Abstract:
An antenna including a conductive loop having a first top surface portion, the conductive loop having a first edge portion interrupted by a gap defining a feed point, a conductive strip having a second top surface, the conductive loop lying in a plane defined by the second top surface, the conductive strip having a second edge portion extending between first and second opposing distal ends, the second edge portion being spaced from the first edge portion, and the second edge portion extending along the first edge portion at a substantially constant distance from the first edge portion, and wherein the conductive strip is electrically isolated from the conductive loop and is structurally configured and positioned relative to the conductive loop to adjust an input impedance of the conductive loop.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a United States national phase application of co-pending international patent application number PCT/CN2011/073130, filed Apr. 21, 2011, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Conventional indoor television antennas generally include two antennas, a loop antenna for UHF reception and a telescopic antenna for VHF reception. Typically, in such a setup, the UHF loop antenna is paired with a 4:1 balun to match the input impedance of the antenna to that of an amplifier and also to convert a balanced antenna output to an unbalanced amplifier input. Further, although a UHF loop antenna will typically boost received signals by some amount, the television receiver will not receive these enhanced signals because the balun attenuates them somewhat. For example, if the gain of the UHF antenna is about 2 dBi and the signal loss due to the balun is 2 dB, the net signal gain is zero. Further, television signals received by UHF and VHF antennas are usually diplexed before they are transmitted to an amplifier. Filters in the diplexer may further attenuate the signal. 
         [0003]      FIG. 1  is a functional block diagram of a conventional indoor television antenna system  100 . The system  100  includes two antennas, a 7.5 inch diameter UHF loop antenna  102  and a VHF telescopic antenna  104 . The loop antenna  102  receives a UHF signal and boosts it by about 2 dBi. The loop antenna output signal  106  is balanced and has an impedance of about  300  ohms as it is passed to a 4:1 balun  108 . The 4:1 balun  108  unbalances and reduces the impedance so that an output signal  110  is unbalanced and has an impedance of about 75 ohms. Further, the 4:1 balun  108  attenuates the antenna output signal  106  by about 2 dB as it passes through. 
         [0004]    The telescopic antenna  104  receives and sends a balanced VHF signal to a 1:1 balun  112 . The 1:1 balun outputs an unbalanced output signal  114 . The UHF output signal  110  and the VHF output signal  114  are then passed, through a diplexer  116 , where the UHF signal is attenuated further by a high-pass filter. The unbalanced signals  110  and  114  are then passed through an unbalanced amplifier  118  that is powered by a power injector  120 . Finally, the UHF and VHF signals are received by a television receiver  122 . Because of the signal loss inherent in the television antenna system  100 , the television picture produced by the UHF signal is often not entirely satisfactory. 
         [0005]    While existing devices, for example those described above, have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. The embodiments of the present disclosure overcome one or more of the shortcomings of the prior art. 
       SUMMARY 
       [0006]    In one exemplary aspect, the present disclosure is directed to an antenna. The antenna may include a conductive loop having a first top surface and a first bottom surface, the first top surface and the first bottom surface being separated by a first thickness, the conductive loop having a first edge portion interrupted by a gap defining a feed point, and the conductive loop being responsive to electromagnetic signals in a frequency band. The antenna may also include a conductive strip having a second top surface and a second bottom surface, the second top surface and the second bottom surface being separated by a second thickness substantially similar to the first thickness, the conductive loop lying in a plane defined by the second top surface, the conductive strip having a first distal end and an opposing second distal end and a second edge portion extending between the first and second distal ends, the second edge portion being spaced from the first edge portion, and the second edge portion extending along the first edge portion at a substantially constant distance from the first edge portion. The conductive strip may be electrically isolated from the conductive loop and may be structurally configured and positioned relative to the conductive loop to adjust an input impedance of the conductive loop. 
         [0007]    In some instances, the second top surface may be substantially coplanar with the first top surface such that the second edge portion opposes the first edge portion. 
         [0008]    In other instances, the second top surface may be substantially perpendicular to the first top surface such that the second edge portion opposes the first top surface. 
