Abstract:
Briefly, in accordance with an embodiment of the invention, an apparatus and method to provide antenna diversity to reduce multipath effects is provided. The apparatus may include a primary antenna and a secondary antenna, wherein the antenna gain of the secondary antenna is greater than the antenna gain of the primary antenna. The method may include selectively switching between either a primary antenna or a diversity antenna to receive signals, wherein a gain of the primary antenna is less than a gain of the diversity antenna.

Description:
BACKGROUND 
     Multipath fading may reduce a radio&#39;s ability to receive signals. Since signals reflect off objects and may arrive at a point in space in-phase and out-of-phase, and may combine with interfering signals, this may result in destructive interference. The destructive interference may result in dead spots, where signals may not be received. Wireless designers are continually searching for alternate ways to reduce problems due to multipath. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The present invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram illustrating a portion of a transceiver in accordance with an embodiment of the present invention; and 
         FIG. 2  is a block diagram illustrating a wireless device in accordance with an embodiment of the present invention. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention. 
     In the following description and claims, the terms “include” and “comprise,” along with their derivatives, may be used, and are intended to be treated as synonyms for each other. In addition, in the following description and claims, the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” may mean that two or more elements are in direct physical or electrical contact. However, “coupled” may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. 
     Turning to  FIG. 1 , an embodiment of a portion of a transceiver  100  is illustrated. Transceiver  100  may comprise a transmitting portion that may include a power amplifier (PA)  110 . In addition, transceiver  100  may include a receiving portion that may include a low noise amplifier (LNA)  120 . Although the scope of the present invention is not limited in this respect, transceiver  100  may be implemented using a direct conversion or a super-heterodyne receiver architecture. For simplicity, all the components of transceiver  100  have not been shown. 
     An antenna  130  may be switchably coupled to an output terminal of PA  110 . In one example, antenna  130  may be coupled to the output terminal of PA  110  via a switch  140 . In this example, if switch  140  is open, then the output terminal of PA  110  may be disconnected from antenna  130 . Conversely, if switch  140  is closed, the output terminal of PA  110  may be connected to antenna  130 . 
     An antenna  150  may be switchably coupled to an input terminal of LNA  120 . In addition, the input terminal of LNA  120  may be selectively coupled to either antenna  130  or antenna  150  using a switch  160 . In one example, switch  160  may be in a first position to disconnect antenna  150  from the input terminal of LNA  120  and to connect antenna  130  to the input terminal of LNA  120 . Alternatively, switch  160  may be in a second position to connect antenna  150  to the input terminal of LNA  120  and to disconnect antenna  130  from the input terminal of LNA  120 . It should be noted that the use of the terms “first position” and “second position” is arbitrary. 
     In one embodiment, switches  140  and  160  may be relatively low resistance switches such as, for example, micro-electromechanical systems (MEMS) switches. A MEMS switch may be a mechanical switch implemented using semiconductor materials and processes. In alternate embodiments, switches  140  and  160  may be implemented using transistors or diodes. For example, switches  140  and  160  may be implemented using PIN diodes, although the scope of the present invention is not limited in this respect. 
     Antennas  130  and  150  may provide “antenna diversity” to reduce problems due to destructive interference from multipath fading or interference signals. Antennas  130  and  150  may be separated by a predetermined distance, e.g., at least about two centimeters (cm), to provide antenna diversity. In one embodiment, antennas  130  and  150  are separated by a distance of at least about 15 cm. The spatial separation of antennas  130  and  150  may decrease the likelihood that both antennas  130  and  150  receive the same combination of multipath-faded signals. 
     In some embodiments, antenna  130  may be used to transmit and receive signals such as, for example, radio frequency (RF) signals, and may be referred to as a primary antenna, a transmit antenna, or a transmit and receive antenna. Antenna  130  may be used to transmit signals over the air. Antenna  150  may be used to receive signals and may be referred to as a secondary antenna, diversity antenna, or a receive only antenna. 
     In one embodiment, antenna diversity may be accomplished by measuring the signal strength of signals received from antennas  130  and  150  using circuitry of transceiver  100  not shown in  FIG. 1 . The signal strength of signals received using antennas  130  and  150  may be compared by circuitry (not shown) of transceiver  100 . In one embodiment, if the signal strength of a signal received using antenna  150  is greater than the signal strength of a signal received using antenna  130 , then antenna  150  may be used to receive signals by connecting the input terminal of LNA  120  to antenna  150  and disconnecting the input terminal of LNA  120  from antenna  130 . 
     Although the scope of the present invention is not limited in this respect, in some embodiments, the output power of PA  110  may be at least about 14 dBm. In one example, the output power of PA  110  may range from about 17 dBm to about 24 dBm. In other embodiments, the output power of PA  110  may be at least about zero dBm or about 4 dBm. For example, some wireless personal area network (WPAN) devices may have an output power of about zero dBm. 
