Variable directivity antenna and method of controlling variable

Details Variable directivity antenna and method of controlling variable Variable directivity antenna and method of controlling variable

1998-09-22

2000-04-11

Wong, Don

Communications: radio wave antennas

Antennas

With radio cabinet

343814, 343815, 343860, H01Q 124, H01Q 2112

Patent

active

060493100

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a variable directional antenna apparatus wherein the directivity of the antenna employed in a radio apparatus such as a portable radio apparatus is varied in order reduce a fall in the intensity of an electric field at a receiving position. The invention also relates to a method of controlling a variable directional antenna.


BACKGROUND ART

In the mobile radio communications of a portable phone or the like, when reflected waves are involved, there may generally be cases in which an electric field is canceled out due to mutual interference between reflected waves and direct waves or interference between reflected waves. Also the intensity of an electric field may fall extremely depending on the location, so that the mobile unit is unable to receive. To avoid such an event, space, polarization and frequency diversity systems have heretofore been used. FIG. 20 illustrates one example of the space diversity system. Reference numerals 1(a) and 1(b) respectively indicate antennas provided at positions where they are away from each other. Reference numeral 2 indicates a receiver and reference numeral 3 indicates a diversity antenna selector switch. The space diversity system is constructed so as to selectively connect that one of the respective antennas 1(a) and 1(b) having a high received level to the receiver 2 through the diversity antenna selector switch 3. In the space diversity system, however, the achievement of sufficient diversity requires sufficient separation of the respective antennas 1(a) and 1(b) from each other, thereby resulting in an increase in the size of the apparatus. Further, a problem arises in that since the selector switch 3 serves so as to switch between high-frequency signals, it is generally expensive and is expensive to replace Also noise is produced when the selector switch 3 is changed over.
Therefore, an apparatus in which the directivity of each antenna is varied to reduce the influence of a reflected wave, has been produced. As has been disclosed in, for example, Japanese Utility Model Application Laid-Open No. 58-26207, .left brkt-top.Antenna apparatus for Mobile Radio Device.right brkt-bot. shown in FIG. 21, a non-feed or parasitic antenna 7 is set between a transmitting antenna 5 electrically connected to a transmitter 4 and a receiving antenna 6 electrically connected to a receiver 2 so as to act as either a reflector or a director. Further, the parasitic antenna 7 is loaded in series with a switching element 8 (or variable impedance element). A drive circuit 9 turns on and off the switching element 8 on and off to vary the current distribution of the corresponding antenna, thereby varying the directivity of the antenna. FIG. 22 is a block diagram showing the well-known principle of a one pair of half-waves (hereinafter called ".lambda./2", where .lambda.:wavelength) in the two-element Yagi type antenna. Reference numeral 5 indicates a power-fed transmitting antenna, reference numeral 7 indicates a non-feed or parasitic antenna, and reference numeral 4 indicates a transmitter. Assuming the electrical length of the feed antenna 5 is taken as .lambda./2, the parasitic antenna 7 is generally activated as a reflector if the electrical length thereof is set so as to be slightly longer than .lambda./2 as shown in FIG. 22(a), whereas if the electrical length thereof is set so as to be slightly shorter than .lambda./2 as shown in FIG. 22(b), the parasitic antenna 7 acts as a director. Thus, when the parasitic antenna 7 is set slightly longer than the transmitting antenna 5 and the receiving antenna 6 as regards electrical length as in FIG. 21, it operates as a reflector. The transmitting antenna 5 exhibits directivity in the direction of the receiving antenna 6 when the switch 8 is brought to an on state, whereas when the switch 8 is turned off, the transmitting antenna 5 exhibits directivity in the direction opposite to that of the receiving antenna 6. When the parasitic antenna 7 is set slightly shorter than the transmitting antenna 5 an

REFERENCES:
patent: 4631546 (1986-12-01), Dumas et al.
patent: 5293172 (1994-03-01), Lamberty et al.
patent: 5767807 (1998-06-01), Prichett

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