Patent Publication Number: US-7586452-B2

Title: Multi-band antenna

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application No. 60/884,945 filed Jan. 15, 2007, which is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention generally relates to a multi-band antenna and specifically to such an antenna integrated in a window. The invention also relates to an antenna for use on multiple cellular telephone bands. 
   2. Description of the Related Art 
   Antennas are commonly integrated in vehicle windows to reduce and/or negate the need for vertical rod antennas (e.g., mast or whip antennas) that project from various surfaces of the vehicle. By utilizing antennas integrated in windows, vehicle manufacturers obtain aesthetically pleasing and streamlined vehicle exteriors as well as reduced wind resistance. Unfortunately, performance of these window integrated antennas has often been deficient. Furthermore, placement of these antennas on glass often obstructs the view of a driver of the vehicle. 
   An antenna suitable for receiving and transmitting on cellular telephone bands is disclosed in U.S. Pat. No. 4,914,447 (the &#39;447 patent). The antenna of the &#39;447 patent includes a plurality of conductive strip segments arranged in a “U-shape” and an “inverted L-shape” connected to the “U-shape”. This antenna functions in a cellular telephone band of 860 MHz to 940 MHz. Unfortunately, the antenna does not perform in other cellular telephone bands. 
   U.S. Pat. No. 4,072,954 (the &#39;954 patent) discloses a dual-band antenna. The antenna is formed of conductive strip segments disposed on a window. The conductive strip segments form a pair of dipole legs, with each leg forming an open loop. The conductive strip segments also form a vertical section disposed between the dipole legs. The antenna of the &#39;954 patent operates primarily in the AM/FM broadcast frequency ranges, and not in the cellular telephone frequency ranges. Furthermore, the antenna of the &#39;954 patent occupies a significant area on the window, thus obstructing the view of the driver. 
   There remains an opportunity for a dual-band antenna, primarily for cellular telephone use, that may be integrated with a window without significantly obstructing the view of the driver. 
   SUMMARY OF THE INVENTION AND ADVANTAGES 
   The subject invention is an antenna including a conductive area formed of conductive material. The conductive area includes at least one peripheral side. The conductive area also defines a slot interrupting the peripheral side to divide the conductive area into a first section and a second section. The second section is spaced from and at least partially surrounds the first section. The first section includes at least one edge adjacent to the slot and the second section includes at least one edge adjacent to the slot. The edges adjacent to the slot are dimensioned for radiating primarily in a first frequency band. The antenna also includes a conductive strip formed of conductive material. The conductive strip is disposed generally co-planar with the conductive area. The conductive strip is connected to the first section along the peripheral side. The conductive strip is dimensioned for radiating primarily in a second frequency band. In the subject invention, the antenna may be integrated with a window. Specifically, the area of conductive material and the strip of conductive material may be disposed on a transparent, non-conductive pane. 
   The antenna provides numerous advantages. First and foremost, the antenna is an effective radiator on multiple frequency bands, particularly multiple cellular telephone bands. Furthermore, when integrated with a window of a vehicle, the antenna has a pleasing aesthetic appearance which is virtually unnoticeable to the driver of the vehicle and thus does not impede the driver&#39;s vision through the window. Also, the antenna is tuned to match the impedance of a transmission line. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is a perspective view of a vehicle including a window having an antenna disposed on a non-conductive pane; 
       FIG. 2  is a top view of a first embodiment of the antenna showing an area of conductive material divided into a first section having a square shape and a second section and a strip of conductive material having a pair of segments; 
       FIG. 3  is a top view of a second embodiment of the antenna showing the strip defining a plurality of closed loops; 
       FIG. 4  is a top view of a third embodiment of the antenna showing the strip defining an open loop; 
       FIG. 5  is a top view of a fourth embodiment of the antenna showing the first section having a triangular shape and the strip forming an “X” pattern; 
       FIG. 6  is a top view of a fifth embodiment of the antenna showing the first section having a circular shape; 
       FIG. 7  is a top view of a sixth embodiment of the antenna showing the strip forming a meander line and monopole branches extending from the meander line; and 
       FIG. 8  is a top view of the sixth embodiment of the antenna showing additional monopole branches extending from the meander line. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an antenna for operating in multiple frequency bands is shown at  10 . Referring to  FIG. 1 , the antenna  10  is preferably integrated with a window  12  of a vehicle  14 . The window  12  is preferably formed of at least one non-conductive pane  16  of transparent material, such as glass. However, other materials may also be suitable for forming the transparent, non-conductive pane  16 , such as, but not limited to, a resin. Those skilled in the art realize that transparent materials allow light rays to be transmitted through in at least one direction such that objects on the other side of the transparent material may be seen. The window  12  may alternatively be utilized in non-vehicle applications such as buildings (not shown). The antenna  10  may also be implemented in non-window applications, including, but not limited to, electronic devices such as cellular phones and terrestrial broadcast receivers. Of course, those skilled in the art realize other applications for the antenna  10 . The antenna  10  is described hereafter as integrated with the window  12 , but this should not be perceived as limiting in any way. 
