Antenna device

Details Antenna device Antenna device

2001-11-08

2003-08-12

Ho, Tan (Department: 2821)

Communications: radio wave antennas

Antennas

With variable reactance for tuning antenna

C343S715000, C343S749000, C343S850000

Reexamination Certificate

active

06606069

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a frequency variable antenna device capable of varying an operating frequency thereof.
BACKGROUND OF THE INVENTION
A monopole antenna device usually operates at a frequency depending on the overall length of a pole, has an expandable structure, and is widely used in a small-sized wireless apparatus.
FIG. 17
shows a conventional monopole antenna device. A monopole antenna element
1
is connected to an signal power terminal
3
through a coupling capacitor
2
. When this antenna device is used as a receiving antenna, a radio wave received through the signal power terminal
3
is supplied into a radio frequency (RF) receiver such as tuner. When the antenna device is used as a transmitting antenna, a transmission signal is supplied into the antenna element from an RF transmitter through the signal power terminal
3
, and is emitted into a free space as a radio wave.
FIG. 18
is a characteristic diagram of a gain against a frequency of this antenna device. In
FIG. 18
, the axis of abscissas
4
represents the frequency, and the axis of ordinates
5
represents the gain. A level
5
a
on the axis of ordinates indicates the reference value of the antenna gain, and a curve
6
shows the gain characteristic of the antenna element. The gain characteristic curve
6
has a relatively uniform characteristic of gain and frequency in a wide frequency range, and however, as the frequency becomes higher, a drop
7
from the reference value
5
a
becomes larger. This antenna device, therefore, hardly obtain a sufficient antenna gain in a wide frequency range.
SUMMARY OF THE INVENTION
An antenna device having a high antenna gain in a desired frequency range is provided.
The antenna device includes an antenna element, a variable capacitor coupled to the antenna element, a resonance circuit including the antenna element and variable capacitor, a tuning voltage supply terminal for supplying a tuning voltage for varying a capacitance of the variable capacitor, and a signal power terminal capable of at least one of sending a signal power to the resonance circuit and receiving a signal power from the resonance circuit.


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