Patent Document

BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The present invention is directed to multi-band antennas. In particular, the present application is directed to a planar inverted-F antenna with selectable frequency responses.  
           [0003]    2. Description of Related Art  
           [0004]    Presently, devices such as mobile communication devices utilize antennas such as planar inverted-F antennas (PIFAs) for the transmission and reception of radio frequency (RF) signals. These mobile communication devices require the capability to transmit in various frequency bands to be compatible with various systems. For example, such systems can operate at 800, 900, 1800, and 1900 MHz. Unfortunately, at best, current antennas used in mobile communication devices can only operate in limited frequency bands. For example, current PIFA antennas can only operate in a dual band and are incapable of operating for more than two frequency bands. Another problem exists in that present antennas for mobile communication devices have limited bandwidth of operation. A further problem exists in that increasing power to present antennas for improved performance results in specific absorption ratio problems.  
           [0005]    Thus, there is a need for an antenna assembly that provides for multiple frequency operation over a wide bandwidth while reducing specific absorption ratio problems.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention provides an antenna assembly for a mobile communication device. The antenna assembly can include a RF connection feed point and a planar radiating element including a conductive area split by a nonconductive gap which divides the planar radiating element into a first arm having an end coupled to the RF connection feed point and a second arm having an end coupled to the RF connection feed point. The antenna assembly can also include a first connection point coupled to the opposite end of the first arm from the RF connection feed point, the first connection point being selectively coupled to an impedance.  
           [0007]    According to another embodiment, the invention provides an antenna assembly for a mobile communication device, including a RF connection feed point, a first arm having an end coupled to the RF connection feed point, a second arm having an end coupled to the RF connection feed point, and tuning circuitry selectively coupled to the opposite end of the first arm from the RF connection point. The tuning circuitry can be a first connection point selectively coupled to a ground. The tuning circuitry can also be an impedance. The antenna assembly can also include means for selectively eliminating the effects of the second arm on the antenna assembly. The means for selectively eliminating can be an impedance coupled to the opposite end of the second arm from the RF connection point. Also, the means for selectively eliminating can be a second connection point coupled to the opposite end of the second arm from the RF connection point, the second connection point being selectively coupled to a ground.  
           [0008]    The antenna assembly can also include a connection leg in close proximity to the RF connection feed point, the connection leg being selectively coupled to a ground. The second arm can be longer than the first arm or the first arm can be longer than the second arm. The first arm can include a section folded substantially perpendicular to the first arm along a length of the first arm. Also, the first arm can include a section folded substantially perpendicular to the first arm at the end of the first arm, wherein the tuning circuitry can be coupled to the section folded substantially perpendicular to the first arm. Furthermore, the second arm can include a section folded substantially perpendicular to the second arm at the end of the second arm.  
           [0009]    Thus, the present invention solves numerous problems with present antennas and provides additional benefits that are apparent in the description below.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The preferred embodiments of the present invention will be described with reference to the following figures, wherein like numerals designate like elements, and wherein:  
         [0011]    [0011]FIG. 1 is an exemplary illustration of an antenna assembly according to a first embodiment;  
         [0012]    [0012]FIG. 2 is an exemplary illustration of an antenna assembly according to a second embodiment of high band mode operation;  
         [0013]    [0013]FIG. 3 is an exemplary illustration of an antenna assembly according to a third embodiment of low band mode operation;  
         [0014]    [0014]FIG. 4 is an exemplary illustration of an antenna assembly system according to a preferred embodiment; and  
         [0015]    [0015]FIG. 5 is an exemplary graph of a frequency response of a specifically tuned antenna assembly. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]    [0016]FIG. 1 is an exemplary illustration of an antenna assembly  10 , such as a planar inverted-F antenna, according to a first embodiment. Such an antenna assembly  10  can be used in, for example, a mobile communication device. The antenna assembly  10  can include a RF connection feed point  100 , a first arm  110 , a first arm end  115 , a folded section  117 , a second arm  120 , a second arm end  125 , a connection leg  130 , and a gap  140 . The feed point  100 , connection leg  130 , and arm ends  115  and  125  may be bent ends, legs, attached legs, connection points, or the like. For example, the first arm end  115  may include a portion of the first arm  110  bent down to a connection point and the second arm end  125  may include a portion of the second arm  120  bent down to a connection point on a printed circuit board or elsewhere. The second arm  120  may be a long arm and the first arm  110  may be a short arm depending on frequencies to be transmitted and received. According to another embodiment, the second arm  120  may be a short arm and the first arm  110  may be a long arm. The first arm  110  and the second arm  120  may define a planar radiating element including a nonconductive gap  140 . The folded section  117  may be located on the first arm  110  or the second arm  120 . Additionally, the folded section  117  may be an attachment to an arm, a bent portion of an arm, a sidewall, or any other section useful for tuning an arm or an antenna for resonating in a desired band. The folded section  117  may be substantially perpendicular to an arm. For example, the folded section  117  may be folded at a substantially right angle, may curve down, or may be otherwise substantially perpendicular to an arm or to a ground plane.  
