(12) United States Patent
`Ying
`
`I 1111111111111111 11111 lllll lllll lllll lllll lllll lllll 111111111111111 11111111
`US006353443Bl
`US 6,353,443 Bl
`*Mar.5,2002
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) MINIATURE PRINTED SPIRALANTENNA
`FOR MOBILE TERMINALS
`
`(75)
`
`Inventor: Zhinong Ying, Lund (SE)
`
`(73) Assignee: Telefonaktiebolaget LM Ericsson
`(publ), Stockholm (SE)
`
`EP
`EP
`EP
`EP
`EP
`EP
`EP
`EP
`
`0 522 806
`0 590 671
`0 593 185
`0 635 898
`0 644 606
`0 660 440
`0 747 989
`0 777 293
`
`1/1993
`4/1994
`4/1994
`1/1995
`3/1995
`6/1995
`12/1996
`6/1997
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by O days.
`
`(List continued on next page.)
`
`OTHER PUBLICATIONS
`
`This patent is subject to a terminal dis(cid:173)
`claimer.
`
`(21) Appl. No.: 09/112,366
`
`(22) Filed:
`
`Jul. 9, 1998
`
`Int. CI.7 .................................................. HOlQ 1/24
`(51)
`(52) U.S. Cl. ............................... 345/702; 343/700 MS;
`343/850; 343/895
`(58) Field of Search .......................... 343/700 MS, 702,
`343/850, 851, 852, 895
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`676,332 A
`1,837,678 A
`2,966,679 A
`2,993,204 A
`3,573,840 A
`4,012,744 A
`4,121,218 A
`4,137,534 A
`4,161,737 A
`4,169,267 A
`
`6/1901 Marconi
`12/1931 Ryder
`12/1960 Harris ........................ 343/895
`7/1961 Macalpine .................. 343/745
`4/1971 Gouillou ..................... 343/745
`3/1977 Greiser ....................... 343/895
`10/1978 Irwin ......................... 343/702
`1/1979 Goodnight .................. 343/752
`7/1979 Albright ..................... 343/749
`9/1979 Wong et al. ................ 343/895
`
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`
`AU
`DE
`EP
`EP
`
`55898 73
`31 29 045
`0 372 720
`0 511 577
`
`11/1974
`10/1982
`6/1990
`11/1992
`
`"A Wideband Dual Meander Sleeve Antenna" by M. Ali et
`al., 1995 IEEE, pp. 1124-1127.
`Patent Abstracts of Japan, JP---0236602, Sep. 30, 1994.
`"Antennas", by J.D. Kraus, (McGraw-Hill Book Co., Inc.)
`pp. 173-178 (1950).
`
`(List continued on next page.)
`
`Primary Examiner-Don Wong
`Assistant Examiner-Shih-Chao Chen
`(74) Attorney, Agent, or Firm-Burns, Doane, Swecker &
`Mathis, L.L.P.
`
`(57)
`
`ABSTRACT
`
`The present invention seeks to overcome the above(cid:173)
`identified deficiencies in the art by providing a built-in
`printed spiral antenna which is small enough to satisfy the
`needs of future compact mobile terminals. According to
`exemplary embodiments, a built-in antenna is provided
`which includes a printed spiral metal strip that is connected
`to the mobile terminal's printed circuit board via a substrate.
`Matching of the antenna is performed by a matching bridge
`which is positioned between a feeding pin and a grounded
`post. By adjusting the length of the matching bridge, the
`matching of the antenna can be changed. In an alternative
`embodiment, a loading resistor is attached to the matching
`bridge in order to enhance the bandwidth of the antenna. The
`size of the antenna of the present invention can be reduced
`to 20-30% of the conventional PIFA antenna (i.e., less than
`½o of the wavelength of the operating frequency). As a
`result, the antenna can be used in a very compact chassis.
`
`20 Claims, 7 Drawing Sheets
`
`Matching bridge 330
`
`PCB
`310
`
`Spiral metal strip
`315
`
`Dielectric substrate
`320
`
`Ground post 335
`
`Antenna feed pin
`325
`
`Ex.1028
`APPLE INC. / Page 1 of 13
`
`

