BACKGROUND OF THE INVENTION Wireless communication systems are well known and include various types of systems, such as cellular telephone systems, paging systems, two-way radio systems, personal communication systems, personal area networks, data systems, and various combinations thereof. Such wireless communication systems are known to include a system infrastructure and wireless communication devices constructed and programmed to operate in the respective system. The system infrastructure includes fixed network equipment, such as base transceiver sites, system controllers, switches, routers, communication links, antenna towers, and various other well-known infrastructure components. The wireless communication devices include an antenna system and other well-known elements, such as transmitters, receivers, processors, memory, user interfaces, and user controls.

The antenna system of many wireless communication devices, such as two-way radios and cellular phones, typically comprise fixed length or retractable helical antennas. Such antennas are typically very efficient due to their position effectively in free space during operation. However, antenna systems of other wireless communication devices are not generally as efficient.

For example, many palmtop computers and PDAs (personal digital assistants) include at least one slot for a PCMCIA (Personal Computer Memory Card International Association) card to expand the functionality of the computer or PDA. Wireless communication companies are working jointly with

manufacturers of PDAs and portable computers to embody wireless communication circuitry and an antenna on such cards to enable the portable computers and PDAs to engage in wireless communication. For various aesthetic and ergonomic reasons, the antenna on a PCMCIA card typically must remain inside the PCMCIA slot and not protrude out of the slot. In addition, many PDAs include doors that close over the PCMCIA slot after inserting or removing a PCMCIA card from the slot. The small aperture for the antenna and the high probability that the antenna will be in an enclosed environment imposes stringent requirements on the selection of antennas for the PCMCIA card. Regardless of whether an electric (E) field antenna or a magnetic (H) field antenna is selected, antenna efficiency is substantially degraded by the PCMCIA slot environment in which the antenna is placed.

In addition to computers or PDAs that employ wireless circuitry and antennas on internally located PCMCIA cards, certain other communication devices, such as pagers, also employ internal antennas. Such internal antennas provide for pleasant device aesthetics (i. e., no external antenna is showing); however, as is known, such internal antennas are often much less efficient than their external, free space counterparts. To overcome the efficiency loss of internal antennas, while maintaining the aesthetic benefits, a radio frequency (RF) field strength enhancer was developed that includes an external antenna element to enhance the efficiency of the internal antenna of a pager. Such an RF field strength enhancer is described in U. S. Patent No. 5,050,236, entitled Radio Frequency (RF) Field Strength Enhancer, which is issued to Colman et al., and assigned to the Assignee of the present invention. The external antenna element of the RF field strength enhancer comprises a discrete inductor in parallel with a tunable capacitor. The inductor and capacitor are attached to a carrying case for the pager. When the pager is inserted into the carrying case, the external antenna element is positioned in close proximity to the internal antenna of the pager, thereby enhancing the efficiency of the overall antenna system.

Although the RF field strength enhancer does enhance the antenna system efficiency in comparison to the efficiency of the internal antenna of the wireless communication device alone, the RF field strength enhancer requires the

wireless communication device to be placed in a carrying case to obtain the antenna enhancement. Thus, a device located out of the carrying case, such as a cellular phone being held by a user during a conversation or a PDA being accessed by its user, does not obtain the antenna efficiency enhancement.

Moreover, the external antenna element includes a tunable impedance that limits the efficiency of the enhancement to a relatively narrow frequency range, thereby requiring manual retuning of the RF field strength enhancer based on the desired operating frequency of the wireless communication device which is being coupled to it.

Therefore, a need exists for a parasitic antenna element that can be permanently attached to a wireless communication device that improves the radiation efficiency and/or gain of the wireless communication device's internal antenna system over a relatively broad frequency range without requiring tuning of the parasitic antenna element.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical block diagram of an exemplary wireless communication device that incorporates a parasitic antenna element in accordance with the present invention.

FIG. 2 is a pattern configuration of conductive traces forming a parasitic antenna element in accordance with a preferred embodiment of the present invention.

