Microstrip-fed monopole antennas loaded with symmetric ENG unit cells

In this paper, a microstrip-fed monopole antenna is loaded with symmetric epsilon negative (ENG) unit cells comprising of shunt spiral inductors to achieve multi-band operation. Two antenna designs have been proposed. In the first design, one symmetric ENG unit cell is integrated with the monopole antenna which leads to generation of a lower order mode in addition to the reference monopole mode. In the second design, monopole is loaded with two symmetric ENG unit cells. The resulting monopole has two lower order modes along with the reference λ/4 resonance of the monopole. The resonance frequencies of the induced lower order modes can be controlled by varying the geometrical parameters of spiral inductors. Prototypes of proposed antennas are fabricated to validate the results obtained in simulation. The measured and simulated results are in good agreement. The proposed antennas exhibit quasi-omnidirectional patterns at all the operating frequencies.