Patent Publication Number: US-6903702-B2

Title: Radio equipment

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to radio equipment and more particularly to radio equipment which can ensure good transmission of radio waves even when the provision of a ground structure (ground) is difficult. 
   2. Prior Art 
   In order to efficiently radiate radio waves from an antenna connected to radio equipment, a circuit of the radio equipment or the body of the device has hitherto been grounded to the earth to provide electrical connection to the earth. 
     FIG. 1  is a schematic diagram showing the construction of a conventional radio transmitter. This radio transmitter  20  includes a signal wave generator  21  for generating a signal wave such as voice, an oscillator  22  for generating a high-frequency carrier, a modulator  23  for modulating the carrier by the signal wave according to a predetermined modulating method, an amplifier  24  for amplifying the modulated wave output from the modulator  23  to provide necessary electric power which is then supplied to an antenna  25 , a power supply wire  26  for supplying electric power to each part, a power supply  27  for supplying electric power through the power supply wire  26 , and a ground wire  29  for grounding a common ground  26 A to the earth  28 . 
   Regarding stable radiation of a modulated wave from the antenna  25 , a common recognition in the art is that minimizing the grounding resistance derived from the ground wire  29  is preferred. When the grounding resistance can be minimized, reference potential high enough to operate the antenna  25  can be ensured and the drive of the antenna  25  can be accelerated to improve the radiation of the radio wave. 
   In the conventional radio equipment, however, when satisfactory grounding cannot be ensured, the reference potential becomes unstable and, consequently, the radiation of the radio wave is lowered. The lowered radiation results in lowered radio transmission efficiency, or otherwise the radio transmission becomes impossible. This tendency is significant particularly under such a condition that the transmission output is low. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the invention to provide radio equipment which can stably radiate radio waves even under ungroundable conditions and, at the same time, can realize good characteristics even under low transmission output conditions. 
   According to the first feature of the invention, radio equipment comprises: 
   an antenna for radiating radio waves; and 
   a ground part configured as an antenna armature so as to be equivalent to the antenna. 
   According to the second feature of the invention, radio equipment comprises: 
   an antenna for radiating radio waves; and 
   a ground part configured in the same form as the antenna. 
   According to the third feature of the invention, radio equipment comprises: 
   an antenna for radiating radio waves; 
   a sensor for measuring a physical quantity and converting the physical quantity to an electric signal which is then output; 
   a transmission circuit for sending the electric signal as the radio wave; 
   a casing for housing therein the transmission circuit and the sensor; and 
   a ground part configured as an antenna armature so as to be equivalent to the antenna. 
   According to the fourth feature of the invention, radio equipment comprises: 
   an antenna for radiating radio waves; 
   a sensor for measuring a physical quantity and converting the physical quantity to an electric signal which is then output; 
   a transmission circuit for sending the electric signal as the radio wave; 
   a casing for housing therein the transmission circuit, said sensor being provided separately from and outside the casing, said sensor and said transmission circuit being connected to a common ground; and 
   a ground part configured as an antenna armature so as to be equivalent to the antenna. 
   According to the fifth feature of the invention, radio equipment comprises: 
   an antenna for radiating radio waves; 
   a ground part configured as an antenna armature so as to be equivalent to the antenna; and 
   a balanced matching part provided between the transmission circuit and the ground part for electrically realizing matching therebetween. 
   According to the radio equipment in each of the first to fifth features of the invention, preferably, the antenna and the ground part each are formed of a conductor having at least one quarter of the wavelength of the radio wave. Further, preferably, the ground part is formed of a copper foil pattern provided on a circuit board. 
   According to the radio equipment in each of the first to fifth features of the invention, the formation of a pseudo-equipotential surface as a ground using a part of the circuit construction of radio equipment can realize the radiation of radio waves with high efficiency even when grounding to the earth is impossible. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail in conjunction with the appended drawings, wherein: 
       FIG. 1  is a schematic diagram showing the construction of a conventional radio transmitter; 
       FIG. 2  is a schematic diagram showing the construction of radio equipment in a first preferred embodiment of the invention; 
       FIG. 3  is a diagram showing the construction of a circuit of an antenna provided in radio equipment; 
       FIG. 4  is a schematic diagram showing the construction of radio equipment in a second preferred embodiment of the invention; 
       FIG. 5  is a perspective view showing a temperature monitoring apparatus in a third preferred embodiment of the invention; 
       FIG. 6  is a block diagram of a circuit in the temperature monitoring apparatus in the third preferred embodiment of the invention; 
       FIG. 7  is a perspective view showing a temperature monitoring apparatus in a fourth preferred embodiment of the invention; 
       FIG. 8  is a block diagram of a circuit in the temperature monitoring apparatus in the fourth preferred embodiment of the invention; and 
       FIG. 9  is a schematic diagram showing the construction of radio equipment in a fifth preferred embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the radio equipment according to the invention will be explained in detail in conjunction with the accompanying drawings. 