FIG. 3 is a pattern configuration of conductive traces forming a parasitic antenna element in accordance with an alternative embodiment of the present invention.

FIG. 4 is a pattern configuration of conductive traces forming a parasitic antenna element in accordance with yet another embodiment of the present invention.

FIG. 5 is a perspective view of a wireless communication device that incorporates a parasitic antenna element in accordance with a preferred embodiment and an alternative embodiment of the present invention.

FIG. 6 is a perspective view of a wireless communication device that incorporates a parasitic antenna element in accordance with yet another embodiment of the present invention.

FIG. 7 illustrates a schematic representation of the parasitic antenna element and internal antenna depicted in FIGs. 5 and 6.

FIG. 8 is a perspective view of an attachable parasitic antenna element in accordance with another embodiment of the present invention.

FIG. 9 is a perspective view of an attachable parasitic antenna element in accordance with one embodiment of the present invention.

FIG. 10 is a perspective view of an attachable parasitic antenna element in accordance with yet another embodiment of the present invention.

FIG. 11 is an exemplary graph of normalized antenna efficiency versus frequency for an internal communication device antenna alone and an antenna system that includes both the internal antenna and a parasitic antenna element in accordance with the present invention.

FIG. 12 is a pattern configuration of conductive traces forming a multi- frequency parasitic antenna element in accordance with an alternate embodiment of the present invention.

FIGs. 13,14,15, and 16 are patterns configurations of conductive traces forming parasitic antenna elements in accordance with alternate embodiments of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Generally, the present invention encompasses a parasitic antenna element and a wireless communication device incorporating the parasitic antenna element. The parasitic antenna element includes a dielectric substrate, such as Mylar or polycarbonate, and a conductive pattern including at least one conductive trace disposed on a surface of the dielectric substrate. The conductive pattern preferably is planar and forms a single electromagnetic loop with overlapping parallel ends that constitute a distributed capacitor for establishing a resonant frequency of the parasitic antenna element. The parasitic antenna element is preferably attached to a housing of a wireless communication device or other wireless electronic device in close proximity to an internal antenna or internal antenna element, or other coupling element of the wireless communication device to enable electromagnetic energy to be coupled between the internal antenna element and the parasitic antenna element, thereby enhancing the gain and/or efficiency of the device's overall antenna system over an operating bandwidth of the device relative to such a gain and/or efficiency of the antenna system without such a parasitic antenna element.

By fabricating the parasitic antenna element as described above, the present invention provides an easily attachable parasitic antenna element for coupling electromagnetic energy to and/or from communication circuitry within the wireless communication device. And the parasitic antenna element serves to enhance the efficiency and/or gain of the antenna system, particularly an antenna system that includes an internal antenna element that, due to size constraints of the internal antenna element or an aperture (e. g., PCMCIA slot) in which the internal antenna element resides, causes the antenna system to be relatively inefficient. Furthermore, in contrast to prior art antenna efficiency enhancement devices, the parasitic antenna element of the present invention can be attached to the wireless communication device without requiring a separate carrying case and provides fixed-tuned,

broadband enhancement through its inclusion of a distributed capacitor to establish the parasitic antenna element's resonant frequency.

The present invention can be more fully understood with reference to FIGs. 1-16, in which like reference numerals designate like items. FIG. 1 illustrates an electrical block diagram of an exemplary wireless communication device 100 in accordance with the present invention. The wireless communication device 100 includes an antenna system 101 which includes a parasitic antenna element 115 and an internal antenna, herein after referred to as an internal antenna element 117, a receiver 103, a processor 105, memory 106, a display 107 or other user interface (e. g., a speaker), and user controls 109. When capable of two-way operation, the communication device 100 further includes a transmitter 111 and can also include an antenna switch 113 or a duplexer 113 in the event half-duplex or full-duplex operation, respectively, is desired. The communication device 100 can comprise a two-way mobile or portable radio, a radiotelephone, a one-way or two-way pager, a wireless data terminal (such as a palmtop computer, a personal digital assistant (PDA), or laptop computer that includes a PCMCIA card for wireless communication), or any combination thereof.