`

`US 6,353,443 Bl
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`6,166,694 A * 12/2000 Ying .......................... 343/702
`
`10/1980 Vo et al. ..................... 343/749
`4,229,743 A
`10/1982 Kaloi ... ... ... .. ... ... . 343/700 MS
`4,356,492 A
`2/1986 Phillips et al. .............. 343/745
`4,571,595 A
`2/1988 Phillips et al. ................ 455/89
`4,723,305 A
`5/1988 Ishino et al. ................ 343/895
`4,742,359 A
`8/1989 Wong et al. ................ 343/828
`4,860,020 A
`9/1989 Johnson, Jr. ................ 343/702
`4,868,576 A
`5/1991 Pireh ........................... 379/59
`5,020,093 A
`4/1993 Elliott et al. ................ 343/702
`5,204,687 A
`6/1993 Hall et al.
`.................. 343/895
`5,216,436 A
`3/1994 Takei et al. ................. 343/895
`5,298,910 A
`5/1994 Lillie et al. ................. 343/791
`5,311,201 A
`5/1994 Bottomley .................. 343/702
`5,317,325 A
`10/1994 Baldry ....................... 343/702
`5,353,036 A
`11/1994 Shoemaker ................. 343/828
`5,363,114 A
`1/1995 Ishihara ...................... 333/129
`5,386,203 A
`7/1995 Liu ............................ 343/723
`5,436,633 A
`8/1995 Itoh et al. ................... 343/702
`5,438,339 A
`8/1995 Makino ...................... 343/702
`5,446,469 A
`9/1995 Marino ....................... 343/895
`5,451,974 A
`11/1995 Takamoro et al. .......... 343/702
`5,467,096 A
`5,471,221 A * 11/1995 Nalbandian et al. . 343/700 MS
`5,479,178 A * 12/1995 Ha ............................. 343/702
`5,532,703 A * 7/1996 Stephens et al. ............ 343/702
`5,546,094 A * 8/1996 Egashira ..................... 343/702
`5,548,827 A * 8/1996 Hanawa et al. ............. 455/129
`5,550,820 A * 8/1996 Baran ........................ 370/60.1
`5,594,457 A * 1/1997 Wingo ........................ 343/702
`5,600,335 A
`2/1997 Abramo ...................... 343/749
`5,612,704 A * 3/1997 Cole .......................... 343/702
`5,635,943 A * 6/1997 Grunwell .................... 343/702
`5,661,496 A * 8/1997 Bak et al. ................... 343/702
`5,764,197 A * 6/1998 Tsuru et al.
`................ 343/895
`5,797,084 A * 8/1998 Tsutu et al. ................... 455/73
`5,892,490 A * 4/1999 Asakura et al. ............. 343/895
`5,903,240 A * 5/1999 Kawahata et al.
`... 343/700 MS
`5,929,825 A * 7/1999 Niu et al.
`................... 343/895
`5,949,385 A * 9/1999 Asakura et al. ............. 343/895
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`FR
`GB
`JP
`JP
`JP
`JP
`JP
`JP
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`
`0 855 759
`0 884 796
`2 664 749
`2175748
`63-219204
`5-7109
`6-37531
`6-90108
`6-152221
`Hl0-173430
`WO93/12559
`WO94/21003
`96/27219
`WO96/38882
`WO97/11507
`WO97/47054
`WO97/49141
`
`7/1998
`12/1998
`1/1992
`12/1986
`9/1988
`1/1993
`2/1994
`3/1994
`5/1994
`6/1998
`* 6/1993
`* 9/1994
`9/1996
`* 12/1996
`* 3/1997
`12/1997
`* 12/1997
`
`OTHER PUBLICATIONS
`
`"Microwave Scanning Antennas", edited by R.C. Hansen,
`Peninsula Publishing, pp. 116-122 (1950).
`European Search Report, File No. RS 102645 US, date of
`mailing, Mar. 31, 1999.
`"FDTD Analysis of Printed Square Spiral Antennas for
`Wireless Communications", J. Chen, et al., IEEE Antennas
`and Propagation Society International Symposium 1997
`Digest, vol. 3, Jul. 14, 1997, pps. 1550-1553.
`"Spectral Domain Analysis of a Square Microstrip Spiral
`Antenna", S.C. Wu, et al., Proceedings of the Antennas and
`Propagation Society Annual Meeting, 1991, vol. 2, Jan.
`1991, pps. 970---973.
`
`* cited by examiner
`
`Ex.1028
`APPLE INC. / Page 2 of 13
`
`

