US006031503A
`6,031,503
`(114) Patent Number:
`United States Patent 55
`Preiss, II et al.
`[45] Date of Patent:
`*Feb. 29, 2000
`
`
`
`4,975,711
`[54] POLARIZATION DIVERSE ANTENNA FOR
`12/1990) Lee voceccccceccseeeeseneesceenenee 343/702
`
`5,486,836
`PORTABLE COMMUNICATION DEVICES
`.. 343/700 MS
`1/1996 Kuffneretal
`
`5,677,698 10/1997 Snowdon...eeecteceeeeeee 343/702
`[75]
`Inventors: Joseph A. Preiss, II, Westford; Terry
`L. McElroy, Hudson; Arnold E. Van
`Doren,Sterling; Stephen R.
`Donaldson, Lincoln; Fernando
`Beltran, Framingham,all of Mass.
`[73] Assignee: Raytheon Company, Lexington, Mass.
`.
`.
`.
`.
`[*] Notice:
`This patent issued on a continued pros-
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`atent
`term provisions of 35 U.S.C.
`vs4(aQ2)
`P
`
`FOREIGN PATENT DOCUMENTS
`0623967 Al
`5/1993 European Pat. Off.
`......... HO01Q 1/36
`0610025 Al
`2/1994 European Pat. Off.
`......... HOSK 5/02
`2292482
`8/1994 United Kingdom .......... HO1Q 1/22
`OTHER PUBLICATIONS
`IBM Technical Disclosure Bulletin; vol. 37 No. 08, Aug.
`1994.
`
`Primary Examiner—Hoanganh Le
`[57]
`ABSTRACT
`
`A communications card having an antenna assembly pro-
`viding polarization diversity for use with a portable com-
`[21] Appl. No.: 08/803,478
`puter is provided. The antenna assembly comprises two
`4.
`folded antennas, which maybe dipolesorslot radiators,that
`Filed:
`[22]
`Feb. 20, 1997
`
`[51] Tint. C17 ccescessssssssssseee H01Q 13/10; HO1Q 1/24—_are disposed orthogonally to one another to provide polar-
`[52] US. Che ceeeeessssscessssseeeee 343/770; 343/767; 343/702
`ization diversity. Signals are carried to and from the antenna
`[58] Field of Search
`343/770, 767
`by microstrip feed lines. The microstrip lines are placed off
`343/702,700MS,725,795 794, 7,
`center along each antenna slot to establish an acceptable
`79 730 846: HO010 B/10, 1PA
`impedance match for the antenna. The feed lines are coupled
`,
`,
`,
`,
`to the communications card by way of coaxial cables. The
`References Cited
`antenna assembly is coupled with the communications card
`in a hinged arrangementthus allowingfor spatial redirection
`of the antenna, if desired.
`
`[56]
`
`U.S. PATENT DOCUMENTS
`3/1984 Burgmyer 0... esc seeee 343/770
`9/1988 Lo et ab. veces 343/700 MS
`
`4,438,437
`4,771,291
`
`15 Claims, 3 Drawing Sheets
`
` 30,
`
`29
`
`
`
`CLT|
`
`
`
`[ALDALLL
`44A 46° 44B
`49
`48 44C 22 43
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`1
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`SAMSUNG 1010
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`SAMSUNG 1010
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`1
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`U.S. Patent
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`6,031,503
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`Feb. 29, 2000
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`Sheet 1 of 3
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`FIG.1
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`U.S. Patent
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`Feb. 29, 2000
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`Sheet 2 of 3
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`6,031,503
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`TRI)
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`VROOPE]
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`U.S. Patent
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`Feb. 29, 2000
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`Sheet 3 of 3
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`6,031,503
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`FIG. 4
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`6,031,503
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`1
`POLARIZATION DIVERSE ANTENNA FOR
`PORTABLE COMMUNICATION DEVICES
`
`FIELD OF THE INVENTION
`
`This invention relates generally to an antenna assembly
`and, more specifically, it relates to a polarization diverse
`antenna assembly for use with small communication devices
`such as laptop computers.
`BACKGROUND OF THE INVENTION
`
`The development of wireless local area networks
`(“WLAN”) for computers has facilitated the use of portable
`devices such as laptop computers for network communica-
`tion. Such computers are small by design and, thus, present
`space constraints for communication units associated with
`them. For example, laptop computers are provided with slots
`in which accessory cards can be inserted. These slots and the
`associated circuitry generally have a prescribed standard
`configuration such as the PCMCIAstandard. A communi-
`cation device used with such a computer must conform to
`this standard.
