Abstract:
A housing antenna is small enough in size so as to be accommodated in a mobile device. The antenna has a number of feeding points that allow the antenna to operate as a number of antennal elements. The antenna is capable of realizing high-speed communication by increasing communication capacity.

Description:
TECHNICAL FIELD 
     The present invention relates to an antenna unit for a wireless communication apparatus, the antenna unit being controlled so as to realize high speed communication by increasing channel capacity while maintaining high communication quality in mobile communication using a mobile telephone or the like, and more particularly to a wireless communication apparatus equipped with a MIMO antenna and/or an adaptive array antenna. 
     BACKGROUND ART 
     As an antenna device employing MIMO (Multi-Input Multi-Output) technique for transmitting and receiving wireless signals of a plurality of channels simultaneously by using a plurality of antennas, a MIMO antenna device is disclosed in Patent Document 1, for example. 
     The conventional MIMO antenna device disclosed in Patent Document 1 includes four groups of antenna elements, the respective groups being arranged at even intervals, and a main body. Each group of antenna elements includes four antenna elements having polarization directions different from each other. Meanwhile, the main body includes a switch section connected to the antenna elements, a signal reception section receiving a reception signal via the switch section, an antenna control section generating a control signal for the switch section, an antenna selection section generating a combination of the antenna elements to inform the antenna control section of information of the selected elements, and an antenna determination section determining, based on the reception signal received by the antenna elements generated by the antenna selection section, a specific combination of the antenna elements to inform the antenna control section of information of the determined elements. 
     The conventional MIMO antenna device with the above-described configuration is intended to reduce correlation between antenna elements and ensure sufficient transmission capacity by determining a combination of the antenna elements in a manner that one antenna element is selected from each group of antenna elements. 
     That is, in the conventional MIMO antenna device, a plurality of antenna elements operate simultaneously and then each of the antenna elements obtains largest possible received power, thereby increasing total transmission rate of a plurality of signal sequences after MIMO demodulation. The MIMO antenna device described in Patent Document 1 achieves this by including more antenna elements in number than channels for concurrent communication and by selecting the antenna elements, each having larger received signal strength therefrom. 
     Such selection of the antenna elements is especially effective in mobile communication in the case where signal intensities of main polarization and cross polarization temporally vary or an arriving angle thereof varies, in accordance with a movement of a mobile station (user) and/or time-dependent change of an ambient environment. Further, a change in the polarization direction can be dealt with by using the antenna elements having different polarization characteristics from each other, and the time-dependent change can be overcome by controlling the antenna elements to be switched. 
     As described above, the MIMO antenna device described in Patent Document 1 including the plurality of groups of antenna elements, each group having the plurality of antenna elements, and can reduce correlation between the antenna elements or increase transmission capacity by causing the switch section to select a combination of the antenna elements having the weakest correlation therebetween or a combination of the antenna elements having the largest transmission capacity. 
     Further, with reference to Patent Documents 2 and 3, an example of a mobile wireless communication apparatus utilizing a portion thereof as an antenna will be described. 
     In a mobile wireless communication apparatus described in Patent Document 2, a part of a conductive housing of the mobile communication apparatus operates as a part of an antenna so as to aim at reduction of production costs, thinning and downsizing by reduction of the number of parts without employing dedicated parts for an antenna. Further, it is possible to configure a larger antenna by causing the housing itself to operate as the antenna, whereby higher sensitivity of the antenna can be expected. According to the mobile wireless communication apparatus described in Patent Document 2, high quality wireless communication can be expected, as to the portable telephone desired to be downsized, by causing the conductive housing to operate as a part of the antenna. 
     A mobile telephone described in Patent Document 3 is aimed at reduction of gain variation depending on a condition of a user&#39;s hand, and configuration of a lip-type mobile telephone  1  is disclosed, where a shield box  14  in the upper housing  3  and an output terminal of a transmission circuit  15  within the lower housing  4  are connected by a flexible cable  9 , and the shield box  14  is used as an antenna (FIG. 3 of Patent Document 3). With such configuration where the shield box  14  is used as the antenna, the gain variation depending on the condition of the user&#39;s hand can be diminished.
     [Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-312381   [Patent Document 2] Japanese Laid-Open Patent Publication No. 2004-274730   [Patent Document 3] Japanese Examined Patent Publication No. 3830773   

     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, the conventional MIMO antenna device described in Patent Document 1 has the following problems. 
     The conventional MIMO antenna device includes, as described above, more antenna elements in number than the channels for the MIMO concurrent communication in order to obtain the largest possible received power, and performs MIMO demodulation by selecting antenna elements having stronger received signal strength from among the included antenna elements. However, a small device such as a mobile telephone in a one-wavelength size or less has a problem. That is, in the case where a plurality of antennas are mounted, a distance between adjacent antennas becomes small, so that radiation efficiency is decreased owing to mutual coupling between antenna elements and to the MIMO communication performed with an antenna array composed of antennas having the same polarization. 
     On the other hand, a conventional mobile wireless communication apparatus as described in Patent Document 2 has the following problems. 
     According to the conventional mobile wireless communication apparatus proposes a construction downsized by using a part of the conductive housing as an antenna, and a construction suitable for a single antenna or switching diversity with a slot antenna. However, the mutual coupling between antenna elements is not a problem since a single antenna operates even in the case of the switching diversity, and thus configuration of an antenna to reduce the mutual coupling is not taken into consideration. That is, the mobile wireless communication apparatus disclosed in Patent Document 2 cannot be used as a MIMO antenna in a MIMO antenna or an adaptive array antenna where a plurality of antennas operate concurrently. 
