Motoo Mizusawa

A compact broad-band helical antenna with two-wire helix

A new method of increasing the bandwidth of normal-mode helical antennas (NMHA) is proposed. The antenna has length of around 0.1 of the target wavelength, and consists of a helix constructed with two flat wire strips. The method exploits the two current modes of the two-wire design to obtain wideband response. Based on an analysis of the equivalent circuits of the two modes and subsequent optimization of design parameters, a final two-strip NMHA design is proposed that is demonstrated to have a bandwidth of 12% in the 760-MHz band at a voltage standing wave ratio of less than 2.

Increasing the bandwidth of a meander line antenna consisting of two strips

Small antennas for handsets in personal communication systems are required. A meander line antenna (MLA) can be used in such systems. The input impedance of the MLA can be easily matched by use of impedance step-up and balance mode impedance loading. But increasing the bandwidth of an MLA through the use of a two-strip geometry has not been accomplished so far. A method for increasing the bandwidth of the 2-strip MLA is described. An equivalent circuit of the MLA is represented by use of the balance mode impedance as an open- or short-circuited shunt stub. On the basis of the equivalent circuit, a numerical analysis of the impedance characteristics of the 2-strip MLA is carried out. In the analysis, the contribution of the parameters of the 2-strip MLA towards increasing the bandwidth are discussed.

A broadband plate antenna with slits

As a small antenna of handsets for personal communication systems, a two-strip meander-line antenna and a normal mode helical antenna have been suggested. The values of quality factors of both antennas are from 20 to 30 when the size of the antennas are smaller than 0.1 wavelength. The quality factor Q is really important to evaluate the bandwidth of an antenna. The bandwidth is in inverse proportion to Q. Therefore, if the quality factor can be small, the bandwidth becomes broadband. A plate antenna whose quality factor is smaller than those of the meander line antenna and the normal mode helical antenna can be obtained with broadband characteristics. In order to realise the impedance matching, the antenna consists of two plates, and the currents of the two plates are produced in imbalance and balance modes. In this paper, the small plate antenna with slits is treated. The impedance characteristics of the antenna is made clear and increasing the bandwidth by using two plates is also discussed.

Numerical analysis of the radiation characteristics of the meander line antennas consisting of two strips

With the development of mobile terminal equipment, the demand for smaller handsets has increased. The size of many devices are decreasing, however, it is difficult to reduce the size of an antenna, that is, there are problems of impedance matching, bandwidth and radiation efficiency with down sizing. Currently, in a personal radio system, a whip antenna, a planar inverted F antenna (PIFA) and a helical antenna in the normal mode are used. The PIFA and helical antenna satisfying the condition that their sizes are smaller than /spl lambda//2/spl pi/ (1 radiansphere) are well known as a reference of a small antenna. The PIFA is not thin, while the normal mode helical antenna needs a matching circuit because of the small radiation resistance. The radiation characteristics of a meander line antenna are described and a method of improving the matching by using two strips are shown. The impedance matching is considered on the basis of its equivalent circuit and an analysis of the current distributions of the meander line antennas is carried out.

Increasing the bandwidth of a two-strip meander-line antenna mounted on a conducting box

A meander-line antenna consisting of two strips (two-strip MLA) is applied to a conducting box as a handset model in order to increase the bandwidth of a built-in antenna. The analysis of an MLA mounted on a conducting box leads to its resonant frequency f/sub r/, and radiation resistance R/sub r/ at f/sub r./ Using the two-strip MLA with balance mode impedance, broadbanding of the antenna in the impedance characteristics is considered.

Increasing the bandwidth of a normal mode helical antenna consisting of two strips

A normal mode helical antenna (NMHA) is usually used for handsets in personal communication systems. As the small NMHA has low radiation resistance, it requires a matching circuit. The matching circuit has loss and the radiation efficiency decreases. An NMHA consisting of two wires (the 2-wire NMHA) has been suggested (Noguchi et al., 1997). The radiation impedance of the 2-wire NMHA can be matched by itself to the characteristic impedance of the feed line. The impedance matching is carried out by use of current modes that include balance and unbalance modes. However, it is difficult to increase the bandwidth of the 2-wire NMHA because reactance components of the antenna can not be eliminated by reactance in the balance mode of two wires. A small meander-line antenna of two strips has been suggested to increase the bandwidth of the antenna without a matching circuit (Noguchi et al., 1997). The reactance component of the antenna can be eliminated by reactance in the balance mode over a wide frequency range. In this paper, a small NMHA consisting of two strips (the 2-strip NMHA) is presented. The method of increasing the bandwidth is applied to this antenna.

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.

Broadband matching of a RFID antenna by using a T-type circuit

RFID usage is steadily increasing in the world, and its frequency bands are assigned in each country. RFID in UHF band is mainly used in 900MHz band. Allocated frequency bands of Europe, the USA and Japan are included from 860 to 960MHz. Broadbanding of the IC and antenna is needed to manage the worldwide RFID frequency band. This paper proposes broadband matching of a RFID antenna by using a T-type circuit. The antenna consists of a meander-line and a T-type circuit that realizes conjugate impedance matching to the IC impedance. Equivalent circuits of the antenna are shown and evaluated by parametric study. Prototype of the antenna is realized and its numerical analyses are examined.

Measurement of a cylindrical dielectric resonator antenna in millimeter wave bands

Recently, the DRA has been researched as an antennas for the millimeter wave band. A feature of the DRA is radiation using the resonance of the dielectric. By choosing the correct dielectric constant, small size and low loss characteristics can be expected compared with past millimeter wave antennas. A millimeter wave band DRA is numerically analyzed by the finite element method, and a prototype DRA is produced. The impedance characteristics are measured using a probe station. The results of experiments and numerical analysis by the finite element method are shown.

Broadbanding of a plate antenna with slits

Handset antennas for mobile radio communications have been small, and its high-performance characteristics over a broadband have been required. With the spread of multimedia, broadband small handset antennas are required too for video communications. In our previous studies, two-wire meander-line, two-wire helical and two-plate antennas have been investigated for the purpose of the broadbanding of the small antennas. By making the antenna element a two-wire structure, it is possible to utilize both the currents in the unbalance and balance modes on the antenna, which results in the broadband characteristics. The radiation resistance of the electrically small antenna (about one tenth of the wavelength) is generally small, and the Q-value then becomes high. Therefore, broadband impedance matching becomes complicated. In this paper, the broadband characteristics are obtained by adding a series impedance element to a small two-plate antenna with slits. The analysis is carried out by using an equivalent circuit of the antenna, and the effect of the impedance added in the series is examined.