   As stated above, the antenna  10  operates in multiple frequency bands. Particularly, the various embodiments of the antenna  10  defined herein each effectively radiate in a first frequency band and a second frequency band. Said another way, the antenna  10  exhibits an acceptable return loss and voltage standing wave ratio (VSWR) in a range of frequencies defining the first and second frequency band. 
   The antenna  10 , as described herein, preferably radiates in frequency bands utilized for cellular/mobile telephone communications. Specifically, the first frequency band is the U.S. “PCS” band, with frequencies ranging from 1850 MHz to 1990 MHz. In the U.S., this band typically supports GSM, CDMA, and D-AMPS systems. The second frequency band is the U.S. “cellular” band, with frequencies ranging from 824 MHz to 940 MHz. In the U.S., this band typically supports AMPS, D-AMPS, CDMA, TDMA, and GSM services. Of course, the dimensions of the antenna  10 , as described in further detail below, may be altered to allow operation of the antenna  10  in other frequency bands and/or additional frequency bands. 
   The antenna  10  includes a conductive area  18  formed of conductive material. The conductive area  18  is preferably disposed on the non-conductive pane  16 . The conductive material is preferably a metal which has properties conducive to conducting electricity. Most preferably, the metal is a silver paste which is disposed on the non-conductive pane  16  in a firing process well known to those skilled in the art. 
   As shown in  FIG. 1 , windows  12  of vehicles  14  often include a region  22  around the edge  20  of the window  12  that is coated with paint or ceramic frit, typically black in color. As shown in  FIG. 1 , the conductive area  18  is preferably disposed adjacent an edge  20  of the window  12  of the vehicle  14 . Most preferably, the conductive area  18  is disposed in the coated region  22  such that the conductive area is not easily viewable on the window  12 . Thus, the conductive area  18  will not impede the vision of the driver any more than is already impeded by the coated region  22 . 
   In the illustrated embodiments, the conductive area  18  is rectangularly-shaped. Of course, the conductive are  18  may form other shapes. The conductive area  18  includes at least one peripheral side  23 . 
   Referring now to  FIG. 2 , the conductive area  18  defines a slot  24 . The slot  24  interrupts the peripheral side  23  and divides the conductive area  18  into a first section  26  and a second section  28 . The first section  26  is spaced from the second section  28 . The second section  28  at least partially surrounds the first section  26 . The second section  28  serves as a ground plane to the antenna  10 . Since the conductive area  18  is disposed adjacent the edge  20  of the window  12 , the metal frame (not shown) of the vehicle  14  may also serve as an extension of the ground plane due to its close proximity to the second section  28 . Furthermore, the metal frame of the vehicle  14  may also be in direct contact with the second section  28 . 
   Preferably, the antenna  10  includes a connector  29  for accepting and supporting a transmission line  30 . The connector  29  includes a first contact (not shown) electrically connected to the first section  26  and a second contact (not shown) electrically connected to the second section  28 . The contacts are electrically isolated from one another. Most preferably, the transmission line  30  is an unbalanced line, such as a coaxial cable. The coaxial cable includes a center conductor (not shown) and a shield (not shown). The connector  29  electrically connects the center conductor to the first section  26  and electrically connects the shield to the second section  28 . Thus, the shield of the transmission line  30  is connected to the ground plane of the antenna  10 . 