`
`Typically, a PCMCIA card used for wireless communi-
`cations has beenfitted with a transceiver and an antenna for
`
`communication by the computer. However, these cards have
`not been completely effective because portable computers
`are often used in complex radio frequency (“RF”) environ-
`ments such as office buildings and the like, where WLAN’s
`are usually installed. These environments include physical
`barriers which give rise to multiple reflections of the signals
`transmitted or received by the computer. The signals travel
`over multiple paths, resulting in interference patterns and
`thus “dead spots”. The radio frequency environment
`is
`further complicated by movement of persons or equipment
`within the environment. Additionally, the portable comput-
`ers will be moved from location to location, thus changing
`the radio frequency environments in which they are to be
`operated.
`It has been proposed to address these problems by using
`a tethered antenna which can be moved bythe user to a
`position where signal strength is sufficient. Such tethered
`designs, however, present an inconveniencein that the tether
`requires the user to continually set up the antenna when
`moving the portable device to a different location. They can
`also give rise to mechanical stress, and resulting failure, of
`the wires used in the tether.
`
`Another proposed solution is the use of multiple antennas
`to provide spatial diversity, so that if one of the antennas is
`in a dead spot, the other one is likely to encounter a usable
`signal. However, spatial diversity has not provided sufficient
`immunity to fading and, thus, such solutions have not been
`effective.
`
`There remains a need for a low cost, morereliable antenna
`assembly which conformsto the available space in a por-
`table communication device, the antenna of which allows
`maximum signal propagation while experiencing minimal
`fading in a dynamic RF environment.
`SUMMARYOF THE INVENTION
`
`The antenna assembly embodying the present invention
`includes a polarization diverse antenna incorporating two
`half-wavelength antennas encased in a plastic housing. The
`housing readily conforms to a communications card for use
`with a portable laptop computer. Specifically, one embodi-
`ment of the antenna assembly is designed for use with a
`transceiver incorporated into a PCMCIA communications
`card that fits within the appropriate card slot in a portable
`computer.
`
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`In its preferred form, the antenna assembly is configured
`to provide a pair of slot radiators. These antennas are
`preferably disposed at right angles to one another such that
`radiation by the respective antennas is orthogonally polar-
`ized. The slot radiators are folded so as to be compatible
`with the dimensions of a PCMCIAcard. The card carries the
`appropriate electronics for the transceiver, i.e. the receiver
`and transmitter electronics.
`
`Each antennais coupled to the transceiver electronics by
`wayof a microstrip feed line. More specifically, one portion
`of the microstrip line is passed across the slot at a selected
`feed point off the center of that slot. The other end of the
`microstrip line is connected from the slot radiator to the
`transceiver electronics by a flexible coaxial cable.
`In operation, if a signal is of a polarization such thatit is
`cross-polarized with one of the slot radiators, it will not be
`cross-polarized with respect
`to the other slot radiator
`because of the polarization diversity of the antennas. Thus,
`at least one of the slot radiators will typically carry a usable
`signal. Moreover, the user can adjust the orientation of the
`antenna by rotating the antenna assembly abouta hinge that
`connects the assembly to the communications card.
`Preferably, a switch automatically controls the selection
`of the antenna to be used, depending upon the signal
`received from each. As will be understood by those skilled
`in the art, the signal will be chosen based upon a predeter-
`mined parameter such as signal-to-noise ratio.
`The antenna assembly provides a low cost, simply made
`antenna for use in a complex RF environment.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention description below refers to the accompa-
`nying drawings, of which:
`FIG. 1 is an isometric view of an antenna assembly
`embodying the invention with the antenna attached to a
`communications card.
`
`FIG. 2 is an isometric view of the antenna assembly of
`FIG. 1 with two, orthogonally placed slot radiators with
`microstrip feed lines depicted in phantom.
`FIG. 3 is a cross section of the antenna assembly taken
`along line A—A of FIG. 2.
`FIG. 4 is a schematic illustration of the ground plane
`conductor of the antenna assembly of the present invention,
`and depicting the microstrip feed lines associated with each
`slot.
