| 摘要 |
<p>A surface acoustic wave filter having a balance/unbalance converting function for improving the degree of balance, and a communication unit comprising it. A longitudinal coupling resonator type surface acoustic wave filter section (501) comprises a first interdigital electrode part (503), a central interdigital electrode part (504), a second interdigital electrode part (505), and first and second reflectors (506, 507) sandwiching them. One comb-shaped electrode at the central interdigital electrode part (504) is divided substantially symmetrically into first and second comb-shaped electrodes (516, 517) along the propagating direction of surface acoustic wave. Between the first and second comb-shaped electrodes (516, 517), at least one of design parameters of the interdigital electrode parts (503, 504, 505) and the reflectors (506, 507) is differentiated between one and the other sides sandwiching an imaginary central axis A orthogonally intersecting the propagating direction of surface acoustic wave.</p> |