   In a first embodiment, as shown in  FIG. 2 , the first section  26  is generally rectangular-shaped and more specifically, square-shaped. Of course, the first section  26  may be implemented in alternative geometric shapes, including, but not limited to, triangular and circular shapes. For example,  FIG. 5  illustrates a fourth embodiment of the antenna  10  showing the first section  26  as generally triangular-shaped. 
   The first section  26  includes at least one edge  31  adjacent to the slot  24 . In the first embodiment, as shown in  FIG. 2 , the first section  26  includes three edges  31  adjacent to the slot  24 . The second section  28  also includes at least one edge  32  adjacent to the slot. In the first embodiment, the second section  28  also includes three edges  32  adjacent to the slot  24 . The edges  31 ,  32  and the slot  24  are dimensioned for radiating primarily in the first frequency band. Said another way, the length of the edges  31 ,  32  and the width of the slot  24  are dimensioned to correspond to a first group of frequencies for which it is desirous to transmit and/or receive RF signals. Specifically, the edges  31  of the first section  26  each have a length of about 10 mm. The slot  24  defines a width of about 2 mm between edges  31 ,  32 . 
   The antenna  10  also includes a conductive strip  34  formed of conductive material. The term “conductive strip”  34  refers to an elongated, thin piece that is longer than it is wide. The conductive strip  34  is disposed generally co-planar with the conductive area  18 . Specifically, a plane (not shown) defined by the conductive strip  34  and a plane (not shown) defined by the conductive area  18  are no more than 10 degrees offset from one another. In the illustrated embodiments, the conductive strip  34  is also disposed on the non-conductive pane  16 , such that the conductive strip  34  and the conductive area  18  are therefore generally co-planar. The conductive strip  34  resembles window defroster heating lines that are common in vehicle windows. Thus, the driver of the vehicle will not significantly notice the conductive strip  34 . 
   The conductive strip  34  is connected to the first section  26  of the conductive area  18  along the peripheral side  23  of the conductive area  18 . The conductive strip  34  is dimensioned for radiating primarily in the second frequency band. In the first embodiment, the conductive strip  34  includes a first segment  36  connected to the first section  26  and extending perpendicularly from the first section  26 . Specifically, the connection of the first segment  36  is generally equidistant from the slot  24 . 
   The conductive strip  34  also includes a second segment  38  connected to the first segment  36  and extending generally perpendicular from the first segment  36 . As such, the second segment  38  is generally parallel to the peripheral side  23  of the area  18 . In the first embodiment, for operating on the frequencies described above, the first segment  36  defines a length of about 62 mm and the second segment  38  defines a length of about 31 mm. The second segment  38  intersects with the first segment  36  at a point about 31 mm from the peripheral side  23  of the conductive area  18 . Either the first or second segments  36 ,  38  can be used for tuning the antenna as a tuning stub. That is, the length of either of the segments  36 ,  38  can be extended or reduced to properly match the impedance of the antenna to the impedance of a coaxial cable, which is typically around 50Ω. 
   The antenna  10  of the first embodiment provides impressive performance characteristics. The antenna  10  achieves a return loss as low as 14 dB in the first frequency band and a return loss between 10 and 22 dB in the second frequency band. This translates to a VSWR of less than 2:1 in both frequency bands. 
   It may be convenient to conceptualize the antenna  10  of the subject invention as a dipole antenna  10 . The dipole antenna  10  includes a first dipole leg (not numbered) and a second dipole leg (not numbered). The first dipole leg radiates primarily in the first frequency band and is formed by the edges  31 ,  32  of conductive material adjacent the slot  24 . The second dipole leg radiates primarily in the second frequency band and is formed by the conductive strip  34 . 
   Of course, the dipole legs do not radiate independently of one another; that is, the dipole antenna  10  must be treated as a consolidated unit. The geometric dimensions of the first dipole leg have an effect on the performance of the antenna  10  in the second frequency band. Likewise, the geometric dimensions of the second dipole leg have an effect on the performance of the antenna  10  in the first frequency band. Changes to the geometric dimensions of just about any component of the antenna  10  will have an effect on the performance of the antenna  10 . 