In the preferred embodiment of the present invention, the receiver 103 is a conventional frequency modulated (FM) receiver for receiving electromagnetic energy (e. g., a radio signal) from the antenna system 100, via the duplexer/antenna switch 113 when so utilized, and for down converting and demodulating the received signal to provide baseband information to the processor 105. The receiver 103 includes well-known components, such as filters, mixers, small-signal amplifiers, a demodulator, and other known elements necessary to receive, down-convert, and demodulate signals in accordance with a communication protocol utilized in the system in which the communication device 100 is operating. The transmitter 111, when used, is also well-known and includes filters, mixers, a modulator, large-signal amplifiers, and other known elements to produce a radio frequency or microwave signal bearing information to be conveyed as electromagnetic energy from the antenna system 101.

The processor 105 comprises one or more microprocessors and/or one or more digital signal processors. The memory 106 is coupled to the processor 105 and preferably comprises a read-only memory (ROM), a random-access memory (RAM), a programmable ROM (PROM), and/or an electrically erasable read-only memory (EEPROM). The memory 106 preferably includes multiple memory locations for storing, inter alia, the computer programs executed by the processor 105, the address or addresses assigned to the wireless communication device 100, and information received for later retrieval by a user of the wireless communication device 100. The computer programs are preferably stored in ROM or PROM and direct the processor 105 in controlling the operation of the wireless communication device 100. The address or addresses of the wireless communication device 100 are preferably stored in an EEPROM. The information received for later retrieval is preferably stored in a RAM.

The processor 105 is preferably programmed to alert the user of the wireless communication device 100 of the device's receipt and storage of information by way of an alerting device (not shown), such as a conventional vibratory or audible alerting mechanism. Once the user has been alerted, the user can invoke functions accessible through the user controls 109 to review the stored information and respond to it as necessary. The user controls 109 preferably comprise one or more of various known input devices, such as one or more individual switches, a keypad, a touch pad, or a touch screen.

Either responsive to signaling from the user controls 109 or automatically upon receipt of certain information from the receiver 103, the processor 105 directs the stored information or received information, as applicable, to the display 107. The display 107 presents the selected information to the user by way of a conventional liquid crystal display (LCD) or other visual display, or alternatively by way of a conventional audible device (e. g., speaker) for playing out audible messages. In addition, the processor 105 can instruct the display 107 to automatically present the user of the wireless communication device 100 with at least a visual indication (e. g., an icon or an icon in combination with a periodic chime) that informs the user that newly received information is stored in the memory 106.

The novelty of the wireless communication device 100 lies in its use of an antenna system 101 that includes a parasitic antenna element 115 in addition to the internal antenna element 117. In a preferred embodiment of the present invention, the internal antenna element 117 comprises an electromagnetic loop antenna resident on a PCMCIA card that has been inserted into a slot in a housing of the wireless communication device 100. Such an electromagnetic loop antenna typically includes a discrete capacitor (not shown) configured in accordance with known techniques to establish a resonant frequency of the internal antenna element 117. The use of a discrete capacitor limits the bandwidth of the internal antenna element 117. The internal antenna element 117 functions to couple electromagnetic energy that is intercepted between the parasitic antenna element 115 and the internal antenna element 117.

All of the elements of the wireless communication device 100 depicted in block diagram form in FIG. 1, except for the parasitic antenna element 115, reside within a housing of the wireless communication device 100. FIGs. 5 and 6 depict perspective views of an exemplary housing 501 and various locations of the parasitic antenna element 115 on the housing 501 in accordance with the present invention.

Due to its position within the housing and the typically small area (e. g., 160 mm2 typical) of the aperture of a PCMCIA slot, which aperture can be enclosed by a door 505 of the housing 501 as illustrated in FIG. 5, the internal antenna element 117 is a relatively inefficient receptor/radiator, especially at frequencies lower than 1 GHZ. To improve the radiation efficiency (and preferably the antenna gain, wherein the antenna gain (G) equals efficiency (e) multiplied by directivity (D)); the wireless communication device 100 of the present invention includes a parasitic antenna element 115 positioned in close proximity to the internal antenna element 117 (e. g., within the near field region of the internal antenna element 117 or adjacent to the internal antenna element 117). The near field region of an antenna is well known and comprises a radial distance that is generally less than 1/2 wavelength away from the antenna at an operating frequency of the antenna.

