Impedance Characteristics Of Antenna Research Articles

Investigation into the impedance characteristics of magnetoelectric antennas

Mechanical antenna is recently considered a novel scheme for realizing very low frequency (VLF) and portable transmitters. In this paper, the impedance characteristics of 1-1 typed and 2-1 typed magnetoelectric (ME) mechanical antennas are systematically studied and compared. Based on measured frequency-impedance curves and the corresponding MBVD (Modified Butterworth-Van Dyke) model, three characteristic frequency points, i.e., the minimum impedance frequency <i>f<sub>m</sub></i>, the series resonance frequency <i>f<sub>s</sub></i> and the resonance frequency <i>f<sub>r</sub></i> are obtained and discussed. On this basis, the influence of driving voltage, bias magnetic field, and the quality factor (Q value) on ME antenna impedance characteristics is experimentally explored. Finally, the reactance components of both 1-1 typed and 2-1 typed ME antenna are collected by referring to the actual working frequency <i>f<sub>d</sub></i>. Experimental results prove that resonant ME antennas are basically pure resistive vibrators, while a ME antenna with high Q value normally fails to support high driving field because of the low resistance (< 100Ω) and the strong nonlinearity. Thus, the field radiation capability in 2-1 typed ME antenna is higher than that of 1-1 typed one. This work provides perspectives for Q value selection and further optimization of a magnetoelectric antenna based on the understanding of its impedance characteristics.

Compact MIMO Antenna for Multiband Mobile Applications

This paper presents a multiple input multiple output (MIMO) antenna for multiband operation based on meander lines with L shaped metallic strip. Meander lines is basically a monopole a antenna loaded with multiple sections of short circuited transmission line that acts as inductor and alter the impedance characteristics of antenna. Antenna size miniaturization of 69 % has been achieved by placing double U slots on the ground plane and a line slot DGS (Defective Ground Structure) is used to reduce the mutual coupling between the antenna elements. The values of envelope correlation coefficient (ECC) and Specific Absorption Rate (SAR) lie well below the specified limit.

Mode-Based Estimation of 3 dB Bandwidth for Near-Field Communication Systems

A new method for estimating the 3 dB bandwidth of near-field communication (NFC) systems using identical electrically small antennas is proposed. The method is based on equivalent circuit representation using the addition theorem, an approach used in the analysis of coupled antennas, and the correction factor derived from antenna impedance characteristics. In addition, variation in the 3 dB bandwidth with respect to the relative position and orientation of the NFC system is investigated using the proposed method.

Impedance characteristics of two-wire helical antenna in normal mode

A helical antenna in normal mode is used as a small antenna for handsets in personal communication systems. When the diameter and axial length of the helical antenna is small compared with the wavelength of the operating frequency, the antenna works in normal mode and has a radiation pattern and linear polarization the same as a monopole antenna. Because the radiation resistance of the antenna is low and the Q-factor is high, the impedance characteristic is a problem. In this paper, a normal-mode helical antenna consisting of two wires is treated and the impedance characteristics of the antenna are analyzed. It is possible to use currents on the helical antenna in balanced and unbalanced modes by use of two wires of the antenna. The analytical results show that the radiation resistance in the unbalanced mode as the radiation mode can be stepped up, and the reactance in the balance mode as transmission-line mode can be used for impedance matching. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(12): 37–44, 1998

Analysis of stripline-fed slot-coupled patch antennas with vias for parallel-plate mode suppression

The paper presents an analysis of slot-coupled stripline-fed patch antennas with vias around the slot to minimize the power launched into the parallel-plate mode. A moment-method scattering formulation is invoked to include the effect of vias on the impedance characteristics of the antenna. Coupling between the stripline feed and the ground-plane slot is obtained by invoking reciprocity. Two design examples were fabricated and the measured input impedances verify the accuracy of the analysis. Vias considerably modify the impedance and resonant characteristics of a patch antenna. The radiation efficiency of patch antennas with and without vias is studied and proper location of the vias is shown to drastically reduce power in the parallel-plate mode.