Patent Publication Number: US-2004053582-A1

Title: Portable radio device having antenna switching function

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to portable radio apparatus having a plurality of antennas and in particular to a technology for switching between transmitting antennas.  
       [0003] 2. Description of the Related Art  
       [0004] A receive signal received by a cell phone  1  as a mobile telecommunication terminal has a variety of transmission paths depending on the reflection of radio waves on the landforms and buildings or other structures. This causes the phenomenon called fading that the phase and amplitude of a receive signal varies due to interference with the receive signal. The cell phone  1  employs diversity reception in order to assure stable reception against the influence of fading.  
       [0005] The diversity reception uses for example two antennas, a main antenna and a sub antenna and secures the stability of radio wave reception by detecting a receiving field strength of each antenna and selecting the antenna having the greater receiving field strength as a receiving antenna.  
       [0006] The cell phone  1  has, for example, an antenna configuration shown in FIGS. 17A and 17B. FIGS. 17A and 17B are explanatory drawings of the antenna arrangement of a related art cell phone. FIG. 17A is a front view of the antenna arrangement. FIG. 17B is a side view of the antenna arrangement.  
       [0007] The cell phone  1  has a whip antenna as a main antenna  2  that may be mounted on the cell phone  1  and located in the upper area of the cell phone  1  and a plane antenna  3  build into the cell phone  1  as a sub antenna.  
       [0008] The whip antenna  2  comprises a helical section  2   a  and a monopole antenna  2   b  and is used as a transmitting/receiving antenna. The plane antenna  3  is for example an inverted-F antenna and is used as a receiving-only antenna. Both antennas are connected to a printed circuit (not shown) built into the cell phone  1  and power is fed to these antennas.  
       [0009] With the aforementioned configuration, when the cell phone  1  receives radio waves, the diversity reception procedure switches between the whip antenna  1  and the plane antenna  3 . When the phone  1  transmits radio waves, a send signal is transmitted from the whip antenna as a transmitting/receiving antenna.  
       [0010] Thus, transmission by the cell phone  1  is performed only via the whip antenna  2 . The transmitting quality solely depends on the whip antenna  2 .  
       [0011] Degradation of the transmitting quality of the whip antenna  2  directly leads to the degradation of the transmitting quality of the cell phone  1 .  
       [0012] Causes of the degradation of the whip antenna  2  includes for example a case where the radiation of a send signal by the whip antenna  2  is hindered by some obstacle around the whip antenna  2 .  
       [0013] Recent reduction in size of the cell phone  1  and the arrangement of the whip antenna  2  on the cell phone  1  have enhanced the possibility that part of a human body, for example the hand of a user comes in contact with the whip antenna  2 . In case part of a human body comes in contact with the whip antenna  2 , the impedance of the whip antenna  2  varies thus preventing radiation of a send signal at a predetermined power.  
       [0014] Contact with a human body is one of the causes of degradation of transmitting quality of the whip antenna  2 .  
       [0015] The invention has been proposed in view of such a situation and aims at providing portable radio apparatus that keeps good transmitting quality.  
       SUMMARY OF THE INVENTION  
       [0016] A portable radio apparatus for attaining the object is portable radio apparatus of a time division multiple access system having a plurality of antennas characterized in that the apparatus comprises  
       [0017] an antenna selector for selecting a transmitting antenna used for transmission from among the plurality of antennas on a per transmitting slot basis and  
       [0018] a switching transmitter for switching between the transmitting antennas on a per transmitting slot basis and outputting a send signal to the transmitting antenna.  
       [0019] According to the portable radio apparatus of the invention, it is possible to switch between transmitting antennas to output a send signal. Thus it is possible to keep a better transmitting quality than when only a single transmitting antenna is used.  
       [0020] Also, switching between transmitting antennas is possible on a per transmitting slot basis thus allowing faster switching between transmitting antennas.  
       [0021] The portable radio apparatus of the invention is characterized in that the each antenna is a transmitting/receiving antenna capable of radio wave transmission/reception and that  
       [0022] the antenna selector selects as the transmitting antenna a receiving antenna determined by the space diversity at radio wave reception.  
       [0023] According to the portable radio apparatus, it is highly possible that an antenna having a better receiving quality has a good transmitting quality in the next transmitting slot. So it is possible to keep the transmitting quality better.  
       [0024] Switching between transmitting antennas is made by selecting an antenna determined by the space diversity at reception on a per transmitting slot basis. This assures quick adaptive switchover to an antenna having a good transmitting quality.  
       [0025] The portable radio apparatus of the invention is characterized in that the antennas include a transmitting/receiving antenna capable of radio wave transmission/reception, a receiving-only antenna capable of radio wave reception only, and a transmitting-only antenna capable of radio wave transmission only, and that  
       [0026] the antenna selector selects as the transmitting antenna another antenna corresponding to the receiving-only antenna capable of radio wave transmission, in case the receiving antenna determined by the space diversity at radio wave reception is the receiving-only antenna.  
       [0027] According to the portable radio apparatus, in case the receiving antenna is a receiving-only antenna, an antenna corresponding to the receiving-only antenna is selected as a transmitting antenna. This allows switching between transmitting antennas.  
       [0028] The portable radio apparatus of the invention is characterized in that the each antenna is a transmitting/receiving antenna capable of radio wave transmission/reception and that  
       [0029] the antenna selector detects the reflected wave of a send signal on at least one antenna of the plurality of antennas by using a directional coupler and selects the transmitting antenna in accordance with the magnitude of the reflected wave detected.  
       [0030] According to the portable radio apparatus, a transmitting antenna is selected in accordance with the magnitude of the reflected wave of a send signal detected by a directional coupler. Thus it is possible to use the reflected wave to detect that an obstacle or human body is in contact with the antenna and select a transmitting antenna having a good transmitting quality based on the magnitude of the reflected wave.  
       [0031] The portable radio apparatus of the invention is characterized in that the antennas include a transmitting/receiving antenna capable of radio wave transmission/reception and a receiving-only antenna capable of radio wave reception only and that  
       [0032] the antenna selector detects the reflected wave of a send signal on at least one antenna of the plurality of antennas by using a directional coupler and selects the transmitting antenna in accordance with the magnitude of the reflected wave detected.  
       [0033] According to the portable radio apparatus, a transmitting antenna is selected in accordance with the magnitude of the reflected wave of a send signal detected by a directional coupler. Thus it is possible to use the reflected wave to detect that an obstacle or human body is in contact with the antenna and select a transmitting antenna having a good transmitting quality based on the magnitude of the reflected wave.  
       [0034] The portable radio apparatus of the invention is characterized in that the switching transmitter has a signal transmitter and an antenna switching section, that  
       [0035] the signal transmitter outputs the send signal to the antenna switching section, and that  
       [0036] the antenna switching section switches the send signal from the signal transmitter to the transmitting antenna based on the selection result of the antenna selector.  
       [0037] According to the portable radio apparatus, it is possible to selectively output a send signal from a signal transmitter to a transmitting antenna by using an antenna switching section.  
       [0038] The portable radio apparatus of the invention is characterized in that the switching transmitter has a signal transmitter and an antenna switching section, that  
       [0039] the signal transmitter has a plurality of output ports for outputting the send signal, directly connects a first output port as the at least one output port out of the plurality of output ports to the antenna capable of radio wave transmission, and connects a second output port as the at least one output port out of the antenna switching section, that  
       [0040] in case the selection result of the antenna selector is the antenna directly connected to the first output port, the signal transmitter outputs the send signal from the first output port, and that  
       [0041] in case the selection result of the antenna selector is the antenna connectable to the second output port by alternating the antenna switching section, the signal transmitter outputs the send signal from the second output port and the antenna switching section switches to the transmit antenna selected by the antenna selector.  
       [0042] According to the portable radio apparatus, there is no switching sections between a first output port and an antenna connected to the first output port so that a send signal output from a first output port is not subject to a transmission loss caused by a contact.  
       [0043] A send signal output from a second output port can be switched to a transmitting antenna by an antenna switching section.  
       [0044] The portable radio apparatus of the invention is characterized in that the plurality of antennas include a whip antenna as a transmitting/receiving antenna provided on the portable radio apparatus so that the whip antenna is capable of being accommodated in the portable radio apparatus and a monopole antenna as a transmitting/receiving antenna built into a housing of the portable radio apparatus.  
       [0045] According to the portable radio apparatus, a whip antenna and a monopole antenna are provided as transmitting/receiving antennas so that either antenna can be used as a transmitting antenna.  