     Further, according to the conventional antenna included in a mobile telephone disclosed in Patent Document 3, only an operation of a single antenna is considered, and configuration of a MIMO antenna or an adaptive array antenna where a plurality of antennas concurrently operate is not considered. 
     Accordingly, an object of the present invention is to provide a wireless communication apparatus for a mobile object, the apparatus having lower mutual coupling between antennas in order to allow a plurality of feed antenna elements to concurrently maintain good reception conditions even if the apparatus is small-sized. 
     Solution to the Problems 
     The present invention is directed to a mobile wireless communication apparatus including a plurality of antenna elements. In order to achieve the above-described object, one embodiment of the present invention includes a rectangular-shaped first conductor section; a second conductor section having the same shape as the first conductor section, arranged in parallel with and spaced from the first conductor section so as to have a predetermined distance therebetween; three short-circuit conductor sections electrically connecting any three edges of the first conductor section with face-to-face three edges of the second conductor section; a ground conductor section spaced by a predetermined distance from the first conductor section; and a wireless communication circuit, wherein a first feeding point on the first conductor section is connected to the wireless communication circuit via a first power supply section arranged between the first conductor section and the ground conductor section, so that the first conductor section and the ground conductor section are allowed to operate as a first antenna element; and a second feeding point on the second conductor section is connected to the wireless communication circuit via a second power supply section arranged between the first conductor section and the second conductor section, so that the first conductor section, the second conductor section and the short-circuit conductor sections are allowed to operate as a second antenna element. 
     When the length of one edge, to which the three short-circuit conductor sections are not connected, is set at a half wavelength of a communication signal, the second antenna element can operate as a half-wavelength slot antenna. Only adjacent two short-circuit conductor sections may be connected to the first and the second conductor sections, and the total length of the adjacent two short-circuit conductor sections may be set at one-half of the communication signal wavelength. Further, a part of a housing of the mobile wireless communication apparatus, the housing being formed of a conductive material, may be used as the first conductor section. Still further, the wireless communication circuit may be mounted on the first conductor section. 
     When one second antenna element is caused to operate at a different frequency, either one of the short-circuit conductor sections may be controlled to be switched in accordance with the frequency. In this case, as the one of the short-circuit conductor sections, a parallel resonant circuit including an inductor and capacitor, a switch circuit controlled by the control section and the like can be employed. 
     Here, the mobile wireless communication apparatus of the present invention can be caused to operate as an adaptive antenna when the mobile wireless communication apparatus further includes an adaptive control circuit executing adaptive control processing on a wireless signal received by each of the First and the second antenna elements to synthesize the adaptively controlled wireless signals; a demodulation circuit demodulating the synthesized wireless signal as well as a wireless signal individually received by each of the first antenna element and the second antenna element; and an apparatus control circuit controlling the adaptive control circuit so as to compare signal integrity obtained from demodulation of the synthesized wireless signal, and signal integrity obtained from demodulation of the wireless signals received by the First and the second antenna elements with each other, and causing the adaptive control circuit to receive a wireless signal having optimum signal integrity determined by the comparison. 
     Further, the mobile wireless communication apparatus of the present invention can be caused to operate as a selection diversity antenna when a mobile wireless communication apparatus further includes a first processing circuit executing adaptive control processing on the wireless signals received by the first and the second antenna elements; a second processing circuit executing selection diversity processing on the wireless signals received by the First and the second antenna elements; and a selection circuit comparing signal integrity of a wireless signal outputted from the first processing circuit, with signal integrity of a wireless signal outputted from the second processing circuit, and selectively outputting a signal having desirable signal integrity. 
     Furthermore, the mobile wireless communication apparatus of the present invention can be caused to operate as a combined diversity antenna when a mobile wireless communication apparatus further includes an adaptive control circuit executing adaptive control processing on a wireless signal received by each of the first and the second antenna elements, and synthesizing the adaptively controlled wireless signals; and an apparatus control circuit detecting phase and amplitude of a wireless signal received by each of the first and the second antenna elements, and controlling the adaptive control circuit so as to perform maximum ratio combining on the wireless signals. 
     Still further, when a mobile wireless communication apparatus further includes a MIMO demodulation circuit executing a MIMO demodulation processing on a wireless signal received by each of the first and the second antenna elements to output one demodulated signal, the mobile wireless communication apparatus of the present invention can be caused to operate as a MIMO antenna. 
     Effect of the Invention  
     According to the above-described present invention, an array antenna can be realized in a small terminal without significantly increasing the number of parts of the antenna. Additionally, the antenna can be enlarged to a large extent by using the housing itself as an antenna. Further, mutual coupling between antennas can be reduced by arranging the short-cut side of the slot antenna so as to face the power supply section for the housing antenna. Still further, a correlation coefficient between antennas can be lowered by arranging antennas so as to have different radiation directivity from each other. Therefore, increase in performance as an array antenna can be expected, and an improved operation of a MIMO antenna and/or an adaptive array antenna can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows diagrams each illustrating an inner structure of a mobile wireless communication apparatus according to a first embodiment of the present invention. 
         FIG. 2  shows a diagram illustrating a structure of a housing antenna  20 . 
         FIG. 3  shows a schematic diagram illustrating directions of currents, a direction of an electric field and a radiation pattern of the housing antenna  20 . 
         FIG. 4  shows a diagram illustrating a structure of a half-wavelength slot antenna  30 . 
         FIG. 5  shows schematic diagrams illustrating a direction and a radiation pattern of an electric field excited at the half-wavelength slot antenna  30 . 
