In this paper, a compact four-element quasi-self-complementary (QSC) ultra-wideband (UWB) multiple-input multiple-output antenna with triple band-notched characteristics is proposed. Coplanar waveguides fed QSC structure is designed as radiation element to achieve wideband and small size. Besides, regular hexagonal split-ring resonators with single negative properties are designed and added on the back of the substrate to obtain high isolation in the whole operating band. Moreover, a double-fork-shaped slit is etched in each radiating element to generate three notched bands covering 3.63–4.24, 5.15–5.98, and 7.17–8 GHz. The experiment results indicate that the isolation of the proposed antenna is higher than 22 dB and the peak gain varies from 2.5 to 6.7 dB in the entire band of 3–18 GHz, which demonstrates that it is suitable for UWB applications.

In this paper, edge-broad-side coupled spiral resonator (EBC-SR) is proposed to enhance the miniaturization of the metamaterial resonators. After a comparative analysis, it is found that the proposed strategy can drastically reduce the electrical size of metamaterial resonators. This is due to the use, at the same time, advantages of edge coupling, broad-side coupling, and self-coupling. A lumped element equivalent circuit model is proposed for the EBC-SR-loaded transmission line. This model is validated by comparing the results of electromagnetic simulations with the circuit simulations using the extracted parameter values. To validate the proposed strategy, a prototype of the EBC-SR embedded inside a drive loop is fabricated. The experimental results are presented with the simulation results.