       [0046] The portable radio apparatus of the invention is portable radio apparatus having a plurality of antennas, comprising an antenna selector for selecting a transmitting antenna used for transmission from among the plurality of antennas and  
       [0047] a switching transmitter for switching between the transmitting antennas and outputting a send signal to the transmitting antenna based on the selection result of the antenna selector, characterized in that  
       [0048] the plurality of antennas include a whip antenna as a transmitting/receiving antenna provided on the portable radio apparatus so that the whip antenna is capable of being accommodated in the portable radio apparatus and a monopole antenna as a transmitting/receiving antenna built into the housing of the portable radio apparatus.  
       [0049] According to the portable radio apparatus, it is possible to switch between transmitting antennas to output a send signal. Thus it is possible to keep the transmitting quality better than when only a single transmitting antenna is used.  
       [0050] Further, a whip antenna and a monopole antenna are provided as transmitting/receiving antennas so that either antenna can be used as a transmitting antenna.  
       [0051] The portable radio apparatus of the invention is characterized in that the monopole antenna is in an approximate L shape having one knee and that the knee is located away from the whip antenna.  
       [0052] According to the portable radio apparatus, a monopole antenna is an inverted-L antenna in an L shape so that the pole length can be increased within a housing.  
       [0053] The knee is located away from the whip antenna. This reduces mutual interference between antennas.  
       [0054] The portable radio apparatus of the invention is portable radio apparatus comprising two housings which can be folded via a hinge, characterized in that  
       [0055] the whip antenna and the monopole antenna are provided in the housings separate from each other.  
       [0056] According to the portable radio apparatus, antennas are provided in separate housings thus reducing mutual interference between antennas. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0057]FIG. 1 is a circuit block diagram of portable radio apparatus in a first embodiment;  
     [0058]FIGS. 2A and 2B show antenna arrangements of portable radio apparatus; FIG. 2A shows an antenna arrangement of portable radio apparatus in the first embodiment; FIG. 2B shows an antenna arrangement of portable radio apparatus in the second embodiment;  
     [0059]FIGS. 3A to  3 E are explanatory drawings of a monopole antenna; FIG. 3A is a front view of a transmitting/receiving antenna; FIG. 3B is a side view of the transmitting/receiving antenna; FIG. 3C is an enlarged front view of a power feeding section; FIG. 3D is an enlarged side view of a power feeding section; FIG. 3E is a sectional drawing of Section A of a power feeding section;  
     [0060]FIG. 4 is a timing chart of portable radio apparatus;  
     [0061]FIG. 5 is a table showing the transmitting antenna gain improvement ratio of portable radio apparatus per grasp state at a first transmitting frequency;  
     [0062]FIGS. 6A to  6 F is an explanatory drawing of a grasp state of portable radio apparatus; FIG. 6A is an explanatory drawing showing a grasp state- 1 ; FIG. 6B is an explanatory drawing showing a grasp state- 2 ; FIG. 6C is an explanatory drawing showing a grasp state- 3 ; FIG. 6D is an explanatory drawing showing a grasp state- 4 ; FIG. 6F is an explanatory drawing showing a grasp state- 6 ;  
     [0063]FIG. 7 is a table showing the transmitting antenna gain improvement ratio of portable radio apparatus per grasp state at a second transmitting frequency;  
     [0064]FIG. 8 is a circuit block diagram of portable radio apparatus in a second embodiment;  
     [0065]FIG. 9 is a circuit block diagram of portable radio apparatus in a third embodiment;  
     [0066]FIG. 10 is a block diagram of a reflected wave detector;  
     [0067]FIG. 11 is a timing chart of portable radio apparatus;  
     [0068]FIG. 12 is a block diagram showing the configuration of portable radio apparatus in the fourth embodiment;  
     [0069]FIG. 13 is a block diagram showing the configuration of portable radio apparatus in the fifth embodiment;  
     [0070]FIG. 14 is a block diagram showing the configuration of portable radio apparatus in the sixth embodiment;  
     [0071]FIG. 15 is a block diagram showing the configuration of portable radio apparatus in the seventh embodiment;  
     [0072]FIG. 16 is a block diagram showing the configuration of portable radio apparatus in the eighth embodiment;  
     [0073]FIGS. 17A and 17B explain an antenna arrangement of a related art cell phone; FIG. 17A is a front view thereof; FIG. 17B is a side view thereof. 
    
    
     [0074] In the drawings, a numeral  10  represents portable radio apparatus,  10   a  an upper housing,  10   b  a lower housing,  10   c  a hinge,  12  a transmitting/receiving antenna,  13  a receiving-only antenna,  14  a transmitting/receiving antenna,  14   a  a knee,  14   b  an antenna slope section,  14   c  an antenna end,  14   c   1  a protrusion,  15  a receiving-only antenna,  16  a space diversity,  18  a controller,  20  a logic circuit,  20   a  an inverter,  20   b  and AND circuit,  22  a signal transmitter,  24  an antenna switching section,  26  an external output terminal,  36  a directional coupler,  38  a reflected wave detector,  38   a  a detection holder,  38   b  a comparator,  38   c  a reference voltage section, Rx a receiving slot, Tx a transmitting slot, BRNC a determination result, ANTDT a reflected wave detecting signal, TxPo a power on signal, SUB 1  a switching signal, and SUB 2  is a switching signal.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0075] The portable radio apparatus of the invention will be described referring to the following drawings.  
     [0076] [First Embodiment] 
     [0077]FIG. 1 is a circuit block diagram of portable radio apparatus in this embodiment. FIGS. 2A and 2B show antenna arrangements of the portable radio apparatus. FIGS. 3A to  3 E are explanatory drawings of a monopole antenna.  
     [0078] The portable radio apparatus  10  of the embodiment comprises units including transmitting/receiving antennas  12 ,  14 , a space diversity  16 , a controller  18  and a logic circuit  20  as an antenna selector, a signal transmitter  22  and an antenna switching section  24  as a switching transmitter, and an external output terminal  26 .  
     [0079] Each unit of the portable radio apparatus.  10  will be detailed.  
     [0080] The transmitting/receiving antennas  12 ,  14  are transmitting/receiving antennas commonly available for transmission and reception. Both antennas are also connected to a receiver (not shown). FIGS. 2A and 2B show examples of antenna arrangement of the transmitting/receiving antennas  12  and  14  in the portable radio apparatus  10 .  
     [0081] The portable radio apparatus  10  in the first embodiment shown in FIG. 2A comprises an upper housing  10   a  and a lower housing  10   b  rotatably coupled via a hinge  10   c  and can be folded.  
     [0082] The transmitting/receiving antenna  12  is a whip antenna mountably provided on the head of the upper housing  10   a.  FIG. 2A shows the state where the transmitting/receiving antenna  12  is housed.  
     [0083] The transmitting/receiving antenna  14  is built into the upper housing  10   a  and its antenna shape is an approximate L shape having one knee  14   a.    
     [0084] The portable radio apparatus  10  in another embodiment or in the second embodiment shown in FIG. 2B is foldable the same as the portable radio apparatus in FIG. 2A. The transmitting/receiving antenna  14  in an approximate L shape is built into the upper housing  10   a.  The transmitting/receiving antenna  12  is a whip antenna provided mountably on the side face of the lower housing  10   b.    
     [0085] The knee  14   a  of the transmitting/receiving antenna  14  each of both portable radio apparatus is located away from the transmitting/receiving antenna  12 .  
     [0086] The shape and configuration of the transmitting/receiving antenna  14  will b described referring to FIGS. 3A to  3 E.  
     [0087]FIG. 3A is a front view of a transmitting/receiving antenna  14 . FIG. 3B is a side view of the transmitting/receiving antenna  14 . FIG. 3C is an enlarged front view of a power feeding section. FIG. 3D is an enlarged side view of a power feeding section. FIG. 3E is a sectional drawing of Section A of a power feeding section.  
     [0088] The transmitting/receiving antenna  14  is a copper foil tape having an approximate constant width and has the knee  14   a,  an antenna slope section  14   b,  and an antenna end  14   c.  The antenna section  14   a  serves as an antenna power feeding section of an antenna and comes in contact with a contact on a printed circuit built into the upper housing  10   a.  The antenna slope section  14   b  is provided to energize the antenna end  14   c  in the direction of the contact when the antenna end  14   c  comes in contact with this contact so as to enhance the contact pressure with the contact thus ensuring contact continuity.  