         [0009]    In other instances, the first edge portion may be substantially parallel to the second edge portion. 
         [0010]    In other instances, the first and second edge portions may be curved and substantially concentric about an axis and wherein the conductive loop is a circle loop. 
         [0011]    In another exemplary aspect, the present disclosure is directed to an antenna system. The antenna system may include a conductive loop having a feed point portion with a first terminal and a second terminal, the conductive loop having a balanced output and a first input impedance. The antenna system may also include an amplifier having a third terminal electrically coupled to the first terminal and a fourth terminal electrically coupled to the second terminal, the amplifier having a balanced input and a second input impedance, wherein the first, second, third, and fourth terminals form a balanced transmission line between the conductive loop and the amplifier. The antenna system may further include a conductive strip adjacent to and spaced from the feed point portion of the conductive loop, the conductive strip being electrically isolated from the loop antenna and being structurally configured and positioned relative to the conductive loop to adjust the first input impedance of the conductive loop to substantially match the second input impedance of the amplifier. The antenna system may additionally include a housing structurally configured to house the conductive loop, the amplifier, and the conductive strip. 
         [0012]    In some instances, the conductive loop includes a first top surface with the feed point portion therein and the conductive strip includes a second top surface that is substantially coplanar with the first top surface. 
         [0013]    In other instances, the conductive loop includes a feed point surface with the feed point portion therein and the conductive strip includes a top surface that is substantially perpendicular to the feed point surface. 
         [0014]    In other instances, the conductive loop includes a first edge portion interrupted by a gap defining the feed point portion and the conductive strip includes a first distal end and an opposing second distal end and a second edge portion extending between the first and second distal ends. The second edge portion may be opposed to and spaced from the first edge portion, the second edge portion extending along the first edge portion at a substantially constant distance from the first edge portion. 
         [0015]    In another exemplary aspect, the present disclosure is directed to a method of receiving television signals. The method may include receiving electromagnetic signals using a conductive loop having a first input impedance and a first edge portion interrupted by a gap defining a feed point. The method may also include transmitting the electromagnetic signals from the conductive loop to an amplifier having a second input impedance over a balanced transmission line electrically coupled to the feed point portion of the conductive loop. The method may further include substantially matching the first input impedance of the conductive loop with the second input impedance of the amplifier using an electrically isolated conductive strip adjacent to and spaced from the feed point portion of the conductive loop, the conductive strip having a second edge portion spaced from and opposing the first edge portion, and the second edge portion extending along the first edge portion at a substantially constant distance. 
         [0016]    In some instances, the substantially matching may include adjusting the first input impedance of the conductive loop from approximately 300 ohms to approximately 75 ohms. 
         [0017]    In other instances, the conductive loop may include a first top surface with the feed point therein and the conductive strip may include a second top surface that is substantially coplanar with the first top surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a functional block diagram of a conventional indoor television antenna system. 
           [0019]      FIG. 2  is a functional block diagram of a television antenna system according to one exemplary aspect of the present disclosure. 
           [0020]      FIG. 3  is a schematic drawing of the planar loop antenna of  FIG. 2  according to one exemplary embodiment of the present disclosure. 
           [0021]      FIG. 4  is an illustration of an example antenna reception pattern of the planar loop antenna of  FIG. 3 . 
           [0022]      FIG. 5  is a schematic drawing of a loop antenna according to another exemplary embodiment of the present disclosure. 
           [0023]      FIG. 6  is a schematic drawing of a circle loop antenna according to another exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications in the described devices, instruments, methods, and any further application of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure. 
         [0025]    As described above, conventional antenna systems typically include a 4:1 balun to match the input impedance of a loop antenna with the input impedance of an amplifier. Exemplary antenna systems according to the present disclosure do not include a 4:1 balun to impedance match, and thus avoid the signal attenuation typically imposed by a balun. Instead, the exemplary antenna systems described herein utilize an impedance matching technique that involves positioning a conductive matching strip near the conductive loop of a loop antenna. These conductive matching strips are electrically isolated from their associated loop antennas and reduce the input impedance of the antennas to match that of the downstream amplifiers. Therefore, the exemplary antenna systems according to the present disclosure may produce a stronger television signal than conventional systems and do so in a more efficient manner. 
