An example radio frequency (RF) charging pad includes: at least one processor for monitoring an amount of energy that is transferred from the RF charging pad to an RF receiver of an electronic device. The pad also includes: one or more transmitting antenna elements that are in communication with the processor for transmitting RF signals to the RF receiver. In some embodiments, each respective transmitting antenna element includes: (i) a conductive line forming a meandered line pattern; (ii) a first terminal of the conductive line for receiving current at a frequency controlled by the processor; and (iii) a second terminal coupled with a component that allows for modifying an impedance value at the second terminal. In some embodiments, the processor adaptively adjusts the frequency and/or the impedance value to optimize the amount of energy that is transferred from the one or more transmitting antenna elements to the RF receiver.