  Operational bandwidth of resonant circuits is limited by the resonator's
size, which is known as the Chu limit. This limit restricts miniaturization of
antennas, as the antenna bandwidth is inversely proportional to its size. Here,
we propose slow time modulation of resistive elements to engineer bandwidth of
small antennas. The temporal modulation of resistance induces virtual impedance
that is fully controlled by the modulation parameters. We show how the virtual
impedance can be used to optimize the frequency response of a resonant circuit,
leading to enhanced matching at multiple frequencies simultaneously. We
experimentally verify the proposed technique, demonstrating enhancement of
radiation of a broadband modulated signal radiated by a small antenna.