`
`DETAILED DESCRIPTION OF AN
`ILLUSTRATIVE EMBODIMENT
`
`As shown in FIG. 1, an antenna housing 10, which
`includes an antenna assembly 11 (FIG. 2) embodying the
`invention, is incorporated into a communications card 12
`used with a portable laptop computer (not shown). The card
`12 is constructed in such a manner as to conform to the
`
`PCMCIAstandard. It includes a digital electronics portion
`14 which is connected to a bus in the computer. The card 12
`also includes an RF electronics section 16 containing a
`suitable transceiver (not shown). The user may be a member
`of a local area network, which is a collection of computers
`that use a consistent protocol to communicate with one
`another. By meansofthe transceiver and the antenna assem-
`bly 11, the user can communicate as a node on the network,
`either directly with another laptop computer which has
`wireless capability, or by way of a commonaccess pointto
`the network, even if the user is not in a fixed location.
`The antenna housing 10 is physically joined to RF elec-
`tronics section 16 by meansof a hinge 20. The hinge allows
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`6,031,503
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`for rotation of the antenna housing 10 about the horizontal.
`This facilitates orientation adjustment of the antenna
`assembly, in addition to the polarization diversity described
`herein.
`In operation,
`the antenna housing 10 is placed
`nominally to a vertical position and, thereafter, is rotated to
`provide an adjustment, as needed,
`in the particular RF
`environment. Suitable lights, such as LED’s 15, can be
`provided to indicate that a usable signal has been obtained.
`When not in use, antenna housing 10 can be folded flat
`against the card body 12 for storage.
`Referring to FIGS. 2 and 3, the antenna assembly 11 is
`configured according to typical printed circuit board tech-
`niques in which two copper sheets, which are adhered to
`either side of a plastic substrate 17, are etched to provide the
`desired conductor configurations. Thus,
`in the antenna
`assembly 11, the upper metal sheet has been etched to form
`two microstrip feedlines 28 and 30. The lower copper sheet
`has been etched to provide a ground plane conductor 22
`containing two apertures which form folded antennas.
`Specifically, the conductor 22 includesa slot radiator 24 and
`an orthogonally-disposed slot radiator 26. The polarization
`of the slot radiator 24 is thus orthogonal to that of the slot
`radiator 26. The slot radiators 24 and 26 are preferably
`configured in a folded arrangement to be compatible with
`the PCMCIAcard dimensions as discussed herein.
`
`As shownin FIGS. 2 and 3, the feed line 28 passes across
`the slot radiator 24 and is connected by plated through-hole
`25 to the conductor 22 at the edge of the radiator. The feed
`line 30 passes across radiator 26 and is connected to the
`conductor 22, at the edge of the plated through-hole 29.
`The feed lines 28 and 30, in turn, are connected to the RF
`section 16 (FIG. 1) with two flexible coaxial cables 32 and
`38, respectively. More specifically, the coaxial cable 32 has
`a center conductor 33 which is soldered to the microstrip
`feed line 28 at a pad 34. The cable 32 also has an outer
`conductor 35 whichis soldered to a ground pad 36, as shown
`in FIG. 2. The ground pad 36 is connected through to
`conductor 22 to complete the circuit for the slot radiator 24.
`Similarly, the coaxial cable 38 has a center conductor 39
`connected to the microstrip feed line 30 at a pad 40. The
`outer conductor 41 is connected to a ground pad 42 which
`connects to conductor 22 to complete the circuit for the slot
`radiator 26.
`
`The entire antenna assembly 11 is encapsulated within a
`plastic casing. In the encapsulation step, the antenna assem-
`bly 11 is made to conform to a curvature in the antenna
`housing 10 (FIG. 1). The coaxial cables 32 and 38 pass
`through the hinge 20 (FIG. 1),which connects antenna
`housing 10 to card 12 for convenience and protection of the
`cables.
`
`A signal which is received or transmitted by the slot
`radiator 24 will be carried by the microstrip feed line 28 and
`cable 32 to the transceiver portion 80 of RF section 16.
`Similarly, a signal transmitted or received by the slot radia-
`tor 26 will be carried by the microstrip feed line 30 and cable
`38 to transceiver portion 80. The switch 82 is contained
`within the transceiver portion 80, which is coupled with each
`of the microstrip feed lines 28 and 30. The switch 82
`includes conventional electronics for comparing the signal-
`to-noiseratio of the signal received by eachslot radiator and
`for selecting the antenna providing the better quality. The
`selected antenna is then used for both transmission and
`reception.
`Referring to FIG. 4, each of the radiators 24 and 26 has
`an electrical length of one-half wave-length. The physical
`dimensionsofthe slot radiators are selected based upon the
`materials utilized.