     FIG. 3  illustrates a second embodiment of the invention. In the second embodiment, the conductive strip  34  forms at least one closed loop  40  of conductive material. The term “closed loop” refers to the conductive strip  34  forming a polygon. The at least one closed loop  40  may form any of several shapes. In the second embodiment, the conductive strip  34  forms three closed loops  40  forming rectangular shapes of various dimensions. Each closed loop  40  is made up of various segments (not numbered). One of the closed loops  40  may share one or more segments, or part of segments, with another of the closed loops  40 . 
   The conductive strip  34  may also include various segments (not numbered) that are not part of one of the closed loops  40 . For instance, as shown in  FIG. 3 , the conductive strip  34  includes segments connecting the closed loops  40  to the first section  26 . The conductive strip  34  also includes segments extending from one of the closed loops  40  and functioning as tuning stubs. 
   The antenna  10  of the second embodiment also provides excellent performance characteristics. The antenna  10  achieves a return loss of nearly 20 dB in the first frequency band and a return loss between 10 and 16 dB in the second frequency band. Again, this translates to a VSWR of less than 2:1 in both frequency bands. 
     FIG. 4  illustrates a third embodiment of the present invention. In the third embodiment, the conductive strip  34  forms an open loop  42  of conductive material. Specifically, the conductive strip  34  includes a first segment  44  having a proximal end  46  and a distal end  48 . The proximal end  46  is connected to the first section  26  of the area  18  and the first segment extends from the peripheral side  23 . A second segment  50  includes a proximal end  52  and a distal end  54 . The proximal end  52  is connected to the distal end  48  of the first segment  44 . The second segment  50  extends perpendicularly from the first segment  44 . A third segment  56  includes a proximal end  58  and a distal end  60 . The proximal end  58  is connected to the distal end  54  of the second segment  50 . The third segment  56  extends perpendicularly from the second segment  50  and towards the area  18 . The conductive strip  34  also includes a fourth segment  62  having a proximal end  64  and a distal end  66 . The fourth segment  62  is connected to the first segment  44  at a point  68  between the proximal and distal ends  46 ,  48  of the first segment  44 . The fourth segment  62  extends generally perpendicular from the first segment  44  and towards the distal end  60  of the third segment  56 . A gap  70  is defined between the distal end  66  of the fourth segment  62  and the distal end  60  of the third segment  56 . 
   The antenna  10  of the third embodiment may also include a stub  72  having a proximal end  74  and a distal end  76  extending away from the peripheral side  23  of the conductive area  18  and towards the gap  70  defined between the third and fourth segments  56 ,  62 . The proximal end  74  is connected to the second section  28 . The distal end  76  terminates at a point about equidistant from the distal end  60  of the third segment  56  and the distal end  66  of the fourth segment  62 . 
   The first, second, and third segments  44 ,  50 ,  56  assist in providing the antenna  10  of the third embodiment resonance at the second frequency band. The fourth segment  62 , the stub  72 , and a portion (not numbered) of the first segment  44  between the proximal end  46  and the fourth segment  62  assist in providing the antenna  10  resonance at the first frequency band. 
   The antenna  10  of the third embodiment provides excellent performance. The antenna  10  achieves a return loss of 14 dB at 824 MHz and 20 dB at 894 MHz, both in the second frequency band. Furthermore, the return loss dips to 30 dB between the above frequencies in the second frequency band. The antenna  10  also provides a return loss of 27 dB at 1.85 GHz and around 35 dB elsewhere in the first frequency band. The return loss values translate to VSWRs of less than 1.4:1 in both frequency bands. 
   A fourth embodiment of the invention is illustrated in  FIG. 5 . In this embodiment, the first section  26  is triangularly-shaped. The triangularly-shaped first section  26  includes at least two edges  31  adjacent to the slot  24 . However, in the fourth embodiment, all three edges  31  of the triangularly-shaped first section  26  are adjacent to the slot to define the slot  24 . The edges  32  of the second section  28  of the fourth embodiment define a generally square shape. As such, portions of the slot  24  define a variable width between the sections  26 ,  28 . Specifically, the width of the slot  24  is highest adjacent the peripheral side  23  of the conductive area  18 . The triangularly-shaped first section  26  provides wideband characteristics to the antenna  10  which allow the antenna  10  to be easily tuned. 
