Y. Ebine’s research while affiliated with Yokohama National University and other places

Repeater systems will become practical in the IMT-2000 system in order to provide service in locations where presently radio waves cannot reach. We have examined an antenna structure, in the form of a patch array antenna of 4 elements, for a repeater (Michishita, N. et al., IEE 12th Int. Conf. Antennas and Propagation, 2003). At the edge of the ground plane is a choke structure, and this structure's parameters effect the FB (front-to-back) ratio. We investigate a 16 element patch array antenna which references the 4 element design method and present the mutual coupling characteristics of the 16 element patch array antennas with chokes. The repression of the FB ratio by a choke is small in the case of the 16 element array, because its side lobe level is large. We examine the effect of restraining the mutual coupling using a binomial and Chebyshev array by controlling the amplitude of each element. The binomial and Chebyshev arrays effect the restraint of the side lobe level, and the mutual coupling can be made less than -100 dB by choosing suitable parameters.

In this paper, we examine the structure of a patch array antenna suitable for repeater systems. An FB (Front to Back) ratio is determined with a choke structure set up at the edge of the ground plane. An FB ratio of 45 dB is realized when the choke parameters are optimized by electromagnetic analysis. The mutual couplings are about 100 dB when the distance between the elements is 4λ. We also discuss the antenna structure of a 4 port feed type and the coupling of a beam tilted antenna, and confirm that the mutual coupling is changed by the FS (Front to Side) ratio of the element. Experimental and calculated results are also compared.

In a repeater antenna for wireless communications, suppression of mutual coupling between transmitting and receiving antenna is required to reduce the weight and size of the antenna system even if the antenna separation is very small. On the other hand, for a dipole antenna backed by a reflector, it has already been proposed that the enhancement of FB (front-to-back) ratio of a dipole antenna can be achieved by optimizing the reflector shape. Miniaturization of the reflector can be achieved by using an optimum size for the FB ratio (see Rikuta, Y. et al., Asia-Pacific Microwave Conference, vol.3, p.1068-71, 2001). An antenna with high FB ratio has little influence on the backward direction. This paper presents the suppression of mutual coupling with a small distance between antennas by using two antennas with high FB ratio back to back. We investigate a rectangular reflector and a dual boxing reflector. The characteristics of mutual coupling of these antennas are calculated by FDTD analysis.

The purpose of this study is to investigate input and radiation characteristics of antennas due to parameters of the dielectric cylindrical radome. Sector antennas occupy an important position in base station antennas. It is necessary to investigate the radome effect for sector antennas. In this paper, we investigate the input and radiation characteristic of a 2 GHz band 120° beam antenna due to the radome's parameters

Indoor wall mounted antennas need to have the cocoon-shaped pattern with the high FB ratio. This cocoon-shaped pattern in the horizontal plane will be used for IMT-2000 indoor base station antennas. This paper proposes the patch antenna with two parasitic elements mounted on the flanged ground plane to obtain the cocoon-shaped pattern with the high FB ratio. The FDTD calculations and the measurements verified the FB ratio of more than 20 dB

We presented the characteristics of the front-to-back (FB) ratio by using a dipole antenna backed by several types of reflector shapes. We simulated the radiation pattern and FB ratio of a dipole antenna by changing the size of rectangular reflector, dual reflector, and boxing reflector. There is an optimum size for each shape of reflector, and FB ratio of the dipole antenna is increased by more than 20 dB. Comparing each shape of the reflector when the width is constant, using a boxing reflector has the best FB ratio of a dipole antenna of about 29 dB

This paper presents the enhancement of FB ratio by optimizing several types of reflector shape which are placed on the back of a dipole antenna for the sector antenna. By optimizing the size of each reflector shape, the FB ratio of dipole antenna is increased by more than 20dB. Comparing each shape for the same width of reflector, a dual box reflector has the best FB ratio of more than 30dB

Typical electrical characteristics of base station antennas are low sidelobe levels and electrical beam tilt capabilities. Previously (1999) we studied a base station antenna of an equally spaced array configuration which can achieve low sidelobe characteristics and electrical beam tilt in 800 MHz to 2000 MHz. In 1500 MHz and 2000 MHz bands, many grating lobes appeared in the case of electrical beam tilt. This paper shows that suppression of grating lobes can be achieved in 1500 MHz and 2000 MHz bands by employing an unequally spaced array antenna configuration

This paper presents a two-layered antenna with dual frequency for indoor micro cellular system. It consists of a upper loop and a bottom center feed patch antenna. FDTD analysis shows that this antenna has two resonant frequencies and the radiation patterns are similar to monopole antenna

In the IMT-2000 system, because the frequency band is around 2 GHz, it is necessary to account for the effect of the dielectric radome in the antenna's design. The far field radiation pattern of an antenna with a dielectric radome also will change from the case of the element only. It is necessary to investigate the change of the antenna's input characteristics and radiation patterns due to a cylindrical radome. We investigated input characteristic of a λ/4 monopole antenna due to the parameters (radius, thickness, permittivity constant) of a dielectric cylindrical radome. We also examined the central frequency and bandwidth ratio due to offset value of element from the center of the cylindrical radome