Abstract:
A grounded, shielded holder for a radio frequency communications card installed in a terminal used in a wireless network includes a built-in antenna for transmitting and receiving radio frequency signals to and from the card. The antenna is formed from the material of the holder itself.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to wireless local area networks and portable or mobile communications equipment such as telephones, computers, personal digital assistants, pagers, and data collection and roaming terminals, as well as stationary equipment such as fixed access points or base stations and, more particularly, to improvements in holding, shielding, grounding and transmitting/receiving radio frequency signals for a communications equipment card used in such mobile and/or stationary equipment. 
     2. Description of the Related Art 
     Wireless local area networks use radio frequency (RF) communications channels to communicate between communications equipment. Each equipment may be a portable or mobile terminal or station, such as a telephone, computer, personal digital assistant, pagers, and data collection and roaming terminal, or a stationary terminal or station, such as a fixed access point or base station. Typically, a multitude of mobile terminals communicate with a plurality of stationary terminals such as host computers. The stationary terminals are, in turn, connected by a wired or wireless channel to a network infrastructure. 
     Wireless and RF protocols are known which support the logical interconnection of portable terminals having a variety of types of communication capabilities to stationary terminals. The logical interconnections are based upon an infrastructure in which at least some of each of the portable terminals are capable of communicating with at least two of the stationary terminals when located within a predetermined range therefrom, each portable terminal being normally associated and in communication with a single one of such stationary terminals. Based on the overall spatial layout, response time, and loading requirements of the network, different networking schemes and communications protocols have been designed so as to most efficiently regulate the communications. 
     One such protocol is set forth in the IEEE Standard 802.11 entitled “ Wireless LAN Medium Access Control  ( MAC )  and Physical Layer  ( PHY )  Specifications ” available from the IEEE Standards Department, Piscataway, N.J., (hereinafter, the “IEEE 802.11 standard”). The IEEE 802.11 standard is directed to wireless local area networks, and in particular specifies the MAC or the data link layer and the PHY or physical link layer. These layers are intended to correspond closely to the two lowest layers of the ISO Basic Reference Model of OSI, i.e., the physical layer and the data link layer. The IEEE 802.11 standard permits communications, at 1 Mbps, 2 Mbps and higher data rates, a medium access technique similar to carrier sense multiple access/collision avoidance (CSMA/CA), a power-save mode for battery-operated mobile stations, seamless roaming in a full cellular network, high throughput operation, diverse antenna systems designed to eliminate “dead spots”, and an easy interface to existing network infrastructures. 
     The current implementations of commercial wireless local area networks utilize a transceiver operating in the 2.4 to 2.4835 GHz spread spectrum band which is the industrial, scientific, and medical (ISM) band allocated for unlicensed use by the U.S. Federal Communications Commission. The current systems utilize one of two basic types of spread spectrum modulation: direct-sequence and frequency-hopping. 
     In a direct-sequence spread spectrum (DSSS) system, each binary bit of data in a data signal is spread over each of 11 discrete frequency channels at the same time, i.e., an 11-bit pseudorandom noise (PN) code. The data of each user is coded using a different PN code so that the signals of different users are orthogonal to each other. Thus, another user&#39;s signal is merely interpreted as noise. The IEEE 802.11 standard provides two modulation formats and data rates in the DSSS system—a basic access rate using differential binary phase shift keying (DBPSK) modulation operating at 1 Mbps, and an enhanced access rate using differential quadrature phase shift keying (DQPSK) modulation operating at 2 Mbps. 
     In a frequency-hopping spread spectrum (FHSS) system, each binary bit of data in the data signal is associated with a group of distinct “chips”, or discrete signal frequency output, in different parts of a frequency band, with a minimum hop of at least 6 MHz (in North America/Europe). The chipping pattern or hopping sequence is a pseudo-random sequence uniformly distributed throughout the band and set forth in the IEEE 802.11 standard. Each access point executes a unique hopping pattern across 79 non-overlapping frequencies at a rate of one hop every 100 milliseconds. There are three sets of hopping patterns specified in the IEEE 802.11 standard for North American/European operations, with each set containing 26 sequences. The sets are selected to minimize the possibility of interference. The RF modulation technique used in the FHSS system is 2-level or 4-level Gaussian-filtered frequency shift keying (GFSK). Frequency-hopping spread spectrum systems are currently preferred over direct sequence for most applications by the majority of users as they allow increased capacity and decreased interference. The FHSS system hops over channels with an effective raw data rate of 1 Mbps or 2 Mbps. Current commercial systems can typically cover from an area of 25,000 to 70,000 square feet with a process gain of 10 dB. The relatively low power output used in such systems is a consequence of limits placed by regulatory agencies. Power output standards currently in effect limits the power output to either 100 mW, 230 mW, or 500 mW depending on the country. 
