Abstract:
A multi-filar helical antenna has an antenna radiant section which has n elements which are wound in spiral, and a phase control part which feeds signal to the n elements with a phase delay of 360°/n each in the order of an arrangement of the n elements or a phase lead of 360°/n each in the order of the arrangement of the n elements.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiple-wire wound helical antenna which is used mainly for a mobile radio device such as a portable telephone. 
     2. Related Art of the Invention 
     The recent years have seen a rapid development of mobile telecommunication such as portable telephones, and as a result, not only portable telephone systems using ground stations are wanted but systems using satellites as well are expected. Meanwhile, an antenna is one of important devices of a portable telephone terminal. 
     In the following, an example of a conventional quadrifilar helical antenna mentioned above will be described with reference to an associated drawing. 
     FIG. 9 is a block diagram showing a conventional quadrifilar helical antenna. In FIG. 9, denoted at  201  is a quadrifilar helical antenna radiant section, denoted at  202  is a 3 dB hybrid, and denoted at  203  is an input/output terminal. An operation of the quadrifilar helical antenna having such a structure will be described below. 
     The quadrifilar helical antenna  201 , when dimensioned to have an appropriate size and fed at the input/output terminal  203  through the 3dB hybrid  202 , exhibits radiation pattern having a conical beam characteristic as that shown in FIG.  10 . 
     However, since the directivity is always upward with such a structure described above, if this antenna is disposed to a portable telephone which utilizes a satellite, the directivity becomes downward with the antenna folded during stand-by, whereby a radio wave from above is failed to be received. 
     SUMMARY OF THE INVENTION 
     In view of such a problem with the conventional technique, the present invention aims at providing a multi-filar helical antenna which exhibits an upward directivity not only when stretched but even when folded as well. 
     The present invention is directed to a multi-filar helical antenna which comprises: an antenna radiant section which comprises n elements which are wound in spiral; and phase control means which feeds a signal to the n elements with a phase delay of 360°/n each in the order of an arrangement of the n elements or a phase lead of 360°/n each in the order of the arrangement of the n elements. 
     The present invention is also directed to a multi-filar helical antenna which comprises: an antenna radiant section which comprises four elements which are wound in spiral; two feed lines which are connected to the antenna radiant section and have substantially the same electrical length with each other; a 3 dB hybrid which comprises four terminals; and two terminating circuits, wherein two on one side out of the four terminals of the 3 dB hybrid are connected to the two feed lines, two on the other side out of the four terminals of the 3 dB hybrid are connected to a switch which switches a connection state with a signal input/output portion, two connection circuits for connecting the switch to two terminals out of the four terminals of the 3 dB hybrid are respectively connected to terminating circuits, and wherein when the signal input/output portion is conducted with either one of two terminals of the 3 dB hybrid as the switch switches over, non-conducting one of the terminals is terminated by one of the terminating circuits which is connected to the non-conducting terminal. 
     With such structures according to the present invention, by means of a switch, it is possible to switch the directivity of an antenna between an upward direction and a downward direction. Hence, when the antenna is attached to a portable radio terminal, it is possible to direct the directivity of the antenna always to above regardless of whether the antenna is stretched or folded. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a quadrifilar helical antenna according to a preferred embodiment of the present invention; 
     FIG. 2 is a circuitry diagram of the quadrifilar helical antenna according to the preferred embodiment of the present invention; 
     FIG. 3 is a structure diagram of the quadrifilar helical antenna according to the preferred embodiment; 
     FIGS. 4 and 5 are views showing a method of feeding signal to the quadrifilar helical antenna according to the preferred embodiment; 
     FIG. 6 is a view showing a radiation pattern of the quadrifilar helical antenna according to the preferred embodiment; 
     FIG. 7 is a circuitry diagram of a phase control circuit of an octafiler helical antenna according to the preferred embodiment of the present invention; 
     FIG. 8 is a view showing the quadrifilar helical antenna according to the preferred embodiment attached to a satellite portable telephone, as it is stretched and folded; 
     FIG. 9 is a block diagram of a conventional quadrifilar helical antenna; and 
     FIG. 10 is a view showing a radiant pattern of the conventional quadrifilar helical antenna. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, the present invention will be described in relation to preferred embodiments, with reference to the associated drawings. 
     FIG. 1 is an abstract circuitry diagram of a quadrifilar helical antenna according to a preferred embodiment of the present invention, and FIG. 2 specifically shows the quadrifilar helical antenna. In FIGS. 1 and 2, denoted at  101  is a quadrifilar helical antenna radiant section, denoted at  102  is a 3dB hybrid, denoted at  103  is a switch, denoted at  104  is an input/output terminal, and denoted at  105  is a control terminal of the switch  103 . 