         FIG. 6  shows a diagram illustrating an exemplary prototype of the housing antenna  20 . 
         FIG. 7  shows a diagram illustrating impedance characteristics of the housing antenna  20  shown in  FIG. 6 . 
         FIG. 8  shows a diagram illustrating a radiation pattern of the housing antenna  20  shown in  FIG. 6 . 
         FIG. 9  shows a diagram illustrating an exemplary prototype of the half-wavelength slot antenna  30 . 
         FIG. 10  shows a diagram illustrating impedance characteristics of the half-wavelength antenna  30  shown in  FIG. 9 . 
         FIG. 11  shows a diagram illustrating a radiation pattern of the half-wavelength antenna  30  shown in  FIG. 9 . 
         FIG. 12  shows a diagram illustrating an exemplary prototype of an antenna array, which is obtained by combining both antennas. 
         FIG. 13  shows a diagram illustrating impedance characteristics of the antenna array shown in  FIG. 12 . 
         FIG. 14  shows a diagram illustrating the reflection characteristics and mutual coupling characteristics of the antenna array shown in  FIG. 12 . 
         FIG. 15  shows a diagram illustrating radiation directivity of the housing antenna  20  in the antenna array. 
         FIG. 16  shows a diagram illustrating radiation directivity of the half-wavelength antenna  30  in the antenna array. 
         FIG. 17  shows a diagram illustrating an inner structure of another mobile wireless communication apparatus according to the first embodiment of the present invention. 
         FIG. 18  shows a diagram illustrating an example of a specific circuit of a short-circuit conductor section  12  used for a mobile wireless communication apparatus according to a second embodiment of the present invention. 
         FIG. 19  shows a diagram illustrating a Smith chart of the circuit shown in  FIG. 18 . 
         FIG. 20  shows a diagram illustrating an example of another specific circuit for realizing the short-circuit conductor section  12 . 
         FIG. 21  shows a diagram illustrating a structure of an adaptive antenna device according to a third embodiment of the present invention. 
         FIG. 22  shows a flowchart illustrating adaptive control processing performed by a controller  103  shown in  FIG. 21 . 
         FIG. 23  shows a diagram illustrating a structure of a selection diversity antenna device according to a fourth embodiment of the present invention. 
         FIG. 24  shows a schematic diagram illustrating a structure of a combined diversity antenna device according to a fifth embodiment of the present invention. 
         FIG. 25  shows a diagram illustrating a structure of a MIMO antenna device according to a sixth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
         
           
               2 ,  3  power supply section 
               4  wireless communication circuit 
               5 ,  6  feedline 
               7 ,  8  conductor section 
               9  ground conductor section 
               10 - 12  short-circuit conductor section 
               20  housing antenna 
               30  slot antenna 
               41  inductor 
               42  capacitor 
               43  switch 
               100   a - d ,  201 ,  202 ,  40   a - c ,  501   a - c ,  507  antenna element 
               101 ,  502  A/D converter circuit 
               102  adaptive control circuit 
               103 ,  405 ,  505  controller 
               104   a - d ,  402   a - c  variable amplifier 
               105   a - d ,  403   a - c  variable phase-shifter 
               106 ,  406  signal synthesizer 
               107  demodulator 
               109  determinator 
               203 ,  204  processing circuit 
               205 ,  206  wave detector 
               207  signal integrity monitoring circuit 
               208  selection circuit 
               404   a - c  received signal wave detector 
               503  MIMO demodulation circuit 
               504  signal level comparison circuit 
               506  wireless transmission circuit 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described in detail with reference to the drawings. Note that with respect to figures for describing the embodiments of the present invention, components having similar functions are denoted by the same reference numerals and repeated description thereof will be omitted. 
     (First Embodiment) 
       FIG. 1  is a front view and a side view each showing an inner structure of a mobile wireless communication apparatus according to a first embodiment of the present invention. In  FIG. 1 , the mobile wireless communication apparatus according to the first embodiment of the present invention includes a first and a second power supply sections  2  and  3 , a wireless communication circuit  4 , a first and a second feedlines  6  and  5 , a first and a second conductor sections  7  and  8 , a ground conductor section  9 , and three short-circuit conductor sections  10  to  12 . The first conductor section  7  and the second conductor section  8  have the same rectangular configuration. 
     The mobile wireless communication apparatus according to the first embodiment includes, as an antenna array, a housing antenna which is obtained by using a part or a conductive housing as an antenna, and a half-wavelength slot antenna which is obtained by using a part of the conductive housing as a ground plane. The first power supply section  2  is a power supply section for supplying power to the housing antenna via the first feedline  6 . The second power supply section  3  is a power supply section for supplying power to the half-wavelength slot antenna via the second feedline  5 . The first and second power supply sections  2  and  3  are connected to the wireless communication circuit  4  and allow wireless communication. The wireless communication circuit  4  includes high-frequency circuits such as a filter, an amplifier and a frequency conversion mixer, and a baseband circuit such as a modulator and a demodulator. 
     First, an operation of a housing antenna  20  will be described with reference to  FIG. 2  and  FIG. 3 , and an operation of a half-wavelength slot antenna  30  will be described with reference to  FIG. 4  and  FIG. 5 , respectively. 
       FIG. 2  shows a schematic structure of the housing antenna  20 . The housing antenna  20  includes a first conductor section  7 , a ground conductor section  9  and a first power supply section  2 . The first conductor section  7  is a ground plane of the upper housing of a flip-type telephone. The ground conductor section  9  is a ground plane of the lower housing of the flip-type telephone. The first power supply section  2  is disposed at a hinge portion connecting the first conductor section  7  and the ground conductor section  9 . 