     In one embodiment, the gain of antenna  150  may be greater than the gain of antenna  130 . Although the scope of the present invention is not limited in this respect, antenna  150  may have a gain of at least about 6 dBi and antenna  130  may have a gain of less than about 6 dBi. In one example, antenna  150  may have a gain of at least about 12 dBi and antenna  130  may have a gain of less than about 3 dBi, although the scope of the present invention is not limited in this respect. In another example, antenna  130  may have a gain of less than about zero dBi, although the scope of the present invention is not limited in this respect. As may be appreciated, in this example, antenna  150  may have a highly directional radiation pattern compared to antenna  130 , and therefore, antenna  150  may be capable of receiving signals at a greater horizontal distance compared to antenna  130 . Generally, increasing the gain of an antenna may result in a relatively higher gain antenna having a more directional radiation pattern that may be capable of receiving signals from a greater horizontal distance, but at less of a vertical distance compared to a lower gain antenna. 
     Although the scope of the present invention is not limited in this respect, in one embodiment, antenna  150  may be a dipole antenna such as, for example, a “stub” or “whip” antenna. In another embodiment, antenna  150  may be a stacked dipole antenna. A stacked dipole antenna may be formed by stacking two or more dipole antennas together. Generally, a stacked dipole antenna may have a greater antenna gain compared to a non-stacked dipole antenna. 
     Although the scope of the present invention is not limited in this respect, in alternate embodiments, antenna  130  may be a dipole antenna, a microstrip patch antenna, or an inverted-F antenna. A patch antenna may be layer of metal, e.g., copper, over a ground plane and may be separated by an insulator material. An inverted-F antenna may be made using a of sheet of metal, e.g., tin or some shielding material, that may be bent in the shape of an “F” but backwards, wherein the center of the “F” is driven, and other side is grounded. 
     Although the scope of the present invention is not limited in this respect, transceiver  100  may be adapted to process a variety of wireless communication protocols such wireless personal area network (WPAN) protocols, wireless local area network (WLAN) protocols, wide area network (WAN) protocols, wireless metropolitan area network (WMAN) protocols, or cellular protocols. 
     In one example, transceiver  100  may be used in a WLAN access point (AP) (not shown). In this example, the output power of power amplifier  110  may be about 24 dBm and antennas  130  and  150  may have a antenna gains of about 6 dBi and about 12 dBi, respectively. A client, e.g., a laptop computer (not shown), may communicate wirelessly with the AP. The laptop may have an output power of about 14 dBm and may have a receive antenna having a gain of about zero dBi. In this example, even though the laptop is transmitting at a relatively low power, the AP may still receive signals from the laptop at relatively large distances since the AP has a relatively high gain receive antenna, i.e., antenna  150 . In addition, even though the laptop is using a relatively lower gain receive antenna in this example, the laptop may still be able to receive signals from the AP since the AP is transmitting signals at a relatively high output power. 
       FIG. 2  is a block diagram of a wireless device  200  in accordance with an embodiment of the present invention. As shown in  FIG. 2 , wireless device  200  may comprise an electronic device  210  that may include a transceiver such as, for example, transceiver  100  described above. Antennas  130  and  150  are illustrated in  FIG. 2 , and the gain of antenna  130  may be less than the gain of antenna  150  as described above. 
     Although the scope of the present invention is not limited in this respect, wireless device  200  may be a personal digital assistant (PDA), a laptop or portable computer with wireless capability, an wireless local area network (WLAN) access point (AP), a web tablet, a wireless telephone, a pager, an instant messaging device, a digital music player, a digital camera, or other devices that may be adapted to transmit and/or receive information wirelessly. In other embodiments, wireless device  200  may be a set-top box, a gateway, or a multimedia center with wireless capability. The gateway may include a digital subscriber line (DSL) modem or a cable modem, and a router. The multimedia center may include a personal video recorder (PVR) and a digital video disc (DVD) player. 
     Wireless device  200  may be used in any of the following systems: a wireless personal area network (WPAN) system, a wireless local area network (WLAN) system, wide area network (WAN), a wireless metropolitan area network (WMAN), or a cellular system, although the scope of the present invention is not limited in this respect. An example of a WLAN network includes the Industrial Electrical and Electronics Engineers (IEEE) 802.11 standard. An example of a WMAN network includes the Industrial Electrical and Electronics Engineers (IEEE) 802.16 standard. An example of a WPAN system includes Bluetooth™ (Bluetooth is a registered trademark of the Bluetooth Special Interest Group). Examples of cellular systems include: Code Division Multiple Access (CDMA) cellular radiotelephone communication systems, Global System for Mobile Communications (GSM) cellular radiotelephone systems, Enhanced data for GSM Evolution (EDGE) systems, North American Digital Cellular (NADC) cellular radiotelephone systems, Time Division Multiple Access (TDMA) systems, Extended-TDMA (E-TDMA) cellular radiotelephone systems, GPRS, third generation (3G) systems like Wide-band CDMA (WCDMA), CDMA-2000, Universal Mobile Telecommunications System (UMTS), or the like. 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.