access icon free Overcoming the Chu lower bound on antenna Q with highly dispersive lossy material

© The Institution of Engineering and Technology
Received 08/07/2017, Accepted 15/01/2018, Revised 13/12/2017, Published 16/01/2018

Beginning with a brief overview of the history of lower bounds on the quality factor Q of antennas and the fundamental relationships between the impedance, bandwidth, and Q of antennas, it is demonstrated by means of RLC circuit models of electrically small antennas that their isolated-resonance quality factors obtained from the ‘Q-energy’ predicts their bandwidths with greater accuracy than the ‘equivalent-circuit’ energies or the ‘electrodynamic’ energies. A generalisation is obtained for quasi-static fields of antennas that facilitate the evaluation of the expressions for the Q-energy. It is verified that the Q-energy cannot be considered stored energy in the highly dispersive lossy material. Nonetheless, using tuning elements containing highly dispersive lossy material, the bandwidth of fifty-per cent (for example) efficient electrically small dipole antennas can be designed with twice the bandwidth predicted by the Chu lower bound for the quality factor of fifty-per cent efficient antennas.

Inspec keywords: Q-factor; dipole antennas; RLC circuits

Other keywords: isolated-resonance quality factors; electrically small dipole antennas; quasistatic fields; dispersive lossy material; Q-energy; Chu lower bound; RLC circuit models

Subjects: Single antennas

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