       FIG. 3  is a schematic diagram showing a direction of a current, a direction of an electric field and a radiation pattern, in the housing antenna  20 . As shown in  FIG. 3 , in the housing antenna  20 , a high-frequency current  24  flows to the first conductor section  7  and to the ground conductor section  9 , whereby radio waves are emitted. The current flows in a similar manner to that of a dipole antenna, and thus, has radiation directivity such as a figure-eight directional sensitivity  25  on a plane (ZY plane) of the sheet of the drawings and non-directional sensitivity on a plane (XY plane) perpendicular to the plane of the sheet. Note that the direction  26  of the electric field of the emitted radio waves is parallel to that of the high-frequency current  24 . 
       FIG. 4  shows a structure of the half-wavelength slot antenna  30 . The half-wavelength slot antenna  30  includes a first conductor section  7 , a second conductor section (top face conductor section)  8 , three short-circuit conductor sections  10  to  12 , and a second power supply section  3 . The first conductor section  7  is arranged parallel to and apart from the second conductor section  8  having a predetermined distance therebetween, and three edges thereof are electrically connected via the three short-circuit conductor sections  10  to  12 , respectively, each conductor section having a width equal to the predetermined distance. That is, the half-wavelength slot antenna  30  is open top box shaped, the short-circuit conductor section  10  forming the bottom face, and the short-circuit conductor section  11 , the short-circuit conductor section  12 , the first conductor section  7  and the second conductor section  8  forming side faces. The second power supply section  3  supplies power between the first conductor section  7  and the second conductor section  8 . The half-wavelength slot antenna  30  is designed such that a length of one edge (line a), to which the short-circuit conductor sections  10  to  12  are not connected, of the first conductor section  7  (or the second conductor section  8 ) is a half of the wavelength of a communication signal. 
     Note that, although the open top box shaped half-wavelength slot antenna  30  is described in the first embodiment, the short-circuit conductor section  11  or the short-circuit conductor section  12  can be omitted. That is, when the total length of two edges (line a and line b), to which the short-circuit conductor sections  10  and  12  are not connected, of the first conductor section  7  is a half of the wavelength of the communication signal, the short-circuit conductor section  11  is unnecessary. Further, when the total length of two edges (line a and line c), to which the short-circuit conductor sections  10  and  11  are not connected, of the conductor section  7  is a half of the wavelength of the communication signal, the short-circuit conductor section  12  is unnecessary. 
       FIG. 5  shows schematic diagrams illustrating a direction and a radiation pattern of an electric field that is excited in the half-wavelength slot antenna  30 . As shown in  FIG. 5 , in the half-wavelength slot antenna  30 , power supply from the second power supply section  3  generates an electric field  35  between the first conductor section  7  and the second conductor section  8 , and the short-circuit conductor section  10  functions as a reflection plate, whereby a high radiation directivity  36  in a Z-direction can be obtained. 
     Next, examples of prototypes of the housing antenna  20  and the half-wavelength slot antenna  30  will be described with reference to  FIG. 6  through  FIG. 11 . 
       FIG. 6  is an exemplary prototype of the housing antenna  20 . In the prototype, a first conductor section  7  and a ground conductor section  9  are rectangular measuring 45 mm×90 mm, and have a distance of 5 mm therebetween. Further,  FIG. 7  and  FIG. 8  show impedance characteristics (input VSWR) and a radiation pattern (XY plane), respectively. From  FIG. 7 , it can be seen that the housing antenna  20  resonates at 1.4 GHz. Note that  FIG. 8  shows a radiation pattern of a frequency of 1.6 GHz. According to  FIG. 8 , slightly higher directivity in an X-direction can be seen. This is because the power supply section is not symmetrical with respect to the antenna. However, it is apparent that non-directional can be substantially obtained. 
       FIG. 9  is an exemplary prototype of a half-wavelength slot antenna  30 . In the exemplary prototype, a first conductor section  7  and a second conductor section  8  are rectangular measuring 45 mm×90 mm, a short-circuit conductor section  10  is rectangular measuring 90 mm×5 mm, and short-circuit conductor sections  11  and  12  are rectangular measuring 45 mm×5 mm. Further,  FIG. 10  and  FIG. 11  show impedance characteristics (input VSWR) and a radiation pattern (XY plane), respectively. From  FIG. 10 , it can be seen that the half-wavelength slot antenna  30  resonates at 1.6 GHz.  FIG. 11  shows a radiation pattern or a frequency of 1.6 GHz. From  FIG. 11 , slightly higher directivity in a Y-direction can be seen. This is because, as shown in  FIG. 5 , the short-circuit conductor section  10  functions as a reflection plate. 
     As described above, the housing antenna  20  and the half-wavelength slot antenna  30  have different radiation directivities from each other, so that it is assumed that correlation coefficient between the antennas is low. Accordingly, desirable array performance can be expected as a MIMO antenna, an adaptive array antenna, and an array antenna of maximum ratio combining or the like. 
     Next, an antenna array formed by combining the housing antenna  20  and the half-wavelength slot antenna  30  will be described. 
       FIG. 12  is an exemplary prototype of an array antenna formed by combining the housing antenna  20  shown in  FIG. 6  and the half-wavelength slot antenna  30  shown in  FIG. 9 . Additionally,  FIG. 13  shows impedance characteristics (input VSWR) of both antennas, and  FIG. 14  shows reflection characteristics and mutual coupling characteristics (transmission characteristics between antennas) of both antennas. 