     FIG. 2  is a schematic diagram showing radio equipment in a first preferred embodiment of the invention. This radio equipment  1  includes a signal wave generator  2  for generating a signal wave such as voice, an oscillator  3  for generating a high-frequency carrier, a modulator  4  for modulating the carrier by the signal wave according to a predetermined modulating method, an amplifier  5  for amplifying the modulated wave output from the modulator  4  to provide necessary electric power, an antenna  6  for radiating the amplified modulated wave as a radio wave, a power supply wire  7  for supplying electric power to each part, a power supply  8  which is a battery for supplying electric power through the power supply wire  7 , and a ground part  9  which is electrically connected to a common ground  7 A and is configured in the same manner as in the antenna  6 . 
   The antenna  6  is provided as a substrate member that can be housed in a casing (not shown) in which the radio equipment  1  can be housed. The antenna  6  includes a folded pattern  6 A formed of a copper foil provided on the surface of a substrate material. The antenna  6  is configured so that the length of the folded pattern  6 A is one quarter of the wavelength λ of the modulated wave. 
   As with the antenna  6 , the ground part  9  is provided as a substrate member and includes a folded pattern  9 A formed of a copper foil provided on the surface of a circuit board  9 B. The ground part  9  is configured so that the length of the folded pattern  9 A is one quarter of the wavelength λ of the modulated wave. 
     FIG. 3  shows the construction of a circuit in an antenna provided in the radio equipment  1 . As shown in the drawing, a dipole antenna  11  of two perfect balanced lines connected to a high-frequency power supply  10  is provided by configuring the antenna and the ground so as to be electrically equivalent to each other based on the folded patterns  6 A and  9 A. This dipole antenna  11  is provided in noncontact with the earth  12 . In this way, a pseudo-antenna having a length of one half of the wavelength λ can be formed by configuring the folded patterns  6 A and  9 A each in a length of one quarter of the wavelength λ. In this case, the antenna gain is about 2 dB, that is, the radiation of the radio wave can be improved. At the same time, the antinoise properties and the arrival distance of the radio wave can be improved. 
     FIG. 4  is a schematic diagram showing radio equipment in a second preferred embodiment of the invention. This radio equipment  1  includes a signal wave generator  2  for generating a signal wave such as voice, an oscillator  3  for generating a high-frequency carrier, a modulator  4  for modulating the carrier by the signal wave according to a predetermined modulating method, an amplifier  5  for amplifying the modulated wave output from the modulator  4  to provide necessary electric power, an antenna  6  for radiating the amplified modulated wave as a radio wave, a power supply wire  7  for supplying electric power to each part, a power supply  8  which is a battery for supplying electric power through the power supply wire  7 , and a ground part  14  which is electrically connected to a common ground  7 A to form a pseudo-equipotential surface. 
   The ground part  14  is provided as an antenna armature in a length (λ/4) necessary for forming a potential equivalent to that of the folded pattern  6 A in the antenna  6 . The ground part  14  may be in the form of a conductor wire, or alternatively may be in the form of a rod member made of a highly electrically conductive metal or a resin member made of an electrically conductive plastic or the like. 
   The provision of the ground part  14  also can configure a pseudo-dipole antenna  11  of two perfect balanced lines shown in FIG.  3  and thus can contribute to improved radiation of radio waves. Therefore, the arrival distance of the radio wave can be improved even in the case of low electric power, and, at the same time, antinoise properties can be improved. 
