Manabu Omiya

Considerations on performance evaluation of cavity-backed slot antenna using the FDTD technique

The finite-difference time-domain (FDTD) method is considered a versatile and efficient tool for the solution of Maxwells equations in complex structures for any time dependence. We show an antenna feed model suitable for performance evaluation of a cavity-backed slot antenna using the FDTD technique. The gap voltage and the coaxial feed models are examined, and their input characteristics and absolute gains are compared. Analytical results show that the input characteristics are estimated with fewer time steps for the coaxial model than for the conventional gap voltage model. Furthermore, we show how to calculate absolute gains and radiation patterns using the coaxial model and a sinusoidal voltage source at the desired frequency. The computed results of the absolute gain converge after the fifteenth period of the voltage source for the coaxial model and are in good agreement with the experimental results. On the other hand, the absolute gain is observed to fluctuate when the gap voltage model is used. The performance evaluation and comparison reveals that the coaxial model is an appropriate feed model for use in the analysis of the performance of the cavity-backed slot antenna using the FDTD technique. The good agreement of the FDTD results with the experimental measurements demonstrates the effectiveness of the model and the method proposed.

Numerical analysis of electromagnetic field distributions in a typical aircraft

The purpose of this study is to develop accurate and reliable estimation method of Electromagnetic field distributions in practical environments including passengers. However, comprehensive measurements in an actual environment cost too much and it is difficult to carry them out precisely. In this paper, large-scale numerical simulations are carried out to examine the electromagnetic fields excited by the 2.45 GHz wireless LAN terminal inside an aircraft. We used a typical aircraft model and employed the FDTD technique and a supercomputer to estimate the field distributions inside the whole area of the cabin. A Large-scale parallel computing technique based upon several node partitions of a supercomputer was used because of its memory and speed capabilities. It is able to give us a good perspective within a reasonable computation time. Furthermore, a simplified histogram estimation method for electric field strength in the cabin was employed to deal with the complicated EMF distributions inside the cabin including passengers.

Slot antenna consisted of two conductive plates and thin wires

The solar power satellite (SPS) was proposed as a sustainable and reusable energy source for mankind in future. This paper discusses a design method of antenna elements whose conductive sidewalls in the conventional model are replaced by thin wires. Such a new configuration makes it easy to produce low profile antenna elements as well as array antennas. Relations between the wire intervals and input characteristics are clarified. It is shown from the study that the method is also available to design the new type of antenna element. This paper describes the geometries of a conventional and a new type of cavity-backed slot antenna, and shows the antenna parameters that realize the impedance matching by using the proposed method. The effectiveness of the design is clarified from computed results. Moreover, the mutual coupling of a nine-element array antenna is considered.

Performance evaluation of cavity-backed slot antennas using the FDTD technique

This paper proposed feed models appropriate for the FDTD evaluation of the input characteristics of the cavity-backed slot antenna. By employing the coaxial model and the gap voltage model, we showed the coaxial model effectively reduced the amount of time steps and did not require the time window function to estimate experimental results of the input characteristics. Compared with the gap voltage model, the coaxial model gives a good estimation of the input impedance by only 3000 time steps. On the other hand, the gap voltage model and time windows required 32768 or 20000 time steps for the accurate estimation. It is concluded that the coaxial model requires only 9 % or 15 % of the time steps required for the gap voltage model. As a result, we concluded the coaxial model is effective for the FDTD analysis of the cavity-backed slot antenna. This technique is easily applicable to the evaluation of mutual coupling and beam steering performance of phased array antennas.

A large-scale numerical simulation of indoor radio wave propagation for a wireless LAN system

Recently, a high-power wireless LAN access point (AP) based on IEEE802.11n/ac standard with a high-speed data transmission rate has been developed. Using this AP makes it possible to build easily wireless networks including a few floors in the adjacent as well as many rooms in a floor. This paper discusses indoor propagation characteristics including received signal strength indicators (RSSI) and propagation channel in a whole office floor based on a large-scale numerical electromagnetic simulations employing the FDTD technique. A precise numerical model with the spatial resolution of 5 mm is developed for the numerical simulation at the frequency of 5 GHz. The calculation are carried out by using the high-performance and high-capacity computer system, HITACHI SR16000 model Ml. As a result, we confirm the validity of numerical simulation related to RSSI and channel modeling. The manner is useful to decide the number of access points as well as their locations for designing wireless networks.

