Patent Publication Number: US-2002002037-A1

Title: Radio communication apparatus and radio communication method

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a radio communication apparatus and a radio communication method, and more particularly, is suitably applied to, for example, a small portable radio.  
       [0003] 2. Description of the Related Art  
       [0004] Recently, a portable radio communicates not only with a ground base station, but also with a satellite base station, and the utilization varies with time in various systems and methods. Under the situation, in addition to communicating using voice, a portable radio can, for example, obtain measured position data by receiving and analyzing a satellite signal from a global positioning system (GPS) satellite, and detecting its current position according to the measured positional data.  
       [0005] As shown in FIG. 1, a portable radio  1  as a terminal in a Personal Digital Cellular (PDC) digital portable telephone system comprises a circuit board (not shown) necessary for radio communication contained in a casing (not shown) made of a nonconductive material. The circuit board is covered with a shielding case  2  as a grounding member.  
       [0006] The portable radio  1 , having the inside circuit board covered with the shielding case  2 , prevents a first power supply circuit  10  mounted on the circuit board as shown in FIG. 2 and other various circuits from adversely affecting one another, a first antenna unit  3  for transmission and reception, a second antenna unit  16  for reception, or other equipment.  
       [0007] The first antenna unit  3  (FIG. 1) comprises a helical antenna  4  and a rod antenna  5 . The rod antenna  5  is designed to slide along the z-axis inside and outside the casing.  
       [0008] The helical antenna  4  is formed by helically winding a conductive wire, and is covered with an antenna cover  4 A made of a non-metallic material, thereby preventing its conductive portion from directly touching a human body portion.  
       [0009] In addition, the rod antenna  5  is made of a conductive wire, formed in a rod shape, and covered with a non-metallic antenna cover  5 A, thereby preventing its conductive portion from directly touching a human body portion.  
       [0010] When the antenna is folded, the rod antenna  5  of the first antenna unit  3  slides along the inner circumference of a first antenna fixture  6  such that the antenna can be stored in the casing, and a bottom surface  4 B of the helical antenna  4  can be held against a top surface  6 A of the first antenna fixture  6 .  
       [0011] When the antenna is extended, the rod antenna  5  of the first antenna unit  3  slides along the inner circumference of the first antenna fixture  6  such that the antenna can be pulled out of the casing, and the lower end (not shown) of the rod antenna  5  can be connected and held by the first antenna fixture  6 .  
       [0012] The first antenna unit  3  is electrically connected to the circuit board covered with the shielding case  2  through the first antenna fixture  6  and a first antenna power supply conductor  7 , and is connected to the first power supply circuit  10  through a first antenna matching circuit  8  and a diversity switch  9  mounted on the circuit board as shown in FIG. 2.  
       [0013] The first antenna matching circuit  8  matches the impedance of the first antenna unit  3  with the impedance of the first power supply circuit  10 .  
       [0014] The second antenna unit  16  is an inverted F plate antenna in which a rectangular radiant conductor  11  having a length of the circumference of about {fraction (1/2)} wavelength is placed little above and substantially parallel to a top surface  2 A of the shielding case  2  through a spacer (not shown).  
       [0015] In the second antenna unit  16 , one end of the radiant conductor  11  grounded to the shielding case  2  by a second antenna short-circuit conductor  12 , and the radiant conductor  11  is electrically connected to a second antenna power supply conductor  13  at a predetermined position on the radiant conductor  11 .  
       [0016] In the second antenna unit  16 , the radiant conductor  11  is electrically connected to the circuit board covered with the shielding case  2  through the second antenna power supply conductor  13 , and is further connected to the first power supply circuit  10  through a second antenna matching circuit  14  mounted on the circuit board, and the diversity switch  9  as shown in FIG. 2.  
       [0017] The second antenna matching circuit  14  matches the impedance on the second antenna unit  16  side with the impedance on the first power supply circuit  10  side.  
       [0018] The first power supply circuit  10  is adapted to generate a transmission signal in a signal format for communication with a ground base station in transmission, supplies the signal to the first antenna unit  3  through the diversity switch  9 , the first antenna matching circuit  8 , the first antenna power supply conductor  7 , and the first antenna fixture  6 , and transmits it through the first antenna unit  3  as an electric wave of 1.5 GHz band to the ground base station.  
