伊藤 公一

In recent years, various types of applications of electromagnetic techniques to microwave thermal therapies have been developed. The authors have been studying the coaxial-slot antenna, which is one of the thin microwave antennas, for the minimally invasive microwave thermal therapies, such as interstitial microwave hyperthermia. From the results of our previous studies, it was clear that the coaxial-slot antenna with two slots generates a localized heating region only around the tip of the antenna. In this paper, we confirm the heating characteristics of the coaxial-slot antennas with two slots from a viewpoint of clinical use, and introduce the results of two clinical trials.

This paper presents a very useful and yet simple method of improving the radiation-pattern distortion of a patch antenna having a finite ground plane. The improvement can be achieved by cutting out the edges of the finite ground plane. This produces a phase shift between the induced equivalent magnetic currents on the edges, thereby causing cancellation in the diffracted fields. We numerically and experimentally examined the effects for some typical patch antennas and confirmed that the ripples in the copolar E plane pattern could be eliminated by using this approach.

The efficiency fractional efficiency bandwidth product (EB) that is expressed as a ratio of the radiation resistance to the absolute value of an input reactance of an antenna is used as a performance, measure for small dielectric-loaded monopole antennas (DLMAs). The dependence of the efficiency bandwidth (EB) on the permittivity of the dielectric loading (i.e., the electrical volume) is experimentally investigated for the first time after we succeed in measuring the small radiation resistance of the DLMAs precisely on the basis of the Wheeler cap method. As a result, it is found that the EBs of some DLMAs are enhanced over a bare monopole antenna and an EB characteristic curve has a maximum point. This result suggests the presence of the optimum electrical volume for the dielectric loading in order to obtain the best EB performance. A calculation by the finite-difference time-domain (FDTD) method is also conducted to confirm the presence of the maximum EB value under a certain condition. A general reason for the existence of the peak value is also explained using a mathematical deduction.