| 摘要 |
<p>A loop antenna (10) is provided with feed means (12,14) and a variable capacitor (C1) to adjust a first resonant frequency of the antenna (10). A reactive network (C2,L2,X) is included which permits the antenna to provide a further resonant frequency. The reactive network comprises a series-resonant circuit (L2,C2) in parallel with a further reactive element (X). The resonant frequency of the series-resonant circuit is arranged to be substantially equal to the first resonant frequency of the antenna as tuned by the capacitor (C1). The reactance (X) thus has no effect at this frequency. Another resonant frequency for the antenna may be adjusted by altering the reactance (X). The arrangement may be extended to provide further resonant frequencies. <IMAGE></p> |