       [0019] The first power supply circuit  10  is adapted to cause the diversity switch  9  to select the first antenna unit  3  or the second antenna unit  16  whichever has a higher received power level in reception, thereby reducing the influence of fading.  
       [0020] Thus, when the first antenna unit  3  is selected by the diversity switch  9 , the first power supply circuit  10  demodulates the signal received by the first antenna unit  3  from the ground base station after receiving it through the first antenna fixture  6 , the first antenna power supply conductor  7 , and the first antenna matching circuit  8 .  
       [0021] On the other hand, when the second antenna unit  16  is selected by diversity switch  9 , the first power supply circuit  10  demodulates the signal received by the second antenna unit  16  from the ground base station after receiving it through the second antenna power supply conductor  13  and the second antenna matching circuit  14 .  
       [0022] At this time, the first antenna unit  3  functions as a vertical mode helical antenna for the z-axis direction linear polarization (vertical polarization) oscillating in the z-axis direction, but substantially undirectionally on the x-y plane whose ground is the shielding case  2  of the helical antenna  4  when the antenna is folded.  
       [0023] Furthermore, the first antenna unit  3  functions as a rod antenna for the z-axis direction linear polarization oscillating in the z-axis direction, but substantially undirectionally on the x-y plane whose ground is the shielding case  2  of the rod antenna  5  when the antenna is extended.  
       [0024] On the other hand, in the second antenna unit  16 , an electric current i 1  flows in the y-axis direction (horizontally) on the radiant conductor  11  to radiate an electric wave of y-axis direction linear polarization (horizontal polarization), and a leakage current i 2 , which is induced by the electric current i 1  flowing on the radiant conductor  11  because the power supply point is close to the shielding case  2 , flows in a large amount in the z-axis direction (vertically) on the shielding case  2  to radiate an electric wave of z-axis direction linear polarization (vertical polarization).  
       [0025] Thus, the second antenna unit  16  dominantly radiates the electric wave of z-axis direction linear polarization (vertical polarization) on the whole. As a result, it functions as an inverted F plate antenna for the z-axis direction vertical polarization, but substantially undirectional on the x-y plane whose ground is the shielding case  2 .  
       [0026] However, the portable radio  1  with the above mentioned configuration is a terminal of a PDC system having a radio communication frequency of 1.5 GHz, and the radio communication frequency of the satellite signal transmitted from the GPS satellite is 1.5 GHz, so their radio communication frequencies match each other.  
       [0027] However, the satellite signal of the GPS satellite is transmitted with circular polarization obtained by combining the vertical polarization and the horizontal polarization, which are orthogonal to each other, with a 90° phase difference, and does not match in polarization the antenna characteristic of the z-axis direction linear polarization (vertical polarization) in the first antenna unit  3  and the second antenna unit  16 .  
       [0028] Therefore, it has been very difficult that the portable radio  1  can receive a satellite signal of circular polarization from a base station of the GPS satellite with an acceptable gain because there is no perfect match of the polarization even if the radio communication frequency for communication with a ground base station matches the radio communication frequency for communication with a base station of the GPS satellite.  
       SUMMARY OF THE INVENTION  
       [0029] In view of the foregoing, an object of this invention is to provide a radio communication apparatus and a radio communication method with a simple configuration capable of obtaining an acceptable gain when communication are established between a ground base station and a satellite base station.  
       [0030] The foregoing object and other objects of the invention have been achieved by the provision of a radio communication apparatus and a radio communication method wherein communication can be accomplished by switching the first communication mode in which the first antenna unit is operated with the first linear polarization characteristic while the second antenna unit is operated with the second linear polarization characteristic, and the second communication mode in which the first antenna unit and the second antenna unit are operated with the circular polarization characteristic by supplying electric power to the first antenna unit and the second antenna unit by the circular polarization generation means with the phase difference of about 90° so as to make the polarization to match with two communication targets having different polarization characteristics at one terminal.  
