| 摘要 |
A unified circuit without using a relay is proposed to resonate an antenna at more than two frequencies. The use of such analog IC switches are common place for transceiver applications in high RF frequencies (500 MHz and above). However, the use of selectively tuned antennas has for the most part been accomplished by the use of latching relays or fixed value components. The IC switch allows for not only the functionality of a single antenna to be either a transmitter and/or a receiver, but also allows, by adding additional switches to select any number of frequencies to resonate the antenna. This frequency resonation could be at fixed frequency points or sweep in either linear or logarithmic steps. The component selection of capacitors for either method would be controlled by a DSP or other microcontroller device. In one embodiment, an antenna for a downhole measurement tool is provided with a tuning circuit couple by a transformer to at least one antenna. The tuning circuit is disposed entirely within and protected by the hollow body of the tool and selectively tunes the antenna to at least three discrete frequencies. Advantageously, no structural modification is made on the outer surface of the tool to accommodate the tuning circuit. In one embodiment, a switching circuit enables a single antenna to function as both a transmitter and a receiver.
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