     [0089] As shown in FIG. 3C and D, the antenna end  14   c  provides a protrusion  14   c   1  of an approximate semispherical shape on the contact face with the contact. The protrusion  14   c   1  comprises, as shown in FIG. 3E, a silicone sponge, a silicone adhesive, a base material (copper foil), and acrylic adhesive. The contact and the copper foil as a base material are electrically continuous via a silicone sponge and a silicone adhesive.  
     [0090] While the transmitting/receiving antenna  14  is composed of a copper foil tape in the above example, in case a flexible printed circuit is present in the housing  10   a,  an antenna element may be formed on the flexible printed circuit and used as a transmitting/receiving antenna  14 .  
     [0091] The space diversity  16  determines the receiving antenna used for a receiving slot based on the receiving field strength of a receive signal received by the transmitting/receiving antenna  12 ,  14  and outputs the receiving antenna determination result BRNC to the controller  18 .  
     [0092] The controller  18  outputs a control signal to a logic circuit  20  in the subsequent stage on input of the determination result BRNC of the receiving antenna output from the space diversity  16 .  
     [0093] The logic circuit  20 , on input of a control signal from the controller  18 , outputs switching signals SUB 1 , SUB 2  for selecting a transmitting antenna to the antenna switching section  24 . The inside of the logic circuit  20  comprises, for example, an inverter  20   a  and an AND circuit  20   b.  Another logic circuit may be used as long as it can output switching signals SUB 1 , SUB 2 . Or, a single is switching signal output may be used to allow instruction on antenna switching to the antenna switching section  24 .  
     [0094] The signal transmitter  22  is a unit for outputting a send signal per transmit slot based on a power on signal TxPo from the controller  18 . The send signal is output to an antenna switching section  24  in the subsequent stage from the output port ANT.  
     [0095] The antenna switching section  24  is a selector switch for selecting a transmitting antenna for outputting a send signal from the output port ANT of the signal transmitter  22  based on the switching signals SUB 1 , SUB 2  from the logic circuit  20 .  
     [0096] The external output terminal  26  is an output terminal for connecting an output signal from the output port EXT to external apparatus (not shown).  
     [0097] This is the end of the explanation on the configuration of the portable radio apparatus  10 .  
     [0098] Next, operation of the portable radio apparatus  10  of the aforementioned configuration will be described referring to FIG. 4. FIG. 4 is a timing chart of portable radio apparatus.  
     [0099] The uppermost slot in the timing chart chronologically shows the timing of a transmitting/receiving antenna slot of a time division multiple access system. The time division multiple access systems include an FDD (Frequency Division Duplex) system where radio wave reception and transmission is made by way of time division and telecommunication frequency differs between reception and transmission, and a TDD (Time Division Duplex) system where the same telecommunication frequency is used for reception and transmission. The invention is applicable to both systems.  
     [0100] Just before the receiving slot Rx is a determination period for the space diversity  16  to determine a receiving antenna. In this determination period, the receiving antenna determination result BRNC is output to the controller  18 . In this embodiment, in case the determination result remains Low (hereinafter abbreviated as L) in a receiving slot Rx from the end of the determination period to next determination period, the transmitting/receiving antenna  12  is selected as a receiving antenna. In case the determination result remains High (hereinafter abbreviated as H), the transmitting/receiving antenna  14  is selected as a receiving antenna.  
     [0101] The period from the receiving slot Rx to next transmitting slot Tx is an idle slot as a transmitting/receiving period irrelevant to channels of the portable radio apparatus  10 .  
     [0102] In the transmitting slot Tx, the signal transmitter  22  is powered when the power on signal TxPo from the controller  18  goes “H” and outputs a send signal from an is output port ANT to an antenna switching section  24 .  
     [0103] At the same time, in case the determination result BRNC is “L”, the controller  18  outputs a control signal so that the switching signal SUB 1  from the logic circuit  20  will be driven “L” and the switching signal SUB 2  will be driven “H”. In case the determination result BRNC is “H”, the controller  18  outputs a control signal so that the switching signal SUB 1  from the logic circuit  20  will be driven “H” and the switching signal SUB 2  will be driven “L”.  
     [0104] The antenna switching section  24 , in case the switching signal SUB 1  from the logic circuit  20  is “L” and the switching signal SUB 2  is “H”, selects a transmitting/receiving antenna  12  as a transmitting antenna (solid line in the antenna switching section  24 ). In case the switching signal SUB 1  from the logic circuit  20  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  24  selects a transmitting/receiving antenna  14  as a transmitting antenna (dotted line in the antenna switching section  24 ).  
     [0105] operation of transmission antenna switching is described referring to the timing chart.  
     [0106] In a receiving slot Rx 1 , the determination result BRNC of the space diversity  16  is “L” so that a transmitting/receiving antenna  12  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 1  is reached, the signal transmitter  22  is powered by way of a power on signal TxPo. In this practice, the switching signal SUB 1  from the logic circuit  20  is “L” and the switching signal SUB 2  is “H” so that the antenna switching section  24  selects a transmitting/receiving antenna  12  as a transmitting antenna.  
     [0107] In the receiving slot Rx 2 , the determination result BRNC of the space diversity  16  is “H” so that a transmitting/receiving antenna  14  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  22  is powered by way of a power on signal TxPo. At the same time, the switching signal SUB 1  from the logic circuit  22  goes “H” and the switching signal SUB 2  goes “L”. Thus the antenna switching section  24  selects a transmitting/receiving antenna  14  as a transmitting antenna.  
     [0108] In the embodiment, a transmitting/receiving antenna selected as a receiving antenna by the space diversity in a receiving slot is selected as a transmitting antenna in a transmitting slot.  
     [0109] It is highly possible that a transmitting/receiving antenna with good receiving quality has a good transmitting in transmission of next transmission slot. Such a transmitting/receiving antenna can keep a better transmitting quality.  
     [0110] Improvement of the transmitting antenna gain per grasp state assumed when the transmitting/receiving antenna  14  of the portable radio apparatus  10  in this embodiment is used as a transmitting antenna will be described referring to FIGS. 5 through 7.  
     [0111]FIG. 5 is a table showing the transmitting antenna gain improvement ratio of portable radio apparatus per grasp state at a first transmitting frequency. FIGS. 6A to  6 F are explanatory drawings of a grasp state of portable radio apparatus. FIG. 7 is a table showing the transmitting antenna gain improvement ratio of portable radio apparatus per grasp state at a second transmitting frequency.  
     [0112] In the measurement of the transmitting antenna gain shown in FIG. 5, the transmitting frequency is 960 MHz (first transmitting frequency). A transmitting antenna as a reference for the transmission antenna gain improvement ratio is a transmitting/receiving antenna  12 . The transmitting/receiving antenna  12  is housed in the main unit while measurement is in progress.  
     [0113] Then, the transmitting/receiving antenna  14  built into the housing is selected and the transmitting antenna gain is compared between the transmitting/receiving antenna  14  and the transmitting/receiving antenna  12 .  
     [0114] The grasp state of portable radio apparatus in FIG. 5 will be described referring to FIGS. 6A to  6 F. Grasp state- 1  “Left hand grasp” shows a state where the user grasps portable radio apparatus  10  with his/her left hand and part of a human body such as a hand is not in contact with the transmitting/receiving antenna  12  and only the left hand is in contact with the main unit of the portable radio apparatus  10 , as shown in FIG. 6A.  
     [0115] Grasp state- 2  “Left hand helical thumb rest” shows a state where the portable radio apparatus  10  is grasped with the thumb of the left hand of the user being in contact with the transmitting/receiving antenna  12  (in details, helical antenna section of the whip antenna), as shown in FIG. 6B.  
     [0116] Grasp state- 3  “Left hand cheek touch” shows a state where the portable radio apparatus  10  is grasped without the fingers of the user&#39;s left hand do not come in contact with the transmitting/receiving antenna  12  while the cheek of a human body is in contact with the receiver side of the portable radio apparatus  10 , as shown in FIG. 6C.  
     [0117] Grasp state- 4  “Right hand helical index finger rest” shows a state where the portable radio apparatus  10  is grasped with the thumb of the left hand of the user being in contact with the transmitting/receiving antenna  12 , as shown in FIG. 6D.  
     [0118] Grasp state- 5  “Right hand cheek touch” shows a state where the portable radio apparatus  10  is grasped without the fingers of the user&#39;s right hand do not come in contact with the transmitting/receiving antenna  12  while the cheek of a human body is in contact with the receiver side of the portable radio apparatus  10 , as shown in FIG. 6E.  
     [0119] Grasp state- 6  “Right hand cheek touch + helical index finger rest” shows a state where the portable radio apparatus  10  is grasped so that the index finger of the user&#39;s right hand comes in contact with the transmitting/receiving antenna  12  while the cheek of a human body is in contact with the receiver side of the portable radio apparatus  10 , as shown in FIG. 6F.  
