Analysis of a Direct Antenna Modulation Transmitter for Wideband OOK With a Narrowband Antenna

The characteristics of a narrowband antenna transmitting a broadband on-off-keyed signal using direct antenna modulation (DAM) are studied. The DAM technique has previously been proposed to generate a broadband signal using a rapidly time-varying antenna, but the signals produced using this technique and its limitations are not well understood. In this paper, we quantitatively compare the performance of a DAM transmitter to a conventional time-invariant transmit antenna. We show that the fall time of an RF pulse produced with the DAM configuration is measurably shorter than with the conventional system; however, the pulse rise time using both systems is identical. The performance of each system is then analyzed in terms of the bit error rate over a simple point-to-point link using analytical models, numerical simulation, and measurement. DAM reduces the intersymbol interference (ISI) by reducing the discharging time; however, the overall performance remains similar to the conventional system because of their similar charging times. While the DAM configuration does radiate a qualitatively broader spectrum as observed in previous studies, this does not translate into quantitative improvement in the characteristics of a transmitted data signal.