         [0017]    The first arm  110  may extend from the feed point  100  to the first arm end  115 . Thus, the feed point  100  is located at one end of the first arm  110  and the first arm end  115  is located at an opposite end of the first arm  110 . Similarly, the second arm  120  may extend from the feed point  100  to the second arm end  125 . Thus, the feed point  100  is located at one end of the second arm  120  and the second arm end  125  is located at an opposite end of the second arm  120 . Such locations are not absolute and are thus, approximate. For example, the second arm end  125  may be located at the side of the second arm  120  at the opposite end of the second arm  120  from the feed point  100 . Additionally, the ends of the arms may be folded substantially perpendicular to the arms. For example, the ends may be bent at an approximate 90-degree angle, may be curved down, may be attached at a right angle, or may be otherwise substantially perpendicular to the arm or a ground plane.  
         [0018]    In operation, the first arm  110  may be a short arm that resonates in one frequency band and the second arm  120  may be a long arm that resonates in another frequency band. The first arm end  115 , the second arm end  125 , and the connection leg  130  can be grounded or ungrounded by switching techniques. According to another embodiment, the first arm end  115 , the second arm end  125 , and the connection leg  130  can be coupled to tuning impedances by switching techniques. Thus, the tuning and structure of the antenna assembly  10  can be altered by various switching techniques. In particular, by adjusting the impedances and/or grounding points located at the arm ends  115  and  125  and the connection leg  130 , a single antenna assembly  10  can be used for radiating in a wider band in numerous frequency bands. For example, impedances can be used to compensate for the lengths of the legs  110  and  120 . Thus, a single antenna can be used for at least quad-band operation. In a particular example, the bandwidth of the antenna assembly  10  is increased in high and low bands and the antenna assembly  10  is capable of radiating in all bands of 800/900 MHz, 1800/1900 MHz, and GPS frequency. Also, the antenna can be tuned by altering lengths and widths of the arms  110  and  120  and the size of the folded section  117  to operate in other frequencies.  
         [0019]    For improved operation and tuning in given frequencies, a ground plane may be extended under the antenna assembly  10  in its length. This can further improve the return loss of the antenna assembly  10  Additional adjustments may be made, such as reducing the height and increasing the width of components of the antenna assembly  10  based on space and tuning requirements.  
         [0020]    [0020]FIG. 2 is an exemplary illustration of an antenna assembly  10  according to a second embodiment of high band mode operation. For example, the antenna assembly  10  may operate in a mode covering both 1800 and 1900 MHz. In high band mode operation, the first arm end  115  may float and the second arm end  125  and the connection leg  130  may be connected to a ground plane  200 . Thus, the second arm  120  can join the first arm  110  to become a second resonator in the high band. Therefore, the two arms can both resonate in the high band and provide for a large bandwidth. For example, the antenna assembly  10  can cover not only 1800 and 1900 MHz, but also cover GPS frequency.  
         [0021]    [0021]FIG. 3 is an exemplary illustration of an antenna assembly  10  according to a third embodiment of low band mode operation. For example, the antenna assembly  10  may operate in a mode covering both 800 and 900 MHz. In low band mode operation, the first arm end  115  may be connected to a ground plane  200  and the second arm end  125  and the connection leg  130  may float. Thus, the first arm  110  may be disabled partially by making it look like high impedance at the feed point  100  looking into that arm. The second arm  120  then resonates as a micro strip line. Therefore, the bandwidth of operation of the antenna assembly  10  in the low band mode significantly increases.  