       [0031] The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0032] In the accompanying drawings:  
     [0033]FIG. 1 is a schematic diagram showing the configuration of the conventional portable radio;  
     [0034]FIG. 2 is a schematic circuit diagram showing the circuitry near the antenna of the conventional portable radio;  
     [0035]FIG. 3 is a schematic diagram showing the configuration of a portable radio according to an embodiment of the present invention;  
     [0036]FIG. 4 is a schematic circuit diagram showing the circuitry near the antenna of the portable radio;  
     [0037]FIG. 5 is a schematic diagram for explaining the current components in the horizontal direction mutually intensified by the first and the second inverted F plate antennas;  
     [0038]FIG. 6 is a schematic diagram showing the radiation pattern of the first antenna unit;  
     [0039]FIG. 7 is a schematic diagram showing the radiation-directivity of the first and second antenna units; and  
     [0040]FIG. 8 is a schematic diagram showing the radiation pattern of the second antenna unit.  
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT  
     [0041] Preferred embodiments of this invention will be described with reference to the accompanying drawings:  
     [0042] (1) Configuration of a Portable Radio  
     [0043] In FIG. 3 in which units corresponding to the units shown in FIG. 1 are assigned the same reference numerals, reference numeral  20  generally denotes a portable radio as a terminal in a Personal Digital Cellular (PDC) digital portable telephone system. A casing (not shown) made of a non-conductive material contains a circuit board (not shown) necessary for radio communication, and the circuit board is covered with a shielding case  2  as a grounding member.  
     [0044] The portable radio  20  having the inside circuit board covered with the shielding case  2 , prevents various circuits mounted on the circuit board from adversely affecting one another, a first antenna unit  3 , a second antenna unit  21 , or other equipment.  
     [0045] The first antenna unit  3  comprises a helical antenna  4  and a rod antenna  5 . The rod antenna  5  is designed to slide along the z-axis inside and outside the casing.  
     [0046] The helical antenna  4  is formed by helically winding a conductive wire, and is covered with an antenna cover  4 A made of a non-metallic material, thereby preventing its conductive portion from directly touching a human body portion.  
     [0047] In addition, the rod antenna  5  is made of a conductive wire, formed in a rod shape, and covered with a non-metallic antenna cover  5 A, thereby preventing its conductive portion from directly touching a human body portion.  
     [0048] When the antenna is folded, the rod antenna  5  of the first antenna unit  3  slides along the inner circumference of a first antenna fixture  6  such that the antenna can be stored in the casing, and a bottom surface  4 B of the helical antenna  4  can be held against a top surface  6 A of the first antenna fixture  6 .  
     [0049] When the antenna is extended, the rod antenna  5  of the first antenna unit  3  slides along the inner circumference of the first antenna fixture  6  such that the antenna can be pulled out of the casing, and the lower end (not shown) of the rod antenna  5  can be connected and held by the first antenna fixture  6 .  
     [0050] The first antenna unit  3  is electrically connected to the circuit board covered with the shielding case  2  through the first antenna fixture  6  and a first antenna power supply conductor  7 .  
     [0051] Furthermore, as shown in FIG. 4, the first antenna unit  3  is electrically connected to the first power supply circuit  10  through the first antenna matching circuit  8 , a communication switch  37 , and the diversity switch  9  mounted on a circuit board when communication are established with a ground base station. In this case, a switch terminal  37 C is connected to a contact point  37 A in the communication switch  37 .  
     [0052] On the other hand, the first antenna unit  3  is electrically connected to a second power supply circuit  36  through the first antenna matching circuit  8 , and the communication switch  37  mounted on a circuit board when communication are established with a base station of a GPS satellite. In this case, the switch terminal  37 C is connected to a contact point  37 B in the communication switch  37 .  
     [0053] The first antenna matching circuit  8  matches the impedance on the first antenna unit  3  side with the impedance on the first power supply circuit  10  side.  
     [0054] On the other hand, a second antenna unit  21  (FIG. 3) comprises a first inverted F plate antenna  22  and a second inverted F plate antenna  23 .  
     [0055] Each of the first inverted F plate antenna  22  and the second inverted F plate antenna  23  comprises a first radiant conductor  24  and a second radiant conductor  25  of a rectangular shape each having a length of the circumference of about {fraction (1/2)} wavelength little above and substantially parallel to a top surface  2 A of the shielding case  2  through a spacer (not shown) and in the y-axis direction (horizontally).  
     [0056] The first inverted F plate antenna  22  is adapted to be resonant by setting the length of the circumference of the first radiant conductor  24  to the electric length of about {fraction (1/2)} wavelength, and the upper right end of the first radiant conductor  24  is grounded to the shielding case  2  by a first inverted F plate antenna short-circuit conductor  26 , and power is applied to the first radiant conductor  24  through a first inverted F plate antenna power supply conductor  27 .  
