Patent ID: 8270537
Filing Date: 2012-09-18
Classification: H01Q,H03F,H03H,H04B,H04L

Abstract:
1. An antenna device that is placed adjacent to an antenna for receiving a high frequency signal and transmits the high frequency signal received by the antenna to a demodulating device through a feeder cable, the antenna device comprising: an amplifying circuit for amplifying the high frequency signal received by the antenna; an impedance matching circuit for matching impedances of the antenna and the amplifying circuit according to a received frequency; a low pass filter for receiving a DC control voltage to be supplied from the demodulating device through the feeder cable, the DC control voltage adjusting a frequency characteristic of the impedance matching circuit within an allowable range corresponding to the received frequency, and for supplying the DC control voltage to the amplifying circuit and the impedance matching circuit after removing a high frequency component from the DC control voltage; and a first clamping circuit for clamping the DC control voltage to a constant voltage, wherein a difference voltage of the DC control voltage and a clamp voltage by the first clamping circuit adjusts a reactance value of at least one variable reactive element incorporated in the impedance matching circuit.