Wide-Band Near-Field Resonance Z-Antennas Using Change In Parasitic Structure and Capacitive Lumped Element as Replacement of Non-Foster Impedance Matching Circuits

Using metamaterials in antenna design leads to interesting features includes size reduction. Although, the antenna miniaturization is the most promising advantage especially in commercial applications, their narrow band effectiveness causes great concern for the future progress. Today, using lumped and parasitic elements for admittance compensation of electrically small antennas (ESA) is a most well-known solution to overcome this problem. In this article, a modified parasitic structure is proposed to enhance the antenna impedance matching over a wide frequency range. Moreover, a new structure based on a capacitive lumped-element has been suggested which is improved the antenna bandwidth significantly. To do this, a Z-shape shaped parasitic element incorporate with an ESA monopole antenna designed, simulated and fabricated. Simulations show great agreement with measurement results. Both simulations and measurements demonstrated that the antenna fractional bandwidth, in the first case was about 5%, which increased up to 81% in modified structure.