Ryo Yamaguchi

Mutual coupling reduction effects of EBG structure located on cylinder surface

EBG (Electromagnetic Band-Gap) structures composed of metal patches arranged at narrow intervals have been studied to apply to microwave components and antennas [1][2]. The EBG structures have the frequency-band-rejection characteristics and it can reduce the undesired radiation of electromagnetic waves [3]. In general, the EBG structure is made on the flat ground plane, and is not examined the design method when put on the curved surface. This paper describes the mutual coupling reduction effects of EBG structures located on cylindrical surface.

Low-profile design of meta-surface by considering filtering characteristics of FSS

A FSS (Frequency Selective Surface) is composed of metal patches arranged in narrow intervals, and has frequency-band-rejection and frequency-band-pass characteristics. It is known that the FSS with the ground plane has PMC (Perfect Magnetic Conductor) characteristics in a specific frequency band. The surface is referred to as a meta-surface and it can control the phase of the wave which is reflected at the surface. This paper proposes a design method to realize a low-profile meta-surface. In the proposed method, the FSS which has low-pass or high-pass filtering characteristics is utilized. The effects of the filtering characteristics of a FSS on PMC characteristics of a meta-surface are described. Based on the calculated results, it is confirmed that the meta-surface can be obtained by using the FSS. In addition, it is found that the thinner and more wideband meta-surface can be achieved by using the FSS which has low-pass filtering characteristics.

Reduction in mutual coupling characteristics of slot-coupled planar antenna due to rectangular elements

In this paper, we proposed a broadband ACPA that integrated a filter function. By installing multiple rectangular elements in the Rx antenna, the mutual coupling between the Tx and Rx antennas was reduced from -24 dB to -29.8 dB(min. -36 dB). At the same time, the broadband resonance of the antenna and external size were maintained after adding the filter function. By investigating the current distribution on the rectangular elements, we found that the current on the second rectangular element changes its direction when the frequency is higher than ftrap. This enables the antenna to function as a low-pass filter.

Gain measurement method for long antenna using numerical compact range concept

A gain measurement method applied to actual measurements of fields at finite distances by using a conventional pattern measurement system and numerical compact range concept was evaluated in order to obtain the gain of a long antenna. Based on the simulation results, the dependency on the distance from an antenna array with elements in a numerical compact range is clarified to show the measurement restrictions for this method. Furthermore, the experiment results in an anechoic chamber show that the dominant deviation in gain occurs due to the offset in the axis parallel to the direction of the actual source element, and the difference in value can be reduced by using a REF of the same length as the AUT.

Reflection Characteristics of Finite EBG Structures on Finite Ground Plane

In this paper, we take up mushroom type EBG structures and clarify the frequency-band-rejection characteristics of the finite EBG structures on the finite ground plane, and we also compare that with the infinite EBG structures and the semi-infinite EBG structures. Here, we analyze the reflection characteristics of a normal incidence plane wave.

Novel specific absorption rate (SAR) measurement system using flat-plane solid phantom

In this paper, the required dimensions of the flat-plane solid phantom are derived using the finite difference time domain (FDTD) method to obtain detailed SAR measurements that are equivalent to standardized procedures using the liquid. The proposed measurement system using the flat-plane solid phantom constructed using ceramic materials is presented and the system is validated by acquiring SAR distributions at 900 MHz for two types of antennas.

A fading generator using rotated scattering slots

MIMO-OTA (Over-the-air) measurement methods of mobile terminals have been recently studied and developed for mobile communications. However, the methods like these for base station antenna have not been often reported. A fading generator using rotated scattering objects has been proposed in my previous study in order to establish an OTA measurement method for MIMO base station emulating radio environment around the base station. This fading generator is based on a near-field Jakes scattering model that is modified from the conventional Jakes model. Although metal patches on the dielectric disc as scattering objects is used to obtain fading waves in the study, slots on the metal disc are newly adopted as scattering objects in order to get the same waves. In this paper, the validity of the proposed generator is clarified by experiments using a prototype.

Azimuth pattern design to reduce interference in overlapping sectors using combined tilt

This paper focused on the effects of the combined tilt to decrease the interference from overlapping sectors in urban areas. The simulation results showed that the characteristics when using a combination of mechanical up-tilt and electrical down-tilt can narrow the azimuth beam patterns. We found that the larger the mechanical up-tilt and number of elements were, the narrower the azimuth beam patterns became. The conditions to avoid a loss in gain due to the grating lobes were shown. The application of the combined tilt to shaped beams that have very sharp curve characteristics was examined. The influence of shaped beams on the coverage areas was investigated, and the effects of decreasing the interference from overlapping sectors and increasing the SIR were shown.

Measurement of current phase distribution for wireless devices using polarization stabilized MO probe

This paper investigates a magneto-optical (MO) probe that has no metal in its construction and comprises a MO crystal and an optical fiber. The MO probe is considered to be well suited to measure the current distribution with high accuracy because of 1) its low level of electromagnetic field invasiveness since no metal is used in its construction, 2) its close proximity to the device under test (DUT), and 3) its micrometer scale sensitive area. The MO probe, however, has a problem in that fluctuation due to optical polarization causes measurement instability. In order to achieve stable measurement, we have proposed employing a polarization stabilized MO probe. In this paper, the current phase measurement employing this probe is performed

Loop antenna for localized exposure of small animals

The observation during exposure is important in assessing temporal changes (microcirculation of blood, skin condition, etc.) in bio-tissue as a result of microwave radiation. For use in such a study, we investigated the use of a loop antenna that is set parallel to the exposure object. Because the loop antenna is thin, flat, and hollow, this antenna can be placed close enough and parallel to the exposure object to achieve microwave exposure during observation. The bio-tissue can be observed through the loop hole. The exposure distribution by the loop antenna is compared to that of other antennas for use in the experiment.