Indoor propagation characteristics at 2.4 GHz for IEEE802.11n wireless local area network

Recently, a high-power wireless LAN access point (AP) based on IEEE802.11n standard with a high-speed data transmission rate of 300 Mbps has been developed. Using this equipment makes it possible to build easily wireless networks including a few floors in the adjacent as well as many rooms in the same floor. This paper discusses indoor propagation characteristics including the relationship between received signal strength indicators (RSSI) and throughputs in several communication environments by measurements and FDTD simulations. As a result, we obtain a linear function expressing the relation between them. Hence we can predict values of data throughput in arbitrary locations from the RSSI distributions. The manner is useful to design number of access points as well as their locations for building wireless networks.

A technique for determining the normalized impedance of slots in the image plane of the image NRDG

This paper presents a method for determining the normalized impedance of a transverse slot in the image plane of the image nonradiative dielectric guide using measurements of the standing wave. The method overcomes the problem of distortion caused by the scattered evanescent fields that are present in the vicinity of the slot. The measurement equipment, its optimum parameters, and aspects necessary for accurate measurements are also discussed. Moreover, the finite-difference time-domain technique is employed to determine the normalized slot impedance, and good agreement is obtained with measured results, confirming the reliability of the method.

Electromagnetic simulations and numerical models for an accurate prediction of indoor radio wave propagation in an office environment

A high-power wireless LAN (WLAN) access point (AP) based on IEEE802.11n/ac standard makes it possible to build easily wireless networks including a few floors in the adjacent as well as many rooms in the same floor. This paper discusses indoor propagation characteristics including received signal strength indicators (RSSI) and channel modeling in the premises of Information Initiative Center, Hokkaido University by measurements and a large-scale numerical simulations. A precise numerical model with reinforced-concrete walls, furniture and so on is developed for the numerical simulation at the frequency of 5200 MHz. Comparing the calculated results with the measurements, we confirm the validity of numerical technique for estimating RSSI and channel modeling in the indoor office environment. Moreover, it is clarified from calculations using two kinds of numerical model with the reinforcing rods in the concrete walls and without them that the indoor propagation channels are significantly influenced by the reinforced-concrete walls. The proposed numerical technique and the numerical model indicate their accuracy in predicting the RSSI and indoor channel model for WLAN.

Estimation of the EMF excitation by cellular radios in actual train carriages - with and without passenger

Precise computer simulations using 800 MHz and 2 GHz transmitters in an actual train carriage are conducted on the electromagnetic field (EMF) distributions excited inside train carriages. With regard to the EMC of the portable radio terminals such as cellular phones and data communication transceivers that transmit RF waves, one of the most important and substantial issues is to prevent the occurrence of unwanted effects on the human health due to the RF exposure from such radio devices (1997) (Kramer et al., 2002). Since the portable radios may be used in various environments, accurate and reliable estimations of EMC in practical environments are required. However, the measurements in the actual environment need enormous costs and it is also difficult to carry out precisely. In this paper, we carry out the precise numerical simulations to examine the EMF actual environment. A simplified histogram estimation method for electric field strength is developed to deal with the complicated EMF distributions. Typical results of FDTD analysis and actual measurement data are then shown. Finally, considerations and conclusions are made

Analysis of the open-ended image NRD guide using FDTD

Simulation is an indispensable means of designing antennas, especially when the evaluation of the antenna characteristics using theoretical analysis is complex or not very accurate. This work proposes an open-ended image nonradiative dielectric (NRD) guide antenna and presents its characteristics obtained using the finite-difference time-domain (FDTD) method. The key features of the FDTD implementation are discussed, particularly the simple and convenient approximate three dimensional modeling of the coaxial feed cable and the excitation probe that were used. The characteristics of the antenna that were determined are the return loss and absolute gain frequency characteristics and the E- and H-plane radiation patterns. Experimental results are used to verify the characteristics obtained using FDTD and are found to be in good agreement.