Image Number 10 for United States Patent #8130061.
A filter being small and having a narrowband filter characteristic is achieved using interdigital-coupled resonators. A first resonator and a second resonator are configured using interdigital-coupled quarter-wavelength resonators respectively. In addition, the first resonator and the second resonator are disposed so as to extend along directions intersecting with each other at a predetermined angle .theta.. Thus, coupling between the resonators is reduced compared with, for example, a case that the first resonator and the second resonator are, as a whole, disposed in parallel to each other. The angle .theta., with which the first resonator and the second resonator are disposed respectively, is adjusted, thereby coupling between the resonators may be made into a desired state. Thus, a desired narrowband filter characteristic is obtained.