     Denoted at  106   a  and  106   b  are circuits for 50 Ω-terminating non-conducting other terminal when one terminal of the switch  103  conducts. Denoted at  107  are feed lines, denoted at  108 ,  109 ,  111   a  and  111   b  are input/output terminals of the 3 dB hybrid  102 , denoted at  112   a  and  112   b  are connection terminals of the switch  103 , and denoted at  113  is a common terminal of the switch  103 . Denoted at  190  is a circuit in which two terminals are connected to the two feed lines  107 , and two output terminals branch out from one of the two terminals and other two output terminals branch out from the other one of the two terminals. Four lines of the helical antenna are connected to the four output terminals, respectively. At the branches, signals are out of phase  180  degrees from each other. 
     A circuit structure of the terminating circuit  106   a  will now be described. Denoted at  121   a  is a d.c. cut capacitor, denoted at  122   a  is a resistor, denoted at  123   a  is a diode, and denoted at  124   a  and  125   a  are control terminals. The d.c. cut capacitor  121   a  is connected between one terminal  111   a  of the 3 dB hybrid  102  and the connection terminal  112   a  of the switch  103 . The terminating circuit  106   a  is described as follows. 
     The resistor  122   a  and the diode  123   a  are connected between the control terminals  124   a  and  125   a,  and the control terminal  124   a  is connected between the d.c. cut capacitor  121   a  and the connection terminal  112   a  of the switch  103 . 
     Like the terminating circuit  106   a,  in the circuit  106   b  as well, a d.c. cut capacitor  121   b  is connected between the terminal  111   b  of the 3 dB hybrid  102  and the connection terminal  112   b  of the switch  103 , and a series circuit of the diode  123   b  and the resistor  122   b  is connected to the connection terminal  112   b  of the switch  103 . Further, the diode  123   b  and the resistor  122   b  which are connected in series to each other are connected between the two control terminals  124   b  and  125   b.    
     Next, a circuit structure of the quadrifilar helical antenna according to the preferred embodiment above will be described. The quadrifilar helical antenna radiant section  101  is connected to the two feed lines  107  ( 108 ,  109 ) which have the same electrical length with each other through a circuit  100 , the feed lines  107  are connected to the terminals  108 ,  109  of the 3 dB hybrid  102 , the terminal  111   a  of the 3 dB hybrid  102  is connected to the connection terminal  112   a  of the switch  103  through the circuit  106   a,  and the terminal  111   b  of the 3 dB hybrid is connected to the connection terminal  112   b  of the switch  103  through the circuit  106   b.  Further, the common terminal  113  of the switch  103  is connected to the input/output terminal  104 . 
     FIG. 3 shows a structure of the radiant section of the quadrifilar helical antenna according to the preferred embodiment. In FIG. 3, denoted at  131  is a hollow cylinder of a resin, while denoted at  132  are antenna elements of metal. The four metal elements are wound around the resin cylinder  131  in spiral with equal pitches between each other and at equal intervals. With respect to the size, a winding diameter is about 0.1 wavelength and a winding pitch is about 0.5 wavelength, for example. In addition,teflon is used as the hollow cylinder  131 , and copper wires are used as the antenna elements  132 , for instance. 
     Now, operations of the quadrifilar helical antenna having such a structure described above will be described with reference to FIGS. 1 through 5. 
     First, operations of the quadrifilar helical antenna will be described with reference to FIGS. 3 through 5. 
     A radiation characteristic of the quadrifilar helical antenna  101  according to the preferred embodiment is a conical beam characteristic and the direction changes depending on the phase of fed signal. Considering coordinate axes as shown in FIG. 4, when the phase of fed signal at the terminal  108  is delayed 90 degrees with respect to the phase of fed signal at the terminal  109 , the directivity is toward a direction +z as denoted at the solid line in FIG.  6 . Meanwhile, when the phase of fed signal at the terminal  109  is delayed 90 degrees with respect to the phase of fed signal at the terminal  108 , the directivity is toward a direction −z as denoted at the dotted line in FIG.  6 . Thus, by switching the phases of fed signal to the terminals  108  and  109 , it is possible to control the direction of the directivity. 
     Such switching of the phases of supplied electricity is realized as associated input terminals are switched by means of the 3 dB hybrid  102 . 
     Now, operations of the circuit according to the preferred embodiment will be described. 
