Takashi Yanagi

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.

Basic study on wideband microstrip patch antenna incorporating matching-stubs onto patch conductor

This study demonstrates a new bandwidth improvement technique using a structure of impedance-matching function which is composed of two series-stubs located on the patch conductor.The effectiveness of the matching stubs on the bandwidth improvement has been confirmed experimentally. The proposed method is especially effective against a thin microstrip patch antenna that it is hard to apply L-probe method.

A Realistic Distributed Circuit Model for EBG Structures Based on Physical Implementations

In this paper a new equivalent circuit for the EBG structure which represent the feature of surface-wave suppression is proposed. The equivalent circuit of the EBG unit cell consists of capacitors, inductors and transmission lines of series branches, as well as a capacitor and an inductor of shunt branch. These equivalent circuit parameters are based on physical implementations of EBG structures. Therefore it is easer to extract the parameters than conventional equivalent circuits. Also, the proposed equivalent circuit can calculate a large-scale EBG structure characteristic without a long computation time although the constitution is simple.