Yoshihide Yamada

A vehicular-mounted vertical space diversity antenna for a land mobile radio

A vertical space-diversity antenna has been developed in order to achieve a diversity scheme while maintaining the simple appearance of a trunk-lid antenna. It is shown that small correlation coefficients can be achieved by a separation of approximately 0.5 wavelengths. Differences in the upper and lower antenna radiation patterns are clarified as being caused by mutual coupling of these antennas, and an incoming wave spread of more than 20 degrees is the main reason for reduction of the correlation coefficients. Field tests in the Tokyo metropolitan area have indicated that adequate correlation coefficients and an adequate received signal level can be achieved. Moreover, calculation estimations are confirmed by the experimental results. >

Mutual coupling reduction between two dipole antennas with parasitic elements composed of composite right-/left-handed transmission lines

In this study, a composite right-/left-handed transmission line (CRLH TL) is used as a parasitic element. It is shown that a right-handed (RH) dipole antenna with the CRLH parasitic element has band rejection characteristics. Moreover, transmission characteristics and electric field distribution confirm that mutual coupling between the two dipole antennas can be reduced by using CRLH parasitic elements between the two antennas.

High gain design of a very small normal mode helical antenna for RFID tags

Recently RFID tags of 900 MHz band are interested in many commercial fields. Tags are requested to be used on liquid bottles, medicine bottles and metallic plates. So, antennas are requested to be made very small and to have properties capable of use in metal proximity. In this paper, important design subjects to achieve very small antennas are summarized and technical solutions are explained first of all. Following this summary, the normal mode helical antenna (NMHA) is selected as a promising antenna that is suitable for achieving high gain in very small size and metal proximity use. Next, useful design data of NMHA to achieve high gain and metal proximity are shown. And an example of achieving a low profile NMHA is shown. In order to ensure realization, measured results of a fabricated antenna is shown. Moreover, the fabricated antenna is applied to the commercial IC chip. Communication distances are compared with that of the commercial tags.

Input impedance increase of a very small meander line antenna

Meander line antennas are commonly used as small antennas in commercial handy phones. In the case of meander line antennas of size less than 0.1 wavelength, input impedances become very small. Hence, antenna efficiencies become very low. Therefore, increase of input impedance is very important. The paper proposes a folded dipole antenna configuration that can increase input impedance. First, antenna configurations less than 0.1 wavelength and their input impedances are clarified through EM simulations. Next, increases of input impedance by folded configurations are shown. An antenna of 0.1 wavelength and its folded configuration were manufactured. Measured and calculated resistances agree rather well. Antenna efficiencies of the conventional meander line antenna and the folded configuration were 28.9% and 67.8%. respectively. Increase of antenna efficiency is ensured by the folded configuration.

A triple-layer patch antenna capable of triple-frequency operation

A triple-layer patch antenna with single feed for triple-frequency operation was designed. Satisfactory VSWR, axial-ratio, gain and radiation patterns were achieved. An important part of this antenna is its through hole feed system. A comparison of measured and calculated gains confirmed that the feeding loss is rather small, which validates the usefulness of the through hole feed. Circular and linear polarization characteristics were successfully achieved. The results confirm that we have developed a low profile antenna with excellent performance.

High performance normal mode helical antennas for RFID tags

A 0.035 wavelength very small normal mode helical antenna is designed to achieve high antenna efficiency. Antenna gain of -3.72dBd is achieved. When this antenna is attached on a metal plate, antenna gain is increased to -0.4dBd. Communication distances of current RFID tags and NMHA tags are measured. In the case of NMHA tags, communication distances comparable to current RFID tags are ensured.

A novel impedance matching structure for a dielectric loaded 0.05 wavelength small meander line antenna

This paper presents high efficiency small meander line antennas for UHF RFID tags. In this paper, we propose a novel feed model to achieve an impedance matching of small meander line antenna as a means of increasing the antenna efficiency

Tunable Phase Shifter Using Composite Right/Left-Handed Transmission Line With Mechanically Variable MIM Capacitors

In the multifrequency base-station antenna, the beam tilt angle becomes frequency-independent due to be accomplished by designing the feeding cable length of the conventional phase shifter. To suppress the interference to the adjacent area in the lower frequency band, the tunable phase shifter that can vary main bean directions in the multifrequency band is proposed in this letter. The different phase shifts can be realized by using the dispersion relation of a composite right/left-handed transmission line. The tunable function is realized by mechanically sliding the patches of the metal-insulator-metal capacitors.

Improvement of Beam Scanning Characteristics of a Dielectric Lens Antenna by Array Feeds

In the Intelligent Transportation System, millimeter waves are used and antennas are required beam scanning ability. In the millimeter wave operation, a lens antenna is one of the prominent candidates which achieves wide angle beam scanning. Wide angle scanning can be achieved by introducing Abbe sine condition to lens surface shaping. Authors designed the shaped lens antenna that could achieve beam scanning ±30°. The narrow beam widths were maintained on the scanning plane. However, the beam widths were broadened on the transverse plane and large gain reduction was appeared. It was clarified that the reason of this beam deterioration was due to the phase delay on the antenna aperture. In this paper, an array feed composed of a group of rectangular horns is employed to compensate the phase delay on the antenna aperture. In designing the array feed, because there were no examples of phase radiation pattern synthesis, a new radiation pattern synthesis method is studied. Ability of the weighting matrix contained in the Least Mean Square synthesis method is paid attention. Adequate weighting matrix is found out. Satisfactory phase radiation pattern that can compensate the phase delay and an adequate amplitude radiation pattern are achieved. As a result, the improvement of scanned beam widths and antenna gains through the array feed are ensured. And adequate horn arrangements of the array feed for improving scanned beam are clarified. Moreover, in order to examine the realization of an actual array feed, the exact electromagnetic simulation is conducted. The validity of the radiation pattern synthesis is clarified.

Estimations of radiation characteristics of an off-focus feed shaped dielectric lens antenna by a ray tracing method

Millimeter waves are planned for use in the near future in next generation mobile communication systems and ITS services. In this paper, a ray tracing method is employed to estimate the radiation characteristics. In the case of a shaped lens, the lens surfaces are given by numerical discrete data. So, it becomes rather difficult to find adequate refraction positions on the lens surfaces. By utilizing formulas of refracted rays and searching procedures of adequate refraction positions of the lens surfaces, ray tracings are achieved. Aperture phase distributions for various off-focus feeds are calculated. The beam shift characteristics are also calculated. Through numerical results, the accuracy of the developed estimation method are ensured.