     [0120] As shown in FIG. 5, comparison of the gain of the transmitting/receiving antenna  14  with that of the transmitting/receiving antenna  12  on a per grasp state basis proved an improvement in the transmitting antenna gain by way of the transmitting/receiving antenna  14 , irrespective of the grasp state employed. In particular, in a case where a finger is placed on the transmitting/receiving antenna  12  and a case where the cheek of a human body is in contact with the receiver side of the portable radio apparatus  10 , a remarkable gain improvement of 14.7 to 22.9 percent is attained.  
     [0121] In a configuration where a transmitting antenna having a better transmitting antenna gain is selected, it is possible to maintain a good transmitting antenna gain by selecting the transmitting/receiving antenna  14  as a transmitting antenna, even when a finger is placed on the transmitting/receiving antenna  12  or when the cheek of a human body is in contact with the receiver side of the portable radio apparatus  10 .  
     [0122] Even in case the transmitting/receiving antenna  14  is a copper foil as described referring to FIGS. 3A to  3 E or in case an antenna element is formed on a flexible printed circuit, the transmitting antenna gain is improved.  
     [0123] Next, In the measurement of the transmitting antenna gain shown in FIG. 7, the transmitting frequency is 1441 MHz (second transmitting frequency). A transmitting antenna as a reference for the transmission antenna gain improvement ratio is a transmitting/receiving antenna  12 . The transmitting/receiving antenna  12  is housed in the main unit and switched to the transmitting/receiving antenna  12  housed in the housing to compare the transmitting antenna gain of the transmitting/receiving antenna  14  with that of the transmitting/receiving antenna  12 .  
     [0124] As shown in FIG. 7, comparison of the gain of the transmitting/receiving antenna  14  with that of the transmitting/receiving antenna  12  on a per grasp state basis proved an improvement in the transmitting antenna gain by way of the transmitting/receiving antenna  14 , in any grasp state other than the grasp state- 1 . In particular, in a case where a finger is placed on the transmitting/receiving antenna  12  and a case where the cheek of a human body is in contact with the receiver side of the portable radio apparatus  10 , a remarkable gain improvement of 19.8 to 39.6 percent is attained.  
     [0125] In a configuration where a transmitting antenna having a better transmitting antenna gain is selected, it is possible to maintain a good transmitting antenna gain by selecting the transmitting/receiving antenna  14  as a transmitting antenna, even when a finger is placed on the transmitting/receiving antenna  12  or when the cheek of a human body is in contact with the receiver side of the portable radio apparatus  10 .  
     [0126] Even in case the transmitting/receiving antenna  14  is a copper foil as described referring to FIGS. 3A to  3 E or in case an antenna element is formed on a flexible printed circuit, the transmitting antenna gain is improved as much as 1.5 to 17.7 percent, except for the grasp state- 1 .  
     [0127] [Second Embodiment] 
     [0128] Next, assume a case where a transmitting/receiving antenna capable of radio wave transmission/reception, a receiving-only antenna capable of radio wave reception only and a transmitting-only antenna capable of radio wave transmission only are included as antennas.  
     [0129]FIG. 8 is a circuit block diagram of portable radio apparatus in a second embodiment. The portable radio apparatus in this embodiment differs from the portable radio apparatus  10  in the first embodiment in that a receiving-only antenna  13  and a transmitting-only antenna are included as antennas. Either the receiving-only antenna  13  and the transmitting/receiving antenna  12  is determined as a receiving antenna by the space diversity  16 . Further, either the transmitting-only antenna  15  and the transmitting/receiving antenna  12  is selected as a transmitting antenna by the antenna switching section  24 .  
     [0130] Features of the other units are the same as those of the portable radio apparatus  10  in the first embodiment. Features and operation of this embodiment will be described.  
     [0131] In a determination period for the space diversity  16  to determine a receiving antenna, the receiving antenna determination result BRNC is output to the controller  18 . In this embodiment, in case the determination result BRNC remains “L” in a receiving slot Rx from the end of the determination period to next determination period, the transmitting/receiving antenna  12  is selected as a receiving antenna. In case the determination result BRNC remains “H”, the receiving-only antenna  13  is selected as a receiving antenna.  
     [0132] In the transmitting slot Tx, in case the switching signal SUB 1  from the logic circuit  20  is “L” and the switching signal SUB 2  is “H”, the antenna switching section  24  selects transmitting/receiving antenna  12  as a transmitting antenna (solid line in the antenna switching section  24 ). In case the switching signal SUB 1  from the logic circuit  20  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  24  selects a transmitting-only antenna  15  (dotted line in the antenna switching section  24 ) as a transmitting antenna. operation of transmission antenna switching will be described referring to the timing chart of FIG. 4.  
     [0133] In a receiving slot Rx 1 , the determination result BRNC of the space diversity  16  is “L” so that a transmitting/receiving antenna  12  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 1  is reached, the signal transmitter  22  is powered by way of a power on signal TxPo. In this practice, the switching signal SUB 1  from the logic circuit  20  is “L” and the switching signal SUB 2  is “H” so that the antenna switching section  24  selects a transmitting/receiving antenna  12  as a transmitting antenna.  
     [0134] In the receiving slot Rx 2 , the determination result BRNC of the space diversity  16  is “H” so that a receiving-only antenna  13  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  22  is powered by way of a power on signal TxPo. At the same time, the switching signal SUB 1  from the logic circuit  22  goes “H” and the switching signal SUB 2  goes “L”. Thus the antenna switching section  24  selects a transmitting-only antenna  15  as a transmitting antenna.  
     [0135] This, in case a transmitting/receiving antenna  12  is selected as a receiving antenna by the space diversity  16 , the transmitting/receiving antenna  12  is also selected as a transmitting antenna. In case a receiving-only antenna  13  is selected as a receiving antenna by the space diversity  16 , the transmitting-only antenna  15  corresponding to the receiving-only antenna is selected as a transmitting antenna.  
     [0136] In this embodiment, it is possible to select as a transmitting antenna an antenna capable of transmission corresponding to an antenna selected as a receiving antenna by the space diversity  16  in the receiving slot.  
     [0137] [Third Embodiment] 
     [0138]FIG. 9 is a circuit block diagram of portable radio apparatus in the third embodiment. FIG. 10 is a block diagram of a reflected wave detector. FIG. 11 is a timing chart of portable radio apparatus.  
     [0139] The portable radio apparatus  30  of this embodiment comprises units including transmitting/receiving antennas  32 ,  34 , a directional coupler  36 , a reflected wave detector  38 , a controller  40  and a logic circuit  41  as an antenna selector, a signal transmitter  44  and an antenna switching section  46  as a switching transmitter, and an external output terminal  48 .  
     [0140] Each unit of the portable radio apparatus  30  will be detailed.  
     [0141] The transmitting/receiving antennas  32 ,  34  are transmitting/receiving antennas commonly available for transmission and reception. Both antennas are also connected to a receiver (not shown). An example of antenna arrangement of transmitting/receiving antennas  32 ,  34  in the portable radio apparatus  30  is the same as the transmitting/receiving antennas  12  and  14  in FIGS. 2A and 2B referred to in the first embodiment. The shape and configuration of the transmitting/receiving antenna  34  are the same as those of the transmitting/receiving antenna  14  in FIGS. 3A to  3 E so that the corresponding description is omitted.  
     [0142] The directional coupler  36  can transmit to the transmitting/receiving antenna  32  with virtually no loss a send signal output from the signal transmitter  44  via the antenna switching section  46  described later. The directional coupler  36  outputs the reflected wave of a send signal irradiated from the transmitting/receiving antenna  32  to the reflected wave detector  38  in the subsequent stage.  
     [0143] For example, assume a case where part of a human body for example the hand comes in contact with (or in close proximity of) the transmitting/receiving antenna  32 . When the hand comes in contact with the transmitting/receiving antenna  32 , the impedance of the transmitting/receiving antenna  32  varies thus preventing radiation of a send signal at a predetermined power, and a reflected wave of the send signal is returned from the transmitting/receiving antenna  32 . Or, the power and amplitude of the reflected wave increases than when the hand is not in contact or not in close proximity.  
     [0144] The reflected wave (dotted line arrow in FIG. 9) is input to the directional coupler  36  in the opposite direction to the send signal (solid line arrow in FIG. 9) thus is output to the reflected wave detector  38  by the directional coupler  36 .  