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`In a typical embodimentof the invention for operation in
`the frequency range of 2.40 to 2.48 GHz, the ground plane
`conductor 22 has one side 60 (FIG. 4) with a length of 1.950
`inches and a second side 61 with a length of 1.2 inches. The
`slot radiator 24 has a longer dimension indicated by refer-
`ence character 62 of 1.0 inch, and a shorter dimension 66 of
`0.435 inches. The width of the radiator 24, which is indi-
`cated by the dimension 68, in FIG. 4 is 0.100 inches. Theslot
`radiator 26 has the same dimensionsasthe slot radiator 24.
`
`the center;
`Ordinarily, a half wave antenna is fed at
`however, in order to match the impedance of the coaxial
`cables 32 and 38, the microstrip feed line 28 is offset from
`the center of the slot radiator 24 by an amountthat provides
`the desired impedance match for the antenna.
`In the
`example, the distance from the end of slot radiator 24 (72)
`in FIG. 4 will be 0.185 inches. The microstrip feed line 28
`has an overall length of 0.75 inches. The microstrip feed line
`30 is similarly offset from the center of the slot radiator 26.
`The distance from the end oftheslot radiator 26 (76) in FIG.
`4 will be 0.090 inches. Microstrip feed line 30 has an overall
`length of one inch. It is formed along the conductor 22 such
`that the arc of angle B shownin FIG. 4 is 30°. The feed line
`is constructed to have a characteristic impedance that
`matches that of the coaxial cable. In this embodiment, the
`physical dimensions set forth above provide an acceptable
`impedance match over an operating frequency range of
`about 2.40 to 2.48 gigahertz (GHz) for each of the antennas
`24 and 26.
`
`A test performed on this embodiment showeda low input
`return loss for each of the two slot radiators 24 and 26. In
`addition, measured results showed that
`the antennas
`achieved better than a 2:1 VSWR (voltage standing wave
`ratio) and more than 20 dB isolation between the radiators
`over the operating frequency range of 2.40 to 2.48 GHz.
`Measurements of the antenna radiation pattern for each slot
`were also conducted. The antenna pattern exhibits the classic
`dipole antenna pattern, but with a null axis orthogonal to the
`length of the slot. Some skewingofthe radiation pattern was
`attributed to curvature in the plastic housing in which the
`antenna is embedded.
`
`the antenna
`typically set
`the user will
`In operation,
`housing 10 to a vertical position. If an acceptable signal is
`not obtained, the antenna housing 10 can berotated until an
`indicator light 15 (FIG. 1) showsthat a signal of sufficient
`quality is obtained.
`It should be understood that an antenna assembly
`embodying the invention can include dipoles instead of slot
`radiators, if desired in a particular application.
`The antenna assembly provides a low-cost, polarization
`diverse antenna assembly which maintains WLAN system
`performance in complex electromagnetic environments such
`as office buildings. The assembly is adapted to be an integral
`feature of a WLAN card which maintains portability and
`compatibility with the PCMCIA standard. The hinged
`arrangement provides additional adjustment capability for
`the antenna assembly.
`The terms and expressions employed herein are used as
`terms of description and not of limitation and there is no
`intention in the use of such terms and expressions, of
`excluding any equivalents or
`the features shown and
`described or portions thereof, but
`it
`is recogmized that
`various modifications are possible within the scope of the
`invention claimed.
`Whatis claimedis:
`
`1. Acommunications card for transmission and reception
`of microwave signals with an associated portable computer,
`the communications card comprising:
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`6,031,503
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`said antenna assembly is encapsulated in a plastic
`housing, said plastic housing being attached to said RF
`section of said card body.
`9. The communications card of claim 8 wherein
`
`said plastic housing is sized to conform to said card body
`in such a mannerthatit can be folded flush against said
`card body for storage when notin use.
`10. The communications card of claim 9 wherein
`
`10
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`15
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`said ground plane conductor is sized to fit within said
`plastic housing and said first and second slot radiators
`are C-shaped, folded slot radiators dimensioned to
`conform to said ground plane conductor.
`11. The communications card of claim 10 wherein
`
`said computer is a PCMCIAportable computer and said
`card body is dimensioned to conform to said card slot
`associated with said portable computer.