     FIG. 5  shows a temperature monitoring apparatus, as radio equipment in a third preferred embodiment of the invention, in which a ground (GND) wire of a temperature sensor provided as a sensor for measuring physical quantity is used as a ground part. In this temperature monitoring apparatus  1 , an amplifier  5  provided as a substrate member, an antenna  6 , a control circuit  16  including an oscillator, a signal wave generator, and a modulator, and a temperature sensor  17  for measuring the temperature of an object to be monitored are housed in a stacked form in a casing  15  formed of polycarbonate. The temperature sensor  17  is housed in the casing  15  so that a part of the temperature sensor  17  is exposed on a bottom  15 A of the casing  15 . The exposed part is brought into contact with the object to be monitored to measure the temperature through the utilization of thermal conduction. The antenna  6  has a folded pattern  6 A of a copper foil provided on the surface of the substrate member. The temperature sensor  17  is connected to the control circuit  16  through a sensor cable  17 A. The sensor cable  17 A includes a power supply wire, a sensor signal wire, and a GND wire which have been integrated by covering with a sheath. A battery  8  is housed in a space provided in the lower part of the control circuit  16 . The antenna  6  and the GND wire each have a length of one quarter of the wavelength λ, i.e., λ/4. 
     FIG. 6  is a block diagram showing a circuit in the temperature monitoring apparatus shown in FIG.  5 . In  FIG. 5  showing the first preferred embodiment and  FIG. 6 , like parts are identified with the same reference numerals, and the overlapped explanation thereof will be omitted. The sensor cable  17 A in the temperature sensor  17  includes a power supply wire  17 B, a sensor signal wire  17 C, and a GND wire  17 D with a length of λ/4. The GND wire  17 D is electrically connected to the common ground  7 A. 
   In this temperature monitoring apparatus, the temperature sensor  17  is attached to an object to be monitored, and a temperature signal measured in a predetermined measurement cycle is converted to a signal wave in a signal wave generator. The signal wave is subjected to ASK (amplitude shift keying) modulation in a modulator, and the modulated wave is amplified to an electric power necessary for transmission. The amplified wave is then sent as a radio wave of 315 MHz from the antenna  6 . The transmitted radio wave is received by a receiver (not shown). Thus, the temperature of the object to be monitored can be remotely grasped. 
   In this temperature monitoring apparatus, the GND wire  17 D in the sensor cable  17 A connected to the temperature sensor  17  housed within the casing  15  is used as a ground part for configuring a pseudo-equipotential surface, and the length of the GND wire  17 D is brought to λ/4. By virtue of this construction, a pseudo-dipole antenna of two perfect balanced lines can be provided. Therefore, the radiation of radio waves can be improved. 
   In the third preferred embodiment, the construction, in which the temperature sensor  17  for measuring the temperature of an object to be monitored is provided as a physical quantity measuring sensor, has been explained. The physical quantity to be measured, however, is not limited to the temperature, and any physical quantity, which can be converted to an electric signal, can be transmitted as a radio wave. Specifically, other measurable physical quantities include, for example, humidity, strain (stress), quantity of light, flow rate, and vibration (acceleration). 
   Further, it should be noted that the length of the GND wire  17 D is not limited to λ/4. For example, the use of two λ/4-long ground wires, i.e., a length of 2×λ/4, may be adopted. In this case, a plurality of maximum amplitude points in an antenna can be ensured. Therefore, radio waves can be more stably radiated. 
     FIG. 7  shows another temperature monitoring apparatus, as radio equipment in a fourth preferred embodiment of the invention, in which a GND wire of a temperature sensor provided as a sensor for measuring physical quantity is used as a ground part. In this temperature monitoring apparatus  1 , an amplifier  5  provided as a substrate member, an antenna  6 , and a control circuit  16  including an oscillator, a signal wave generator, and a modulator are housed in a stacked form in a casing  15  formed of polycarbonate. A temperature sensor  17  is externally provided separately from the casing  15 . The antenna  6  has a folded pattern  6 A of a copper foil provided on the surface of the substrate member. The temperature sensor  17  is connected to the control circuit  16  through a sensor cable  17 A. The sensor cable  17 A includes a power supply wire, a sensor signal wire, and a GND wire which have been integrated by covering with a sheath. A battery  8  is housed in a space provided in the lower part of the control circuit  16 . The antenna  6  and the GND wire each have a length of λ/4. 
     FIG. 8  is a block diagram showing a circuit in the temperature monitoring apparatus shown in FIG.  7 . In  FIG. 5  showing the first preferred embodiment and  FIG. 8 , like parts are identified with the same reference numerals, and the overlapped explanation thereof will be omitted. The sensor cable  17 A in the temperature sensor  17  includes a power supply wire  17 B, a sensor signal wire  17 C, and a GND wire  17 D with a length of λ/4. The GND wire  17 D is electrically connected to the common ground  7 A provided within the casing  15 . 