     The switch  103 , in response to a control voltage at the control terminal  105 , switches the connection terminals  112   a  and  112   b  as a terminal to conduct with the common terminal  113 . For example, when a voltage at the control terminal  105  is at a high level, the common terminal  113  and the connection terminal  112   a  conduct with each other, whereas when a voltage at the control terminal  105  is at a low level, the common terminal  113  and the connection terminal  112   b  conduct with each other. 
     Now, a case in which voltages at the control terminals  105 ,  124   b  and  125   a  are at a high level and voltages at the control terminals  124   a  and  125   b  are at a low level will be considered. In this situation, the switch  103  allows the common terminal  113  and the connection terminal  112   a  to conduct with each other. For transmission, for instance, a signal inputted at the input/output terminal  104  is supplied to the 3 dB hybrid  102  through the terminal  111   a.  As a result, the phase of an output at the terminal  109  lags 90 degrees with respect to the phase of an output at the terminal  108  as shown in FIG.  5 . Hence, a radiation characteristic of the antenna as that denoted at the dotted line in FIG. 6 is obtained. In addition, since the diode  123   a  is off and the diode  123   b  is on at this stage, the terminal  111   b  of the 3 dB hybrid  102  is terminated at the resistor  122   b.  When the resistor  122   b  has 50 Ω, the terminal  111   b  is 50 Ω-terminated. 
     Conversely, voltages at the control terminals  105 ,  124   b  and  125   a  are at a low level and voltages at the control terminals  124   a  and  125   b  are at a high level, the switch  103  allows the common terminal  113  and the connection terminal  112   b  to conduct with each other. Hence, a signal inputted at the input/output terminal  104  is supplied to the 3 dB hybrid  102  through the terminal  111   b.  As a result, the phase of an output at the terminal  108  lags 90 degrees with respect to the phase of an output at the terminal  109  as shown in FIG.  4 . Therefore, a radiation characteristic of the antenna as that denoted at the solid line in FIG. 6 is obtained. Since the diode  123   a  is on and the diode  123   b  is off at this stage, the terminal  111   a  of the 3 dB hybrid  102  is terminated at the resistor  122   a.  When the resistor  122   a  has 50 Ω, the terminal  111   a  is 50 Ω-terminated. 
     In this manner, although switch-over performed by the switch makes one of the terminals  111   a  and  111   b  of the 3 dB hybrid  102  a terminal which does not pass a signal, the one of the terminals is terminated with the terminating resistor. 
     As described above, according to the preferred embodiment, the switch is disposed before the 3 dB hybrid which is used to feed signal to the quadrifilar helical antenna, and therefore, it is possible to switch the directivity of radiation pattern of the antenna between the direction +z and the direction −z. Further, since the terminal which does not carry a signal received from the 3 dB hybrid is terminated at switching, this operation is more stable. 
     Where the quadrifilar helical antenna  101  according to the preferred embodiment is attached to a satellite portable telephone  133  as shown in FIG. 8 in a foldaway fashion, as the directivity of radiation pattern is switched between when the antenna  101  is stretched and when the antenna  101  is folded, the antenna can always receive an radio wave from above. In this case, a mechanical switch  191  may be disposed in the vicinity of a supporting point around a base of the antenna  101 , so that when the antenna  101  is manipulated, a control signal is sent to the control terminal  105  from this switch and the switch  103  accordingly switches over. 
     As described above, when a switch is disposed before the feed circuit of the quadrifilar helical antenna, it is possible to switch the directivity of radiation pattern of the antenna between an upward direction and a downward direction. Further, when the quadrifilar helical antenna  101  according to the present invention is attached to a satellite portable telephone, it is possible to switch the directivity of radiation pattern of the antenna depending on whether the antenna is stretched or folded, and hence, to direct the directivity of radiation pattern of the antenna always to an upward direction. Still further, at switching, as the terminal which does not carry a signal received from the 3 dB hybrid is terminated, the operation becomes more stable. 
     While the preferred embodiment described above requires that the hollow resin cylinder  131  is made of teflon, this is not limiting. Instead, the cylinder may be made of other resins such as polypropylene. Further, while the foregoing has described that copper wires are used as the antenna elements  132 , a similar effect is maintained even when metal elements are printed or plated directly on the hollow resin cylinder  131 . 
     The present invention does not limit the number of wound wires to four. Rather, eight wires may be wound, in which case the phase control circuit may be designed as shown in FIG.  7 . More specifically, using one 3 dB hybrid, two 45-degree phase-distributors and two switches, it is possible to form the phase control circuit.