     From  FIG. 13 , it can be seen that the antenna array resonates at 1.6 GHz. According to  FIG. 13 , in comparison with  FIG. 7  and  FIG. 10 , impedance characteristics of the antenna array are almost unchanged. That is, it can be seen that two antennas forming the antenna array are hardly affected by one another. This is because the short-circuit conductor sections  10  to  12  provided between the first power supply section  2  of the housing antenna  20  and the power supply section  3  of the half-wavelength slot antenna  30  improve shielding effect. 
     Accordingly, each antenna can be designed independently, which provides an effect of easing designing of each antenna. Further, according to  FIG. 14 , it can be seen that the mutual coupling characteristics are −35 dB and below. Accordingly, an electric power of one antenna absorbed by the other antenna is less than or equal to a tenth, so that decrease of radiation efficiency of the one antenna is up to −0.5 dB. As a result, desirable radiation efficiency with low deterioration can be realized. 
       FIG. 15  and  FIG. 16  show radiation directivities of the housing antenna  20  and the half-wavelength slot antenna  30 , respectively, when both function as an antenna array. Although the radiation directivity of the half-wavelength slot antenna  30  shown in  FIG. 16  is slightly lower in comparison with the case of individual functioning, the housing antenna  20  and the half-wavelength slot antenna  30  can obtain the directivity similar to that of the individual case, and variation of directivity is small in the case of functioning as an antenna array. 
     As described above, the mobile wireless communication apparatus according to the first embodiment of the present invention can realize an antenna which has small mutual coupling between antennas and different directivities to obtain desirable array characteristics, and the mobile wireless communication apparatus according to the First embodiment of the present invention is most suitable for a compact mobile wireless communication apparatus. 
     The example where the wireless communication circuit  4  is mounted on the ground conductor section  9  is described in the First embodiment. However, as shown in  FIG. 17 , the wireless communication circuit  4  may be mounted on the first conductor section  7 . Such configuration allows the second feedline  5  wired to the second power supply section  3  to be shortened. Further, since the first conductor section  7  becomes a common ground of the first power supply section  2  and the second power supply section  3 , the stabilization and a simple construction of the ground can be advantageously realized. 
     Additionally, although, in the first embodiment, the flip-type mobile wireless communication apparatus as shown in  FIG. 1  is described as an example, the antenna array configuration of the present invention is applicable to a mobile wireless communication apparatus having other various structures (non-flip type, slide type). 
     Further, when a part of the housing of the mobile wireless communication apparatus is formed of a conductive material, the part can be used as the first conductor section  7 . 
     (Second Embodiment) 
     A mobile wireless communication apparatus according to a second embodiment of the present invention allows the half-wavelength slot antenna  30  to resonate at different frequencies by switching the short-circuit conductor section  12  (or the short-circuit conductor section  11 , hereinafter referred to similarly) of the mobile wireless communication apparatus according to the first embodiment. 
     In order to achieve resonances at two frequencies, the short-circuit conductor section  12  of the half-wavelength slot antenna  30  is caused to be an open circuit in the case of resonance at a first frequency, and is caused to be a short circuit in the case of resonance at a second frequency. As a result, two orthogonal resonant modes can be realized. 
       FIG. 18  is a diagram showing a specific circuit example of the short-circuit conductor section  12 . 
       FIG. 18  is a parallel resonant circuit consisting of an inductor  41  and a capacitor  42 , where impedance reaches an infinite value at a resonant frequency, resulting in an open-circuit condition. A Smith chart under such a condition is shown in  FIG. 19 . In the example, magnitude of each of the inductor  41  and the capacitor  42  is determined so as to resonate at a first frequency f 1 . The circuit is in an open-circuit condition at a first frequency f 1 , and in low impedance and short circuited at a second frequency f 2 , which is higher than the first frequency f 1 . 
     On the other hand, the short-circuit conductor section  12  may be replaced with a switch  43  shown in  FIG. 20 . In such a case, the switch  43  is connected at the time of operation at the first frequency, the switch  43  is open at the time of operation at the second frequency. 
     As described above, the mobile wireless communication apparatus according to the second embodiment of the invention uses, for the short-circuit conductor section  12 , a circuit where impedance is changed in accordance with a frequency, whereby resonance at two frequencies can be achieved in one apparatus. 
     (Third Embodiment) 
       FIG. 21  is a diagram showing a structure of an adaptive antenna device according to a third embodiment of the present invention. In  FIG. 21 , the adaptive antenna device according to the third embodiment includes four antenna elements  100   a - d , an analog/digital converter circuit (A/D converter circuit)  101 , an adaptive control circuit  102 , a controller  103 , a determinator  109 , and a demodulator  107 . The housing antenna  20  and the half-wavelength slot antenna  30  described in the first embodiment are used for two of the four antenna elements  100   a - d.    
     In  FIG. 21 , a wireless signal received by each of the antenna elements  100   a - d  is inputted to both of the A/D converter circuit  101  and the adaptive control circuit  102 . The A/D converter circuit  101  includes A/D converters corresponding to the antenna elements  100   a - d . respectively, and converts analog wireless signals received by the antenna elements  100   a - d  to digital signals, respectively to output the converted results to the controller  103 . 
     The adaptive control circuit  102  includes four variable amplifiers  104   a - d , four variable phase-shifters  105   a - d  and a signal synthesizer  106 . The amount of variable amplification of the variable amplifiers  104   a - d  and the amount of phase shift of the variable phase-shifters  105   a - d  are controlled by the controller  103 . A wireless signal received by the antenna element  100   a  is outputted via the variable amplifier  104   a  and the variable phase-shifter  105   a , a wireless signal received by the antenna element  100   b  is outputted via the variable amplifier  104   b  and the variable phase-shifter  105   b , a wireless signal received by the antenna element  100   c  is outputted via the variable amplifier  104   c  and the variable phase-shifter  105   c , and a wireless signal received by the antenna element  100   d  is outputted via the variable amplifier  104   d  and the variable phase-shifter  105   d , to the signal synthesizer  106 , respectively. The signal synthesizer  106  synthesizes (adds) the inputted four wireless signals so as to output the result to the demodulator  107 . 