         [0026]      FIG. 2  is a functional block diagram of a television antenna system  200  according to one exemplary aspect of the present disclosure. The television antenna system  200  includes a UHF loop antenna  202 , an amplifier  204 , a power injector  206  to power the amplifier, and a television receiver  208 . In the illustrated embodiment, the loop antenna  202  and the amplifier  204  are contained in a housing  205 , but, in alternative embodiments, the antenna and amplifier may be spaced apart in different housings. Note that a patent application entitled “Configurable Antenna System and Method” filed on ______ under attorney docket number 2030.454 discloses an antenna system with a housing and is hereby incorporated by reference in its entirety. The loop antenna  202  is operable to receive digital television signals with wavelengths between approximately 470 MHz and 725 MHz. In other embodiments, however, the loop antenna  202  may be operable to receive TV signals in other wavelength ranges. Additionally, in the illustrated embodiment, the loop antenna  202  has a gain of approximately 2 dBi, but alternatively, it may have a smaller or larger gain. The loop antenna  202  further has a balanced output and an input impedance  210 . The loop antenna  202  will be described in greater detail in association with  FIG. 3 . As shown in  FIG. 2 , the loop antenna  202  sends received UHF signals to an amplifier  204 . The amplifier  204  is a low noise amplifier operable to amplify the UHF signals received from the loop antenna  202 . The amplifier  204  has a balanced input and an input impedance  212 . As shown in  FIG. 2 , the amplifier transmits the amplified UHF signal to the television receiver  208  where it is decoded to produce a television picture. 
         [0027]    Notably, the input impedance  210  of the loop antenna  202  matches the input impedance  212  of the amplifier  204 . In the illustrated embodiment, the input impedance  210  is approximately 75 ohms and the input impedance  212  is also approximately 75 ohms. In alternative embodiments, the input impedance of the amplifier may be approximately 50 ohms and the input impedance of the loop may be adjusted accordingly by a matching strip (described below) to match it. Thus, because both the loop antenna  202  and the amplifier  204  have approximately the same input impedances and both are balanced circuits, no balun is required between the loop antenna and amplifier. That is, electromagnetic signals may be passed directly from the loop antenna to the amplifier over a balanced transmission line. As a result, the approximately 2 dBi gain of the loop antenna  202  is passed to the amplifier  204  without being attenuated by a balun. In this manner, the UHF signal passed to the television receiver  208  may be improved by at least 2 dB. Although input impedances of approximately 75 ohms and 50 ohms are described above, other input impedances, both higher and lower, are contemplated. 
         [0028]      FIG. 3  is a schematic drawing of the planar loop antenna  202  of  FIG. 2  according to one exemplary embodiment of the present disclosure. The loop antenna  202  includes a conductive loop  250  with a feed point  252  and a conductive matching strip  254 , both of which are housed in housing  209 . In the current embodiment, the amplifier  204  is also housed in the housing  209 , but, for the sake of clarity, the amplifier is not shown in  FIG. 3 . The matching strip  254  is electrically isolated from the loop  250  by a dielectric, for example, air. In general, by virtue of its position with respect to the loop  250 , the matching strip  254  is operable to lower the input impedance  210  of the antenna  202  so that it approximately matches the input impedance  212  of the amplifier  204 . 
