Radiation Efficiency Improvement for Electrically Small and Low-Profile Antenna by Stacked Elements

Radiation efficiency of an electrically small and low-profile meandered-line antenna is enhanced by stacked elements. The proposed antenna uses a capacitive feed structure and two meandered elements. The lower meandered element is stacked with another meandered element at a very close distance of 25 μm (1.4 × 10^-4 λ₀, where λ₀ = 175.2 mm is the wavelength at the resonant frequency of 1.71 GHz). This antenna consists of an air gap and three dielectric substrates including a thin polyimide film. As a result, this antenna has 2 mm height from the ground plane and has a ka value of 0.476 <; 0.5 (k: wavenumber at the resonant frequency; a: radius of a sphere surrounding the antenna). This electrically small and low-profile antenna achieves a radiation efficiency of 79% and 77% in simulated and measured results, respectively.