     The demodulator  107  demodulates the synthesized wireless signals inputted from the signal synthesizer  106 , by using a predetermined digital demodulation method, to a baseband signal that is the demodulated signal, and outputs the demodulated result to the output terminal  108  and the determinator  109 . The determinator  109  determines an error rate based on a reference pattern, which is included in the inputted baseband signal and is within a predetermined reference pattern period, and outputs the error rate to the controller  103 . The controller  103  uses an adaptive control method, which will be described in detail, to control the adaptive control circuit  102  such that a wireless signal having the optimum signal integrity is received and demodulated. 
     Note that, in  FIG. 21 , basic configuration for processing a wireless signal, a high-frequency filter, a high-frequency amplifier, a high-frequency circuit, an intermediate-frequency circuit, and a signal processing circuits are omitted. That is, in the adaptive control circuit  102 , processing may be executed at a carrier frequency or at an intermediate frequency. Further, the configuration order of the components, that is, the variable amplifiers  104   a - d  and the variable phase-shifters  105   a - d  in the adaptive control circuit  102  may be reversed. 
     First, an adaptive control method in the adaptive antenna device will be described below. The adaptive antenna device uses an adaptive control technique to maximize a radiation pattern of an antenna toward a direction of arrival of a desired radio wave (i.e., to substantially direct the main beam in the radiation pattern toward the direction of the desired wave), and to direct NULL in the radiation pattern toward a direction of an interference wave which causes interference (i.e., to substantially direct NULL in the radiation pattern toward the direction of the interference wave), thereby achieving a stable wireless communication. Generally, the adaptive antenna device performs controlling to obtain the maximum desired signal power and the minimum interference signal power, by providing a wireless signal received by each of the antenna elements  100   a - d , (or an intermediate-frequency signal frequency converted from the wireless signal) with an amplitude difference and a phase difference. 
     Each of the antenna elements  100   a - d  generally receives a thermal noise component together with a desired wave. Further, a co-channel interference wave having a common frequency radiated from a neighboring base station, or a delay wave which is temporally delayed because of having been arrived via a detour route, though it is a desired wave, may be received. The delay wave deteriorates, as a ghost, for example, appearing on a television receiver, quality of a screen display in an analog wireless communication system such as television broadcasting or radio broadcasting. On the other hand, a thermal noise component, the co-channel interference wave and the delay wave affect a digital wireless communication system as a bit error rate, and directly deteriorate signal integrity. Here, assuming that a desired wave power is C, a thermal noise power is N, and power of an interference wave including a co-channel interference wave and the delay wave is 1, the adaptive antenna device performs adaptive control to favorably maximize C/(N+1) in order to improve signal integrity. 
     Next, a specific operation of the adaptive control apparatus will be described. 
     A wireless signal received by each of the antenna elements  100   a - d  is converted in the A/D converter circuit  101  to a digital signal x(t) (a signal vector having four parameters in the case of the present embodiment) to be inputted to the controller  103 . The controller  103  determines amplitude amounts and shift amounts of the variable amplifiers  104   a - d  and the variable phase-shifters  105   a - d  in the adaptive control circuit  102 , respectively, and the amplitude amounts and the shift amounts allow a wireless signal y(t), outputted from the adaptive control circuit  162 , to have the optimum signal integrity. 
     A method for calculating a weighting coefficient including the amplitude amount and shift amount will be described. Note that, the weighting coefficient Wi is defined by the following formula (1) based on an amplitude amount Ai and a shift amount φi.
 
 Wi−Ai ×exp( j×φi )  (1)
 
     Here, j represents an imaginary unit. Additionally, i takes values 1 through 4, corresponding to systems for processing wireless signals received by the antenna elements  100   a - d , respectively. A method for calculating the weighting coefficient Wi will be shown by defining weighting coefficient vector W that has the weighting coefficient Wi as a component thereof. 
     Although there are several methods for calculating the weighting coefficient Wi, an example using Least Means Squares (LMS) will be described. In the method, the adaptive antenna device preliminarily stores a reference signal r(t) that is a signal sequence included in a known desired wave, and performs control such that the signal sequence included in the received wireless signal become close to the reference signal r(t). Here, an example where the reference signal r(t) is preliminarily stored in the controller  103  will be shown. Specifically, the controller  103  controls the adaptive control circuit  102  so as to multiply a wireless digital signal x(t) by the weighting coefficient w(t) including components of an amplitude amount and a phase shift amount. A residual error e(t) between a multiplication result obtained by multiplying the weighting coefficient w(t) by the wireless digital signal x(t) and the reference signal r(t) is calculated from the following formula (2).
 
 e ( t )= r ( t )− W ( t )× x ( t )  (2)
 
     Here, the residual error e(t) takes a positive or negative value. Accordingly, a minimum square value of the residual error e(t), calculated by the above-described formula (2), is calculated by repeating the calculation recursively. That is, the weighting coefficient w(t, m+1), obtained by repeating a calculation multiple times (m+1 limes), can be obtained by the following formula (3) based on the m-th weighting coefficient w(t, m).
