A non-Foster Solution to Broadband Directive Radiation Pattern in Huygens and Magnetoelectric Antennas

Classical Huygens source that contains a short dipole and a small loop is very attractive antenna due to its subwavelength size, low profile and unidirectional radiation pattern with a theoretical directivity of 4.77dBi. However, inherent requirement of a 90° phase shift between a dipole and loop excitation currents causes a narrow bandwidth with cardiod directive radiation pattern. In this contribution, it is shown that well-known Chu’s equivalent circuits of a short dipole and a small loop provide clear physical picture of the requirements for the 90° phase shift. Moreover, the combination of Chu’s equivalent circuits with non-Foster elements leads to broadband cardiod radiation pattern as well as broadband impedance matching. This approach can also be used for construction of a broadband magnetolectric antenna. Proposed idea is tested by circuit-theory simulations, full-wave simulations, and experiments.