VARIABLE DIRECTIVITY ANTENNA AND METHOD OF CONTROLLING VARIABLE DIRECTIVITY ANTENNA

摘要

Described herein is a variable directional antenna apparatus wherein an electrical length of a parasitic antenna of a paired two-element Yagi antenna is varied to change antenna directivity. A radio device (12) outputs a received signal corresponding to the intensity of an electric field received by a first antenna. A control circuit (15) outputs a control signal to a variable impedance circuit (14) according to the result of detection of the received signal so as to change the impedance of the variable impedance circuit (14) according to the control signal. Thus, an electrical length of a second antenna (13) placed in parallel away from the first antenna (10) is changed to thereby activate the second antenna as a director or reflector, whereby antenna directivity is varied.