Teruo Onishi

Biological Tissue-Equivalent Agar-Based Solid Phantoms and SAR Estimation Using the Thermographic Method in the Range of 3-6 GHz

In this paper, the electrical constants of a biological tissue-equivalent agar-based solid phantom from 3.0 to 6.0GHz are described. The developed phantom can reproduce the electrical constants of biological tissues from 3.0 to 6.0 GHz, and it is not necessary to change the phantom for each frequency band in the range of 3.0 to 6.0 GHz during the measurements. Moreover, adjustments to the dielectric constants of the phantom at 3.0, 3.8, 5.2, and 5.8 GHz are presented. The constants of this phantom can be adjusted mainly by using polyethylene powder and sodium chloride. The phantom can be used to evaluate the Specific Absorption Rate (SAR) as well as the antenna characteristics in the range of 3.0 to 6.0 GHz. Furthermore, the effect of the electrical constants of the phantom on the SAR is investigated. The investigation of SAR measurements is performed on the phantom at 5.2 GHz using the thermographic method. Calculations using the FD-TD method and the finite difference method based on the heat conduction equation are carried out in order to evaluate the thermal diffusion in the measurements using the thermographic method. The measured and calculated results are in good agreement. There is evidence that the thermal diffusion influences the SAR estimation at 5,2 GHz more than in a lower frequency range even though this method basically does not depend on the frequency.

Consideration on the characteristics of antennas close to lossy objects

Recently mobile telephone terminals have been used not only for voice but also data. This tendency suggests that there can be various positions of the telephone near a human body other than the ear. From this point of view, it is very interesting to know how much the characteristics of the antennas mounted on the telephone are changed in each case. Therefore, in this paper a basic investigation into the characteristics (input impedance, radiation efficiency and SAR) of an antenna with consideration of the relative positions between the antenna and the object is presented. In particular directions of two different nulls of the radiation pattern in the far-field are chosen as the positions. Various numerical simulated results for different locations are obtained and discussed.

On the performances of simple circularly polarized beam-switching, 3-element and 4-element patch array antennas for mobile satellite broadcasting/communication

Two types of array antennas operating at the 2.6 GHz-band, which can be used for the MSB (mobile satellite broadcasting), are presented. Both are formed of square patches with truncated comers and generate circular polarization. After finding the value of substrate relative permittivity giving the best results, numerical simulations concerning the two antennas were performed. The first array antenna is made of three elements and aims at a reduced size. Its performance is satisfactory in terms of axial ratio in the elevation plane and in terms of minimum gain, but not at low elevation angle. Then a second array, composed of four patches, was analyzed and gave better results. The axial ratio is satisfactory and the minimum gain is better than for the first array, though still under the specification at low elevation angles. Extra simulations revealed that the minimum gain could reach the required 3 dBi at low elevation angles if one of the feeding sources is turned off. This case is still under investigation. As both antennas are interesting, depending on the user, and considering the promising results, it is planned to confirm them by performing measurements.

Simple Electronically-steered On-board Stacked-type Dual-band Patch Array Antenna for Engineering Test Satellite VIII Applications

In this paper, two simple electronically-steered on-board satellite-tracking circularly polarized stacked-type dual-band patch array antennas for mobile satellite communications are numerically investigated. The configurations of the novel antennas are shown and their performances are discussed. The first model is fed by probes while the second one is fed by microstrip line. The gain obtained for an elevation angle of 48 is 6.4 dBic at the receiving frequency and the gain is 5.7 dBic at the transmitting frequency for the former model. Additionally, the axial ratio at both frequencies is around 4 dB. Regarding the latter model, for the same elevation angle, the gain is 6.4 dBic for the transmission but only 3.3 dBic for the reception. However with this model the axial ratio is satisfactorily less than 3 dB.