The parasitic antenna element 115 is preferably constructed of a planar conductive pattern printed, deposited, etched, or otherwise disposed on a dielectric substrate, such as Mylar or polycarbonate. In such an embodiment, the dielectric substrate can be attached to the interior or exterior surface of the wireless communication device housing (e. g., using a known adhesive) in close proximity to the internal antenna element 117 to obtain the desired efficiency enhancement. In contrast to the internal antenna element 117, the parasitic antenna element 115 preferably includes a distributed capacitance to adjust the quality factor (Q) and resonant frequency of the parasitic antenna element 115 and thereby enable reasonably broadband operation of the parasitic antenna element 115 without the necessity of external tuning. Since in the preferred embodiment of the present invention, both the parasitic antenna element 115 and the internal antenna element 117 are electromagnetic loop antennas that magnetically couple electromagnetic energy between each other during operation of the wireless communication device 100. Various exemplary locations for the parasitic antenna element 115 on the wireless communication device housing, and various conductive pattern implementations of the parasitic antenna element 115 are described below.

In a preferred embodiment of the present invention, the parasitic antenna element 115 has a resonant frequency slightly higher than the resonant frequency of the internal antenna element 117. For example, when the desired operating frequency range of the wireless communication device 100 is between 700 Megahertz (MHz) to 1000 MHz, the resonant frequency of the parasitic antenna element 115 would be by way of example, 1050 MHz, and the resonant frequency of the internal antenna element 117 is tunable over the 700 MHz to 1000 MHz operating frequency range. Although the parasitic antenna element 115 preferably has a slightly higher resonant frequency than the internal antenna element 117, improved efficiency performance can be obtained for parasitic antenna element resonant frequencies that are greater than or equal to the resonant frequency of the internal antenna element 117. In addition, to being able to achieve a broadband efficiency enhancement (e. g., over a 35% bandwidth at 850 MHz), the parasitic antenna element 115 is preferably

constructed to include distributed capacitance to establish its resonant frequency and keep its Q low relative as compared to the Q of the internal antenna element 117, particularly when the internal antenna element 117 is a typical electromagnetic loop antenna resident on a PCMCIA card.

FIGs. 2-4 depict various embodiments for the conductive pattern that can be used to form the parasitic antenna element 115 which is used to couple to an internal antenna element 117 in accordance with the present invention.

Other embodiments will be described in detail below. Referring first to FIG. 2, the parasitic antenna element 115 includes a conductive pattern formed by one or more contiguous conductive traces 202,204,206,208,210 arranged to form a single electromagnetic loop. In the embodiment depicted in FIG. 2, trace 202 and trace 210 form the beginning trace and the end trace, respectively, of the single electromagnetic loop and are substantially in parallel with one another and separated by a predetermined distance 212. It will be appreciated the overlap between trace 202 and trace 210 form a distributed capacitor which is used to establish the resonant frequency of the parasitic antenna element 115.

The magnitude of the distributed capacitor is controlled by the amount of overlap and spacing provided between trace 202 and trace 210 in a manner well known to one of ordinary skill in the art. The widths and lengths of the conductive traces 202,204,206,208,210 depend upon the thickness and dielectric constant of a dielectric substrate material 201 upon which the traces 202, 204,206,208,210 are disposed or otherwise attached in combination with the housing to which the dielectric substrate material 201 is attached, and the desired input impedance, resonant frequency and bandwidth of the parasitic antenna element 115.