`

`U.S. Patent
`
`Mar. 5, 2002
`
`Sheet 1 of 7
`
`US 6,353,443 Bl
`
`i_
`, - - - - - - - - - - , w
`
`l~◄---L---~►ft
`
`FIG. 1A
`
`PRIOR ART
`
`I◄
`
`0.4 L
`
`►I
`
`FIG. 1 B
`
`PRIOR ART
`
`Ex.1028
`APPLE INC. / Page 3 of 13
`
`

`

`U.S. Patent
`
`Mar. 5, 2002
`
`Sheet 2 of 7
`
`US 6,353,443 Bl
`
`250
`
`230
`
`200
`
`~
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`I world I
`c JC)
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`210
`
`240
`
`220
`
`FIG. 2
`
`Ex.1028
`APPLE INC. / Page 4 of 13
`
`

`

`U.S. Patent
`
`Mar.5,2002
`
`Sheet 3 of 7
`
`US 6,353,443 Bl
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`C.
`..... Cl)
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`Ex.1028
`APPLE INC. / Page 5 of 13
`
`

`

`U.S. Patent
`
`Mar.5,2002
`
`Sheet 4 of 7
`
`US 6,353,443 Bl
`
`Grounded
`post 335
`
`Matching
`bridge
`330
`
`Feeding
`pm
`325
`
`Grounded
`post 335
`
`Chip
`resistor
`560
`
`Feeding
`pm
`325
`
`Metallic
`strip 315
`
`FIG. 4
`
`Matching bridge 330
`
`Metallic
`strip 315
`
`FIG. 5
`
`Ex.1028
`APPLE INC. / Page 6 of 13
`
`

`

`U.S. Patent
`
`Mar.5,2002
`
`Sheet 5 of 7
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`US 6,353,443 Bl
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`Ex.1028
`APPLE INC. / Page 7 of 13
`
`

`

`U.S. Patent
`
`Mar.5,2002
`
`Sheet 6 of 7
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`US 6,353,443 Bl
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`Ex.1028
`APPLE INC. / Page 8 of 13
`
`

`

`U.S. Patent
`
`Mar.5,2002
`
`Sheet 7 of 7
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`US 6,353,443 Bl
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`Ex.1028
`APPLE INC. / Page 9 of 13
`
`

