Direct Antenna Modulation: A Novel Pathway in Developing High Efficiency Bandwidth Electrically Small Antennas

The increasing need to improve bandwidth and efficiency in antennas is a continuous topic of research in RF systems. However, when it comes to physical platforms that are electrically small relative to the desired frequency of operation, balancing miniaturization, bandwidth, and efficiency is both challenging and often counterintuitive. To overcome these challenges, this dissertation proposes utilizing a Direct Antenna Modulated (DAM) electrically small antenna (ESA). Here, we propose using efficiency-bandwidth product in theoretically analyzing and in measuring the improvement of DAM over a conventional capacitively loaded loop antenna (CLLA). To quantify the benefits of DAM, a prototyped antenna with DAM (0.0275λ x 0.0251λ) was designed and successfully transmits a Binary-Frequency Shift Keying (BFSK) signal centered at 75 MHz. Though transistor parasitics reduce the possible efficiency-bandwidth product improvement, β, of DAM, measurements show the key importance of maintaining proper switching synchronization to achieve system bandwidths beyond the antenna’s impedance bandwidth. The DAM system achieves significant measured efficiency-bandwidth product improvement, β, up to 5 over bit rates of 700 kbps to 7 Mbps. Moreover, another important characteristic in these transmitters is their power handling capability. Therefore, the BFSK DAM system was also simulated and tested up to 40 dBm of input RF power. Both the simulations and measurements show the capability of DAM to transmit up to 40 dBm due to the complementary symmetrical topology of the antenna. Furthermore, to improve the spectral efficiency of BFSK DAM, another prototyped antenna, 0.018λ x 0.02λ, was designed to transmit a 4FSK signal at 35 MHz. Because 4FSK is a higher order modulation technique, the design can exhibit twice the bit rate of a BFSK DAM system. These results show that such a topology provides a roadmap in attaining even higher modulation orders, thus, higher spectral efficiency