Electromagnetically coupleed small broadband rectangular disk-loaded monopole antenna

Abstract

Electrically small antennas are much smaller than a radiant sphere and they have a narrow bandwidth because the quality factor, Q, of antenna is very high. Therefore, the reduction of Q is an important factor in the design of electrically small antennas. It has been reported that Q of the antenna can be reduced, thereby increasing the bandwidth, by effective use of the volume of a smallest sphere that can enclose the antenna. We present a small broadband antenna which consists of a rectangular disk-loaded monopole and a probe with a rectangular spiral strip line monopole. The broad impedance bandwidth is achieved through the electromagnetic coupling between these two monopoles that generate two resonances within close frequency ranges. Even though the electrical dimensions of the antenna are very small (11 mm /spl times/ 11 mm /spl times/ 11 mm, or 0.075/spl lambda//sub 0/ /spl times/ 0.075/spl lambda//sub 0/ /spl times/ 0.075/spl lambda//sub 0/), the measured impedance bandwidth for VSWR<2 is 336 MHz with the center frequency at 2.038 GHz.