To provide a tunable filter in which a pass band is variable in a wide frequency region, the pass band can be continuously varied, insertion loss is small, an interrupting characteristic is steep, downsizing is possible, and reliability and reproducibility are excellent.
The tunable filter comprises a filter body 11 and a control circuit 12 for controlling the filter body 11. Feedback control for controlling the capacity of variable capacitors 7, 9 in the filter body 11 is continuously performed during communication in accordance with the oscillation frequency in a first and a second voltage controlled oscillators 13, 14 as a monitor circuit, thereby making it possible to obtain a stable filter characteristic without being affected by a frequency drift or the like due to a temperature rise in a device.
OHARA RYOICHI
ABE KAZUHIDE
YOSHIDA HIROSHI
TSURUMI HIROSHI
Hidetoshi Tachibana
Yasukazu Sato
Hiroshi Yoshimoto
Yasushi Kawasaki