     [0057] The first inverted F plate antenna power supply conductor  27  is attached at the optimum position such that the input impedance is matched with various circuits on the circuit board when power is supplied to the first radiant conductor  24 .  
     [0058] An end point  24 A on the first radiant conductor  24  farthest from the first inverted F plate antenna power supply conductor  27  has high impedance because a further current does not flow, and the short-circuit point of the first radiant conductor  24  connected to the first inverted F plate antenna power supply conductor  27  has low impedance of substantially 0 Ω.  
     [0059] Therefore, the first inverted F plate antenna  22  can be adjusted by moving the first inverted F plate antenna power supply conductor  27  between the positions of high impedance and low impedance to obtain the optimum input impedance.  
     [0060] On the other hand, in the second inverted F plate antenna  23 , a second inverted F plate antenna short-circuit conductor  28  and a second inverted F plate antenna power supply conductor  29  are connected to the second radiant conductor  25  as the first inverted F plate antenna short-circuit conductor  26  and the first inverted F plate antenna power supply conductor  27  are connected to the first radiant conductor  24 .  
     [0061] Thus, the second antenna unit  21  is provided such that the first inverted F plate antenna  22  and the second inverted F plate antenna  23  which have the same configurations and the same antenna characteristics can be symmetrical.  
     [0062] At this time, in the second antenna unit  21 , the first radiant conductor  24  and the second radiant conductor  25  are electrically connected to a circuit board covered with the shielding case  2  through the first inverted F plate antenna power supply conductor  27  and the second inverted F plate antenna power supply conductor  29 , and the second radiant conductor  25  is connected to the second power supply circuit  36  through a second antenna matching circuit  31 , a balun (balanced-to-unbalanced transformer)  32 , a communication switch  33 , a phase shifter  34 , and a combine  35  on the circuit board as shown in FIG. 4.  
     [0063] In addition, as shown in FIG. 4, the second antenna unit  21  is connected to the first power supply circuit  10  through the second antenna matching circuit  31 , the balun  32 , the communication switch  33 , and the diversity switch  9  mounted on the circuit board when communication are established with a ground base station. In this case, in the communication switch  33 , a switch terminal  33 C is connected to a contact point  33 A.  
     [0064] On the other hand, the second antenna unit  21  is connected to the second power supply circuit  36  through the second antenna matching circuit  31 , the balun  32 , the communication switch  33 , the phase shifter  34 , and the combiner  35  mounted on the circuit board when communication are established with a base station of a GPS satellite. In this case, in the communication switch  33 , a switch terminal  33 C is connected to a contact point  33 B.  
     [0065] The second antenna matching circuit  31  matches the impedance on the second antenna unit  21  side with the impedance on the second power supply circuit  36  side.  
     [0066] The balun  32  prevents an unbalanced current from being caused by the difference in excitation state by performing a balanced to unbalanced converting process between the second antenna unit  21  which is operated as a balanced antenna and an unbalanced circuit at and after the communication switch  33  connected through an unbalanced transmission line when the first radiant conductor  24  and the second radiant conductor  25  in the second antenna unit  21  are operated as antennas. Power is applied to the first radiant conductor  24  and the second radiant conductor  25  with a phase difference of 180°.  
     [0067] Practically, if power is applied to the first inverted F plate antenna power supply conductor  27  and the second inverted F plate antenna power supply conductor  29  with a phase difference of 180° in the second antenna unit  21  as shown in FIG. 5, then a current component  24   i   1  flowing through the first radiant conductor  24  and a current component  25   i   1  flowing through the second radiant conductor  25  intensify each other for a moment in the horizontal direction (y-axis direction), and a current component  24   i   2  flowing through the first radiant conductor  24  and a current component  25   i   2  flowing through the second radiant conductor  25  intensify each other for a moment in the horizontal direction (y-axis direction), thereby mutually intensifying the current components flowing through the two radiant conductors  24  and  25  only in the horizontal direction.  
     [0068] In the current components flowing through the first and second radiant conductors  24  and  25 , the current components  24   i   2  and  25   i   1  nullify each other in the vertical direction (z-axis direction), and the current components  24   i   1  and  25   i   2  nullify each other in the vertical direction, thereby attenuating the current components in the vertical direction.  