     [0145] Next, the reflected wave detector  38  will be described referring to FIG. 10. The reflected wave detector  38  comprises a detection hold section  38   a,  a comparator  38   b  and a reference voltage section  38   c.  The detection hold section  38   a  detects a reflected wave output from the directional coupler  36  and holds the detected voltage Vdet of the reflected wave in the transmitting slot period. The comparator  38   b  compares the detected voltage Vdet of the reflected wave received from the detection hold section  38   a  with the reference voltage Vref received from the reference voltage section  38   c.  In case the detected voltage Vdet is greater than the reference voltage Vref, the reflected wave detecting signal ANTDT is output as an “H” signal. In case the detected voltage Vdet is smaller than the reference voltage Vref, the reflected wave detecting signal ANTDT is output as an “L” signal.  
     [0146] The controller  40  outputs a control signal to a logic circuit  42  in the subsequent stage on input of the reflected wave detecting signal ANTDT output from the reflected wave detector  38 .  
     [0147] The logic circuit  42 , on input of a control signal from the controller  40 , outputs switching signals SUB 1 , SUB 2  for selecting a transmitting antenna to the antenna switching section  46 . The inside of the logic circuit  42  S comprises, for example, an inverter  42   a  and an AND circuit  42   b.  Another logic circuit may be used as long as it can output switching signals SUB 1 , SUB 2 . Or, a single switching signal output may be used to allow instruction on antenna switching to the antenna switching section  46 .  
     [0148] The signal transmitter  44  is a unit for outputting a send signal per transmit slot based on a power on signal TxPo from the controller  40 . The send signal is output to an antenna switching section  46  in the subsequent stage from the output port ANT.  
     [0149] The antenna switching section  46  is a selector switch for selecting a transmitting antenna for outputting a send signal from the output port ANT of the signal transmitter  44  based on the switching signals SUB 1 , SUB 2  from the logic circuit  42 .  
     [0150] The external output terminal  48  is an output terminal for connecting an output signal from the output port EXT to external apparatus (not shown).  
     [0151] This is the end of the explanation on the configuration of the portable radio apparatus  30 .  
     [0152] Next, operation of the portable radio apparatus  30  of the aforementioned configuration will be described referring to FIG. 11. FIG. 11 is a timing chart of portable radio apparatus.  
     [0153] The uppermost slot in the timing chart chronologically shows the timing of a transmitting/receiving antenna slot of a time division multiple access system.  
     [0154] The period from the receiving slot Rx to next transmitting slot Tx is an idle slot as a transmitting/receiving period irrelevant to channels of the portable radio apparatus  30 .  
     [0155] In the transmitting slot Tx, the signal transmitter  44  is powered when the power on signal TxPo from the controller  40  goes “H” and outputs a send signal from an output port ANT to an antenna switching section  46 .  
     [0156] The antenna switching section  46 , in case the switching signal SUB 1  from the logic circuit  42  is “L” and the switching signal SUB 2  is “H”, selects a transmitting/receiving antenna  32  as a transmitting antenna (solid line in the antenna switching section  46 ). In case the switching signal SUB 1  from the logic circuit  42  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  46  selects a transmitting/receiving antenna  34  as a transmitting antenna (dotted line in the antenna switching section  46 ).  
     [0157] operation of transmission antenna switching is described referring to the timing chart.  
     [0158] When the receiving slot Rx 1  and the idle slot are passed and a transmitting slot Tx 1  is reached, the signal transmitter  44  is powered. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  38  is “L”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  32  is smaller than the reference voltage Vref, so that a control signal from the controller  40  drives the switching signal SUB 1  from the logic circuit  42  “L” and the switching signal SUB 2  “H”. The antenna switching section  46  selects a transmitting/receiving antenna  32  as a transmitting antenna.  
     [0159] In the receiving slot Rx 2 , the reflected wave detecting signal ANTDT goes “L”. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  44  is powered. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  38  is “H”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  32  is greater than the reference voltage Vref, so that a control signal from the controller  40  drives the switching signal SUB 1  from the logic circuit  42  “H” and the switching signal SUB 2  “L”. The antenna switching section  46  selects a transmitting/receiving antenna  34  as a transmitting antenna.  
     [0160] In case the reflected wave on the transmitting/receiving antenna  32  is output to the reflected wave detector  38  by the directional coupler  36  and the voltage Vdet detected by the reflected wave detector  38  is smaller than the reference voltage Vref, the transmitting/receiving antenna  32  is selected as a transmitting antenna. In case the detected voltage Vdet is greater than the reference voltage Vref, the transmitting/receiving antenna  34  is selected as a transmitting antenna.  
     [0161] In this embodiment, in case the reflected wave is smaller than a predetermined value, the transmitting/receiving antenna  32  is selected as a transmitting antenna. In case the reflected wave is greater than a predetermined value, it is assumed that part of a human body, for example the hand of a user has come in contact with (or in close proximity of) the transmitting/receiving antenna  32 , then the transmitting/receiving antenna  34  is selected as a transmitting antenna instead of the transmitting/receiving antenna  32 . This allows use of an antenna with a higher antenna gain as a transmitting antenna.  
     [0162] In this embodiment, even after the transmitting/receiving antenna  34  is selected as a transmitting antenna, it is possible to output a send signal from the transmitting/receiving antenna  32  each time a transmitting slot starts and detect the level of the reflected wave on the transmitting/receiving antenna  32  then switch between transmitting antennas. By doing so, it is possible to switch between transmitting antennas by using the reflected wave on the transmitting/receiving antenna  32  as a switching reference.  
     [0163] While a directional coupler is connected to only the transmitting/receiving antenna  32  in this embodiment, It is possible to connect a directional coupler to the transmitting/receiving antenna  34  also (connect a reflected detector as well) and compare the outputs of reflected waves from both directional couplers with each other. Or, it is possible to compare each reflected wave with each reference voltage thus determining switchover of a transmitting antenna in a comprehensive way.  
     [0164] [Fourth Embodiment] 
     [0165] The fourth embodiment of the invention will be described referring to FIG. 12.  
     [0166]FIG. 12 is a block diagram showing the configuration of portable radio apparatus in the fourth embodiment.  
     [0167] The portable radio apparatus in the fourth embodiment differs from the portable radio apparatus  30  in the third embodiment in that a receiving-only antenna  33  capable of radio wave reception only and a transmitting-only antenna  35  capable of radio wave transmission only are included as antennas. The receiving-only antenna  33  is connected to a receiver circuit. Either the transmitting-only antenna  35  and the transmitting/receiving antenna  32  is selected as a transmitting antenna by the antenna switching section  46 .  
     [0168] Features of the other units are the same as those of the portable radio apparatus  30  in the third embodiment. Features and operation of this embodiment will be described.  
     [0169] In the transmitting slot Tx, in case the switching signal SUB 1  from the logic circuit  42  is “L” and the switching signal SUB 2  is “H”, the antenna switching section  46  selects transmitting/receiving antenna  32  as a transmitting antenna (solid line in the antenna switching section  46 ). In case the switching signal SUB 1  from the logic circuit  42  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  46  selects a transmitting-only antenna  35  (dotted line in the antenna switching section  46 ) as a transmitting antenna. operation of transmission antenna switching will be described referring to the timing chart of FIG. 11.  
     [0170] When the receiving slot Rx 1  and the idle slot are passed and a transmitting slot Tx 1  is reached, the signal transmitter  44  is powered. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  38  is “L”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  32  is smaller than the reference voltage Vref, so that a control signal from the controller  40  drives the switching signal SUB 1  from the logic circuit  42  “L” and the switching signal SUB 2  “H”. The antenna switching section  46  selects a transmitting/receiving antenna  32  as a transmitting antenna.  
     [0171] In the receiving slot Rx 2 , the reflected wave detecting signal ANTDT goes “L”. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  44  is powered. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  38  is “H”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  32  is greater than the reference voltage Vref, so that a control signal from the controller  40  drives the switching signal SUB 1  from the logic circuit  42  “H” and the switching signal SUB 2  “L”. The antenna switching section  46  selects a transmitting-only antenna  35  as a transmitting antenna.  
     [0172] In case the reflected wave on the transmitting/receiving antenna  32  is output to the reflected wave detector  38  by the directional coupler  36  and the voltage Vdet detected by the reflected wave detector  38  is smaller than the reference voltage Vref, the transmitting/receiving antenna  32  is selected as a transmitting antenna. In case the detected voltage Vdet is greater than the reference voltage Vref, the transmitting-only antenna  35  is selected as a transmitting antenna.  