`

`US 6,353,443 Bl
`
`1
`MINIATURE PRINTED SPIRAL ANTENNA
`FOR MOBILE TERMINALS
`
`RELATED APPLICATION
`
`This application is related to U.S. patent application Ser.
`No. 09/112,152 to Ying, filed Jul. 9, 1998, and entitled
`"Printed Twin Spiral Dual Band Antenna", which is incor(cid:173)
`porated herein by reference.
`
`BACKGROUND
`
`The present invention relates generally to radio commu(cid:173)
`nication systems and, in particular, to a miniature printed
`spiral antenna which can be incorporated into a portable
`terminal.
`The cellular telephone industry has made phenomenal
`strides in commercial operations in the United States as well
`as the rest of the world. Growth in major metropolitan areas
`has far exceeded expectations and is rapidly outstripping
`system capacity. If this trend continues, the effects of this
`industry's growth will soon reach even the smallest markets.
`Innovative solutions are required to meet these increasing
`capacity needs as well as maintain high quality service and
`avoid rising prices.
`Throughout the world, one important step in the advance(cid:173)
`ment of radio communication systems is the change from
`analog to digital transmission. Equally significant is the
`choice of an effective digital transmission scheme for imple(cid:173)
`menting the next generation technology, e.g., time division
`multiple access (TDMA) or code division multiple access
`(CDMA). Furthermore, it is widely believed that the first
`generation of Personal Communication Networks (PCNs),
`employing low cost, pocket-sized, cordless telephones that
`can be carried comfortably and used to make or receive calls
`in the home, office, street, car, etc., will be provided by, for
`example, cellular carriers using the next generation digital
`cellular system infrastructure.
`To provide an acceptable level of equipment
`compatibility, standards have been created in various
`regions of the world. For example, analog standards such as
`AMPS (Advanced Mobile Phone System), NMT (Nordic
`Mobile Telephone) and ETA CS and digital standards such as
`D-AMPS (e.g., as specified in EIA/TIA-IS-54-B and
`IS-136) and GSM (Global System for Mobile Communica(cid:173)
`tions adopted by ETSI) have been promulgated to standard(cid:173)
`ize design criteria for radio communication systems. Once
`created, these standards tend to be reused in the same or
`similar form, to specify additional systems. For example, in
`addition to the original GSM system, there also exists the
`DCS1800 (specified by ETSI) and PCS1900 (specified by
`JTC in J-STD-007), both of which are based on GSM.
`However, the most recent evolution in cellular commu(cid:173)
`nication services involves the adoption of additional fre(cid:173)
`quency bands for use in handling mobile communications,
`e.g., for Personal Communication Services (PCS) services.
`Taking the U.S. as an example, the Cellular hyperband is
`assigned two frequency bands ( commonly referred to as the
`A frequency band and the B frequency band) for carrying
`and controlling communications in the 800 MHz region. The
`PCS hyperband, on the other hand, is specified in the United 60
`States to include six different frequency bands (A, B, C, D,
`E and F) in the 1900 MHz region. Thus, eight frequency
`bands are now available in any given service area of the U.S.
`to facilitate communication services. Certain standards have
`been approved for the PCS hyperband (e.g., PCS1900 65
`(J-STD-007)), while others have been approved for the
`Cellular hyperband (e.g., D-AMPS (IS-136)).
`
`20
`
`15
`
`2
`Each one of the frequency bands specified for the Cellular
`and PCS hyperbands is allocated a plurality of traffic chan(cid:173)
`nels and at least one access or control channel. The control
