| 摘要 |
An internal monopole antenna intended for small-sized radio devices (RD). It comprises a radiating main element (220) and parasitic element (230). The main element has a resonance frequency both in the lower and upper operating band of the antenna, and the parasitic element has a resonance frequency in the upper operating band. The length of the part (221) of the main element, which corresponds to its lower resonance, is increased by shaping the element so that the third harmonic of the basic resonance frequency lowers relatively close to the other resonance frequencies in the upper operating band. The shift of the lower resonance frequency of the main element, which takes place at the same time, is compensated by adding a serial capacitor to the feed circuit of the antenna. The part of the main element, which corresponds to its upper resonance, is divided into two arms (222, 223) so that one (223) of these arms is the part of the main element nearest to the parasitic element. The upper operating band of an antenna can be made wider compared with the corresponding known antennas, because said harmonic resonance is utilized in the antenna matching in the upper operating band. In addition, a relatively strong coupling can exist between the main (220) and parasitic (230) element without degradation in the antenna matching in the upper operating band, in which case the parasitic element becomes smaller compared with the known technique and its unfavourable coupling to the other conductive parts of the radio device reduces. |
