Dynamic adaptation of power emissivity for mobile microstrip antennas in a variable impedance environment with microcontroller

In this paper a qualitative and quantitative study of emissivity control for micro-strip type microwave antennas using adaptive correction of the transmission power when the wave impedance of the propagation medium is not constant and it is influenced by nearby moving conductive objects or by objects with different reflection or absorption ispresented. We propose a dynamic adaptation module controlled by a microcontroller for the microwave transmission circuit. The microcontroller reads the current variation for a fixed current level of the emitter which contains the information about the propagation efficiency of the electromagnetic wave and generates a RF carrier amplitude control signal. The mathematical model of a micro-strip antenna working in a certain emission band and the dynamic hardware adaptation possibility for the power of the emission so that the medium influence will not affect the minimum useful power needed by the receiver are considered. The main idea is to create an algorithm to reduce the supplemental RF emitter energy consumption working in open waveguide (air or vacuum) and whose antennae are not perfectly adapted or are moving, such as wireless devices or GSM antennae. For these particular cases, the surrounding objects having the physical dimension of the emitting antenna behave like receivers and will absorb totally or partially the energy emitted. The phenomenon considered is the one of reappearing of the reflected waves in the antenna, which will change the antenna circuit similar to a supplemental reactive load in the emitting circuit. The effect in this case is the increase of the absorbed electrical power in the final RF stage. Measuring the current is a challenge because two steps are needed; a pre-scaling and a final scaling using a voltage zoom by temporally modifying the voltage references of the ADC converter. Finally, the solution proposed in this paper consists in the very precise periodic measurement in the final RF circuit by using a shunt resistor connected to the ground; when a supplemental charge appears, the microcontroller will change (increase or reduce) the amplitude of the RF carrier so that the reflected wave's amplitude returning to the antenna is subsequently smaller. The system uses an experimental model with a process microcontroller with a 10 bits ADC.