`12. A polarization diverse antenna assembly for use with
`a computer device, for the transmission and reception of
`microwave communications with a transceiver associated
`
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`5
`(A) a transceiver portion including receiver and transmit-
`ter electronics for communication of said signals to and
`from said computer;
`(B) a polarization diverse antenna assembly having:
`1) a first antenna and an orthogonally-disposed second
`antenna with each antenna being substantially omni-
`directional about a first axis;
`2) a single metal sheet adhered to a plastic substrate,
`said metal sheet comprising a ground plane
`conductor, and the first and second antennas being
`first and second slot radiators formed in said metal
`sheet, said slot radiators being unobstructed on both
`sides so that signals may be radiated and received
`from both sides of said ground plane conductor;
`(C) a card body sized for insertion into a card slot in the
`portable computer, said card body having an RF section
`including said transceiver portion, and a digital elec-
`tronics portion which provides a connection to the
`computer, and said antenna assembly being attached to
`said RF section of said card body in a hinge
`arrangement, whereby the radiation pattern of said
`with the computer, the antenna assembly comprising:
`antenna assembly is adjustable for obtaining maximum
`(A) a first antenna and an orthogonally-disposed second
`signal quality by rotation of said antenna assembly
`antenna with each antenna being substantially omnidi-
`about said hinge arrangement;
`25 rectional aboutafirst axis;
`(D) coupling means disposed between said transceiver
`(B) a single metal sheet adhered to a plastic substrate, said
`portion and said antenna assembly for communicating
`metal sheet comprising a ground plane conductor, and
`signals between said transceiver portion and said
`the first and second antennasbeingfirst and second slot
`antenna assembly.
`radiators formed in said metal sheet, said slot radiators
`2. The communications card of claim 1 wherein
`being unobstructed on both sides so that signals may be
`radiated and received from both sides of said ground
`plane conductor;
`(C) coupling means disposed between said transceiver
`and said first and second antennas for communicating
`signals between said transceiver and said first and
`second antennas; and
`(D) hinge arrangement connecting said antenna assembly
`to said transceiver portion in such manner that the
`spatial direction of said antenna assembly is adjustable
`by rotation of said antenna assembly about said hinge
`arrangement for obtaining maximum signal quality.
`13. The antenna assembly of claim 12 wherein said first
`and secondslot radiators are C-shaped, folded slot radiators
`dimensioned to conform to said ground plane conductor.
`14. The antenna assembly of claim 12 wherein
`said coupling means includesa first microstrip feed line
`coupled at one end to said transceiver portion and
`connected at an other end acrosssaid first slot radiator,
`50
`and a second microstrip feed line coupled at one end to
`said coupling means includesafirst and second coaxial
`said transceiver portion and connected at an other end
`cable connected from said first and second microstrip
`across said second slot radiator, and said first and
`feed lines, respectively, of said antenna assembly, to
`second microstrip feed lines are offset from a center of
`said transceiver portion.
`each ofsaid first and secondslot radiators, respectively,
`6. The communications card of claim 5 wherein:
`by a predetermined amountto set the impedance char-
`said first coaxial cable has an outer conductor connected
`acteristics of said antenna assembly.
`to a first ground pad disposed on said ground plane
`15. The antenna assembly of claim 14 further comprising
`conductor, and a center conductor connected to said
`a card body sized for insertion in to a card slot in said
`one end of said first microstrip feed line, and said
`computer device, said card body having an RFsection
`second coaxial cable has an outer conductor connected
`including said transceiver, and a digital electronics
`portion which provides a connection to said associated
`computer device, and said ground plane conductor
`including said first and second antennasis encapsulated
`in a plastic housing, said plastic housing being attached
`to said RF section of said card body.
`*
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`said coupling meansincludesa first microstrip feed line
`coupled at one end to said transceiver portion and
`connected at an other end acrosssaid first slot radiator,
`and a second microstrip feed line coupled at one end to
`said transceiver portion and connected at an other end
`across said second slot radiator.
`4. The communications card of claim 3 wherein
`
`said transceiver portion includes a switch for selecting
`between signals received from said first antenna and
`said second antenna based upon the signal-to-noise
`ratio of the signal so produced by eachofsaid first and
`second antennas.
`3. The communications card of claim 1 wherein
`
`said first and said second microstrip feed lines are offset
`from a center of each of said first and second slot
`
`radiators, respectively, by a predetermined amount to
`set the impedance characteristic of said antenna assem-
`bly.
`5. The communications card of claim 3 wherein
`
`to a second ground pad disposed on said ground plane
`conductor, and a center conductor connected to said
`one end of said second microstrip feed line.
`7. The communications card of claim 5 wherein
`said first and second coaxial cables are housed within said
`
`hinge arrangement.
`8. The communications card of claim 1 wherein
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