Antennas in platforms where the physical dimensions are significantly smaller than the wavelength of the frequency of interest are limited to narrowband operations. A technique that enables transmission of such signals through narrowband antennas is called Direct Antenna Modulation (DAM). DAM utilizes switching circuitry to directly modulate the antenna at its maximum energy moments synchronized with the input RF signal. In this paper, we propose a method of attaining higher-order, N, frequency shift keyed, NFSK, modulation through a high Quality-factor electrically small antenna to achieve higher bit rates and better spectral efficiency within an instantaneous bandwidth. A DAM antenna transmitting a frequency shift keyed signal using four carrier frequencies, 4FSK, was designed, prototyped, and measured. Its electrical size is 0.018λ x 0.02λ. A pseudorandom 8-bit and 16-bit sequence were transmitted through the 4FSK DAM antenna and received in the far-field. The results show that such a topology provides a roadmap in attaining even higher modulation orders, thus, higher spectral efficiency. INDEX TERMS electrically small antennas, direct antenna modulation, time-varying electromagnetics, high-efficiency bandwidth antenna

No abstract

Antennas constrained to platforms that require miniaturisation, significantly smaller than the wavelength of the desired frequency, are inefficient radiators and limited to narrowband operations. To overcome these limitations, a technique called direct antenna modulation (DAM), is incorporated with electrically small antennas to enable transmission of high-bandwidth signals through narrowband antennas. DAM utilises switching circuitry to directly modulate the antenna at its corresponding peak energy moments all while being synchronised to the input signal, yet previous iterations were susceptible to low transmit powers due to limitations in the switching network's power handling capability and tremendous coupling between transistor ports that results in an ambiguous switching signal at the gate. A frequency shift keyed (FSK) DAM antenna topology is proposed, which is capable of high-power transmission through a geometrically symmetrical switching circuitry integrating pairs of complementary GaN transistors. The symmetry assists in removing coupling among transistor ports to effectively switch the transistors OFF and ON without regard to the input RF power. The authors' theoretical analysis agrees with our simulations and far-field measurements which show the FSK DAM antenna topology is capable of transmit powers up to −1 dBm given a 42 dBm of input RF power.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.