         [0029]    In more detail, in the illustrated embodiment, the loop  250  and the matching strip  254  are sheets of 0.2 mm thick zinc metal, but, in other embodiments they may be another conductive metal such as, for example, copper or aluminum or an alloy and may be of a different thickness. It should be noted that the conductive metal may be any conductive metal, and is not limited to those explicitly referenced here. The loop  250  has a width  256  and a height  258 , which, in the illustrated embodiment are both 190.5 mm (i.e. loop  250  is a square loop). Further, the conductive portion of the loop  250  has a width  260 , which, in the illustrated embodiment is 28.575 mm. Further, the matching strip  254  has a length  262  and a height  264 , which, in the illustrated embodiment are respectively 158.75 mm and 12.7 mm. With respect to the orientation of the matching strip  254  relative to the loop  250 , an edge of the matching strip extends in a parallel manner along an opposing edge of the loop  250  that contains the feed input  252 . In other words, all points along the edge of the matching strip  254  are spaced from opposing points on the feed point edge of the loop by an equal distance  266 . In the illustrated embodiment, the distance  266  between the matching strip  254  and the loop  250  is 12.7 mm. Further, a planar surface  268  of loop  250  and a planar surface  270  of the matching strip  254  are aligned along the same plane (i.e. coplanar) within the housing  209 . A gap in the planar surface  268  defines the feed point  252 . In the illustrated embodiment, contact points (terminals)  272  and  274  are disposed on either side of the feed point  252  and electrically couple the loop  250  to the amplifier  204 . 
         [0030]    As mentioned above, the matching strip  254  is operable to affect the input impedance of the loop  250 . More specifically, the placement of the matching strip  254  near the loop  250  disturbs the distribution of the loop&#39;s magnetic field and, in turn, affects the loop&#39;s impedance. In the illustrated embodiment, the placement of the matching strip  254  12.7 mm below the feed-input  252  of the loop  250  lowers the loop&#39;s inherent impedance of approximately 300 ohms to approximately 75 ohms. The structural characteristics of the matching strip  254  and its position and orientation relative to the loop  250  determine the amount of disturbance to the loop&#39;s magnetic field. Thus, changing at least one of the distance of the matching strip  254  from the loop  250 , the orientation of the loop&#39;s planar surface  268  with respect to the strip&#39;s planar surface  270 , the length  262  of the matching strip, and the height  264  of the matching strip may affect the input impedance  210  of the antenna  202 . 
         [0031]    Further, the placement of the matching strip  254  near the loop  250  does not significantly alter the antenna reception pattern with respect to conventional loop antennas. In the illustrated embodiment, the antenna  202  is “omni-directional” and has a “figure 8” antenna pattern at UHF frequencies. For example, at 589 MHz, the loop antenna  202  has a “figure 8” antenna pattern  280  shown in  FIG. 4 . 
         [0032]    The impedance matching technique using a conductive matching strip as described above is not limited to the loop and strip configuration shown in  FIG. 3 . For example, with reference now to  FIG. 5 , illustrated is a schematic drawing of a loop antenna  300  according to another exemplary embodiment of the present disclosure. Like the loop antenna  202  of  FIG. 3 , the loop antenna  300  includes a conductive loop  302  with a feed point  304  and a conductive matching strip  306  that is electrically isolated from the loop  302  by air. And, like the matching strip  254  of  FIG. 3 , the matching strip  306  is operable to lower the input impedance of the antenna  300  so that it approximately matches the input impedance of a down-stream balanced amplifier. However, in the embodiment of  FIG. 5 , the matching strip  306  is not co-planar with the loop  302 . Specifically, the loop  302  includes a planar feed point surface  308  with a gap that defines the feed point  304 . And, as illustrated in  FIG. 5 , the matching strip  306  includes a planar surface  310  that is approximately perpendicular to the planar surface  308  in loop  302 . As such, the plane defined by the planar surface  310  of the matching strip  306  passes through the conductive loop  302 . 
