Antenna Tuning Unit

Abstract

A system, apparatus, and method directed to impedance matching an antenna with a transmitter for non-directional radio beacons. The apparatus includes an L-type impedance network comprising non-capacitive elements and at least one variable inductor on each branch of the impedance network. Also, system, apparatus, and method directed to providing a low power signal for tuning the antenna. The apparatus includes an impedance matching network and a signal generator. Also, a system, apparatus, and method directed to providing an estimate of near-field strength of a signal from an antenna. The apparatus includes an impedance matching network, a near-field signal strength detector, and microcontroller configured to estimate the near-field signal strength. Corresponding systems includes using the respective apparatuses between an antenna and a transmitter. Corresponding methods are directed to the use of the apparatuses and systems.

1 . An apparatus for maintaining a constant radio signal strength, the apparatus comprising:
 a. at least one sensor configured to estimate at least one radio signal strength of a radio signal from an antenna; and   b. a microcontroller configured to receive the at least one estimated radio signal strength and to transmit a signal strength indication to a radio transmitter.   
     
     
         2 . The apparatus of  claim 1 , wherein the at least one sensor comprises a near-field signal strength detector. 
     
     
         3 . The apparatus of  claim 1 , wherein the at least one sensor comprises a plurality of sensors, and wherein the signal strength indication is a weighted average of the plurality of radio signal strengths estimated by the plurality of sensors. 
     
     
         4 . The apparatus of  claim 3 , wherein each of the plurality of sensors is disposed at a different location from every other of the plurality of sensors. 
     
     
         5 . The apparatus of  claim 3 , wherein the weighted average is based on distances between the antenna and each of the plurality of sensors. 
     
     
         6 . A system for maintaining a constant radio signal strength, the apparatus comprising:
 a. a radio transmitter configured to transmit a transmitter signal to an antenna;   b. at least one sensor configured to estimate radio signal strength of a radio signal from the antenna; and   c. a microcontroller configured to receive the estimated radio signal strength from the sensor and to transmit the estimated radio signal strength to the radio transmitter.   
     
     
         7 . The system of  claim 6 , further comprising:
 a. a closed loop controller configured transmit a power adjustment signal to the radio transmitter based on a difference between the estimated radio signal strength and a target radio signal strength.   
     
     
         8 . The system of  claim 6 , wherein the at least one sensor comprises a near-field signal strength detector. 
     
     
         9 . The system of  claim 6 , wherein the at least one sensor comprises a plurality of sensors, and wherein the observed radio signal strength is a weighted average of the observed radio signal strengths estimated by the plurality of sensors. 
     
     
         10 . The system of  claim 9 , wherein each of the plurality of sensors is disposed at a different location from every other of the plurality of sensors. 
     
     
         11 . The system of  claim 9 , wherein the weighted average is based on distances between the antenna and each of the plurality of sensors. 
     
     
         12 . The system of  claim 6 , further comprising:
 a. an impedance matching network electrically connected between the radio transmitter and the antenna.   
     
     
         13 . The system of  claim 12 , wherein the impedance matching network is an L-type network comprising only noncapacitive impedance elements. 
     
     
         14 . The system of  claim 13 , wherein the impedance matching network comprises two branches with at least one variable inductor in each branch. 
     
     
         15 . The system of  claim 6 , further comprising:
 a. a signal generator configured to transmit a signal through the impedance matching network separate from the radio transmitter.   
     
     
         16 . The system of  claim 15 , wherein the signal generator is configured to limit the signal to a power level below a threshold that is harmful to humans. 
     
     
         17 . A method for maintaining a constant radio signal strength from an antenna powered by a radio transmitter, the method comprising:
 a. estimating a signal strength of a radio signal using at least one sensor; and   b. transmitting the estimated signal strength to the radio transmitter.   
     
     
         18 . The method of  claim 17 , further comprising:
 a. comparing the at least one estimated signal strength with a target signal strength; and   b. adjusting the input power from the radio transmitter to the antenna based on the comparison.   
     
     
         19 . The method of  claim 17 , wherein the at least one sensor comprises a near-field signal strength detector. 
     
     
         20 . The method of  claim 17 , wherein the adjustment step is configured to reduce a difference between the estimated signal strength and a target signal strength. 
     
     
         21 . The method of  claim 17 , wherein the at least one sensor comprises a plurality of sensors, and wherein the estimating step comprises using a weighted average of the estimated signal strengths estimated by each of the plurality of sensors. 
     
     
         22 . The method of  claim 21 , wherein each of the plurality of sensors is disposed at a different location from every other of the plurality of sensors. 
     
     
         23 . The method of  claim 21 , wherein the weighted average is based on distances between the antenna and each of the plurality of sensors.