     In a spread spectrum system, one can multiplex users by assigning them different spreading keys. Such a system is called a code division multiple access (CDMA) system. Most wireless local area network products are not CDMA systems since users belonging to the same wireless local area network utilize the same spreading key. Instead, as noted above, the media access protocol (MAC) set forth in the IEEE 802.11 standard provides that use access to the channel is multiplexed in time using nearly the same Carrier Sense Multiple Access (CSMA) protocol as in the Ethernet. 
     Each of the aforementioned terminals utilize a communications equipment card which essentially comprises a radio frequency transceiver circuit for implementing the desired RF protocol, and an antenna, especially the classical λ/4 monopole antenna as typified by the whip antenna. For increased miniaturization and sensitivity to electro-magnetic fields, inverted L- and F-antennas have been proposed to replace the monopole antenna. 
     The known antennas are connected to the transceiver circuits by being mounted on printed circuit boards that carry the circuits, by being loosely connected by cables or end caps, or by being encapsulated in shielded housings. Such methods are disadvantageous because they increase the occupied space factor and are therefore unsuitable for applications where a high degree of miniaturization is desired. 
     SUMMARY OF THE INVENTION 
     OBJECTS OF THE INVENTION 
     Accordingly, it is a general object of this invention to provide a highly suitable, miniaturized communications equipment component capable of performing multiple functions previously performed by multiple components. 
     Still another object of the present invention is to enable a single component to hold a radio frequency communications card, to shield the card from electro-magnetic interference, to transmit/receive radio frequency signals with a built-in antenna, and to serve as a ground plane for the antenna. 
     A still further object of the present invention is to reduce manufacturing and assembly costs for such components. 
     FEATURES OF THE INVENTION 
     In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention resides in a component for a radio frequency communications card, comprising a holder constituted of an electrically conductive material, such as sheet metal, for holding and shielding the card from radio frequency interference. The holder has a main portion lying in a plane which extends over the card and a pair of side portions integral with the main portion and extending over the side edges of the card. The main and side portions bound a compartment in which the card is slidably received and held. An end portion abuts against a leading edge of the card in a fully received, held position for the card. A plurality of mounting portions on the side portions are used for fixing the position of the holder in a communications equipment. 
     The component includes a built-in antenna constituted of the same material as, and being of one-piece with, the holder, and is operative for transmitting/receiving radio frequency signals to and from the card. The antenna is formed from the main portion itself. Specifically, an antenna portion is cut or stamped out of the main portion, but not completely removed therefrom. The antenna portion is bent out of the plane of the main portion and leaves behind a cutout that extends through the main portion. Preferably, the antenna portion has a first part extending generally perpendicularly to the main portion, a second part extending generally parallel to the main portion, and a feeding point connected to the main portion and to the second part, thereby configuring the antenna as an F-antenna. 
     The holder includes a grounding contact for grounding the holder and enabling the plane of the main portion to serve as a ground plane for the antenna. At least one of the side portions and the end portion, and preferably each of the side and end portions of the holder, is provided with the grounding contact which extends along the respective side and end portion and makes contact with a grounded area on the card. 
     In the preferred embodiment, two F-antennas are formed side-by-side in the main portion. A resilient tongue between the antennas resiliently bears against the card for a more secure holding and grounding of the card. 
     The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective, exploded view of a component according to this invention and a communications card prior to its introduction into the component; 
     FIG. 2 is a bottom plan view of the component of FIG. 1; 
     FIG. 3 is a sectional view taken on line  3 — 3  of FIG. 1 after the introduction of the card; and 
     FIG. 4 is a sectional view taken on line  4 — 4  of FIG. 1 after the introduction of the card. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, reference numeral  10  generally identifies a communications card having a printed circuit board  12  and a radio frequency transceiver circuit thereon. The transceiver circuit executes the RF protocol described above, especially the IEEE 802.11 standard, and includes a plurality of integrated circuit chips identified by reference numerals  14 ,  16 ,  18  which are visible on an upper surface of the board in FIG. 1, and additional chips located underneath a perforated cover plate  20  that at least partly shields the chips underneath the cover plate from radio frequency interference, as well as still more chips on the opposite, lower surface of the board. The connections among the chips have not been illustrated so as not to encumber the drawing. 
     FIG. 1 also shows grounded areas or conductive strips  22 ,  24  extending along the opposite sides of the upper surface of the board. Similar conductive strips  34 ,  36  extend along the opposite sides of the lower surface of the board. Another conductive strip  38  extends transversely across the lower surface of the board at a leading end  26  of the card. A multi-pin connector  28 , such as a sixty-eight pin PCMCIA connector, which serves as a handle, is located at a trailing end of the card. A pair of antenna connectors  30 ,  32  is mounted and accessible at the leading end  26  of the card. 
     In accordance with this invention, a multi-functional component  40  performs various electrical and mechanical functions for the card  10 . The component  40  is, first of all, a holder for receiving the card  10  slidably inserted in a longitudinal direction A, and for securely holding the inserted card in a held position. The holder includes a main portion  42  generally lying in a plane, a pair of side portions  44 ,  46  spaced transversely apart along a transverse direction perpendicular to the longitudinal direction, and an end portion  48  (see FIG. 3) extending at least partly along the transverse direction at a closed end  50  of the holder. The opposite end  52  is open to receive the card. 
