Small Wideband Double-Loop Antennas Using Lumped Inductors and Coupling Capacitors

Miniature footprint double-loop antennas, loaded with lumped inductors and coupling capacitors, are introduced. Through band diagram analysis, it is shown that frequency separation between the two radiating modes can be controlled to achieve wider bandwidth. For verification, three wideband antennas are designed by adjusting the inductive and capacitive loadings to create resonances at two closely spaced frequencies around 2.45 GHz. The first antenna is fabricated on a 125-mil-thick Rogers TMM10i substrate and has 2.1% |S₁₁| <; -10-dB bandwidth with >;1.2 dB gain using a λ₀/9.8 × λ₀/9.8 × λ₀/39.4 footprint. It is shown that the antenna has 49% smaller footprint area than a standard patch and exhibits the same bandwidth performance at the expense of lower gain. The second antenna is fabricated on a reduced-size substrate comparable to its footprint size. This antenna still exhibits the same bandwidth performance as the standard patch. The third antenna is on a 250-mil-thick substrate and exhibits 14.7% bandwidth and 4.34 dB gain with λ₀/9.8 × λ₀/9.8 × λ₀/19.7 footprint.