Providing distributed capacitance through the use of parallel adjacent trace 202 and trace 210 as shown in FIG. 2 enables the parasitic antenna element 115 to operate satisfactorily over a broad bandwidth relative to the bandwidth of the internal antenna element 117 and relative to the bandwidth of communication channels over which the wireless communication device 100 receives and/or transmits information. For example, a parasitic antenna element 115 constructed as depicted in FIG. 2 and having a resonant frequency

of 1000 MHz can provide a gain enhancement of 5 decibels (db) over a 115 MHz bandwidth for a typical PCMCIA card antenna. Considering the typical communication channel includes information transmitted and received within only a 25 kHz bandwidth, the parasitic antenna element 115 can be used with many different narrowband wireless communication devices to enhance the efficiency and gain of the narrowband wireless communication devices without the necessity of re-tuning the resonant frequency of the parasitic antenna element 115 for each narrowband wireless communication device.

In the event that sufficient capacitance cannot be obtained to establish a desired resonant frequency using the embodiment depicted in FIG. 2, the parasitic antenna element 115 can be configured with a conductive pattern as shown in FIG. 3. Similar to the embodiment of FIG. 2, the conductive pattern of FIG. 3 includes multiple contiguous traces 302,304 and 306, and 308, 310 and 312 that are arranged to form a single electromagnetic loop on a dielectric substrate 201. However, in contrast to the pattern depicted in FIG. 2, the pattern depicted in FIG. 3 includes two or more distributed capacitors formed by two or more sets of parallel traces (e. g., parallel trace 302 and trace 312 forming one capacitor, and parallel trace 306 and trace 308 forming the other capacitor). Continuity of the electromagnetic loop is established through the capacitive coupling of electromagnetic energy between the parallel trace 302 and trace 312, and parallel trace 306 and trace 308. The distance 314 and 316 between the parallel traces establishes the capacitance of each distributed capacitor. It will be appreciated that the distance 314 and 316 can be of the same magnitude, or can be different magnitudes, depending upon the capacitance required to resonate the electromagnetic loop The two distributed capacitors of the pattern of FIG. 3 are connected electrically in parallel thereby providing for an increased amount of capacitance as compared to the pattern of FIG. 2. Therefore, the pattern of FIG. 3 is particularly useful for lower antenna resonant frequencies.

FIG. 4 depicts yet another conductive pattern for the parasitic antenna element 115. This pattern is particularly useful for dual band operation of the parasitic antenna element 115. The pattern includes two capacitively coupled

tuning stubs, tuning stub 402 and tuning stub 404 that function to establish a second resonant frequency of the parasitic antenna element 115 at a frequency that is higher than a first resonant frequency of the parasitic antenna element 115 not incorporating the tuning stubs. Thus, the tuning stubs effectively reduce the size of the electromagnetic loop and, therefore, the inductance in the electromagnetic loop at a frequency (i. e., the second resonant frequency) at which the capacitive impedance between the tuning stubs is very small. The separation 406 between the tuning stubs, and the lengths of the sections of stub 402 and stub 404 that overlap to provide capacitive coupling are determined in accordance with known techniques based on the desired second resonant frequency of the parasitic antenna element 115.

As noted above, FIGs. 5 and 6 illustrate perspective views of exemplary wireless communication devices that incorporate a parasitic antenna element 115 in accordance with various embodiments of the present invention.

Referring first to FIG. 5, an exemplary wireless communication device 500, is depicted that includes a housing 501 with a door 505 which conceals a slot 507 into which a wireless PCMCIA card can be inserted. The wireless PCMCIA card can include a printed circuit board 503 to which is attached an internal antenna element 117. The wireless communication device 500 also includes the circuitry depicted in FIG. 1, although such circuitry is not shown in FIG. 5. The circuitry of FIG. 1 can reside entirely on printed circuit board 503, but more preferably resides partially on printed circuit board 503 (e. g., internal antenna element 117, duplexer/antenna switch 113 (if utilized), receiver 103, transmitter 111 (if utilized), and a portion of the processor 105 and the memory 106) and partially on one or more other circuit boards (not shown) permanently attached inside the housing 501.

The parasitic antenna element 115 preferably comprises a conductive pattern forming a single electromagnetic loop and is preferably positioned in close proximity to (e. g., within a near field region of) the internal antenna element 117. The conductive pattern preferably includes at least one distributed capacitance to establish a resonant frequency of the parasitic antenna element 115. Various exemplary conductive pattern embodiments for forming the

parasitic antenna element 115 were described above with respect to FIGs. 2-4.