         [0033]    In more detail, in the illustrated embodiment, the loop  302  and the matching strip  306  are sheets of 0.2 mm thick zinc metal, but, in other embodiments they may be another conductive metal such as, for example, copper or aluminum or an alloy and may be of a different thickness. It should be noted that the conductive metal may be any conductive metal, and is not limited to those explicitly referenced here. The loop  302  has a width  312  and a height  314 , which, in the illustrated embodiment are both 177.8 mm (i.e. loop  302  is a square loop). Further, the planar conductive surface  308  of the loop  302  has a depth  316 , which, in the illustrated embodiment is 6 mm. Further, the matching strip  306  has a length  318  and a height  320  (of planar surface  310 ), which, in the illustrated embodiment are 165.1 mm and 12 mm, respectively. With respect to the orientation of the matching strip  306  to the loop  302 , an edge of the matching strip extends in a parallel manner along the surface  308  of the loop. More specifically, all points along the edge of the matching strip  306  are spaced from the opposing points on the surface  308  by an equal distance  322 . In the illustrated embodiment, the distance  322  between the matching strip  306  and the loop  302  is 3 mm. Additionally, the antenna reception pattern for the antenna  300  is omni-directional and similar to the “figure 8” pattern shown in  FIG. 4 . Further, contact points (terminals) may be disposed on either side of the feed point  304  to electrically couple the loop  302  to an amplifier, such as amplifier  204  in  FIG. 2 . 
         [0034]    The impedance matching technique using a conductive matching strip is also not limited to square loop antennas, such as antennas  202  and  300  shown in  FIGS. 3 and 5 . This impedance matching technique may be used with other shape loop antennas, such as rectangle loop antennas and circle loop antennas. 
         [0035]    With reference now to  FIG. 6 , illustrated is a schematic drawing of a circle loop antenna  350  according to another exemplary embodiment of the present disclosure. Like the loop antenna  202  of  FIG. 3 , the loop antenna  350  includes a conductive loop  352  with a feed point  354  and a conductive matching strip  356  that is electrically isolated from the loop  352  by air. And, like the matching strip  254  of  FIG. 3 , the matching strip  356  is operable to lower the input impedance of the loop  352  so that it approximately matches the input impedance of a balanced amplifier electrically coupled to terminals on the feed point  354 . 
         [0036]    In more detail, in the illustrated embodiment, the loop  352  and the matching strip  356  are sheets of 0.2 mm thick zinc metal, but, in other embodiments they may be another conductive metal such as, for example, copper or aluminum or an alloy and may be of a different thickness. It should be noted that the conductive metal may be any conductive metal, and is not limited to those explicitly referenced here. The loop  352  has an interior radius  358 , which, in the illustrated embodiment is 172.5 mm. Further, the loop  302  has a planar surface  360  of width  362 , which, in the illustrated embodiment is 18 mm. The matching strip  356  has a planar surface  364  of width  366 , which, in the illustrated embodiment is 16 mm. Further, the matching strip is a semi-circle with interior radius  368  as measured from the same center point (axis) as the loop  352 . In the illustrated embodiment, the interior radius  368  is 212.5 mm. With respect to the orientation of the matching strip  356  to the loop  352 , an edge of the matching strip and an opposing edge of the loop containing the feed point  354  are substantially concentric. In other words, all points along the edge of the matching strip are equidistant from opposing points along the outside edge of loop  352 . Specifically, in the illustrated embodiment, the matching strip  356  extends 90° about the center point of the loop  352  and, by virtue of its radius  368 , is spaced from the loop by 22 mm Further, a planar surface  360  of loop  352  and a planar surface  364  of the matching strip  356  are aligned along the same plane (i.e. coplanar). A gap in the planar surface  360  defines the feed point  354 . Contact points (terminals) may be disposed on either side of the feed point  354  to electrically couple the loop  352  to an amplifier, such as amplifier  204  in  FIG. 2 . 
         [0037]    Although illustrative embodiments have been shown and described, wide ranges of modifications, changes, and substitutions are contemplated in the foregoing disclosure and in some instances, some features of the present disclosure may be employed without a corresponding use of the other features. For example, in some embodiments, the components of an antenna according to the present disclosure may have different dimensions than the antennas shown in  FIGS. 3 ,  5 , and  6 . And, the matching strips in some embodiments may be oriented and positioned relative to their associated loops in a different manner than in the described embodiments. For example, the matching strips may lie in a plane oblique to the loop. Further, the impedance matching technique described herein may be applied in different types of antenna systems, such as outdoor antenna systems, commercial antenna systems, large scale antenna systems, and any other antenna systems that would benefit from impedance matching without the use of a balun. It is understood that such variations may be made in the foregoing without departing from the scope of the present disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the present disclosure.