     [0173] In this embodiment, in case the reflected wave is smaller than a predetermined value, the transmitting/receiving antenna  32  is selected as a transmitting antenna. In case the reflected wave is greater than a predetermined value, it is assumed that part of a human body, for example the hand of a user has come in contact with (or in close proximity of) the transmitting/receiving antenna  32 , then the transmitting-only antenna  35  is selected as a transmitting antenna instead of the transmitting/receiving antenna  32 . This allows use of an antenna with a higher antenna gain as a transmitting antenna.  
     [0174] [Fifth Embodiment] 
     [0175] The fifth embodiment of the invention will be described referring to FIG. 13.  
     [0176]FIG. 13 is a circuit block diagram of portable radio apparatus in the fifth embodiment.  
     [0177] The portable radio apparatus  50  of this embodiment comprises units including transmitting/receiving antennas  52 ,  54 , a space diversity  56 , a controller  58  and a logic circuit  60  as an antenna selector, a signal transmitter  62  and an antenna switching section  64  as a switching transmitter, and an external output terminal  66 .  
     [0178] Each unit of the portable radio apparatus  50  will be detailed.  
     [0179] The transmitting/receiving antennas  53 ,  54  are transmitting/receiving antennas commonly available for transmission and reception. Both antennas are also connected to a receiver (not shown). An example of antenna arrangement of transmitting/receiving antennas  52 ,  54  in the portable radio apparatus  50  is the same as the transmitting/receiving antennas  12  and  14  in FIGS. 2A and 2B referred to in the first embodiment. The shape and configuration of the transmitting/receiving antenna  54  are the same as those of the transmitting/receiving antenna  14  in FIGS. 3A to  3 E so that the corresponding description is omitted.  
     [0180] The space diversity  56  determines the receiving antenna used for a receiving slot based on the receiving field strength of a receive signal received by the transmitting/receiving antenna  52 ,  54  and outputs the receiving antenna determination result BRNC to the controller  58 .  
     [0181] The controller  58  outputs a control signal to a logic circuit  60  in the subsequent stage on input of the determination result BRNC of the receiving antenna output from the space diversity  56 .  
     [0182] The logic circuit  60 , on input of a control signal from the controller  18 , outputs switching signals SUB 1 , SUB 2  for selecting a transmitting antenna to the antenna switching section  64 . The inside of the logic circuit  60  comprises, for example, an inverter  60   a  and an AND circuit  60   b.  Another logic circuit may be used as long as it can output switching signals SUB 1 , SUB 2 . Or, a single switching signal output may be used to allow instruction on antenna switching to the antenna switching section  64 .  
     [0183] The switching signal SUB  1  from the logic circuit  60  is also output to a signal transmitter  62  described later and performs switching so as to output a send signal to an output port ANT as a first output port or an output port EXT as a second output port.  
     [0184] The signal transmitter  62  is a unit for outputting a send signal per transmit slot based on a power on signal TxPo from the controller  58 . The send signal is output to the transmitting/receiving antenna  52  via the output port ANT based on the switching signal SUB 1  or to the antenna switching section  64  via the output port EXT.  
     [0185] The antenna switching section  64  is a selector switch for selecting a transmitting antenna for outputting a send signal from the output port ANT of the signal transmitter  62  based on the switching signals SUB 1 , SUB 2  from the logic circuit  60 .  
     [0186] The external output terminal  66  is an output terminal for connecting an output signal from the output port EXT to external apparatus (not shown) via the antenna switching section  64 .  
     [0187] This is the end of the explanation on the configuration of the portable radio apparatus  50 .  
     [0188] Next, operation of the portable radio apparatus  50  of the aforementioned configuration will be described referring to FIG. 4. FIG. 4 is a timing chart of portable radio apparatus.  
     [0189] The uppermost slot in the timing chart chronologically shows the timing of a transmitting/receiving antenna slot of a time division multiple access system.  
     [0190] Just before the receiving slot Rx is a determination period for the space diversity  56  to determine a receiving antenna. In this determination period, the receiving antenna determination result BRNC is output to the controller  58 . In this embodiment, in case the determination result remains “L” in a receiving slot Rx from the end of the determination period to next determination period, the transmitting/receiving antenna  52  is selected as a receiving antenna. In case the determination result remains “H”, the transmitting/receiving antenna  54  is selected as a receiving antenna.  
     [0191] The period from the receiving slot Rx to next transmitting slot Tx is an idle slot as a transmitting/receiving period irrelevant to channels of the portable radio apparatus  50 .  
     [0192] In the transmitting slot Tx, the signal transmitter  62  is powered when the power on signal TxPo from the controller  58  goes “H”.  
     [0193] At the same time, in case the determination result BRNC is “L”, the controller  58  outputs a control signal so that the switching signal SUB 1  from the logic circuit  60  will be driven “L” and the switching signal SUB 2  will be driven “H”. In case the determination result BRNC is “H”, the controller  58  outputs a control signal to the logic circuit  60  so that the switching signal SUB 1  from the logic circuit  60  will be driven “H” and the switching signal SUB 2  will be driven “L”.  
     [0194] The signal transmitter  62 , in case the switching signal SUB 1  from the logic circuit  60  is “L”, outputs a send signal to the transmitting/receiving antenna  52  from the output port ANT. In case the switching signal SUB 1  is “H”, the signal transmitter  62  outputs a send signal from the output port EXT.  
     [0195] The antenna switching section  64 , in case the switching signal SUB 1  from the logic circuit  60  is “L” and the switching signal SUB 2  is “H”, selects an external output terminal  66  (solid line in the antenna switching section  64 ). In case the switching signal SUB 1  from the logic circuit  60  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  64  selects a transmitting/receiving antenna  54  as a transmitting antenna (dotted line in the antenna switching section  64 ).  
     [0196] Thus, in case the transmitting/receiving antenna  52  is selected as a transmitting antenna (switching signal SUB 1  is “L”), a send signal is output from the output port ANT. In case the transmitting/receiving antenna  54  is selected as a transmitting antenna (switching signal SUB 1  is “H”), a send signal is output from the output port EXT, and the antenna switching section  64  switches to the transmitting/receiving antenna  54 .  
     [0197] operation of transmission antenna switching is described referring to-the timing chart of FIG. 4.  
     [0198] In a receiving slot Rx 1 , the determination result BRNC of the space diversity  56  is “L” so that a transmitting/receiving antenna  52  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 1  is reached, the signal transmitter  62  is powered by way of a power on signal TxPo. In this practice, the switching signal SUB 1  from the logic circuit  60  is “L” and the switching signal SUB 2  is “H” so that the signal transmitter  62  outputs a send signal to the transmitting/receiving antenna  52  from the output port ANT. The antenna switching section  64  selects the external output terminal  66 .  
     [0199] In the receiving slot Rx 2 , the determination result BRNC of the space diversity  56  is “H” so that a transmitting/receiving antenna  54  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  62  is powered by way of a power on signal TxPo. At the same time, the switching signal SUB 1  from the logic circuit  60  goes “H” and the switching signal SUB 2  goes “L”. Thus the signal transmitter  62  outputs a send signal from the output port EXT and the antenna switching section  64  selects the transmitting/receiving antenna  54  as a transmitting antenna.  
     [0200] In the embodiment, a transmitting/receiving antenna selected as a receiving antenna by the space diversity  56  in a receiving slot is selected as a transmitting antenna in a transmitting slot.  
     [0201] It is highly possible that a transmitting/receiving antenna with good receiving quality has a good transmitting in transmission of next transmission slot. Such a transmitting/receiving antenna can keep a better transmitting quality.  
     [0202] There is no switching sections between the output port ANT and the transmitting/receiving antenna  52  so that a send signal output from output port ANT is not subject to a transmission loss caused by a contact.  
     [0203] [Sixth Embodiment] 
     [0204] The sixth embodiment of the invention will be described referring to FIG. 14.  
     [0205]FIG. 14 is a block diagram of portable radio apparatus in the sixth embodiment.  
     [0206] The portable radio apparatus in this embodiment differs from the portable radio apparatus  50  in the first embodiment in that a receiving-only antenna  53  and a transmitting-only antenna  55  are included as antennas. Either the receiving-only antenna  53  and the transmitting/receiving antenna  52  is determined as a receiving antenna by the space diversity  56 . Further, either the transmitting-only antenna  55  and the transmitting/receiving antenna  52  is selected as a transmitting antenna.  
     [0207] Features of the other units are the same as those of the portable radio apparatus  50  in the fifth embodiment. Features and operation of this embodiment will be described.  