With respect to positioning of the parasitic antenna element 115, as depicted in FIG. 5, the parasitic antenna element 115 can be positioned on a top, exterior surface of the housing 501 just above the internal antenna element 117; or the parasitic antenna element 115 can be alternatively positioned on an inside or outside surface of the PCMCIA door 505, which for purposes of example shows the parasitic antenna element 115 positioned on the inside surface of the door 505. In this instance, it will be appreciated that the parasitic antenna element 115 is in close proximity to the internal antenna element 117 only when the PCMCIA door 505 is closed. When both the internal antenna element 117 and the parasitic antenna element 115 are electromagnetic loops as shown in FIG. 5, magnetic coupling is the mechanism for exchanging electromagnetic energy between the parasitic antenna element 115 and the internal antenna element 117.

Therefore, the parasitic antenna element 115, and the internal antenna element 117 would be oriented to maximize the magnetic coupling between them.

When the parasitic antenna element 115 is affixed to the housing 501 as described above, it will be appreciated that the housing 501 typically includes a recess into which the parasitic antenna element 115 can by placed. The recess provides protection to the edges of the substrate of the parasitic antenna element 115 and insures the parasitic antenna element 115 is properly positioned relative to the internal antenna element 117 A further embodiment of the present invention is a wireless communication device 600 that includes a parasitic antenna element 115 as illustrated in FIG. 6. In this embodiment, unlike the embodiment shown in FIG.

5, the wireless communication device 600 does not include a door as described above. In the example shown, the parasitic antenna element 115 is affixed to the surface of the housing 501 about the slot 507 into which the PCMCIA card is inserted.

FIG. 7 is an equivalent schematic representation of the parasitic antenna element 115 and the internal antenna element 117 depicted in FIGs. 5 and 6. The parasitic antenna element 115 effectively comprises an inductor 701 (i. e., the effective inductance in the electromagnetic loop) in parallel with a fixed

capacitor 703 (i. e., the effective capacitance of the distributed capacitor (s) formed by the adjacent parallel electromagnetic loop traces (e. g., traces 202 and 210)). The internal antenna element 117 effectively comprises an inductor 705 (i. e., the effective inductance of the electromagnetic loop) in parallel with a capacitor 707 (e. g., a discrete capacitor electrically connected across the electromagnetic loop). The inductors 701,705 are appropriately oriented to magnetically couple electromagnetic energy between them. The resonant frequency of the parasitic antenna element is (2 [ (L) (C)]-1/2. where L is the inductance of inductor 701 and C is the capacitance of capacitor 703. The resonant frequency of the internal antenna element is (2/)- [(L) (C)]-', where L is the inductance of inductor 705 and C is the capacitance of capacitor 707. As discussed above, the resonant frequency of the parasitic antenna element 115 is preferably slightly higher than the resonant frequency of the internal antenna element 117.

Unlike prior art antenna efficiency enhancement devices that include tunable discrete capacitors, the present invention, through the use of distributed capacitance, provides broadband enhancement and therefore does not require tuning of the resonant frequency of the parasitic antenna element 115 over a relatively wide bandwidth (about 35% at 850 MHz). The elimination of the need to tune the resonant frequency of the parasitic antenna element 115 enables the parasitic antenna element to be inconspicuously positioned on an inside or outside surface of the wireless communication device's housing, or on the bottom side of a device label, while still providing substantial antenna efficiency and/or gain enhancement.

FIGs. 8, 9, and 10 illustrate perspective views of attachable parasitic antenna elements 115 in accordance with the present invention. The parasitic antenna element 800 of FIG. 8 includes a substrate 201 having a top surface 803 and a bottom surface 805. The substrate 201 preferably comprises a Mylar (polyester) or polycarbonate material, but may alternatively comprise other known materials, such as Teflon, Kapton0 (polyimide), polystyrene, or paper.