   In this temperature monitoring apparatus, the temperature sensor  17  is attached to an object to be monitored, and a temperature signal measured in a predetermined measurement cycle is converted to a signal wave in a signal wave generator. The signal wave is subjected to ASK modulation in a modulator, and the modulated wave is amplified to an electric power necessary for transmission. The amplified wave is then sent as a radio wave of 315 MHz from the antenna  6 . The transmitted radio wave is received by a receiver (not shown). Thus, the temperature of the object can be remotely grasped. 
   In this temperature monitoring apparatus, the GND wire  17 D in the sensor cable  17 A connected to the temperature sensor  17 , which is externally provided separately from the casing  15 , is used as a ground part for configuring a pseudo-equipotential surface, and the length of the GND wire  17 D is brought to λ/4. By virtue of this construction, a pseudo-dipole antenna of two perfect balanced lines can be provided. Therefore, the radiation of radio waves can be improved. Further, since the temperature sensor  17  is provided separately and apart from the casing  15  and, in this state, is connected through a sensor cable  17 A, unlike the integral structure in which the temperature sensor  17  is housed in the casing  15 , there is no fear of the follow-up property of the sensor  17  with respect to a temperature change being deteriorated by heat drawing of the object to be monitored depending upon the heat capacity based on the material and shape of the casing  15 . 
   Also in the fourth preferred embodiment, the length of the GND wire  17 D is not limited to λ/4, and, for example, the use of two λ/4-long ground wires, i.e., a length of 2×λ/4, may be adopted. 
     FIG. 9  is a schematic diagram showing radio equipment in a fifth preferred embodiment of the invention. In this radio equipment  1 , a line  14 A with a length of λ/8 is provided as a balanced matching part between a common ground  7 A and a ground part  14 . The other construction and function are the same as those explained above in connection with the second preferred embodiment ( FIG. 4 ) of the invention, and, in  FIGS. 4 and 9 , like parts are identified with the same reference numerals for omitting the overlapped explanation of the like parts. 
   The power supply wire  7  and the common ground  7 A provided in the radio equipment  1  sometimes cause an electric moment depending upon the scale and the resistance value of the battery  8  as the power supply. In some cases, the occurrence of the electric moment hinders the distribution of voltage in the antenna  6  or the ground part  14 . This sometimes makes it impossible to provide the function of a λ/2-long antenna and results in remarkably deteriorated radiation of radio waves. The provision of the line  14 A with a length of λ/8 can cope with the occurrence of the electric moment. That is, the provision of the line  14 A can provide balanced matching and can ensure operation of the λ/2-long antenna as a whole. The λ/8-long line  14 A may be formed of a copper foil pattern near the GND wire  7 A, or alternatively may be formed by winding a conductor wire. In these cases, the same effect can be attained. 
   In the circuit construction of the above radio equipment, in order to stably radiate radio waves from the antenna  6 , a given level of difference in impedance should be ensured between the antenna and the battery  8  as the power supply. According to studies conducted by the present inventor, in each of the above preferred embodiments, good transmission characteristics can be provided when the impedance of the antenna  6  is 50 Ω and the impedance of the battery  8  is 5 to 7 Ω. This demonstrates that the impedance of the power supply is preferably not less than 10% of the impedance of the antenna  6 . 
   The construction of each of the above preferred embodiments uses an antenna as a substrate member having a folded pattern formed of a copper foil. Alternatively, the antenna may have a structure having a rod element made of a highly electrically conductive metal material or an antenna having an antenna pattern formed of a copper foil on a film base. The part provided as a ground may also have the same construction as the antenna or a construction which can form an electric field equivalent to that of the antenna and consequently can form an equipotential surface. 
   The invention has been explained by taking the construction of a transmitter as an example. The invention, however, can also be applied to a transmitter-receiver. 
   As described above, according to the radio equipment of the invention, a ground part electrically equivalent to an antenna is provided to form an equipotential surface. By virtue of this construction, radio waves can be stably radiated even under ungroundable conditions, and good characteristics can be provided even under low transmission output conditions. 
   The invention has been described in detail with particular reference to preferred embodiments, but it will be understood that variations and modifications can be effected within the scope of the invention as set forth in the appended claims.