     [0069] If the directions of the currents flowing through the first radiant conductor  24  and the second radiant conductor  25  are inverted in the second antenna unit  21  for the next moment, the current components flowing through the two radiant conductors  24  and  25  intensify each other only in the horizontal direction, which is inverse to the above mentioned case, thereby attenuating the current components in the vertical direction.  
     [0070] With the current flowing through the first radiant conductor  24  and the second radiant conductor  25 , an induced current flows through the shielding case  2 , which is a grounding conductor, through the first inverted F plate antenna short-circuit conductor  26  and the second inverted F plate antenna short-circuit conductor  28 .  
     [0071] That is, since currents (current components  24   i   1  and  24   i   2 ) flow from the first inverted F plate antenna short-circuit conductor  26  to the first radiant conductor  24 , an induced current flows to the first inverted F plate antenna short-circuit conductor  26  through the shielding case  2 . Similarly, since currents (current components  25   i   1  and  25   i   2 ) flow to the second inverted F plate antenna short-circuit conductor  28  through the second radiant conductor  25 , an induced current starts flowing from the second inverted F plate antenna short-circuit conductor  28  through the shielding case  2 .  
     [0072] Thus, in the second antenna unit  21 , the induced current flowing through the shielding case  2  mainly to the first inverted F plate antenna short-circuit conductor  26  and the second inverted F plate antenna short-circuit conductor  28  almost nullify each other, thereby preventing the leakage current i 2  from flowing in the z-axis direction (vertical direction) through the shielding case  2  as in the second antenna unit  16  in the conventional portable radio  1  (shown in FIG. 1).  
     [0073] (1-1) Communications with Base Station on Ground  
     [0074] A portable radio  20  generates a transmission signal in a signal format for communication with a ground base station through the first power supply circuit  10  in transmitting data when communication are established with the ground base station, the power is applied to the first antenna unit  3  through the diversity switch  9 , the first antenna matching circuit  8 , the first antenna power supply conductor  7 , and the first antenna fixture  6 , and the signal is transmitted to the ground base station as an electric wave of 1.5 GHz band from the first antenna unit  3 .  
     [0075] At this time, the first antenna unit  3  has radiation-directivity as shown in FIGS. 6 and 7, functions as a vertical mode helical antenna for the z-axis direction vertical polarization substantially undirectional on the x-y plane whose ground is the shielding case  2  of the helical antenna  4  when the antenna is folded, and functions as a rod antenna for the z-axis direction linear polarization (vertical polarization) oscillating in the z-axis direction, but substantially undirectionally on the x-y plane whose ground is the shielding case  2  of the rod antenna  5  when the antenna is extended.  
     [0076] Therefore, the first antenna unit  3  has directivity of obtaining desired communication with a ground base station, and matches in polarization with the ground base station, thereby obtaining desired antenna characteristics.  
     [0077] The portable radio  20  connects the switch terminal  33 C of the communication switch  33  to the contact point  33 A when receiving data, connects the switch terminal  37 C of the communication switch  37  to the contact point  37 A, then compares the received power level in the first antenna unit  3  and the second antenna unit  21  by a control unit (not shown), switches a switch terminal  9 C of the diversity switch  9  between connection points  9 A and  9 B based on the comparison result, selects the first antenna unit  3  or the second antenna unit  21  whichever has a higher received power level when receiving data, and reducing the influence of fading.  
     [0078] Practically, when the portable radio  20  selects the first antenna unit  3  using the diversity switch  9 , it receives a base station signal from a ground base station received by the first antenna unit  3  using the first power supply circuit  10  through the first antenna fixture  6 , the first antenna power supply conductor  7 , the first antenna matching circuit  8 , and the communication switch  37 , and demodulates it using the first power supply circuit  10 .  
     [0079] Similarly, when the portable radio  20  selects the second antenna unit  21  using the diversity switch  9 , it receives a base station signal from a ground base station received by the second antenna unit  21  using the first power supply circuit  10  through the first inverted F plate antenna power supply conductor  27 , the second inverted F plate antenna power supply conductor  29 , the second antenna matching circuit  31 , the balun  32 , and the communication switch  33 , and demodulates it using the first power supply circuit  10 .  
     [0080] At this time, the second antenna unit  21  has radiation-directivity as shown in FIGS. 7 and 8, and functions as a dipole antenna of y-axis direction linear polarization (horizontal polarization) oscillating in the y-axis direction, but substantially undirectional on the x-z plane.  