In the embodiment depicted in FIG. 8, the conductive pattern 807 forming the resonant portion of the parasitic antenna element 800 is formed by depositing,

screen printing, electroplating, etching or otherwise disposing conductive material, such as a metallic foil or a conductive ink onto a surface of a dielectric substrate 201 (preferably the bottom surface 805 to allow the pattern 807 to remain inconspicuous to a user of the electronic or wireless communication device 500) and information 809 identifying the wireless or electronic device, such as model number, manufacturer's logo, serial number, warning label, or other information, is printed on the opposing surface of the substrate 201 (preferably the top surface 803). It will be appreciated that the method by which the conductive pattern 807 is deposited on the substrate 201 is dependent upon the nature of the actual material being utilized. After at least the conductive pattern 807 has been deposited on a surface 805 of the substrate 201, an adhesive, such as a 3M pressure sensitive (PSA) adhesive, is applied to the surface 805 containing the pattern 807 to enable the surface 805 to be attached to the housing 501 of the device 500. Once attached to the housing 501 via the adhesive, the surface 805 of the substrate 201 containing the conductive pattern 807 is in contact with the housing 501 in an area substantially adjacent to any internal coupling or antenna 117. Although the conductive pattern 807 is preferably disposed on a bottom surface 805 of the substrate 201 to enable the pattern 807 to remain inconspicuous to a user of the electronic device 500, such a location of the pattern 807 is not required pursuant to the present invention and the pattern 807 can alternatively be disposed on the top surface 803 of the substrate 201. When disposed of on the top surface 803 of the substrate 201, a thin clear or opaque film (not shown) can be disposed thereon to protect the pattern 807, and to provide a surface upon which the identifying information 809 is disposed.

As depicted in FIG. 8, the area of the bottom surface 805 of the substrate 201 onto which the conductive pattern 807 is printed can be small in comparison to the overall area of the bottom surface 805 of the substrate 201. Such might be the case when the pattern 807 is disposed on the bottom surface 805 of a relatively large adhesive label substrate that includes the manufacture's logo, the device model number, the device serial number, or any other additional information on the substrate's top surface 803. Alternatively, as depicted in FIG.

9, the area of the surface 905 of the substrate 201 onto which the conductive pattern 907 is printed can be substantially equal to the overall area of the surface 905 of the substrate 201. Such might be the case when the pattern 907 is disposed on the bottom surface 905 of a relatively small adhesive label substrate 201 that includes only the manufacturer's name or device serial number on the substrate's top surface 903.

In an alternate embodiment, as shown in FIG. 10, a substrate 201 having a top surface 1003 and a bottom surface 1005 includes a cut-out 1011 through which a PCMCIA card can be inserted into the slot 507 in the housing 501, shown in FIG. 6. The composition of the parasitic antenna element 1007 is as described above. Identifying information 1009 identifying the wireless communication device, such as, a manufacturer's logo, or other information, can be printed on the opposing surface of the substrate 201 (preferably the top surface 1003).

Computer simulations and anechoic chamber testing have shown that the addition of a parasitic antenna element 115 as described above increases the efficiency of an antenna system 101 as shown in FIG. 1 relative to the efficiency of an internal antenna element 117 alone. A graph 1200 of normalized efficiency versus frequency for one such computer simulation is depicted in FIG. 11 for a parasitic antenna element 115 configured as shown in FIG. 2 and disposed on the top exterior surface of the wireless communication device housing 501, one millimeter (mm) away from an internal antenna element 117 as generally shown in FIG. 5. The internal antenna element 117 is an electromagnetic loop antenna typically embodied in a PCMCIA card. The parasitic antenna element 115 has a resonant frequency of 980 MHz and a Q of 60 and the internal antenna element 117 has a resonant frequency of 930 MHz and an unloaded Q of 60.

As shown in FIG. 11, the normalized efficiency 1203 of the antenna system 101 including the parasitic antenna element 115 is as much as six decibels (db) better than the normalized efficiency 1201 of the antenna system including only the internal antenna element 117. In addition, the efficiency enhancement provided by the parasitic antenna element 115 remains over a

relatively broad frequency range (approximately 300 MHz for a parasitic element resonant frequency of 980 MHz).

