New Subwavelength Profile Monopole-Type Antenna

In this paper, we present a new low-profile (λ/40) compact antenna for the S-band frequency range (around 2.1 GHz). The main features are high efficiency (>90%), vertical polarization, and omnidirectional radiation patterns. The antenna was designed using a low-profile vertical monopole element with a standard metallic reflector plane. Top-loading techniques with symmetrical coplanar folded-slot dipoles (λ
_g
/2) and four vertical shorting pins placed at appropriate locations achieved the desired antenna matching impedance-bandwidth. The overall dimension of the antenna is 0.32λ × 0.32λ × 0.025λ. A prototype of the designed antenna was fabricated and fully characterized. The experimental results are in good agreement with the numerical calculations. The measured field radiation patterns are similar to those of standard vertical monopole antenna with a maximum normalized gain of 3.7 dB at 2.1 GHz and a bandwidth of 5% (S
¹¹
<; -10 dB).