   The conductive strip  34  of the fourth embodiment presents an “X” or cross-shaped feature. Specifically, the conductive strip  34  includes a first segment  78  having a proximal end  80  and a distal end  82 . The proximal end  80  is connected to the first section  26  at the peripheral side  23  and extends generally perpendicular from the area  18 . A second segment  84  intersects with the distal end  82  of the first segment at an intersection point  86 . A third segment  88  intersects with the second segment  84  at the intersection point  86 . The second and third segments  84 ,  88  define the “X” or cross shape of this embodiment. Preferably, the second and third segments  84 ,  88  each define a 45° angle with the first segment  78 . The second segment  84  also includes a pair of ends  90 . A fourth segment  92  extends towards the area  18  of conductive material from one of the ends  90  of the second segment  84 . The fourth segment  92  is preferably disposed generally parallel to the first segment  78 , however, this parallel disposition is not strictly required. 
   The first segment  78 , the fourth segment  92 , and a portion of the second segment  84  between the intersection point  86  and the fourth segment  92  provide resonance at the second frequency band. The first, second, and third segments  78 ,  84 ,  88  provide resonance at the first frequency band. The antenna  10  of the fourth embodiment also provides superb performance. The antenna  10  achieves a return loss of 11 dB at 824 MHz and 12 dB at 894 MHz while dipping to 30 dB in the second frequency band. The antenna  10  also provides a return loss of 12 dB at 1.85 GHz. The return loss values translate to VSWRs of less than 1.8:1 in both frequency bands. 
     FIG. 6  illustrates a fifth embodiment of the invention. In the fifth embodiment, the first section  26  defines a circular-shape. As such, the first section  26  has a single, continuous edge  31 . 
     FIG. 7  illustrates a sixth embodiment of the invention. In the sixth embodiment, the conductive strip  34  includes a meander line  94 . The meander line  94  extends “upwards” and downwards” as the conductive strip  34  extends away from the first section  26 . Specifically, the meander line  94  includes at least one horizontal component  96  and at least one vertical component  98 . In the embodiment illustrated in  FIG. 7 , the meander line  94  includes four horizontal components  96  and four vertical components  98 . The horizontal components  96  are generally perpendicular to the peripheral side  23  of the conductive area  18  while the vertical components  98  are generally parallel to the peripheral side  23 . The length of each horizontal component is 25.2 mm and the length of each vertical component is 12.5 mm. Of course, the number and lengths of the components  96 ,  98  are determined by performance requirements and the desired frequency bands and may be different based on the specific application. 
   The antenna  10  of the sixth embodiment also includes a first monopole branch  100  and a second monopole branch  102 . The monopole branches  100 ,  102  may serve to assist the resonance of the antenna  10  at specific frequencies and/or to match the impedance of the antenna  10  to the impedance of the transmission line  30 . The first monopole branch  100  extends from the meander line  94 . Specifically, in the embodiment illustrated in  FIG. 7 , the first monopole branch  100  extends generally perpendicularly from the horizontal component  96  adjacent the first section  26  of the conductive area  18 . The first monopole branch  100  preferably has a length of 76.9 mm. The second monopole branch  102  also extends generally perpendicular from the meander line  94  and specifically from the horizontal component  96  adjacent the first section  26 . The second monopole branch  102  preferably has a length of 40.6 mm. The antenna  10  of this sixth embodiment achieves a return loss greater than or equal to 10 dB and a VSWR of less than 2:1 in the first and second frequency bands. 
   Those skilled in the art realize that the length, position, and intersection angles of the monopole branches  100 ,  102  may be different based on the specific application. Furthermore, additional monopole branches  104  may also be utilized, as is shown in  FIG. 8 . As with the first and second monopole branches  100 ,  102 , these additional monopole branches  104  assist the antenna  10  in resonance on additional frequencies. 
   The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.