`channel is used to control or supervise the operation of
`5 mobile stations by means of information transmitted to and
`received from the mobile stations. Such information may
`include incoming call signals, outgoing call signals, page
`signals, page response signals, location registration signals,
`voice channel assignments, maintenance instructions, hand-
`10 off, and cell selection or reselection instructions as a mobile
`station travels out of the radio coverage of one cell and into
`the radio coverage of another cell. The control and voice
`channels may operate using either analog modulation or
`digital modulation.
`The signals transmitted by a base station in the downlink
`over the traffic and control channels are received by mobile
`or portable terminals, each of which have at least one
`antenna. Historically, portable terminals have employed a
`number of different types of antennas to receive and transmit
`signals over the air interface. For example, monopole anten(cid:173)
`nas mounted perpendicularly to a conducting surface have
`been found to provide good radiation characteristics, desir(cid:173)
`able drive point impedances and relatively simple construc(cid:173)
`tion. Monopole antennas can be created in various physical
`25 forms. For example, rod or whip antennas have frequently
`been used in conjunction with portable terminals. For high
`frequency applications where an antenna's length is to be
`minimized, another choice is the helical antenna.
`Presently, antennas for radio communication devices,
`30 such as mobile phones, are mounted directly on the phone
`chassis. However, as the size and weight of portable termi(cid:173)
`nals continue to decrease, the above-described antennas
`become less advantageous due to their size. As a result,
`built-in antennas will be necessary for these future compact
`35 portable terminals which are capable of operating in a 300
`MHz to 3000 MHz frequency range.
`Conventional built-in antennas currently in use in mobile
`phones include microstrip patch antennas and planar
`inverted-F antennas. Microstrip antennas are small in size
`40 and light in weight. The planar inverted-F antenna (PIFA)
`has already been implemented in a mobile phone handset, as
`described by K. Qassim, "Inverted-F Antenna for Portable
`Handsets", IEE Colloqium on Microwave Filters and Anten(cid:173)
`nas for Personal Communication Systems, pp.3/1-3/16,
`45 February 1994, London, UK. And, more recently, Lai et al.
`has published a meandering inverted-F antenna (WO
`96/27219). This antenna has a size which is about 40% of
`that of the conventional PIFA antenna.
`FIGS. lA and lB illustrate the conventional planar patch
`50 antenna compared to the meandering inverted-F antenna
`described in Lai et al. The conventional planar patch antenna
`of FIG. lAhas both a size and length equal to, for example,
`a quarter wavelength of the frequency to which the antenna
`is to be made resonant. The conventional planar patch
`55 antenna also has a width of W. The meandering inverted-F
`antenna, illustrated in FIG. lB, also has a length equal to a
`quarter wavelength of the resonant frequency and a width
`equal to W; however, the size of the meandering inverted-F
`antenna is reduced to about 40% of the size of the conven-
`tional planar patch antenna. This reduction in size is attrib(cid:173)
`utable to the antenna's meandering shape.
`As mobile phones become smaller and smaller, both
`conventional microstrip patch and PIFA antennas are still
`too large to fit the future small phone chassis. This is
`particularly problematic when next generation phones need
`multiple antennas for cellular, wireless local area network,
`GPS and diversity.
`
`Ex.1028
`APPLE INC. / Page 10 of 13
`
`

`

`US 6,353,443 Bl
`
`5
`
`3
`SUMMARY
`
`The present invention seeks to overcome the above(cid:173)
`identified deficiencies in the art by providing a built-in
`printed spiral antenna which is small enough to satisfy the
`needs of future compact mobile terminals. According to
`exemplary embodiments, a built-in antenna is provided
`which includes a printed spiral metal strip that is connected
`to the mobile terminal's printed circuit board via a substrate.
`Matching of the antenna is performed by a matching bridge
`which is positioned between a feeding pin and a grounded
`post. By adjusting the length of the matching bridge, the
`matching of the antenna can be changed. In an alternative
`embodiment, a loading resistor is attached to the matching
`bridge in order to enhance the bandwidth of the antenna. The
`size of the antenna of the present invention can be reduced
`to 20-30% of the conventional PIFA antenna (i.e., less than
`½o of the wavelength of the operating frequency). As a
`result, the antenna can be used in a very compact chassis.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`DETAILED DESCRIPTION
`
`FIG. 2 illustrates a radio communication device 200 in 50
`which the built-in antenna of the present invention may be
`implemented. Communication device 200 includes a chassis
`210 having a microphone opening 220 and speaker opening
`230 located approximately next to the position of the mouth
`and ear, respectively, of a user. A keypad 240 allows the user
`to interact with the communication device, e.g., by inputting
`a telephone number to be dialed. The communication device
`200 also includes a built-in antenna assembly 250, the
`details of which will be described below.
`FIG. 3 illustrates the built-in antenna assembly according
`to an exemplary embodiment of the present invention. The
`built-in antenna, according to the present invention, includes
`a printed metallic strip 315 which is configured in an inner
`spiral shape and is attached to the printed circuit board
`(PCB) 310 of the communication device via a dielectric
`substrate 320. The inner spiral shape allows for a reduction
`in size over the conventional planar patch and meandering
`
`The above objects and features of the present invention
`will be more apparent from the following description of the
`preferred embodiments with reference to the accompanying
`drawings, wherein:
`FIGS. lA and lB illustrate the conventional planar patch
`antenna compared to the conventional meandering
`inverted-F antenna;
`FIG. 2 illustrates a radio communication device in which
`the antenna of the present invention may be implemented; 30
`FIG. 3 illustrates the built-in antenna according to a first
`embodiment of the present invention;
`FIG. 4 illustrates a top view of the built-in spiral antenna
`of the present invention;
`FIG. 5 illustrates the built-in spiral antenna according to
`a second embodiment of the present invention;
`FIG. 6 illustrates the VSWR performance of a miniature
`printed spiral antenna of the present invention designed for
`a W-Lan application;
`FIG. 7 illustrates the VSWR performance of a miniature
`printed spiral antenna of the present invention designed for
`operation in the GSM band; and
`FIG. 8 illustrates the VSWR performance of the miniature 45
`printed spiral antenna of FIG. 7 implementing the resistor
`enhancement technique of the present invention.
`
`35
`
`40
`
`4
`inverted-F antennas. By forming the printed metallic strip in
`an inner spiral shape, the size of the antenna, according to
`the present invention, can be reduced to about 20% of the
`conventional planar patch antenna while still maintaining a
`length of¼ wavelength. One skilled in the art will appreciate
`that the length of the printed metallic strip of the present
`invention is not limited to ¼ wavelength, but other lengths
`may be chosen, such as ½ wavelength.
`The printed spiral metallic strip 315 is fed by an antenna
`10 feed pin 325 at the end of the outer turn of the spiral. One
`skilled in the art will appreciate that the current on the spiral
`metallic strip 315 decays from the feeding point 325 to the
`other end of the metallic strip. As a result, the antenna has
`higher radiation efficiency when the current is distributed
`15 mostly in the outer edge of the antenna.
`As illustrated in FIG. 3 and in the top view of the antenna
`set forth in FIG. 4, the built-in antenna also includes a
`matching bridge 330 positioned between the feeding pin 325
`and the grounded post 335. The matching bridge 330 acts to
`20 tune the antenna and forms a small loop antenna between the
`feeding pin 325 and grounded post 335. Tuning of an
`antenna refers to matching the impedance seen by an
`antenna at its input terminals such that the input impedance
`is seen to be purely resistive, i.e., it will have no appreciable
`25 reactive component. The tuning of the antenna system of the
`present invention is performed by measuring or estimating
`the input impedance associated with the antenna and pro(cid:173)
`viding an appropriate impedance matching circuit (i.e., the
`matching bridge). The matching of the antenna, according to
`the present invention, can be adjusted by changing the length
`of the matching bridge 330. This is accomplished by simply
`changing the location of the grounded post 335. The length
`of the matching bridge is generally in the order of 0.0H. to
`0.lA.
`As is evident from FIG. 3, the printed spiral antenna is
`positioned over the PCB and forms a spiral slot between the
`spiral metallic strip 315 and the PCB 310. One skilled in the
`art will appreciate that it is the spiral slot that forms the main
`radiator ( or sensor) of the present antenna system.
`The resonant frequency and bandwidth of the built-in
`antenna of the present invention are dependent upon the area
`and thickness of the dielectric substrate, the type of dielec(cid:173)
`tric material selected (i.e., the dielectric constant), the spiral
`length of the metallic strip and the rate of expansion of the
`spiral. Generally, the length of the printed spiral metallic
`strip is selected to be approximately ¼ wavelength of the
`frequency band to which the antenna is to be tuned. One
`skilled in the art will appreciate, however, that other lengths
`may be chosen, such as ½ wavelength. One skilled in the art
`will also appreciate that an increase in the area or thickness
`of the dielectric substrate or the tightness of the spiral (i.e.,
`the rate of the expansion of the spiral) or a decrease in the
`value of the dielectric constant results in an increase in the
`55 bandwidth which can be achieved.
`As is evident from FIG. 3, the spiral antenna of the present
`invention can be mounted at the edge of the PCB which
`provides for better radiation efficiency and bandwidth. In
`addition, the PCB space requirement for the spiral antenna
`60 is minimized due to its small size.
`The antenna assembly of the present invention works as
`a magnetic antenna. As a result, the spiral metal strip creates
`nearly circular polarized waves (as opposed to linear polar(cid:173)
`ized waves achieved by the conventional antennas described
`65 above with respect to FIGS. lA and lB) when the rate of
`expansion of the spiral (i.e., the tightness of the spiral) is
`chosen properly. This would be advantageous in a multipath
`
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`5
`environment, such as mobile radio communications, and in
`satellite (e.g., GPS) communications where circular polar(cid:173)
`ized signals are generally used. Moreover, as a magnetic
`antenna, there is less interference from the human body.
`FIG. 5 illustrates the built-in spiral antenna according to
`a second embodiment of the present invention. One skilled
`in the art will appreciate that a printed antenna on a ground
`plane has a narrower bandwidth than the bandwidth of the
`earlier-described conventional monopole or dipole antenna.
`The bandwidth of such a printed antenna can be enhanced by
`introducing some loss into the system. This is evident from
`the fact that loss always indicates a lower Q-factor and thus
`a higher bandwidth. The following equation illustrates the
`relationship between the Q-factor and the achievable band(cid:173)
`width:
`
`Q-fO/BW
`where fO is the center frequency and BW is the bandwidth.
`According to an exemplary embodiment of the present
`invention, a loading resistor 560 is connected in series to the
`matching bridge 330 in order to introduce loss into the 20
`system. In the alternative, the same result can be achieved by
`connecting the resistor 560 in parallel to the grounded post
`335. The resistor of the present invention can be either a chip
`resistor or a resistor film. The resistor introduces loss in the
`antenna's radiated power which results in broader band- 25
`width.
`The resistor value can be selected in order to satisfy
`particular design requirements. In a situation where high
`efficiency is needed (i.e., loss is to be kept small), a small
`resistor value should be used. However, in a situation where 30
`a wide bandwidth is critical, a larger resistor value should be
`used.
`In order to illustrate the effectiveness of the present
`invention, FIGS. 6-8 set forth results of simulations for
`exemplary built-in spiral antennas. The antennas in the 35
`simulations were mounted on a printed circuit board via a
`dielectric substrate. In the first simulation, the results of
`which are illustrated in FIG. 6, a design for a W-LAN
`application was considered. The printed spiral antenna had
`a length of 0.082 wavelength, a width of 0.08 wavelength
`and a height of 0.04 wavelength. The bandwidth of the
`antenna was 5.3% for a VSWR less than 2.5:1. FIG. 6
`illustrates the VSWR performance of the antenna of the
`present invention for the first simulation. It is evident from
`FIG. 6 that the antenna achieves approximately 130 MHz for 45
`a 2.45 GHz band, which would satisfy the requirements for
`a W-LAN application.
`In the second simulation, the antenna was designed for
`operation in the GSM band. The length of the printed spiral
`antenna was 0.073 wavelength (22 mm), the width was 50
`0.067 wavelength (20 mm) and the height was 0.04 wave(cid:173)
`length (12 mm). The bandwidth of the antenna was 4.2% for
`a VSWR less than 2.5:1. In this simulation, the antenna
`achieved approximately 40 MHz for the GSM band which
`would not satisfy the requirements for a GSM application. 55
`FIG. 7 shows the VSWR performance for this design.
`In the third simulation, bandwidth enhancement was
