Abstract:
In a radio unit having an antenna, a receiver and a transmitter, the present invention comprises a detector for detecting at least one signal of a receiving call and a sending call; and a gain switcher for switching gain of the antenna, based on a detection result of the detection means.

Description:
This is a continuation of application Ser. No. 08/466,576 filed on Jun. 6, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a radio unit for a mobile station used in mobile communications and more particularly, to a portable radio unit. 
     Among conventional radio units for mobile stations used in mobile communications, the portable radio unit carried by a user has been provided with a built-in retractable antenna with its length shortened by λ/2 or λ/4. Such a radio unit, for example, a radio phone system, is required to keep its antenna fully extended as much as the unit is allowed to the limit for keeping good receiving sensitivity during standby and communication periods. 
     Carrying the portable radio unit leaving its antenna fully extended is generally inconvenient for a user. So it is likely to be carried in a bag or in a pocket with its antenna retracted. Assuming that there is a call for the user while he/she is carrying it with its antenna retracted, communication between a base station of control signal for connecting the call and the destination radio unit is executed with the antenna left retracted. When the antenna is retracted, its gain is lowered. In case the user stands in a place of low electric field of transmission wave from the base station, it is likely to cause receiving failure, resulting in deteriorating receiving call rate. In case of giving a call by the radio unit with its antenna retracted may also deteriorate connection rate. 
     A means for enhancing the receiving sensitivity while the antenna of the portable radio unit is kept retracted has been disclosed in Japanese Patent Laid-Open No. 252326(1990). This Japanese Patent Laid Open No. 252326 (1990) relates to a cordless phone system provided with a base set and a hand set. In the above art, an electric wave between the base and hand sets may be selected to be the one with excellent S/N ratio (power ratio of signal to noise), for example, FSK, ASK, PSK, and MSK during standby period other than communication period. The receiving band of the hand set is further decreased to improve the S/N ratio in a weak electric field. 
     This system, however, requires a modulation means of a different electric wave mode such as SSB and FM, which further needs specific circuit construction, resulting in increased manufacturing cost. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a portable radio unit that enhances receiving sensitivity at receiving or origination a call to improve connectability with the radio base station even when the radio unit is carried with its antenna retracted. 
     The object of the present invention is achieved by a portable radio unit having an antenna, a receiver and a transmitter, comprising: detection means for detecting at least one signal of a receiving call and a sending call; and gain switching means for switching gain of the antenna, based on a detection result of the detection means. 
     Moreover, it is preferable that the gain switching means comprises means for extending the antenna and switching the gain of the antenna. 
     The present invention extends the antenna partly if it is retracted when the detection means has detected a receiving call or a sending call. 
     By this, the gain of antenna is switched, receiving sensitivity is increased and connectability with a radio base station is increased, too. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and drawings, in which: 
     FIG. 1 is a block diagram of an embodiment of a portable radio unit of the present invention. 
     FIG. 2 is a sectional view of a switch part of the embodiment of the portable radio unit of the present invention. 
     FIG. 3 is a sectional view of a switch part of the embodiment of the portable radio unit of the present invention. 
     FIG. 4 is a sectional view of a switch part of the embodiment of the portable radio unit of the present invention. 
     FIG. 5 is a flowchart showing a receiving process executed by the portable radio unit of the present invention. 
     FIG. 6 is a view for explaining an antenna pattern when the antenna is extended (“pop up”) to improve reception. 
     FIG. 7 is a view showing an antenna pattern when the antenna is extended (“pop up”) to improve reception. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention is described referring to drawings. 
     FIG. 1 is a block diagram of a portable radio unit according to the present invention. This embodiment assumes that a portable radio unit based on the invention is used for a mobile unit of a portable phone system, that is a handy phone. 
     Referring to FIG. 1, a portable phone system is briefly explained. 
     When power is turned on, the portable phone  100  is set to a standby status. An antenna  102  is kept in the retracted position. Under the standby status, the antenna  102  always receives a receiving control channel sent from a radio base station (not shown). The receiving control channel contains a receiving signal and any other information required to give a call. 
     The signal received by the antenna  102  is demodulated in a receiver  103 , and transmitted to a control section  106 . 
     In order to give a call by the portable phone  100 , signals generated in the control section  106  are modulated and amplified in a transmitter  104 , and transmitted to the radio base station (not shown) from the antenna  102 . 
     Under the standby status, when a detection section  105  of the control section  106  detects a receiving call signal, the detection section  105  sends a switch control signal to a switch  101 . The switch  101  is actuated to extend the antenna  102  partially from its fully retracted position (this action is hereinafter referred to as “pop up”). Since the antenna  102  pops up responding to the detection of the receiving call signal, succeeding receiving/transmitting with the radio base station may be executed with excellent receiving sensitivity. 
     While in case of giving a call, the antenna  102  of the portable phone  100  is expected to be extended. Even when starting the call without extending the antenna  102 , the detection section  105  of the control section  106  is so designed to send a switch control signal to the switch  101  upon detection of a transmission signal, thus popping up the antenna  102 . Although the antenna  102  is still partially retracted, sending/receiving with the radio base station may be executed under the condition of enhanced receiving sensitivity. 
