Variable directivity antenna and variable directivity antenna system using the antennas

A variable directivity antenna comprising:

• a first antenna group including first and second antennas for receiving a radio wave in a first frequency band, said first and second antennas being disposed in parallel and spaced by a distance less than a half of a wavelength in said first frequency band, said first and second antennas exhibiting an 8-shaped directivity along a line perpendicular to the length direction thereof;
• a second antenna group including third and fourth antennas for receiving a radio wave in said first frequency band, said third and fourth antennas being disposed in parallel with and spaced by said distance from each other, and exhibiting an 8-shaped directivity along a line perpendicular to the length direction thereof, said third and fourth antennas being disposed perpendicular to said first and second antennas;
• first phase shifting means for adjusting phases of received signals from said first and second antennas and combining the phase-adjusted signals in such a manner that the resultant signal selectively assumes a first directivity state in which said resultant signal exhibits a directivity in a first direction which is from said first antenna toward said second antenna, and a second directivity state in which said resultant signal exhibits a directivity in a second direction which is from said second antenna toward said first antenna;
• second phase shifting means for adjusting phases of received signals from said third and fourth antennas and combining the phase-adjusted signals in such a manner that the resultant signal selectively assumes a third directivity state in which said resultant signal exhibits a directivity in a third direction which is from said third antenna toward said fourth antenna, and a fourth directivity state in which said resultant signal exhibits a directivity in a fourth direction which is from said fourth antenna toward said third antenna;
• and
• signal combining means for adjusting in value and combining an output signal of said first phase shifting means in said first or second directivity state and an output signal of said second phase shifting means in said third or fourth directivity state, and providing an output signal exhibiting a directivity in a selected one of said first through fourth directions and directions between said first through fourth directions.