     [0208] In a determination period for the space diversity  56  to determine a receiving antenna, the receiving antenna determination result BRNC is output to the controller  58 . In this embodiment, in case the determination result BRNC remains “L” in a receiving slot Rx from the end of the determination period to next determination period, the transmitting/receiving antenna  52  is selected as a receiving antenna. In case the determination result BRNC remains “H”, the receiving-only antenna  53  is selected as a receiving antenna.  
     [0209] In the transmitting slot Tx, the signal transmitter  62 , in case the switching signal SUB 1  from the logic circuit  60  is “L”, outputs a send signal to the transmitting/receiving antenna  52  from the output port ANT. In case the switching signal SUB 1  is “H”, the signal transmitter  62  outputs a send signal from the output port EXT.  
     [0210] The antenna switching section  64 , in case the switching signal SUB 1  from the logic circuit  60  is “L” and the switching signal SUB 2  is “H”, selects an external output terminal  66  (solid line in the antenna switching section  64 ). In case the switching signal SUB 1  from the logic circuit  60  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  64  selects a transmitting-only antenna  55  (dotted line in the antenna switching section  64 ).  
     [0211] operation of transmission antenna switching is described referring to the timing chart of FIG. 4.  
     [0212] In a receiving slot Rx 1 , the determination result BRNC of the space diversity  56  is “L” so that a transmitting/receiving antenna  52  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 1  is reached, the signal transmitter  62  is powered by way of a power on signal TxPo. In this practice, the switching signal SUB 1  from the logic circuit  60  is “L” and the switching signal SUB 2  is “H” so that the signal transmitter  62  outputs a send signal to the transmitting/receiving antenna  52  from the output port ANT. The antenna switching section  64  selects the external output terminal  66 .  
     [0213] In the receiving slot Rx 2 , the determination result BRNC of the space diversity  56  is “H” so that a receiving-only antenna  53  is selected as a receiving antenna. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  62  is powered by way of a power on signal TxPo. At the same time, the switching signal SUB 1  from the logic circuit  60  goes “H” and the switching signal SUB 2  goes “L”. Thus the signal transmitter  62  outputs a send signal from the output port EXT and the antenna switching section  64  selects the transmitting-only antenna  55  as a transmitting antenna.  
     [0214] This, in case a transmitting/receiving antenna  52  is selected as a receiving antenna by the space diversity  56 , the transmitting/receiving antenna  52  is also selected as a transmitting antenna. In case a receiving-only antenna  53  is selected as a receiving antenna by the space diversity  56 , the transmitting-only antenna  55  corresponding to the receiving-only antenna  53  is selected as a transmitting antenna.  
     [0215] In this embodiment, it is possible to select as a transmitting antenna an antenna capable of transmission corresponding to an antenna selected as a receiving antenna by the space diversity  56  in the receiving slot.  
     [0216] There is no switching sections between the output port ANT and the transmitting/receiving antenna  52  so that a send signal output from output port ANT is not subject to a transmission loss caused by a contact.  
     [0217] [Seventh Embodiment] 
     [0218]FIG. 15 is a circuit block diagram of portable radio apparatus in the seventh embodiment.  
     [0219] The portable radio apparatus  70  of this embodiment comprises units including transmitting/receiving antennas  72 ,  74 , a directional coupler  76 , a reflected wave detector  78 , a controller  80  and a logic circuit  82  as an antenna selector, a signal transmitter  84  and an antenna switching section  86  as a switching transmitter, and an external output terminal  88 .  
     [0220] Each unit of the portable radio apparatus  70  will be detailed.  
     [0221] The transmitting/receiving antennas  72 ,  74  are transmitting/receiving antennas commonly available for transmission and reception. Both antennas are also connected to a receiver (not shown). An example of antenna arrangement of transmitting/receiving antennas  72 ,  74  in the portable radio apparatus  70  is the same as the transmitting/receiving antennas  12  and  14  in FIGS.  2 A and  2 B referred to in the first embodiment. The shape and configuration of the transmitting/receiving antenna  74  are the same as those of the transmitting/receiving antenna  14  in FIGS. 3A to  3 E so that the corresponding description is omitted.  
     [0222] The directional coupler  76  can transmit to the transmitting/receiving antenna  32  with virtually no loss a send signal output from the signal transmitter  84  described later. The directional coupler  76  outputs the reflected wave of a send signal irradiated from the transmitting/receiving antenna  72  to the reflected wave detector  78  in the subsequent stage.  
     [0223] For example, assume a case where part of a human body for example the hand comes in contact with (or in close proximity of) the transmitting/receiving antenna  72 . When the hand comes in contact with the transmitting/receiving antenna  72 , the impedance of the transmitting/receiving antenna  72  varies thus preventing radiation of a send signal at a predetermined power, and a reflected wave of the send signal is returned from the transmitting/receiving antenna  72 . Or, the power and amplitude of the reflected wave increases than when the hand is not in contact or not in close proximity.  
     [0224] The reflected wave (dotted line arrow in FIG. 15) is input to the directional coupler  76  in the opposite direction to the send signal (solid line arrow in FIG. 15) thus is output to the reflected wave detector  78  by the directional coupler  76 .  
     [0225] The reflected wave detector  78 , in case the detected voltage Vdet is greater than the reference voltage Vref, outputs the reflected wave detecting signal ANTDT as an “H” signal. In case the detected voltage Vdet is smaller than the reference voltage Vref, the reflected wave detector  78  outputs the reflected wave detecting signal ANTDT as an “L” signal. Configuration of the reflected wave detector  78  is the same as that of the reflected wave detector  38  of the third embodiment shown in FIG. 10, and the corresponding description is omitted.  
     [0226] The controller  80  outputs a control signal to a logic circuit  82  in the subsequent stage on input of the reflected wave detecting signal ANTDT output from the reflected wave detector  78 .  
     [0227] The logic circuit  82 , on input of a control signal from the controller  80 , outputs switching signals SUB 1 , SUB 2  for selecting a transmitting antenna to the antenna switching section  86 . The inside of the logic circuit  82  comprises, for example, an inverter  82   a  and an AND circuit  82   b.  Another logic circuit may be used as long as it can output switching signals SUB 1 , SUB 2 . Or, a single switching signal output may be used to allow instruction on antenna switching to the antenna switching section  86 .  
     [0228] The switching signal SUB  1  from the logic circuit  82  is also output to a signal transmitter  84  described later and switches output of a send signal between the output port ANT as a first output port and the output port EXT as a second output port.  
     [0229] The signal transmitter  84  is a unit for outputting a send signal per transmit slot based on a power on signal TxPo from the controller  80 . The send signal is output to the transmitting/receiving antenna  72  via the output port ANT based on the switching signal SUB 1  or to the antenna switching section  84  via the output port EXT.  
     [0230] The antenna switching section  86  is a selector switch for switching a send signal from the output port ANT of the signal transmitter  84  to the transmitting/receiving antenna  74  based on the switching signals SUB 1 , SUB 2  from the logic circuit  82 .  
     [0231] The external output terminal  88  is an output terminal for connecting an output signal from the output port EXT to external apparatus (not shown) via the antenna switching section  84 .  
     [0232] This is the end of the explanation on the configuration of the portable radio apparatus  70 .  
     [0233] Next, operation of the portable radio apparatus  70  of the aforementioned configuration will be described referring to FIG. 11. FIG. 11 is a timing chart of portable radio apparatus.  
     [0234] The uppermost slot in the timing chart chronologically shows the timing of a transmitting/receiving antenna slot of a time division multiple access system.  
     [0235] The period from the receiving slot Rx to next transmitting slot Tx is an idle slot as a transmitting/receiving period irrelevant to channels of the portable radio apparatus  70 .  
     [0236] In the transmitting slot Tx, the signal transmitter  84  is powered when the power on signal TxPo from the controller  80  goes “H”.  
     [0237] At the same time, in case the reflected wave detecting signal ANTDT is “L”, the controller  80  outputs a control signal to the logic circuit  82  so that the switching signal SUB 1  from the logic circuit  82  will be driven “L” and the switching signal SUB 2  will be driven “H”. In case the reflected wave detecting signal ANTDT is “H”, the controller  58  outputs a control signal so that the switching signal SUB 1  from the logic circuit  60  will be driven “H” and the switching signal SUB 2  will be driven “L”.  
     [0238] The signal transmitter  84 , in case the switching signal SUB 1  from the logic circuit  82  is “L”, outputs a send signal to the transmitting/receiving antenna  72  from the output port ANT. In case the switching signal SUB 1  is “H”, the signal transmitter  84  outputs a send signal from the output port EXT.  
