Test Data
The picture above shows data for and simulations of the RF current source driving a loop antenna (see RF_antenna.brd and RF_antenna_B.brd). The blue and red curves correspond to low-signal and large-signal response, respectively. The dashed curve is a lumped-element simulation of the RF-Current-Source as depicted in Circuit Diagram with Lc<\sub> and Cp<\sub> adjusted to fit the data. The dotted curve uses the formula for a loop antenna to guess Lc<\sub> = 220 nH, but all other parameters are the same as for the dashed curve. The dash-dotted curve is a simulation of the loop antenna when it is terminated with 50 Ohms and driven by an RF power amplifier (assumed to be a perfect AC voltage source).
The picture above shows data for the "linked-D" antennas (see RF_antenna.brd and RF_antenna_B.brd). The blue and red curves show the small-signal response of the two different antenna layouts on each board. The two current sources were setup with all the same component values, so the different response of the two antennas is likely caused by slightly different inductance.