Toru Fukasawa

Extended S-Parameter Method Including Radiation Pattern Measurements of an Antenna

Coaxial cables connected to the antenna frequently affect the characteristics of the antenna. Although the S-parameter method is one of the most effective methods of reducing the influence of the coaxial cables, it has so far only been applied to impedance measurements. We propose an extended S-parameter method that can also be applied to radiation pattern measurements of amplitude and phase. In this method, two cables are connected to an antenna, and the excitation coefficients of the two cables are obtained from the S-parameters under the condition where the unbalanced current of the coaxial cables is reduced. From array patterns generated with these excitation coefficients, we can obtain the radiation patterns with a reduced unbalanced current of the coaxial cables. We apply this method to dipole antennas and a helical antenna on a small housing. Our simulated and measured results demonstrate the validity of the proposed method and 20 dB reduction of the influence of the coaxial cables.

Decoupling networks composed of lumped elements for diversity/MIMO antennas

We show design equations for decoupling networks composed of lumped elements. These equations are valid for arbitrary two-element antenna arrays and plane-symmetrical three-element antenna arrays. The decoupling networks consist of series susceptances and shunt susceptances. We design small two-element and three-element antenna arrays with the decoupling networks, and verify the design equations by performing measurements and simulations. The sizes of the two-element and three-element antenna arrays including the ground planes are 0.12λ_c × 0.18λ_c and 0.25λ_c × 0.21λ_c, respectively. We confirm high isolation is achieved by the decoupling networks.

Optimization of cross polarization characteristics for dual-polarized patch antennas

Base station dual-polarized patch antennas for cellular mobile radio require us to decrease cross-polarization for the planes tilted from the horizontal plane. We report the cross polarization characteristics in the tilted planes, and derive analytically that there exists the optimum substrate permittivity to achieve low cross-polarization. Moreover, we validate these characteristics both by FDTD simulations and by experiments.

Analysis of whip antenna fed by a slot antenna with electromagnetic coupling

In this paper, a new type of antenna without the contact feed point is proposed for mobile information terminals. The whip antenna is excited by the built-in antenna with electromagnetic coupling. The built-in antenna acts as a radiator when the whip antenna is pulled in. The built-in antenna acts as not only a radiator but also an exciter for the whip antenna when the whip antenna is extended. In this antenna, the shortcoming of the conventional antenna with contact feed point disappears. The slot antenna on a small conductor plate and a dipole antenna are proposed for the built-in antenna and the whip antenna, respectively. The slot antenna is easily manufactured by an etching technology with low cost. Further, it can be made of very thin conductor film on the substrate, so it is very light.

Simplified adaptive impedance matching circuit using measurement of standing wave amplitude

This paper presents a novel adaptive impedance matching circuit using measurement of standing wave amplitude. This circuit is realized with a simpler structure than the conventional techniques. The reflection phase range can be identified by comparing the standing wave amplitudes measured at some detectors on the feed line. The reflection phase measurement method is verified by the experiments. And, for the reflection amplitude, it is possible to identify the range by using the same circuit. Moreover, the control of this adaptive matching circuit does not need a digital computer. The presented circuit can improve the mismatch loss by more than 1.2dB when VSWR=4.

Characteristics of a dipole antenna on a housing without a balun

We have proposed the dipole antenna on a housing without a balun, shown the condition and mechanism to reduce unbalanced mode. The dipole antenna without a balun under the condition can improve the radiation efficiency. We have also shown the experimental results and confirmed the validity of the calculation.

One-element diversity antenna with reactance-switching circuit for mobile phones

We have proposed a novel type of diversity antenna construction for compact mobile telephones. The proposed diversity antenna basically consists of one excitation element, the conducting-plate, and the reactance-switching circuit connecting between the end of the element and the conducting-plate, and need not install two excitation elements. We have demonstrated numerically and experimentally that the current phase distribution and radiation pattern can be controlled by appropriately switching the reactance value of the reactance-switching circuit. Our next works are to establish an optimum design theory and to investigate the performance in talking and browsing situations.