     Referring to FIG. 2, the “pop up” action is described. FIGS. 2 to  4  represent sectional views of an example of a switch  101  (See FIG. 1) placed in an enclosure  111  of the portable phone  100 . FIG. 2 shows that the antenna  102  is retracted. FIG. 3 shows that the antenna  102  is popped up. FIG. 4 shows that the antenna  102  is extended. 
     As FIG. 2 shows, the switch  101  comprises a supporting rod  127  loosely attached to a bottom of a mold  126 , a spring  128  provided about a periphery of the supporting rod  127 , a piston  123  which is so set to move inside or outside of the mold  126  through a space formed in a side wall of the mold  126 , a spring  124  provided about a periphery of the piston  123  with its left end fixed thereto, a latch  122  attached to an inner wall of the mold  126  opposite to the piston  123  so as to rotate in relation to a bearing point A, and an electromagnet  125  placed outside the mold  126  opposite to the piston  123 . 
     The latch  122  is weakly pressed clockwise by a spring (not shown) attached to the bearing point A. The bottom end of the antenna  102  is supported by a supporting board  127   a  attached to a top end of the supporting rod  127  within the mold  126 . 
     When the electromagnet  125  is not energized, the piston  123  receives rightward force applied by the spring (not shown) attached in the electromagnet  125  to be placed as FIG.  2  and FIG. 4 show. 
     A right end of the spring  124  reaches inside of the mold  126  to press the latch  122  rightward, i.e., counterclockwise against the weak clockwise suppressive force of the latch  122 . 
     In order to retract the antenna  102 , it is pushed downward with one&#39;s hand. As FIG. 2 shows, the bottom end of the antenna  102  contacts with the supporting board  127   a  to push down the supporting rod  127  against a spring  128 . When the spring  128  is contracted to bring the supporting board  127   a  to be pushed down to the level lower than that of the bottom end of the latch  122 , restoring force of the spring  124  causes the latch  122  to rotate counterclockwise with respect to bearing point A. Even though the supporting board  127   a  is released from the downward pressure applied by the antenna  102 , the latch  122  serves to keep it in a position as shown in the drawing. 
     Under the above condition, when the detection section  105  shown in FIG. 1 detects a receiving call signal or a sending call signal, a switch control signal is sent to a switch  101  to supply a signal to the terminals  120  and  121  of the electromagnet  125 . 
     As FIG. 3 shows, the electromagnet  125  is energized to attract the piston  123  leftward against restoring force of the spring within the electromagnet  125 . By this, the spring  124  attached to the piston  123  moves leftward to cause its right end away to move from the latch  122 . Accordingly the rightward force applied to the latch  122  is released to rotate clockwise to the bearing point A, being disconnected from the supporting board  127   a.  The supporting rod  127  is pushed up by a restoring force of a spring  128  to raise the antenna  102  upward. That is, the antenna  102  pops up. 
     When the switch control signals are used to execute the pop up, the electromagnet  125  is de-energized to return the piston  123  to the original position by restoring force of the spring within the electromagnet  125 , as shown in FIG.  3  and FIG.  4 . 
     When the antenna  102  is fully extended at standby or communication period, bottom end of the antenna  102  is raised to a level higher than the position to which the supporting board  127   a  reaches through restoring force of the spring  128  (shown in alternate long and short line) as shown in FIG.  4 . Even when pop up is executed, i.e., the supporting rod  127  is pushed upward upon detection of the receiving/sending call, the supporting board  127   a  is not brought into contact with the bottom end of the antenna  102 , which causes no problem. 
     Sequential operations of the portable radio unit  100  of FIG. 1 at receiving a call are described referring to a flowchart of FIG.  5 . 
     Once the portable radio unit is set to the standby status, it always receives a receiving control channel. When receiving a broadcasting from a radio base station on the receiving control channel (F- 1 ), the detection section  105  of the control section  106  determines whether or not the received signal contains the receiving call signal calling up its own station (F- 2 ). If it determines that the received signal contains no receiving call signal calling up its own station, the process returns to step (F- 1 ) to wait until receiving the next broadcasting. If it is judged that the receiving call signal is contained, the detection section  105  sends a switch control signal to a switch  101  (F- 3 ). The antenna  102  then pops up to execute a call receiving process (F- 4 ) as aforementioned referring to FIG.  3 . 
     Characteristics of the antenna  102 , especially to λ/2 antenna, at popping up is described referring to FIG.  7 . 
     As FIG. 6 shows, it is assumed that “x” denotes the direction extending vertically to a front operation side of the portable radio unit  100 , and “y” denotes the direction extending vertically to its side surface. Supposing that a circle A 1  is designated as 0 dB d  standard (gain based on dipole antenna) as shown in FIG. 7, radiation pattern of the radio waves in x and y directions results in −4 dB d  (circle A 2 ) when the antenna  102  is fully extended. When the antenna  102  is retracted (circle A 4 ), it results in about −10 dB d . 
     Contrary to this, in case the antenna  102  pops up (circle A 3 ), it results in −7 db d , thus improving its receiving sensitivity by approximately 3 dB d  compared with the case with its antenna retracted. As a result, connectability with the radio base station is improved, allowing to facilitate receiving/transmitting therewith. 
     As described above, the portable radio unit of the present invention allows to enhance connection rate with the radio base station by improving the receiving sensitivity upon detection of the receiving/sending call even if the antenna is kept retracted.