applications. Mobile devices may include any of a number of cellular wireless and handheld devices such as mobile phones, smart phones and tablet computers running mobile software and capable of supporting a number of networking and messaging protocols. User computers and computing devices may include laptop computers and general purpose personal computers running a standard operating system, for example Such a system also may include a number of workstations running any of a variety of commercially-available operating systems and other known applications for purposes such as development and database management. These devices also may include other electronic devices, such as dummy terminals, thin-clients, gaming systems, and other devices capable of communicating via a network. 
     The environment may include a variety of data stores and other memory and storage media as discussed above. These may reside in a variety of locations, such as on a storage medium local to (and/or resident in) one or more of the computers or remote from any or all of the computers across the network. In a particular set of embodiments, the information may reside in a storage-area network (“SAN”) familiar to those skilled in the art. Similarly, any necessary files for performing the functions attributed to the computers, servers, or other network devices may be stored locally and/or remotely, as appropriate. Where a system includes computerized devices, each such device may include hardware elements that may be electrically coupled via a bus, the elements including, for example, at least one central processing unit (CPU), at least one input device (e.g., a mouse, keyboard, controller, touch screen, or keypad), and at least one output device (e.g., a display device, printer, or speaker). Such a system may also include one or more storage devices, such as disk drives, optical storage devices, and solid-state storage devices such as random access memory (“RAM”) or read-only memory (“ROM”), as well as removable media devices, memory cards, flash cards, etc. 
     Such devices also may include a computer-readable storage media reader, a communications device (e.g., a modem, a network card (wireless or wired), an infrared communication device, etc.), and working memory as described above. The computer-readable storage media reader may be connected with, or configured to receive, a computer-readable storage medium, representing remote, local, fixed, and/or removable storage devices as well as storage media for temporarily and/or more permanently containing, storing, transmitting, and retrieving computer-readable information. The system and various devices also typically will include a number of software applications, modules, services, or other elements located within at least one working memory device, including an operating system and application programs, such as a client application or Web browser. It should be appreciated that alternate embodiments may have numerous variations from that described above. For example, customized hardware might also be used and/or particular elements might be implemented in hardware, software (including portable software, such as applets), or both. Further, connection to other computing devices such as network input/output devices may be employed. 
     Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will appreciate other ways and/or methods to implement the various aspects and embodiments. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the disclosure as set forth in the claims.