A moderate gain extremely short HF monopole antenna

An extremely short HF monopole antenna with moderate gain is presented. The height and lateral dimension of the proposed antenna are λ/300 and λ/100 × λ/100 at 20 MHz, respectively. The antenna is designed using two short in-phase vertical elements. To achieve in-phase radiation from the short vertical pins a modified T-type 180 degree phase shifter utilizing a capacitive impedance inverter is used [1]. An important advantage of the proposed antenna is omnidirectional radiation pattern and high gain. It is found that the gain of the proposed antenna is about 6 dB higher than that of the conventional spiral-shaped inverted-F antenna on high dielectric-constant substrate (ε=10.2) occupying the same volume but about 200 times heavier.