| 摘要 |
An antenna ( 11 ) includes a patch antenna element ( 22 ) capacitively coupled to a load patch ( 27 ). A switch ( 33 ) connects the load patch ( 27 ) to one of one or more strip lines ( 35, 37, 40 ), each of which has a different length. Each strip lines causes the load patch ( 27 ) to have a different impedance, with one causing a short circuit, one causing an open circuit, and one causing an impedance in between these extremes. Different impedances of the load patch ( 27 ) cause different frequencies of operation of the antenna patch ( 22 ) by virtue of the capacitive coupling therebetween. The antenna ( 11 ) is thereby tuneable to three separate frequencies. Other frequency bands are unaffected by virtue of the location of the load patch ( 27 ) relative to the antenna patch ( 22 ). By allowing tuning by way of controlling the impedance of the load patch ( 27 ), the antenna arrangement can be made smaller than a corresponding passive antenna operable at the same frequencies. By using an N throw switch, N strip lines of different lengths can be connected, each giving rise to a different operating frequency.
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