     [0081] Therefore, since the second antenna unit  21  is different from the first antenna unit  3  in directivity and polarization, it can perform a receiving process with an acceptable gain although an electric wave transmitted from a ground base station through a multi-path changes in reception direction and polarization.  
     [0082] (1-2) Communications with Base Station of GPS Satellite  
     [0083] When the portable radio  20  establishes communication with a base station of a GPS satellite, it connects the switch terminal  33 C of the communication switch  33  to the contact point  33 B, and connects the switch terminal  37 C of the communication switch  37  to the contact point  37 B.  
     [0084] When the portable radio  20  establishes communication with a base station of a GPS satellite, the portable radio  20  is not, for example, performing a communicating process through the ground base station, and a control unit periodically and automatically performs the communication.  
     [0085] In this status, the portable radio  20  transmits a satellite signal component from the GPS satellite received by the first antenna unit  3  to the combiner  35  through the first antenna matching circuit  8  and the communication switch  37 , and transmits the satellite signal component from the GPS satellite received by the second antenna unit  21  to the combiner  35  through the second antenna matching circuit  31 , the balun  32 , the communication switch  37 , and the phase shifter  34 .  
     [0086] The phase shifter  34  transmits the satellite signal component received by the second antenna unit  21  to the combiner  35  with the phase of the components shifted by 90°. Practically, the phase shifter  34  adjusts and shifts the phase of the satellite signal component by 90° when the combiner  35  performs a combining process with a change of the phase by various factors such as the length of the line from the phase shifter  34  to the combiner  35 , etc. taken into account.  
     [0087] The combiner  35  combines the satellite signal component received by the first antenna unit  3  with the satellite signal component received by the second antenna unit  21  with a phase difference of about 90°, and transmits a resultant composed signal to the second power supply circuit  36 . The second power supply circuit  36  computes the current position by demodulating the received composed signal and analyzing the demodulation result.  
     [0088] With an antenna characteristic of the first antenna unit  3  of the z-axis direction linear polarization (vertical polarization) undirectional on the x-y plane as shown in FIGS. 6 and 7, and with an antenna characteristic of the second antenna unit  21  of the y-axis direction linear polarization (horizontal polarization) undirectional on the x-z plane as shown in FIGS. 7 and 8, the polarization of the first antenna unit  3  is orthogonal to the polarization of the second antenna unit  21 .  
     [0089] In this case, the portable radio  20  has no radiation-directivity in the y-axis direction as in the second antenna unit  21  as shown in FIG. 7 but has radiation-directivity in the x-axis direction as in the first antenna unit  3  and the second antenna unit  21 . Therefore, it has the antenna characteristic of radiation-directivity in the x-axis direction.  
     [0090] With the x-axis direction of the portable radio  20 , that is, the front or the back of a terminal, set toward the base station of the GPS satellite, the first antenna unit  3  has horizontal polarization to the ground, and the second antenna unit  21  keeps the horizontal polarization, but they remains orthogonal to each other.  
     [0091] Therefore, with the x-axis direction of the portable radio  20 , that is, the front or the back of a terminal, set toward the base station of the GPS satellite, the first antenna unit  3  and the second antenna unit  21  can receive a satellite signal of circular polarization by dividing it into two polarization components orthogonal to each other.  
     [0092] Then, the portable radio  20  can receive a satellite signal of circular polarization transmitted from a base station of the GPS with an acceptable gain by the combiner  35  combining the satellite signal component received by the first antenna unit  3  with the satellite signal component received by the second antenna unit  21  with the phase shifted by 90° by the phase shifter  34 .  
     [0093] (2) Operation and Effect of Embodiment  
     [0094] With the above mentioned configuration, when the portable radio  20  establishes communication with a ground base station, it switches into the first communication mode by connecting the switch terminal  33 C of the communication switch  33  to the contact point  33 A and connecting the switch terminal  37 C of the communication switch  37  to the contact point  37 A, then switches the switch terminal  9 A of the diversity switch  9  into the first antenna unit  3  or the second antenna unit  21  whichever is higher in received power level, thereby efficiently receiving a base station signal from the ground base station.  