From the description above, it will be appreciated that the application of a parasitic antenna element disposed on a dielectric substrate need not be limited to a single element. FIG. 12 shows a pattern configuration of conductive traces forming at least part of a multi-frequency parasitic antenna element in accordance with an alternate embodiment of the present invention.

As shown in FIG. 12, three parasitic antenna elements are formed on the planar dielectric substrate 201. A first parasitic antenna element 1201 is tuned for operation over a first frequency range fl, a second parasitic antenna element 1203 is tuned for operation over a second frequency range f2, and a third parasitic antenna element 1205 is tuned for operation over a third frequency range f3, wherein fl > f2 > f3. The frequency ranges to which the parasitic antenna elements are tuned can be overlapping, thereby extending the frequency range over which the wireless communication device can be tuned, or the frequency ranges can be widely separated to accommodate different bands of operation.

FIGs. 13 through 16 show alternate embodiments of the parasitic antenna element in accordance with the present invention. As shown in FIG. 13, the shape of the parasitic antenna element need not be restricted to a rectangular shape, but can include other shapes as well, such as a single turn parasitic antenna element having a circular shape (as shown), or an oval or elliptical shape (not shown). As shown in FIG. 14, the parasitic antenna element can be configured with multiple turns for use at lower operating frequencies. The multiple turns can be fabricated on different layers of the dielectric substrate, connected by feed through vias. The parasitic antenna element can also incorporate wide conductor elements, as shown in FIGs. 15 and 16. Such"fat" loops can provide lower Q and consequently wider bandwidths than provided by thin wire geometries. It will be appreciated that other parasitic antenna element configurations utilizing planar conductor patterns on a thin attachable substrate can be utilized as well.

The present invention encompasses a parasitic antenna element and a wireless communication device incorporating the parasitic antenna element.

With the present invention, wireless communication devices, such as laptop computers, palmtop computers, and PDAs, that obtain their wireless functionality through the use of radio circuitry resident on insert able PCMCIA cards, can obtain improved antenna performance and, therefore, wider operating range by incorporating the parasitic antenna element of the present invention as an attachable element. When such a parasitic antenna element is included in the wireless communication device's antenna system, the parasitic antenna element serves to enhance the efficiency and/or gain of the antenna system, particularly when the antenna system includes an internal antenna element that, due to size constraints of an aperture (e. g., PCMCIA slot) in which the internal antenna element resides, is relatively inefficient. It will be appreciated, the parasitic loop element can be utilized on other electronic devices, which incorporate an internal loop antenna as well.

Furthermore, by being disposed directly on a thin adhesive substrate, such as provided by a label, the parasitic antenna element of the present invention maintains a very low profile and, therefore, meets the ergonomic requirements of most users. Still further, when disposed on the back of a device label, the parasitic antenna element provides the desired efficiency enhancement while being virtually undetectable by the device user.

Moreover, since the parasitic antenna element of the present invention is directly attachable to the wireless communication device, the present invention does not require the use of a carrying case or other additional housing to position the parasitic antenna element in close proximity to an internal antenna element of the wireless communication device in contrast to prior art antenna efficiency enhancement techniques. Lastly, in contrast to prior art manually tuned antenna enhancement devices, the present invention provides fixed-tuned, broadband antenna enhancement through the parasitic antenna element's inclusion of a distributed capacitor to establish the parasitic antenna element's resonant frequency. And finally, placement of the parasitic antenna element is simplified by combining the parasitic antenna element, as

described above, into a label which is placed within a recess already provided within the housing of the wireless communication device.

While the foregoing constitute certain preferred and alternative embodiments of the present invention, it is to be understood that the invention is not limited thereto and that in light of the present disclosure, various other embodiments will be apparent to persons skilled in the art. Accordingly, it is to be recognized that changes can be made without departing from the scope of the invention as particularly pointed out and distinctly claimed in the appended claims which shall be construed to encompass all legal equivalents thereof.