         [0022]    [0022]FIG. 4 is an exemplary illustration of an antenna assembly connection switching system  40  according to a preferred embodiment. It is understood that other embodiments may be employed for switching the connections to the antenna assembly  10 , such as a programmable logic gate array, processor switching, micro-electromechanical switches, or any other circuits or means for switching electrical and RF connections. The antenna assembly system  40  can include capacitors  401 - 404 , diodes  411 - 414 , resistors  421 - 424 , an OR gate  430 , and an inverter  440 . The assembly system  40  is merely exemplary and may be designed in various ways. For example, the selection of logic devices may depend on the logic signals available from the logic circuits in selecting a particular band. As another example, XOR gates, AND gates, NAND gates, or other logic circuitry may be used depending on received signals and design choices. The present capacitors, diodes, and resistors can be selected for appropriate coupling and to resonate unwanted reactances. For example, the capacitors  401 - 403  may be over 100 pF and the resistances  421 - 423  may be over 1 k ohm.  
         [0023]    In operation, the OR gate  430  may receive selection signals for selecting a mode of operation. According to one embodiment, the OR gate  430  may receive DCS and PCS selection lines. For example, logical ones and zeros may be sent to the inputs of the OR gate  430  to select specific modes of operation illustrated in the truth table in Table 1. In this case, when either of the selection lines is high, the operation can be for high band frequencies. When both selection lines are low, the operation can be for low band frequencies.  
                                                         TABLE 1                                           Second               Connection       Arm End   First Arm           Leg 130   Feed Point 100   125   End 115                                     800/900 MHz   Float   Signal with match   Float   GND       1800/1900   GND   Signal without   GND   Float       MHz       match                  
 
         [0024]    Also, Table 1 illustrates that the state of the legs in one mode of operation can be the reversal of the other. Thus, the other is a negation of the first mode. Therefore, if either DCS mode or PCS mode is selected for a high band 1800/1900 MHz mode of operation, a logical one will exist at the output of the OR gate. This logical one will turn on the diodes  411  and  413  based on well known electrical circuitry principles. In particular, the diodes  411  and  413  will be forward biased. Thus, the connection leg  130  and the second arm end  125  will be grounded. At the same time, a logical zero will exist at the output of the inverter  440  to turn off the diode  412 . In particular, the diode  412  will be turned off. Therefore, the first arm end  115  will not be grounded. In this case, a matching component is not needed to turn off diode  414  to disable capacitor  404  because the capacitor  404  is a matching component for low band operation. For example, the truth table can change if the goal is to tune the antenna to perform without a matching circuit in the low band and with a matching circuit in the high band. Thus, the circuit may be altered accordingly. As further example, depending on intended use, a capacitance of 2.2 pF may be used for appropriately tuning the antenna assembly  10  in low band mode of operation. If neither DCS or PCS mode is selected, a logical zero will exist at the output of the OR gate  430  and a low band 800/900 MHz mode of operation will be enabled. Thus, opposite components are grounded and not grounded as indicated in Table 1 above. In actual practice, the ground points of diodes  411  and  413  may be connected to the output of the inverter  440  as opposed to the ground to ensure the diodes are reverse biased and in off mode with certainty.  
         [0025]    [0025]FIG. 5 is an exemplary graph  50  of a frequency response of a specifically tuned antenna assembly  10 . The graph  50  illustrates the response of the antenna assembly in a high band mode  510  and in a low band mode  540 . For example, the high band mode  510  can include DCS frequencies of 1710-1880 Hz and PCS frequencies of 1850-1990 Hz. Thus, point  520  illustrates the performance at 1710 Hz and point  530  illustrates the performance at 1990 Hz. As another example, the low band mode  540  can include AMPS and TDMA frequencies of 824-894 Hz and EGSM frequencies of 880-960 Hz. Thus, point  550  illustrates the performance at 824 Hz and point  560  illustrates the performance at 960 Hz. Performance may vary according to the height of the antenna from a ground plane. For example, the present performance can be achieved for a ground plane 9.5 mm below the antenna. Well-known techniques of antenna tuning can be utilized to retune the antenna assembly  10  for other frequencies of operation.  
         [0026]    While this invention has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in the other embodiments. Accordingly, the preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.

Technology Category: h