Near-field probe for adaptive antenna tuning

A new concept of using near-field probes to detected radiated power for feedback in adaptive tuning systems is presented. As the probe is in the near field, it samples both stored reactive energy, as well as far field radiated energy. As such, specific principals must be considered for proper design. It is shown that for an electrically small VHF/UHF antenna a properly designed near-field probe is capable of accurately sampling far field radiated power up to 400 MHz. While this limitation exists for the specific presented prototype, design principals extend to any frequency of interest. Advantages over traditional Su minimizing topologies include lower cost as only one power detector is required, lower insertion loss for the antenna tuner as no directional couplers are used, and flexibility in design degrees of freedom.