Summary
International Symposium on Antennas and Propagation
2008
Session Number:3C21
Session:
Number:3C21-5
Validation of Gain Measurement in the Liquid Based on Extended Friis Transmission Formula
Naoto Ikarashi, Nozomu Ishii, Ken-ichi Sato, Lira Hamada, Soichi Watanabe,
pp.-
Publication Date:2008/10/27
Online ISSN:2188-5079
Summary:
Because the higher frequency band will be used for the mobile communication devices, it is required to establish the technique of calibrating the electric probes for their SAR (Specific Absorption Rate) assessment, especially over 3GHz. For the conventional calibration with rectangular waveguide system commonly used in 300MHz-3GHz [1], the tip size of the probe cannot be ignored so that the calibration is more inaccurate as the frequency is higher. The authors have developed an alternative calibration without using the waveguide system [2]?[4]. For our calibration, first, the far-field gain of the reference antenna operated in the tissue-equivalent liquid is measured, and then the electric field radiated by the antenna is related to the output voltage of the electric probe [1]. For the gain measurement, the S parameters between the two antennas with linear alignment are measured, and the far-field gain is determined by use of the two-antenna method based on the Friis transmission formula in the conducting medium [2], [5]. The decay of the fields in the liquid [1], [3] is too large to receive the signal radiated by the transmitting antenna in its far-field region. For higher frequency over 3GHz, this nature makes the transmittable distance shorter in terms of the wavelength in the liquid. To overcome this difficulty, the authors have examined the technique of estimating the far-field gain of the antenna in the liquid by using S 21 measured in the near-field region and curve-fitting based on extended Friis transmission formula in the conducting medium that we proposed [3], [4]. In this paper, the dynamic range of the measurement system is enhanced by inserting the amplifier in front of the transmitting antenna and increasing its input power to measure S 21 in the far-field region with a vector network analyzer. Then, the far-field gain, that is, the absolute gain estimated by using S 21 measured in the near-field region is compared with that by using S 21 measured in the far-field region. This fact leads to the validity of our technique of estimating the far-field gain of the antenna in the liquid.