     The holder includes a plurality of side mounting portions or side lugs  54 ,  56  and corner mounting portions or corner lugs  58 ,  60 . Each lug has an opening through which a fastener is inserted to fixedly secure the holder in a housing of a communications equipment. Once the card  10  has been inserted into the open end  52  of the holder until the leading end abuts against the closed end  50  to define the held position, the card and the holder are fixed in position by the fasteners extending through the openings of the lugs  54 ,  56 ,  58 ,  60 . 
     The holder is constituted of an electrically conductive material, preferably a sheet metal, such as tinned or chromium-plated steel. As shown in FIGS. 2 and 4, the lower edges  64 ,  66  of the side portions  44 ,  46  are bent upwardly, and extend at least partly along the longitudinal direction. These lower edges  64 ,  66  make electro-mechanical contact with the conductive strips  34 ,  36  on the side edges at the lower surface of the board  12 . These strips  34 ,  36  are electrically grounded so that the main portion  42  serves as an antenna ground plane, as described below. 
     As shown in FIGS. 2 and 3, the lower edge  68  of the end portion  48  is bent upwardly and extends at least partly along the transverse direction. The lower edge  68  makes electro-mechanical contact with the conductive strip  38  on the leading end at the lower surface of the board. The strip  38  is likewise electrically grounded to insure that the main portion  42  serves as an antenna ground plane. 
     The holder  40  also has a built-in antenna  70  constituted of the same material as, and being of one-piece with, the holder, for conducting radio frequency signals to and from the card. Antenna  70  is made from the material of the main portion  42 . Specifically, a first pair of parallel cuts  72  spaced apart by a predetermined transverse width, a second pair of parallel cuts  74  spaced apart by a greater transverse width, and a pair of inclined cuts  76  located between and connecting the cuts  72 ,  74  are formed through the main portion  42  and define an antenna portion which is connected to the main portion only at a hinge or fold line  78 . The antenna portion is folded about fold line  78  to form a vertical part  80  of a predetermined height, and is folded again about another fold line  82  to form a horizontal part  84  of a predetermined area. The bending of the vertical and horizontal antenna parts  80 ,  84  out of the plane of the main portion  42  forms therein a cutout  86  of complementary contour to the antenna parts. Vertical part  80  is perpendicular to the main portion  42 . Horizontal part  84  is parallel to the main portion  42 . 
     The antenna  70  includes an electrically insulating spacer  88  positioned between the horizontal part  84  and the main portion  42 . A cable includes a wire  92  having one end connected to the horizontal part  84  at a feeding point  90 , as well as being connected to the main portion  42  at grounding point  94 . The opposite end of the wire  92  has an RF connector  96  which is plugged into the antenna connector  30  on the card  10 . 
     Antenna  70  is configured as an inverted F-antenna. The sum of the height of vertical part  80  and the area of horizontal part  84  is equal to λ/4. The different widths for the parts  80 ,  84  improve the directivity of the antenna. The usual practice in the design of an F-antenna is to make the height of the vertical part  80  equal to about λ/10. The grounded main portion  42  serves as the ground plane for the antenna. Antennas, other than F-antennas, can be built into the holder. For example, an inverted L-antenna or a slot antenna can be employed. 
     In the preferred embodiment, another inverted F-antenna  100  is built into the main portion  42  and is located in a side-by-side relationship with the first antenna  70 . The use of two antennas and the selection of the antenna receiving the more power are employed in a diversity circuit on the board  12  for improved reception. The second antenna  100  may be essentially identical in structure and function to the first mentioned antenna  70 , and hence, like reference numerals have been omitted from the drawing in order not to encumber the same. An RF connector  102  is plugged into the antenna connector  32  on the card. 
     However, the second antenna can also be designed to radiate in another polarity or angle as compared to the first antenna. The second antenna can also be different in type, such as an L-antenna, a slot, a dipole, or any other tuned radiating element. 
     The holder  40  is a unitary piece of sheet material operative for holding the card  10 , for grounding the card, for having antennas for transmitting and receiving RF signals, and also for shielding the chips on the card from electromagnetic interference. The form factor of the component  40  is very compact. Antennas are no longer separate components mounted on, or separately connected to, printed circuit boards and accommodated within enclosures, but instead, are built into the card holder. 
     A resilient tongue or tab  104  is formed by three slits in the main portion  42  between the two antennas. The tongue resiliently bears against the apertured plate  20  to not only insure that the card is snugly held by the holder, but also to insure that the grounded and shielded connection of the holder also extends to the plate  20 . 
     It will be understood that each of the elements described above, or two or more together, also may find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in a multi-functional component for holding, shielding, grounding and transmitting/receiving radio frequency signals for a communications equipment card for wireless networks, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims: