United States Patent [191
`Matero et al.
`
`I Illll 111111111111111111111011111111111111111111H 1111111111111
`US005768691A
`5,768,691
`[HJ Patent Number:
`Jun. 16, 1998
`[451 Date of Patent:
`
`[54] ANTENNA SWITCHING CIRCUITS FOR
`RADIO TELEPHONES
`
`[75]
`
`Inventors: Jonna Matero. Oulu; Matti L Kangas,
`Oulunsalo, both of Finland
`
`[73) Assignee:. Nokia Mobile Phones Limited, Salo,
`Finland
`
`(21] Appl No.: 692,496
`
`Aug. 7, l!J96
`
`[22] Filed:
`Int. CL 6
`...... _. .............................................. HMB 1/44
`(51]
`(52] U.S. CI. ·······--······--·····--· 455n8; 455/84; 333/101;
`370/280
`(58] Field of Search ............................ 333/101. 103-104;
`455n3. 78. 82. 83. 84. 575, 132. 212. 99,
`129, 345; 370/276, 277, 278, 280. 282.
`294
`
`[56]
`
`References Cited
`
`U.S. PATENf DOCUMENfS
`
`4,955.039
`5,079,520
`5,291,474
`5,301,367
`
`9/1990 Rother et al .............................. 375fi5
`1/1992 Rapeli ................................. 331/100 A
`3/1994 Ikonen et al .............................. 370/30
`4/1994 Heinonen .................................. 455n6
`
`611994 Rapeli ..................................... 332/103
`5,325,075
`1/1995 Ishihara ..................................... 455182
`5,386,203
`2/1995 Vimpari .................................... 370/30
`5,390,168
`5,471,652 11/1995 Hulkko ...................................... 455n6
`
`FOREIGN PATENf DOCUMENTS
`
`0305603 Al
`0541305 Al
`0581573 Al
`WO 94/14247
`
`3/1989 European Pat. Oft' ..
`5/1993 Enropean Pat. Oft' ..
`2/1994 European Pat. Oft' ..
`6/1994 WIPO .
`
`Primary Examiner-Nguyen Vo
`Attome~ Agent, or Firm-Perman & Green. LLP
`ABSTRACT
`
`[57]
`
`Disclosed are various embodiments of circuitry for coupling
`first and second transceivers of a dual band radio telephone
`to integral and external antennas. The circuitry uses imped(cid:173)
`ance matching lengths of transmission lines and switches
`arranged to provide a minimum insertion loss. Also dis(cid:173)
`closed is an embodiment for use with a single band radio
`telephone, such as a digital TDMA radio telephone that
`either transmits or receives at any given time. Also disclosed
`is an antenna switching arrangement for a dual band phone
`that eliminates a requirement for duplexers.
`
`17 Claims, 6 Drawing Sheets
`
`I
`
`r
`
`ANT SWITCH J
`
`ANT SWITCH 2
`
`L
`
`lo
`EXT. ANTENNA
`
`7
`I- -
`..J
`
`- 14
`
`L2
`
`LJ
`
`7
`1---16
`..J
`
`Po
`
`...__
`
`rx....,
`rx....,
`
`rx...,,
`,-..,__,.
`rx...,,
`
`[>
`
`r-x....,
`,-..,__,.
`r-x....,
`
`6
`BAND f
`
`5
`
`9
`
`<]
`
`C>
`
`6'
`
`BAND 2
`
`...__
`rx...,,
`__ rx...,, ___ 5,
`
`rx...,,
`,-..,__,.
`rx...,,
`
`9'
`
`<J
`~ - - ANT SWITCH
`CONTROL
`LINES
`
`Ex.1023
`APPLE INC. / Page 1 of 12
`
`

`

`Jun. 16, 1998
`
`Sheet 1 of 6
`
`2
`
`U.S. Patent
`FIG. 1
`PRIOR ART
`ANTENNA SYSTEM
`' RECEIVER FRONT END.
`TRANSMITTER POWER AMPLIFIER - (cid:173)
`BAND 1
`
`5,768,691
`
`4
`
`RECEIVER IF PARTS.
`SYNTHESIZER.
`MODULATOR
`
`J
`
`RECEIVER FRONT END.
`TRANSMITTER POWER AMPLIFIER - (cid:173)
`BAND 2
`
`FIG. 2
`PRIOR ART
`
`TO ANTENNA
`1
`
`FIG. 3
`PRIOR ART
`
`RECEIVER FRONT END
`.---[>
`,,......._
`rx...,
`rx...,
`~ ,,......._
`~ 5
`~ ,,......._
`~ TRANSMITTER POWER AMPLIFIER
`. _ _ _ _ - - - - I <J
`9
`
`6
`
`rx...,,
`"'--'
`rx...,,
`
`I
`
`rx...,,
`"'--'
`rx...,,
`
`6
`BAND 1
`
`rx...,,
`5
`,-.,,_...,
`rx...,,
`' - - - - - - . 1 <]
`~-+-'r 7 ANT SWITCH
`---,o
`_J
`~ - - - - -< [>
`
`L
`
`9
`
`...-x....,
`,-.,,_...,
`rx_,.
`
`rx...,,
`~ 5'
`rx..,
`
`6'
`BAND 2
`
`' - - - - - - . 1 <]
`
`9'
`
`Ex.1023
`APPLE INC. / Page 2 of 12
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 2 of 6
`
`5,768,691
`
`FIG. 4
`PRIOR ART
`
`I
`
`. . - - - - - - - 1 [>
`
`6
`
`5
`BAND 1
`
`rx...,
`~
`riv
`
`..-x.,.
`~ ..-x.,.
`
`' - - - - - - - - - I <J
`
`9
`
`..-x.,.
`,,..._,__,
`..-x.,.
`
`6'
`
`5'
`BAND 2
`
`lo
`EXT. ANTENNA
`
`._____ <J
`.__ _ _ _ _ _ _ _ _ ANT SWITCH
`...__ _ _ _ _ _ _ _ _ _ _ _ CONTROL
`LINES
`
`9'
`
`FIG. 5
`DUAL BAND
`ANTENNA
`SYSTEM
`
`12b
`
`12
`
`[>
`
`rx...,
`"'--'
`rx...,
`
`rx...,
`"'--'
`rx...,
`
`rx...,
`,,..._,__,
`rx...,
`
`12c
`
`6
`5 BAND!
`
`9
`
`<]
`
`[>
`
`rx...,
`,,..._,__,
`rx...,
`
`rx...,
`"'--'
`rx...,
`
`rx...,
`~ ,,,.__,
`
`5'
`
`6'
`BAND 2
`
`9'
`
`<]
`
`Ex.1023
`APPLE INC. / Page 3 of 12
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 3 of 6
`
`5,768,691
`
`FIG. 6
`
`r
`
`7
`1---14
`_j
`
`L2
`
`LJ
`
`7
`f--- -16
`_j
`
`ANT SWITCH I
`
`ANT SWITCH 2
`
`L
`
`la
`EXT ANTENNA
`
`FIG. 7
`
`L2
`
`LJ
`
`L4
`
`lo
`EXT ANTENNA
`
`,....,,_
`rx...,
`6
`rx...,
`.......ia-rx....,---1---5 BAND I
`~
`rx...,
`
`...._______. <]
`
`9
`
`...---1-----1 [>
`
`,....,,_
`rx...,
`rx...,
`
`rx...,
`~ rx...,
`La--v-5'
`rx...,
`~
`rx.....,
`
`6'
`
`BAND 2
`
`9'
`
`~ - - ANT SWITCH
`CONTROL
`LINES
`
`- [>
`
`9
`
`rx...,
`"----'
`rx...,
`
`6'
`
`BAND 2
`
`erx..., 5'
`~ rx...,
`9'
`~ <]
`ANT SWITCH
`.__ _ _ CONTROL
`LINES
`
`Ex.1023
`APPLE INC. / Page 4 of 12
`
`

`

`U.S. Patent
`Jun. 16, 1998
`FIG. B
`r - - - - - - - - - ,
`PRIOR ART:
`I
`
`Sheet 4 of 6
`
`5,768,691
`
`Pl
`
`rx..,
`20
`
`~ 1
`I
`: BAND 2
`l
`I
`I
`I
`I
`L_L _______ _J
`I
`Tx/Rx
`
`FIG. 9
`PRIOR ART
`
`l
`
`11- -
`
`r
`'l
`L
`ANT. SWITCH 2
`
`la
`EXT. ANTENNA
`
`r-------7
`,~[>-
`I
`rx..,
`I
`. - - - -1 " " ' - '
`rx..,
`I ..__,__
`I
`I
`6
`7
`711
`f.- -10
`I
`BAND 1
`i/vr. SWITCH I :
`1~<]-
`I - - -
`5 b - -
`______ _J
`'--------Tx/Rx
`'---------~NT/EXTANT
`CONTROL
`
`5a
`
`r-1 I ~
`I
`I
`I
`I
`L
`
`L - - - - 1~
`
`rx..,
`""'-'
`rx..,
`
`9
`
`FIG. 10
`'
`
`r - - - - - - - - - - - ,
`I ~[>-
`l - - - -1 rx..,
`! 10 ~
`~
`1--.--
`I 1
`5a
`6
`1 .....1-~
`I
`7
`1
`1
`I
`.__I____..
`I
`I
`_J ANT SWITCH 1 I
`I
`I
`I
`LI
`L2
`I
`I
`: -------~
`I.--<]--,
`I
`I - -
`5b
`JI..._
`1
`I
`la ~-'-4-4-
`NJT SW!T()-1 2 I
`EXT. ANTENNA
`i
`1-Tx/Rx
`L _ _ _ _ _ _ _ _ _ __J
`~ - - - - - - -
`
`rx..,
`,,,......_,,
`
`~
`
`9
`
`Ex.1023
`APPLE INC. / Page 5 of 12
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`FIG. Ila
`A
`I
`
`1
`
`Lt
`
`L4
`
`L5
`
`Sw/
`LRx
`
`Sw2
`LTx
`
`Rx SLOT
`
`SwJ
`HRx
`
`Sw4
`HTx
`
`Sheet 5 of 6
`FIG. lib
`A
`'
`I LI
`
`L4
`
`L5
`
`lo-<g)
`
`LB
`
`IDLE
`
`10\g)
`
`LB
`
`IDLE
`
`5,768,691
`
`Sw!
`LRx
`
`Sw2
`LTx
`
`Tx SLOT
`
`SwJ
`HRx
`
`HTx
`Sw4
`
`FIG. 120
`A
`I
`
`I
`
`-------
`
`..----.Swf
`LRx
`
`~~Sw2
`~-r-----
`L Tx
`
`I
`
`FIG. 12b
`_____ sw,
`A
`--------+--
`I
`LR x
`~-----
`
`..-----. Sw2
`LTx
`
`Rx SLOT
`
`Tx SLOT
`
`LI
`
`L2
`
`SwJ
`HRx
`
`Sw4
`HTx
`
`LI
`
`L2
`
`SwJ
`HRx
`
`Sw4
`HTx
`
`lo\9)
`
`IDLE
`
`lo~ IDLE
`
`Ex.1023
`APPLE INC. / Page 6 of 12
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 6 of 6
`
`5,768,691
`
`FIG. 130
`A
`'
`I
`
`----
`
`~-sw,
`LRx
`
`~-Sw2
`~ - -+ -
`LT x
`
`IDLE
`
`L!
`
`L2
`,,____,SwJ
`HRx
`- - - - - - t - - - ; - - - _ _
`
`~-Sw4
`- - - - - - - - , 1 - - - - + -
`H T x
`
`1
`
`FIG. 13b
`A
`,,__..Swl
`I
`-------1-
`LRx
`------1-
`
`.------. Sw2
`LTx
`
`LI
`
`- - - - - - ! ~ - 1 -
`
`IDLE
`L2
`.-------. SwJ
`HRx
`
`~---Sw4
`HT X
`~ - - - - 1 - - t - - . . .
`
`la --«2) Rx SLOT
`
`la-cQJ
`
`Tx SLOT
`
`FIG. 140
`A
`I
`
`1
`
`FIG. 14b
`A
`1
`
`f
`
`Sw!
`LRx
`
`Sw2
`LTx
`
`IDLE
`
`LI
`
`L2
`
`SwJ
`HRx
`
`Sw4
`HTx
`
`LI
`
`L2
`
`Sw/
`LRx
`
`Sw2
`LTx
`
`IDLE
`
`SwJ
`HRx
`
`Sw4
`HTx
`
`lo""\Q) Rx SLOT
`
`10\9)
`
`Tx SLOT
`
`Ex.1023
`APPLE INC. / Page 7 of 12
`
`

`

`5,768.691
`
`1
`ANTENNA SWITCHING CIRCUITS FOR
`RADIO TELEPHONES
`
`FIELD OF THE INVENTION
`This invention relates generally to methods and apparatus
`for connecting radio frequency (RF) circuits to one or more
`antennas and. in particular, to circuits used in single and dual
`band radio telephones, such as cellular telephones.
`
`20
`
`25
`
`2
`duplex filters, or duplexers, 5 and 5'), which thereby enables
`an optimum performance on both bands. However, the high
`insertion loss and required linearity can overshadow the
`benefit of this arrangement, and make its use undesirable for
`5 many applications.
`Reference can also be made to FIG. 4 for illustrating a
`conventional approach for implementing antenna switching
`in a dual band mobile phone, when an external antenna
`connector la is required. That is, the antenna 1 may be an
`10 integral or master antenna that is provided as part of the
`mobile phone. while antenna connector la is also provided
`to enable the mobile phone to be connected to a second,
`external antenna. In addition to the Band 1 and Band 2
`transceiver circuitry shown in FIG. 3. a second antenna
`switch 11 is connected in series with the band switch 10, and
`suitable antenna switch control lines are provided from a
`controller (not shown) of the mobile phone to control the
`state of the antenna switches 10 and 11. Assuming that the
`second switch 11 is also an electronic switch. it can be
`appreciated that the total insertion loss can be doubled over
`the FIG. 3 configuration. This in turn compounds at least the
`power consumption and receiver sensitivity problems that
`were described above with respect to FIG. 3.
`FIG. 9 illustrates a conventional antenna/external antenna
`switching arrangement for a single band digital (e.g ..
`TDMA) mobile phone. The first antenna switch 10 functions
`as a transmit/receive switch for the receiver and transmitter.
`and is coupled to a receive bandpass filter Sa and a transmit
`bandpass filter Sb. The second antenna switch 11 is
`employed for switching between the antenna 1 and the
`external antenna connector la. As in the embodiment of
`FIG. 4, a significant disadvantage of this technique is the
`doubling of the insertion loss due to the two serially coupled
`antenna switches 10 and 11.
`
`BACKGROUND OF THE INVENTION
`In a dual band mobile phone the operational bandwidth of
`the antenna presents a difficult problem. By example, such
`a mobile phone may need to be operable in the 800 MHz
`band (e.g., analog AMPS) at one time, and then in the 1.9
`GHz band (e.g., digital PCN) at another time. Preferably, a 15
`single antenna is used for both bands. However, due to the
`large difference in operational frequencies conventional dual
`band mobile phones typically provide a separate receiver
`front end and a separate transmitter power amplifier section
`for each band.
`FIG. 1 illustrates one such conventional construction for
`a dual band mobile phone. A single antenna system 1 is
`connected to a Band 1 receiver front end and transmitter
`power amplifier block 2, and is also connected to a Band 2
`receiver front end and transmitter power amplifier block 3.
`Blocks 2 and 3 are both connected to a common, further
`block 4 that contains the receiver IF circuits, frequency
`synthesizer(s). modulators. demodulators. etc. Not shown in
`FIG. 1 are the remaining portions of the mobile phone, such
`as the keypad. display, user interface controller. etc.
`In some dual band phones, such as a dual band phone that
`includes a digital TDMA portion, the TDMA transmitter and
`receiver sections are connected to the antenna 1 through a
`duplex filter 5. as is illustrated in FIG. 2. In this case the 35
`duplex filter 5 is connected to an input of a receiver amplifier
`(), which has an output connected to a bandpass filter 7 and
`a first IF mixer 8. while also being connected to the output
`of a transmitter power amplifier 9.
`In conventional practice the required band switching has
`been accomplished with a mechanical relay or switch 10, as
`is shown in FIG. 3. In FIG. 3 the circuitry shown in FIG. 2
`is duplicated for each band, with the Band 2 circuits being
`designated with prime symbols ('). At any given time the
`switch 10 connects either the Band 1 or the Band 2 trans- 45
`ceiver circuitry to the antenna 1.
`However, this approach has at least two significant dis(cid:173)
`advantages. First. the use of a mechanical switch has the
`disadvantage of requiring a large and bulky component with
`a slow switching time. To overcome this problem the 50
`mechanical switch can be replaced with an electronic switch,
`such as a FEf or a pin diode. However, the use of an
`electronic switch is disadvantageous in that it introduces a
`significant insertion loss into the RF path. A typical insertion
`loss for an electronic switch is on the order of 0.5 dB. This 55
`insertion loss must be compensated for by using a higher
`transmitter power which. in turn. increases the power con(cid:173)
`sumption and reduces the battery life of the mobile phone.
`Furthermore. if operation in one of the bands is required to
`be a duplex analog mode, the antenna switching circuitry 60
`must exhibit a high degree of linearity to avoid spurious
`responses generated by the transmitter signal within the
`antenna switch 10. Also. the receiver sensitivity is impaired
`since the switch insertion loss also degrades the receiver
`noise figure.
`One benefit of the approach shown in FIG. 3 is that it
`provides good isolation between band filters (in this case the
`
`30
`
`OBJECTS OF THE INVENTION
`It is a first object of this invention to provide an improved
`mobile phone that overcomes the foregoing and other prob-
`40 lems.
`It is a further object of this invention to provide embodi(cid:173)
`ments of circuitry for coupling both single band and dual
`band mobile phones to two antennas. and that avoids the
`doubling of the insertion loss due to the use of two series(cid:173)
`connected electronic switches.
`It is another object of this invention to provide embodi(cid:173)
`ments of switching circuitry for coupling a dual band mobile
`phone to two antennas. without requiring a duplexer.
`
`SUMMARY OF THE INVENTION
`
`The foregoing and other problems are overcome and the
`objects of the invention are realized by antenna switching
`circuitry in accordance with embodiments of this invention.
`In a first embodiment of this invention there is provided
`antenna switching circuitry for use in a radio telephone of a
`type that includes a first transceiver operable in a first
`frequency band and a second transceiver operable in a
`second frequency band. The radio telephone further includes
`a first antenna port and a second antenna port. The antenna
`switching circuitry includes a first pair of transmission lines
`(Ll and IA) each having a first node coupled to an input/
`output port of the first transceiver. A second node of LI is
`switchably coupled to the first antenna port and a second
`65 node of IA is switchably coupled to the second antenna port.
`The radio telephone further includes a second pair of trans(cid:173)
`mission lines (L2 and 13) each having a first node coupled
`
`Ex.1023
`APPLE INC. / Page 8 of 12
`
`

`

`5,768,691
`
`4
`port. The first switch further has a second switching state for
`coupling the output port of the transmitter to the first antenna
`port through the second node of Ll. In the first switching
`state of the first switch the second node of Ll is open-
`5 circuited. Also included is a second switch that is operated
`in phase with the first switch. and that has a first switching
`state for coupling the output port of the transmitter to the
`second antenna port. The second switch further has a second
`switching state for coupling the input port of the receiver to
`10 the second antenna port through the second node of U. In
`the first switching state of the second switch the second node
`of L2 is open-circuited. In this embodiment there is only one
`switch in series between one of the antenna ports and the
`input of the receiver or the output of the transmitter. The
`lengths of the transmission lines are as follows: Ll=Al2 for
`the second frequency band (transmit band) and L2=Al2 for
`the first frequency band (receive band).
`Also disclosed is an antenna switching arrangement for a
`dual band phone that eliminates a requirement for duplexers,
`while enabling individual ones of four switches to be
`separately optimized for their intended function (transit or
`receive) and also frequency band.
`
`20
`
`25
`
`3
`to an input/output port of the second transceiver. A second
`node of L2 is switchably coupled to the first antenna port and
`a second node of L3 is switchably coupled to the second
`antenna port. The switching is accomplished such that when
`the second node of Ll is coupled to the first antenna port, the
`second node of both L2 and 1A is open circuited and the
`second node of L3 is coupled to the second antenna port.
`When the second node of L2 is coupled to the first antenna
`port, the second node of both Ll and L3 is open circuited
`and the second node of 1A is coupled to the second antenna
`port.
`The lengths of the transmission lines are as follows
`Ll=L4=Al2 for the first frequency band; and L2=L3=Al2 for
`the second frequency band.
`The first frequency band can include a frequency of about 15
`800 MHz, for example the first transceiver may be used for
`duplex FM analog signals, and the second frequency band
`can include a frequency of about 1900 MHz, and may be
`used for TDMA. phase modulated signals.
`In a further embodiment of this invention a first pair of
`transmission lines (Ll and L2) each has a first node coupled
`to the first antenna port. a second node of Ll is switchably
`coupled to the input/output port of the first transceiver, and
`a second node of L2 is switchably coupled to the input/
`output node of the second transceiver. A second pair of
`transmission lines (L3 and IA) each has a first node coupled
`to the second antenna port. a second node of L3 is switch(cid:173)
`ably coupled to the input/output port of the first transceiver.
`and a second node of IA is switchably coupled to the 30
`input/output node of the second transceiver. In this
`embodiment. when the second node of Ll is coupled to the
`input/output port of the first transceiver, the second node of
`both L2 and L3 is open circuited and the second node of IA
`is coupled to the input/output port of the second transceiver.
`When the second node of L2 is coupled to the input/output
`port of the second transceiver, the second node of both Ll
`and IA is open circuited and the second node of L3 is
`coupled to the input/output port of the first transceiver.
`For this embodiment the lengths of the transmission lines 40
`are as follows: L2=L4=A/2 for the first frequency band, and
`Ll=L3=Al2 for the second frequency band, such that the
`transmission line that is left open-ended has a length of )J2
`for the frequency band in use.
`Further in accordance with this embodiment the second 45
`node of Ll and the second node of L3 are coupled through
`a first switch to the input/output port of the first transceiver.
`and the second node of L2 and the second node of IA are
`coupled through a second switch to the input/output port of
`the second transceiver. In this case the first switch is selected 50
`to minimize an insertion loss for frequencies within the first
`frequency band, and the second switch is selected to mini(cid:173)
`mize an insertion loss for frequencies within the second
`frequency band.
`In a still further embodiment of this invention there is 55
`disclosed antenna switching circuitry for use in a radio
`telephone of a type that includes a transmitter operable in a
`first frequency band when transmitting and a receiver oper(cid:173)
`able in a second frequency band when receiving. The radio
`telephone further includes a first antenna port and a second 60
`antenna port. In this embodiment the antenna switching
`circuitry includes a pair of transmission lines (Ll and L2)
`each having a first node and a second node. A first node of
`L2 is coupled to an input port of the receiver and ·a first node
`of Ll is coupled to an output port of the transmitter. Also 65
`included is a first switch having a first switching state for
`coupling the input port of the receiver to the first antenna
`
`35
`
`BRIEF DESCRIPI1ON OF THE DRAWINGS
`The above set forth and other features of the invention are
`made more apparent in the ensuing Detailed Description of
`the Invention when read in conjunction with the attached
`Drawings. wherein:
`FIG. 1 is block diagram that illustrates a portion of a
`conventional dual band mobile phone;
`FIG. 2 is a simplified schematic diagram of a conventional
`receiver front end and transmitter power amplifier that are
`coupled to an antenna through a duplexer;
`FIG. 3 is a simplified schematic diagram of a portion of
`a conventional dual band mobile phone that includes two
`receiver front ends, transmitter power amplifiers. and
`duplexers that are coupled to an antenna through an antenna
`switch;
`FIG. 4 illustrates a conventional arrangement for coupling
`the circuitry of FIG. 3 to one of two antennas;
`FIG. 5 illustrates a first embodiment of this invention that
`eliminates the antenna switch of FIG. 4 through the use of
`a single. dual band antenna with two feed lines;
`FIG. 6 illustrates one of the preferred embodiments of this
`invention that employs impedance matching lengths of
`transmission line to couple the duplexers to two antenna
`switches;
`FIG. 7 illustrates a presently preferred embodiment of this
`invention that also employs impedance matching lengths of
`transmission line;
`FIG. 8 illustrates a conventional circuit that can be
`employed in the embodiment of FIGS. 6 and 7 in place of
`the Band 2 (TDMA) duplexer;
`FIG. 9 illustrates a conventional arrangement for coupling
`to one of two antennas in a single band mobile phone;
`FIG. 10 illustrates a preferred embodiment of this inven(cid:173)
`tion for coupling to one of two antennas in a single band
`mobile phone. and that also employs the impedance match(cid:173)
`ing lengths of transmission line;
`FIGS. lla and llb illustrate a switching arrangement for
`a lower frequency band using the integral antenna for a
`receive slot and a transmit slot. respectively;
`FIGS. 12a and 12b illustrate a switching arrangement for
`the lower frequency band using the external antenna for the
`receive slot and the transmit slot, respectively;
`
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`5.768,691
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`5
`FIGS. 13a and 13b illustrate a switching arrangement for
`an upper frequency band using the integral antenna for the
`receive slot and the transmit slot, respectively; and
`FIGS. 14a and 14b illustrate a switching arrangement for
`the upper frequency band using the external antenna for the
`receive slot and the transmit slot, respectively.
`
`5
`
`20
`
`25
`
`6
`L2=L3=,J2 for the frequency of Band 2.
`By example, and assuming that the frequency of Band 1
`is 800 MHz and that the frequency of Band 2 is 1900 MHz.
`then the length of LI and I.A can be about 95 mm. and the
`length of L2 and L3 can be about 45 mm. In the presently
`preferred embodiment of the invention Ll-IA are electri(cid:173)
`cally conductive traces that are disposed on a printed circuit
`board dielectric substrate. The electrically conductive traces
`can be fabricated as meander lines, and their total lengths
`can be reduced through the use of lumped impedance
`elements to achieve the equivalent phase shift. With these
`dimensions the open end of the transmission lines reflects a
`high impedance at the duplex filter antenna ports PO and Pl.
`As illustrated in FIG. 6, if it is desired to use the Band 1
`circuitry with the antenna 1, or the Band 2 circuitry with the
`external antenna connector la. the lines L2 and I.A are open
`ended, and the signal path through switches 14 and 16 is to
`the antenna 1 for the Band 1 circuitry (through Ll) and to the
`external antenna connector la for the Band 2 circuitry
`(through L3). If it is desired instead to use the Band 1
`circuitry with the external antenna connector la. or the Band
`2 circuitry with the antenna 1. then the antenna switch
`control line is energized to place the moveable contact of
`both switches 14 and 16 to the lower position. In this case
`the lines LI and L3 are open ended. and the signal path
`through switches 14 and 16 is to the antenna 1 for the Band
`2 circuitry (through L2) and to the external antenna con(cid:173)
`nector la for the Band 1 circuitry (through I.A).
`FIG. 7 illustrates a presently preferred embodiment of this
`invention that also employs the impedance matching lengths
`of transmission line (LI-L4). However, in FIG. 7 the
`switches 14 and 16 are moved so as to be located between
`the lengths of transmission line and the duplexers 5 and 5'.
`In addition, and as is shown. the switches 14 and 16 are
`operated out of phase.
`The lengths of the transmission lines LI-L4 between the
`antenna ports and the switches in the embodiment of FIG. 7
`are as follows:
`L2=L4=,J2 for the frequency of Band I; and
`LI=L3=Al2 for the frequency of Band 2.
`As illustrated in FIG. 7, if it is desired to use the Band 1
`circuitry with the antenna 1. or the Band 2 circuitry with the
`external antenna connector la. the lines L2 and L3 are open
`ended, and the signal path through switches 14 and 16 is to
`the antenna 1 for the Band 1 circuitry (through LI) and to the
`external antenna connector la for the Band 2 circuitry
`(through L4). If it is desired instead to use the Band 1
`circuitry with the external antenna connector la. or the Band
`2 circuitry with the antenna 1. then the antenna switch
`control line is energized to place the moveable contact of
`switch 14 to the lower position and the moveable contact of
`switch 16 to the upper position. In this case the lines LI and
`I.A are open ended. and the signal path through switches 14
`and 16 is to the antenna 1 for the Band 2 circuitry (through
`L2) and to the external antenna connector la for the Band 1
`circuitry (through L3).
`It should be noted that, in the embodiment of FIG. 7, the
`switch 14 is only required to carry the frequency of the Band
`1 signal, while the switch 16 is only required to carry the
`frequency of the Band 2 signal. For the example where the
`Band 1 frequency is about 800 MHz and the Band 2
`frequency is about 1900 MHz, it can be appreciated that the
`switches 14 and 16 can be separately optimized for their
`respective frequency bands. That is. a single switch that is
`selected for a minimum insertion loss at 800 MHz may
`exhibit a higher loss at 1900 MHz. The embodiment of FIG.
`7 avoids this potential problem by enabling both switches to
`
`DEfAil..ED DESCRIPTION OF THE
`INVENTION
`FIG. 5 illustrates a first embodiment of this invention that 10
`eliminates the antenna switch of FIG. 3 through the use of
`a single, dual band antenna 12. In the embodiment of FIG.
`5 there are two feedlines, preferably each having an imped(cid:173)
`ance of 50 ohms. A first feedline 12a connects the Band 1
`f 15
`( e.g .• 800 MHz analog) duplexer 5 to a first element 12b o
`the dual band antenna 12. A second feedline 12c connects
`the Band 2 (e.g .• 1.9 GHz TDMA) duplexer 5' to a second
`element 12d of the dual band antenna 12. The elements 12b
`and 12d are each electrically optimized for operation in their
`respective bands, and may be disposed on a common
`antenna substrate or core and separated by a suitable dielec(cid:173)
`tric material. The antenna elements 12b and 12d are so
`implemented that the electrical isolation between them is
`sufficiently high to prevent loading between the antenna
`ports of the dual band RF sections.
`This embodiment eliminates the insertion loss due to the
`use of band or antenna switches, and thus also eliminates the
`need to compensate for the insertion loss with a higher
`transmitter power. Furthermore, since antenna band switch-
`ing is accomplished without mechanical or electrical delays.
`it is well suited for use in applications where fast hand-offs
`between bands are required. Also. no antenna switching
`control signals need to be generated or routed, no additional
`printed circuit board area is required to implement the
`antenna band switching function. and no spurious responses
`are generated. since there are no nonlinear components
`involved. Also. the high degree of isolation between elec(cid:173)
`trical antennas that can be achieved makes possible the use
`of conventional duplex or band filters in the antenna circuits
`on both bands. Also, the receiver sensitivity is improved
`since the absence of the switch insertion loss does not
`degrade the receiver noise figure.
`FIG. 6 illustrates one of the presently preferred embodi(cid:173)
`ments of this invention that employs lengths of transmission 45
`line (LI-I.A) to couple the duplexers 5 and 5' to two antenna
`switches 14 and 16. The embodiment of FIG. 6 thus over(cid:173)
`comes the problems associated with the conventional
`approach shown in FIG. 4 for connecting to two different
`antennas, such as the integral antenna 1 and the external 50
`antenna connector la. Although the embodiment of FIG. 6
`employs the two electronic switches 14 and 16 ( or mechani-
`cal switches if so desired), there is only one switch in the RF
`signal path. As such. the insertion loss is not doubled as in
`the case of FIG. 4. The antenna 1 and the external antenna 55
`that is connected to the antenna connector la are assumed to
`be two-band antennas each having a single feedline. An
`external booster amplifier can also be coupled to the external
`antenna connector la if so desired.
`When the antenna 1 is in use the unused band circuitry is 60
`always coupled to the external antenna connector la. If
`external antenna connector la is in use, then the unused
`band circuitry is always coupled to antenna 1. Preferably, the
`antenna impedance for both bands is 50 ohms. The lengths
`of the transmission lines Ll-L4 from the duplex filters 5 and 65
`5' to the antenna switches 14 and 16 are as follows:
`Ll=L4=Al2 for the frequency of Band I; and
`
`30
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`40
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`5,768,691
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`10
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`7
`be separately specified for their respective frequency bands.
`As such. for many applications the embodiment of f1G. 7
`may be preferred over the embodiment of FIG. 6.
`The presently preferred embodiment of this is not limited
`for use only with a FM/fDMA phase modulated (AMPS/
`IDMA) dual band mobile phone. but can be used as well
`with, by example. an AMPS/CDMA mobile phone. as well
`as with an AMPS/NAMPS/CDMA mobile phone.
`Furthermore, and referring to f1G. 10, the teaching of this
`invention applies as well to single band mobile phones, such
`as digital (e.g., TDMA) mobile phones that transmit at one
`time in one band of frequencies and that receive at another
`time in another band of frequencies. In FIG. 10 only one
`control signal is employed as compared to the embodiment
`of FIG. 9. and the lengths of transmission line Ll and L2 are
`connected as shown. When operating with the integral
`antenna 1 the antenna switches 10 and 11 are operated in
`phase to couple the integral antenna 1 to the receiver 6
`through switch 10 when receiving (the illustrated position)
`and to couple the integral antenna 1 to the transmitter 9.
`through switch 10 and LI, when transmitting. The unused
`transmitter is coupled to the external antenna coupler la
`through switch 11 when receiving. and the unused receiver
`is coupled to the external antenna coupler la through switch
`11 and L2 when transmitting. When operating with the
`external antenna the polarity of the control signal is
`reversed, the receiver or transmitter in use is coupled to the
`external antenna coupler la. and the unused receiver or
`transmitter is coupled to the integral antenna 1. In either case
`there is only one electronic switch in the receive or transmit 30
`path to the active antenna, and thus the insertion loss is about
`one half of the insertion loss of the embodiment of FIG. 9.
`The lengths of the transmission lines Ll and L2 from the
`filters 5a and Sb in the embodiment of f1G. 10 are as
`follows:
`Ll='Al2 for the transmit band of frequencies; and
`L2=Al2 for the receive band of frequencies.
`As is illustrated in FIG. 8 for the case where. by example.
`the Band 2 is a TDMA band, the duplexer 5' can be replaced
`with a TR switch 18. a receive filter 20, and a transmit filter
`22. The TR switch 18 is controlled with a TX/RX signal for
`setting the switch to either couple the receiver front end or
`the transmitter power amplifier output to the node Pl. Such
`an arrangement is known in the prior art. and can be used to
`replace a conventional duplex filter in a TDMA mobile
`phone. Since the filtering requirements for the TX and RX
`band filters in TDMA mobile phones are not as stringent as
`in the case analog mode mobile phones. it is possible to
`achieve an adequate level of performance with this arrange(cid:173)
`ment This circuit can replace the duplex filter S' in FIGS. 3.
`4, 5. 6 and 7. If Band 1 is also a TDMA-only band. then the
`duplex filter 5 in the above mentioned Figures can also be
`replaced with this circuit.
`Reference is now made to f1GS. lla. llb. 12a, l2b, 13a.
`13b. 14a and 14b for illustrating. in accordance with a
`further embodiment of this invention. preferred antenna
`switching circuitry for a dual band TDMA-based digital
`cellular phone. It should be noted that the same concepts
`may be used also in a single band mobile phones. although
`the advantages are not as great
`In f1GS. 11-14 the following nomenclature is used:
`lRx=lower band r