 
 W ( t,m+ 1)= W ( t,m )+ u×x ( t )× e ( t,m )  (3)
 
     Here, u is referred to as step size, and the repetition count of calculation, which allows the weighting coefficient w to converge to minimum value, is advantageously reduced when the step size u is large, but has a disadvantage that the weighting coefficient w fluctuates near the minimum when the step size u is too large. Accordingly, special attention should be paid depending on the system for selection of the step size U. On the contrary, the weighting coefficient w stably converges to the minimum when the step size u is small. However, the repetition count of calculation increases. When the repetition count increases, it takes a long time to obtain the weighting coefficient. In the case where calculation time of the weighting coefficient w takes longer than time (a few milliseconds) during which surrounding environment changes, improvement in signal integrity by the weighting coefficient w cannot be achieved. Consequently, it is necessary to select highest possible speed and more stable convergence condition when the step size u is determined. Further, the residual error e (t, m) is defined by the following formula (4).
 
 e ( t,m )= r ( t )− W ( t,m )× x ( t )  (4)
 
     The formula (3) is updated in a recurring manner by using the value in the formula (4). Note that the maximum number of repetition of calculation for obtaining the weighting coefficient w is set such that time to calculate the weighting coefficient is not longer than switching time of a wireless system. 
     Here, a method for an adaptive control of the wireless communication system based on the Least Means Squares method is described as an example, but the present invention is not limited to this method, and RLS (Recursive Least Squares) method, or SMI (Sample Matrix Inversion) method, for example, which allow faster determination, for example, can be employed. Although determination can be performed faster by the methods, calculation in the determinator  109  becomes complicated. Further, in the case where the modulating method of a signal sequence is a constant envelope modulation, like a digital phase modulation, having a constant envelope, CMA (Constant Modulus Algorithm) can be employed. 
       FIG. 22  is a flowchart showing adaptive control processing performed by a controller  103  shown in  FIG. 21 . 
     In  FIG. 22 , first, the controller  103  obtains, from the A/D converter circuit  101 , data received by each of the antenna elements  100   a - d  (step S 1 ). Next, the controller  103  calculates an amplitude amount and a phase shift amount, required for the adaptive control, based on the obtained received data (step S 2 ), and controls the adaptive control circuit  102  based on the calculated amplitude amount and phase shift amount (step S 3 ). The demodulator  107  demodulates the received signals outputted from the adaptive control circuit  102  (step S 4 ). The determinator  109  determines signal integrity of the received signal demodulated by the demodulator  107  (step S 4 ). The controller  103  obtains signal integrity, that is error rate, determined by the determinator  109  (step S 4 ). As a result, the controller  103  then determines the obtained error rate is greater than or equal to a predetermined threshold value (step S 5 ). 
     In the case where the error rate is determined to be greater than or equal to 10 −5  in step S 5 , the controller  103  obtains again, from the A/D converter circuit  101 , the received data received by each of the antenna elements  100   a - d  (step S 1 ). On the other hand, in the case where the error rate is determined to be less than 10 −5  in step S 5 , the controller  103  controls the adaptive control circuit  102  to obtain an error rate of each of the antenna elements  100   a - d  in the individual operation (step S 6 ). 
     Here, the antenna elements  100   a - d  in the individual operation means a state where only one of the antenna elements  100   a - d  operates. For example, the antenna element  100   a  in the individual operation means that only the antenna element  100   a  operates and the antenna elements  100   b - d  are not in operation. In this case, specifically, an amplification amount of a variable amplifier  104   a  is set at “1” and phase shift amount of a variable phase-shifter  115   a  at “0”, and an amplification amount of a variable amplifier  104   a  at “0”. 
     Finally, the controller  103  compares an error rate at the time when the adaptive control synthesis is outputted, with an error rate of the signal received by each of the antenna elements  100   a - d  in the individual operation, and selects the optimum error rate to control the adaptive control circuit  102  so as to receive a received signal having the selected optimum error rate (step S 7 ). 
     Note that, in  FIG. 22 , it is desirable to wait for a predetermined time when processing returns from step S 5  to step S 1 , and/or from step S 7  to step S 1 . 
     As described above, in the adaptive antenna device according to the third embodiment of the present invention, error rates are checked while adaptive control is performed by using four antenna elements  100   a - d . The error rate of each of the antenna elements  100   a - d  in the individual operation is measured when the error rate is under a predetermined threshold value, and the adaptive control circuit  102  is controlled so as to receive a received signal having the optimum error rate. Such switching control between the adaptive control and the individual operation of each of the antenna elements makes it possible to constantly select the received signal having the optimum signal integrity. 
     (Fourth Embodiment) 
       FIG. 23  is a diagram showing configuration of a selection diversity antenna device according to a fourth embodiment of the present invention. In  FIG. 23 , the selection diversity antenna device according to the fourth embodiment includes two antenna elements  201  and  202 , two processing circuits  203  and  204 , a signal integrity monitoring circuit  207  and a selection circuit  208 . The housing antenna  20  and the half-wavelength slot antenna  30 , described in the first embodiment, are used as the two antenna elements  201  and  202 . 
     First, a wireless signal received by each of the antenna elements  201  and  202  is inputted to both of the processing circuits  203  and  204 . The processing circuit  203  performs adaptive control processing on the inputted wireless signals to output the results to the wave detector  205  and the signal integrity monitoring circuit  207 . Here, the processing circuit  203  maintains desirable signal integrity by suppressing interference waves in the received wireless signals. That is, the processing circuit  203  is significantly effective when a delay wave and/or a co-channel interference wave arrive from a neighboring base station. Additionally, the processing circuit  204  performs selection diversity processing on the inputted wireless signal to output the result to the wave detector  206  and the signal integrity monitoring circuit  207 . Here, the processing circuits  204  maintains the desirable signal integrity by selecting a wireless signal having greater received power from among the received wireless signals received by the antenna elements  201  and  202 , respectively. That is, the processing circuit  204  produces a great effect when a change in the received power is great like in the case of fading. 