     [0095] On the other hand, when the portable radio  20  receives a satellite signal from a GPS satellite, it switches into the second communication mode by connecting the switch terminal  33 C of the communication switch  33  to the contact point  33 B and connecting the switch terminal  37 C of the communication switch  37  to the contact point  37 B, then sets it in the x-axis direction, that is, sets the front or back of the terminal toward the base station of the GPS satellite, thereby matching in the directivity with the base station of the GPS satellite.  
     [0096] At this time, the portable radio  20  can receive a satellite signal of circular polarization transmitted from a GPS satellite with an acceptable gain by the z-axis direction linear polarization of the first antenna unit  3  and the y-axis direction linear polarization of the second antenna unit  21  with the z-axis direction linear polarization component of the satellite signal received by the first antenna unit  3  and the y-axis direction linear polarization component of the satellite signal received by the second antenna unit  21  composed with a phase difference of 90°.  
     [0097] Thus, the portable radio  20  switches the communication switches  33  and  37 , and matches in directivity with a ground base station and a base station of a GPS satellite by changing the direction of the terminal, thereby appropriately using the first antenna unit  3  and the second antenna unit  21  between the ground base station and the base station of the GPS satellite. Thus, an acceptable gain can be obtained when radio communication are established between the ground base station and the base station of the GPS satellite.  
     [0098] With the above mentioned configuration, the portable radio  20  switches the communication switches  33  and  37  to match in polarization with a ground base station or of a GPS satellite, thereby appropriately selecting the first antenna unit  3  or the second antenna unit  21  to obtain an acceptable gain in communicating with the ground base station or of the GPS satellite.  
     [0099] (3) Other Embodiments  
     [0100] In the above mentioned embodiments of the present invention, the second antenna unit  21  of the portable radio  20  as a radio communication apparatus comprises the first inverted F plate antenna  22  and the second inverted F plate antenna  23 . However, the present invention is not limited to this application, but the second antenna unit  21  can be configured, as long as it has an antenna characteristic similar to that of the second antenna unit  21 , by any antenna in various shapes such as first and second inverted L antennas, first and second helical antennas, etc. with a power supply point provided at a position at which two radiant conductors can be opposite and symmetric. With this configuration, the effects according to the above mentioned embodiments can also be obtained.  
     [0101] According to the above mentioned embodiment, the second antenna unit  21  comprises the balun  32 . However, the present invention is not limited to this application, but it is not always necessary to use a balun only if a balunce circuit can be connected to the second antenna unit  21  functioning as a balunce antenna.  
     [0102] Furthermore, according to the above mentioned embodiments, the second antenna unit  21  receives a satellite signal transmitted along circular polarization from a base station of a GPS satellite. However, the present invention is not limited to this application, but the second antenna unit  21  can receive a satellite signal from a satellite base station in various other communication systems.  
     [0103] According to the above mentioned embodiments of the present invention, the second antenna unit  21  receives a satellite signal transmitted along circular polarization from a base station of a GPS satellite. However, the present invention is not limited to this application, but a signal can be transmitted along circular polarization to a satellite base station in various other communication system.  
     [0104] In this case, using the second power supply circuit  36 , the combiner  35 , and the phase shifter  34  of circular polarization generation means, the power of the transmission signal provided from the second power supply circuit  36  can be distributed by the combiner  35 , and applied to the first antenna unit  3  and the second antenna unit  21  with a phase difference of about 90° through the phase shifter  34 . Thus, the antenna characteristics of the first antenna unit  3  and the second antenna unit  21  can be combined and converted into the circular polarization characteristic for transmission to a satellite base station.  
     [0105] Furthermore, according to the above mentioned embodiments of the present invention, the first communication mode and the second communication mode are switched by the communication switches  33  and  37  as communication switching means. However, the present invention is not limited to this application, but the first communication mode and the second communication mode can be switched using various other communication switching means capable of switching the modes by software, etc.  
     [0106] According to the above mentioned embodiments of the present invention, the control unit and the diversity switch  9  as diversity reception means switches into the first antenna unit  3  or the second antenna unit  21  whichever has a higher received power level. However, the present invention is not limited to this application, but the first antenna unit  3  and the second antenna unit  21  can be switched into each other by various other diversity reception means capable of switching the antennas by software, etc.  
     [0107] While there has been described in connection with the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be aimed, therefore, to cover in the appended claims all such changes and modifications as fall within the true spirit and scope of the invention.