Masakazu Ikeda

A spiral antenna backed by an electromagnetic band-gap material

A spiral antenna backed by an electromagnetic band-gap material, referred to as the EBG spiral antenna, has been analyzed using the finite-difference time domain method. The analysis shows that, even though the antenna height is less than one-quarter wavelength, the EBG spiral can radiate a CP wave. The spiral, which supports first mode radiation at 6 GHz, is found to have a frequency bandwidth of 11% for a 3-dB axial ratio criterion. Within this axial-ratio bandwidth, the gain variation is 4.1 dB.

Monofilar and quadrifilar helical antennas wound on dielectric rods

This paper presents monofilar and quadrifilar helical antennas wound on dielectric rods. These antennas are designed for radiating circularly polarized waves. The finite-difference time domain method, formulated using a rectangular coordinate system (x, y, z), is used to analyze the helical antennas. The radiation pattern, input impedance, and gain are evaluated and discussed.

A half-moon antenna

This work presents a half-moon antenna (HMA), which is composed of two semi-circular top and bottom conducting plates joined by a rectangular conducting plate. The HMA has a wide radiation beam. Radiation in the y-z plane (in the E plane) is hemispherical with a half-power beam width (HPBW) of more than 200/spl deg/. Radiation in the x-y plane (in the H plane) forms a sector beam with an HPBW of more than 100/spl deg/. To reduce the backward radiation and improve the gain, chokes are added to the HMA. An increase in the gain of approximately 1 dB is obtained. In order to obtain a tilted beam, the radius of the bottom plate is reduced. The maximum beam direction of the tilted beam /spl theta//sub max/ is not sensitive to frequency. Within a frequency range of 11 to 14 GHz (24%), /spl theta//sub max/=167/spl deg//spl plusmn/2/spl deg/. The gain is found to be G=9.5/spl plusmn/0.5 dBi within this same frequency range.