     [0239] The antenna switching section  86 , in case the switching signal SUB 1  from the logic circuit  82  is “L” and the switching signal SUB 2  is “H”, selects an external output terminal  88  (solid line in the antenna switching section  86 ). In case the switching signal SUB 1  from the logic circuit  82  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  86  selects a transmitting/receiving antenna  74  (dotted line in the antenna switching-section  86 ).  
     [0240] Thus, in case the transmitting/receiving antenna  72  is selected as a transmitting antenna (switching signal SUB 1  is “L”), a send signal is output from the output port ANT. In case the transmitting/receiving antenna  74  is selected as a transmitting antenna (switching signal SUB 1  is “H”), a send signal is output from the output port EXT, and the antenna switching section  86  switches to the transmitting/receiving antenna  74 .  
     [0241] operation of transmission antenna switching will be described referring to the timing chart of FIG. 11.  
     [0242] When the receiving slot Rx 1  and the idle slot are passed and a transmitting slot Tx 1  is reached, the signal transmitter  84  is powered by a power on signal TxPo and a send signal is output to the transmitting/receiving antenna  72  from the output port ANT. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  78  is “L”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  72  is smaller than the reference voltage Vref, so that a control signal from the controller  80  drives the switching signal SUB 1  from the logic circuit  82  “L” and the switching signal SUB 2  “H”. The antenna switching section  86  selects an external output terminal  88  and the transmitting/receiving antenna  72  is selected as a transmitting antenna.  
     [0243] In the receiving slot Rx 2 , the reflected wave detecting signal ANTDT goes “L”. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  84  is powered by a power on signal TxPo and a send signal is output to the transmitting/receiving antenna  72  from the output port ANT. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  78  is “H”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  72  is greater than the reference voltage Vref, so that a control signal from the controller  80  drives the switching signal SUB 1  from the logic circuit  82  “H” and the switching signal SUB 2  “L”. The antenna switching section  86  selects a transmitting/receiving antenna  74  as a transmitting antenna.  
     [0244] In case the reflected wave on the transmitting/receiving antenna  72  is output to the reflected wave detector  78  by the directional coupler  76  and the voltage Vdet detected by the reflected wave detector  78  is smaller than the reference voltage Vref, the transmitting/receiving antenna  72  is selected as a transmitting antenna. In case the detected voltage Vdet is greater than the reference voltage Vref, the transmitting/receiving antenna  74  is selected as a transmitting antenna.  
     [0245] In this embodiment, in case the reflected wave is smaller than a predetermined value, the transmitting/receiving antenna  72  is selected as a transmitting antenna. In case the reflected wave is greater than a predetermined value, it is assumed that part of a human body, for example the hand of a user has come in contact with (or in close proximity of) the transmitting/receiving antenna  72 , then the transmitting/receiving antenna  74  is selected as a transmitting antenna instead of the transmitting/receiving antenna  72 . This allows use of an antenna with a higher antenna gain as a transmitting antenna.  
     [0246] There is no switching sections between the output port ANT and the transmitting/receiving antenna  72  so that a send signal output from output port ANT is not subject to a transmission loss caused by a contact.  
     [0247] In this embodiment, even after the transmitting/receiving antenna  74  is selected as a transmitting antenna, it is possible to output a send signal from the transmitting/receiving antenna  72  each time a transmitting slot starts and detect the level of the reflected wave on the transmitting/receiving antenna  72  then switch between transmitting antennas. By doing so, it is possible to switch between transmitting antennas by using the reflected wave on the transmitting/receiving antenna  72  as a switching reference.  
     [0248] While a directional coupler is connected to only the transmitting/receiving antenna  72  in this embodiment, It is possible to connect a directional coupler to the transmitting/receiving antenna  74  also (connect a reflected detector as well) and compare the outputs of reflected waves from both directional couplers with each other. Or, it is possible to compare each reflected wave with each reference voltage thus determining switchover of a transmitting antenna in a comprehensive way.  
     [0249] [Eighth Embodiment] 
     [0250]FIG. 16 is a block diagram showing the configuration of portable radio apparatus in the eighth embodiment.  
     [0251] The portable radio apparatus in the eighth embodiment differs from the portable radio apparatus  70  in the seventh embodiment in that a receiving-only antenna  73  capable of radio wave reception only and a transmitting-only antenna  75  capable of radio wave transmission only are included as antennas. The receiving-only antenna  73  is connected to a receiver circuit. Either the transmitting-only antenna  75  and the transmitting/receiving antenna  72  is selected as a transmitting antenna.  
     [0252] Features of the other units are the same as those of the portable radio apparatus  70  in the seventh embodiment. Features and operation of this embodiment will be described.  
     [0253] In the transmitting slot Tx, the signal transmitter  84 , in case the switching signal SUB 1  from the logic circuit  60  is “L”, outputs a send signal to the transmitting/receiving antenna  72  from the output port ANT. In case the switching signal SUB 1  is “H”, the signal transmitter  84  outputs a send signal from the output port EXT.  
     [0254] The antenna switching section  86 , in case the switching signal SUB 1  from the logic circuit  82  is “L” and the switching signal SUB 2  is “H”, selects an external output terminal  66  (solid line in the antenna switching section  86 ). In case the switching signal SUB 1  from the logic circuit  82  is “H” and the switching signal SUB 2  is “L”, the antenna switching section  86  selects a transmitting-only antenna  75  (dotted line in the antenna switching section  86 ).  
     [0255] operation of transmission antenna switching will be described referring to the timing chart of FIG. 11.  
     [0256] When the receiving slot Rx 1  and the idle slot are passed and a transmitting slot Tx 1  is reached, the signal transmitter  84  is powered by a power on signal TxPo and a send signal is output to the transmitting/receiving antenna  72  from the output port ANT. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  78  is “L”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  72  is smaller than the reference voltage Vref, so that a control signal from the controller  80  drives the switching signal SUB 1  from the logic circuit  82  “L” and the switching signal SUB 2  “H”. The antenna switching section  86  selects an external output terminal  88  and the transmitting/receiving antenna  72  is selected as a transmitting antenna.  
     [0257] In the receiving slot Rx 2 , the reflected wave detecting signal ANTDT goes “L”. When the idle slot is passed and a transmitting slot Tx 2  is reached, the signal transmitter  84  is powered by a power on signal TxPo and a send signal is output to the transmitting/receiving antenna  72  from the output port ANT. In this practice, the reflected wave detecting signal ANTDT of the reflected wave detector  78  is “H”, that is, the detected voltage Vdet of the reflected wave on the transmitting/receiving antenna  72  is greater than the reference voltage Vref, so that a control signal from the controller  80  drives the switching signal SUB 1  from the logic circuit  82  “H” and the switching signal SUB 2  “L”. The antenna switching section  86  selects a transmitting-only antenna  75  as a transmitting antenna.  
     [0258] In case the reflected wave on the transmitting/receiving antenna  72  is output to the reflected wave detector  78  by the directional coupler  76  and the voltage Vdet detected by the reflected wave detector  78  is smaller than the reference voltage Vref, the transmitting/receiving antenna  72  is selected as a transmitting antenna. In case the detected voltage Vdet is greater than the reference voltage Vref, a transmitting-only antenna  75  is selected as a transmitting antenna.  
     [0259] In this embodiment, in case the reflected wave is smaller than a predetermined value, the transmitting/receiving antenna  72  is selected as a transmitting antenna. In case the reflected wave is greater than a predetermined value, it is assumed that part of a human body, for example the hand of a user has come in contact with (or in close proximity of) the transmitting/receiving antenna  72 , then the transmitting-only antenna  75  is selected as a transmitting antenna instead of the transmitting/receiving antenna  72 . This allows use of an antenna with a higher antenna gain as a transmitting antenna.  
     [0260] There is no switching sections between the output port ANT and the transmitting/receiving antenna  72  so that a send signal output from output port ANT is not subject to a transmission loss caused by a contact.  
     [0261] While the invention has been described in details and referring to specific embodiments, those skilled in the art will understand that various modifications or changes may be made to the invention without departing from the spirit and scope of the invention.  
     [0262] This patent application is based on the Japanese patent application filed Dec. 15, 2000 (Japanese Patent Application No. 382466/2000) which is herein incorporated as a reference.  
     [0263] Industrial Applicability  
     [0264] According to this portable radio apparatus, it is possible to switch between transmitting antennas to output a send signal. Thus it is possible to keep a better transmitting quality than when only a single transmitting antenna is used.  
     [0265] Also, switching between transmitting antennas is possible on a per transmitting slot basis thus allowing faster switching between transmitting antennas.