`introduced to the GSM band antenna set forth above by
`attaching a 1 ohm chip resistor to the matching bridge of the
`antenna. As a result, the bandwidth of the antenna is 60
`increased to 9.3% (about 88 MHz). The VSWR performance
`for this simulation is illustrated in FIG. 8. The performance
`of this bandwidth enhanced antenna would satisfy the
`requirements for a GSM application; however, the antenna's
`gain is reduced approximately 3 dB.
`The foregoing has described the principles, preferred
`embodiments and modes of operation of the present inven-
`
`6
`tion. However, the invention should not be construed as
`being limited to the particular embodiments discussed
`above. For example, while the antenna of the present inven(cid:173)
`tion has been discussed primarily as being a radiator, one
`5 skilled in the art will appreciate that the printed miniature
`spiral antenna would also be used as a sensor for receiving
`information at specific frequencies. Thus, the above(cid:173)
`described embodiments should be regarded as illustrative
`rather than restrictive, and it should be appreciated that
`10 variations may be made in those embodiments by workers
`skilled in the art without departing from the scope of the
`present invention as defined by the following claims.
`what is claimed is:
`1. A communication device for use in a radio communi-
`15 cation system, said device comprising:
`a microphone opening for allowing the communication
`device to receive auditory information from a user;
`a speaker opening for allowing the communication device
`to transmit auditory information to said user;
`a keypad;
`an antenna comprising a printed spiral metallic strip,
`wherein said antenna is a built-in antenna; and
`a matching bridge for matching an input impedance of
`said antenna.
`2. The communication device of claim 1 wherein the
`matching of said antenna is adjusted by changing a length of
`the matching bridge.
`3. The communication device of claim 1 wherein said
`printed spiral metallic strip is fed with a current at an end of
`an outer turn of said printed spiral metallic strip.
`4. The communication device of claim 1 further compris(cid:173)
`ing a printed circuit board onto which said built-in antenna
`is mounted.
`5. The communication device of claim 1 wherein a length
`of said printed spiral metallic strip is selected to be approxi(cid:173)
`mately ¼ wavelength of the frequency band to which the
`antenna is to be tuned.
`6. A communication device for use in a radio communi-
`40 cation system, said device comprising:
`a microphone opening for allowing the communication
`device to receive auditory information from a user;
`a speaker opening for allowing the communication device
`to transmit auditory information to said user;
`a keypad;
`an antenna comprising a printed spiral metallic strip,
`wherein said antenna is a built-in antenna;
`a matching bridge for matching an input impedance of
`said antenna; and
`a loading resistor attached to said matching bridge for
`enhancing a bandwidth of said antenna.
`7. A communication device for use in a radio communi(cid:173)
`cation system, said device comprising:
`a printed circuit board mounted on
`communication device;
`a substrate attached to said printed
`having a predetermined thickness;
`an antenna mounted on said substrate and comprising a
`printed spiral metallic strip, wherein said antenna is a
`built-in antenna; and
`a matching bridge for matching an input impedance of
`said antenna.
`8. The communication device of claim 7 wherein a length
`65 of said printed spiral metallic strip is selected to be approxi(cid:173)
`mately ¼ wavelength of the frequency band to which the
`antenna is to be tuned.
`
`circuit board and
`
`a chassis of said
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`5
`
`a chassis of said
`
`circuit board and
`
`7
`9. The communication device of claim 7 wherein a
`bandwidth of said antenna depends on a size of said printed
`spiral metallic strip and the thickness and dielectric constant
`of said substrate.
`10. A communication device for use in a radio commu-
`nication system, said device comprising:
`a printed circuit board mounted on
`communication device;
`a substrate attached to said printed
`having a predetermined thickness;
`an antenna mounted on said substrate and comprising a
`printed spiral metallic strip, wherein said antenna is a
`built-in antenna; and
`a matching bridge for matching an input impedance of
`said antenna and located between a feeding point and a
`grounded post.
`11. The communication device of claim 10 wherein the
`matching of said antenna is adjusted by changing a length of
`the matching bridge.
`12. The communication device of claim 10 further com(cid:173)
`prising a loading resistor attached to said matching bridge
`for enhancing a bandwidth of said antenna.
`13. The communication device of claim 10 wherein said
`matching bridge forms a loop antenna between said feeding 25
`point and said grounded post.
`14. An antenna for a radio communication device, said
`antenna comprising:
`a printed spiral metallic strip;
`a matching bridge for matching an input impedance of 30
`said antenna; and
`a loading resistor attached to said matching bridge;
`wherein said antenna is a built-in an