     Here, the signal integrity monitoring circuit  207  determines signal integrity of a baseband signal which is a wireless signal adaptively controlled and modulated by the processing circuit  203 , and signal integrity of a wireless signal on which selection diversity processing is performed by the processing circuit  204 . Next, the selection circuit  208  selects, based on the determination result of the signal monitoring circuit  207 , a baseband signal from a wave detector  205  or  206  corresponding to a signal having more desirable signal integrity and outputs the selected baseband signal to the output terminal  209 . 
     As described above, the selection diversity antenna device according to the fourth embodiment of the present invention can solve both of two main factors, that is, interference waves and fading, for deterioration in signal integrity of the received signal in a mobile communication system. 
     (Fifth Embodiment) 
       FIG. 24  is a schematic diagram showing a configuration of a combined diversity antenna device according to a fifth embodiment of the present invention. In  FIG. 24 , the combined diversity antenna device includes three antenna elements  401   a - c , variable amplifiers  402   a - c , variable phase-shifters  403   a - c , a signal synthesizer  406 , a received signal wave detectors  404   a - c  and a controller  405 . The variable amplifiers  402   a - c  are amplifiers having positive or negative amplification and can operate as attenuators. The housing antenna  20  and the half-wavelength slot antenna  30 , described in the first embodiment, are used as two of the three antenna elements  401   a - c.    
     In  FIG. 24 , each wireless signal received by each of the antenna elements  401   a - c  is inputted to both variable amplifiers  402   a - c  and received signal wave detectors  404   a - c . Each of the received signal wave detectors  404   a - c  detects phase and amplitude of a wireless signal to output the detected data to the controller  405 . The controller  405 , using a well-known adaptive control method, controls amplification amounts of the variable amplifiers  402   a - c  and phase shift amounts of the variable phase-shifters  403   a - c  so as to achieve max ratio combined of the three wireless signals received by the antenna elements  401   a - c . That is, the variable amplifiers  402   a - c  amplify or attenuate the wireless signals corresponding to ratio between the wireless signals, while the variable phase-shifters  403   a - c  align phases of the wireless signals and output the results to the signal synthesizer  406 . The signal synthesizer  406  performs in-phase combination by maximum ratio combining on the inputted three wireless signals and outputs the result to the output terminal  407 . 
     As described above, the combined diversity antenna device according to the fifth embodiment of the present invention makes it possible to obtain the stable received power. 
     (Sixth Embodiment) 
       FIG. 25  is a diagram showing configuration of a MIMO antenna device according to a sixth embodiment of the present invention. In  FIG. 25 , a MIMO device according to the sixth embodiment includes three feed antenna elements  501   a - c , an analog/digital converter circuit (A/D converter circuit)  502 , a MIMO demodulation circuit  503 , a signal level comparison circuit  504 , a controller  505 , a wireless transmission circuit  506  and a transmission antenna element  507 . The housing antenna  20  and the half-wavelength slot antenna  30  described in the first embodiment are used as two of the three feed antenna elements  501   a - c.    
     The three feed antenna elements  501   a - c  are provided to respectively receive three different wireless signals transmitted from base station equipment (not shown) on the MIMO transmission side using a predetermined MIMO demodulation method. Each of the feed antenna elements  501   a - c  inputs the received wireless signal to the A/D converter circuit  502 . The A/D converter circuit  502  includes three A/D converters corresponding to the inputted wireless signals, respectively, and the A/D converters individually perform A/D conversion processing on the respective wireless signals and outputs the processed signals (hereinafter referred to as received signals) to both of the MIMO demodulation circuit  503  and the signal level comparison circuit  504 . 
     The MIMO demodulation circuit  503  performs MIMO demodulation processing on the three received signals to output one demodulated signal. The signal level comparison circuit  504  compares signal levels of the three received signals to output result data of the comparison to the controller  505 . The controller  505  may change, depending on the result of the MIMO adaptive control processing, a MIMO communication method used in the base station equipment on the MIMO transmission side and used in the MIMO demodulation circuit  503 . That is, the controller  505  transmits a control signal, by using the wireless transmission circuit  506  and the antenna element  507 , to request the base station equipment on the MIMO transmission side to change MIMO demodulation method used in the base station equipment on the MIMO transmission side, and additionally cause the MIMO demodulation circuit  503  to change the MIMO demodulation method used therein. 
     It is desirable that the MIMO antenna device according to the sixth embodiment includes, in the first stage of the A/D conversion circuit  502 , a high-frequency filter for separating a signal, having a predetermined frequency, from each of the wireless signals received by the feed antenna elements  501   a - c , and a high-frequency amplifier for amplifying a signal when necessary. Further, it is desirable that the MIMO antenna device according to the sixth embodiment includes, in the first stage of the MIMO demodulation circuit  503 , a high frequency circuit such as a mixer for converting a frequency of each of the received signals outputted from the A/D converter circuit  502 , an inter-mediate frequency circuit, the processing circuits, and the like when necessary. Note that the above-described components are omitted in the present specification and drawings for simplicity. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a wireless communication apparatus, for example, equipped with a MIMO antenna and/or an adaptive array antenna, and especially suitable, for the case of controlling mobile communication using a mobile telephone and the like so as to maintain desirable communication quality while realizing high-speed communication by increasing communication capacity.