The increasing need to improve the 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 challenging and often counterintuitive. 

To overcome these challenges, a direct antenna modulated (DAM) electrically small antenna (ESA) is proposed. By introducing time variance, the antenna system operates outside the linear time invariant regime and is not subject to traditional design and performance constraints.

J. P. Dytioco Santos, F. Fereidoony, M. Hedayati and Y. E. Wang, "High Efficiency Bandwidth VHF Electrically Small Antennas Through Direct Antenna Modulation," in IEEE Transactions on Microwave Theory and Techniques, vol. 68, no. 12, pp. 5029-5041, Dec. 2020, doi: 10.1109/TMTT.2020.3016381.

A novel liquid crystal (LC) based technology is introduced to achieve a high figure of merit (FOM) phase shifter that works at sub-6 GHz frequencies. The phase-shifting mechanism is enabled through the phase constant variation in the main microstrip line, loaded periodically by a variable equivalent capacitance controlled by a bias voltage. 

M. A. Panahi, L. Yeung, M. Hedayati and Y. E. Wang, "Sub-6 GHz High FOM Liquid Crystal Phase Shifter for Phased Array Antenna," in IEEE Journal of Microwaves, vol. 2, no. 2, pp. 316-325, April 2022, doi: 10.1109/JMW.2022.3152208.

Antenna arrays as receivers can achieve greater SNR, but elements must be spaced more than half wavelength apart. Meanwhile, closely spaced antenna arrays face the tradeoff between mutual coupling and impedance matching bandwidth. But by combining multiple techniques, wideband supergain array receiver can be designed.

Active directive matching: connect transmitter to receiver without matching network to achieve broadband noise matching and lower noise figure

Mode-based beamforming: allocation of orthogonal radiation modes in highly coupled arrays as individual information channels

L. Kun Yeung and Y. Ethan Wang, "Theory of Broadband Super Sensitivity Receiving With Closely Spaced Antenna Arrays," in IEEE Transactions on Antennas and Propagation, vol. 72, no. 11, pp. 8294-8306, Nov. 2024, doi: 10.1109/TAP.2024.3455776.