A. Sakitani

Stacked microstrip antenna with wide band and high gain

A microstrip antenna composed of radiating, matching, and director elements is presented. The director element increases the gain of the antenna, while the matching element widens the frequency bandwidth of the input impedance. By adjusting the distance between the matching element and the radiating element by varying the height of the former element, the input impedance of the antenna is matched to the output impedance of the feed line. The proposed antenna, therefore, has wider impedance bandwidth and higher gain than the single-patch antenna. Since this antenna can be directly fed from the back of the ground plane, the feed circuit is simpler than that of the planar array antenna. For mobile communications, the stacked microstrip antenna array is useful when a gain of about 8 approximately 12 dBi is required.<<ETX>>

A design of AM/FM mobile telephone triband antenna

In vehicles, antennas for AM/FM broadcasting (BC) and cellular mobile telephone (MT) are usually mounted on the cars body. However, a triband antenna which can be used for both AM/FM BC and MT is more desirable to decrease the number of antennas. An outline of the general design for the AM/FM MT triband antenna with coils is described. Next, the design of a new triband antenna with double sleeves instead of coils is presented. The double sleeves consist of two coaxial lines connected in series. It is shown that the triband antenna with double sleeves has good characteristics, including radiation patterns and voltage standing-wave ratio (VSWR). >

Simplified expressions for the near fields of a magnetic frill current

The simplified expressions for the electromagnetic field of the near zone from the magnetic frill are derived. In these formulas, E_{\rho} and H_{\phi} are expressed as a single integration of the complete elliptical integrals of the first and second kinds. Furthermore the closed form of E_{z} is obtained approximately. Their accuracy is checked numerically by comparing with Tsais, and significant improvement in efficiencies is obtained.

Analysis of coaxial collinear antenna: recurrence formula of voltages and admittances at connections

A method for the analysis of the coaxial collinear antenna made of transposed coaxial sections of arbitrary length is presented. The excitation terms of the integral equation for the current distribution of this antenna are expressed by using a known impressed voltage, and these are computed recursively by computer. Calculated values of current distributions and input impedances are found to agree with measured results, and the validity of the presented method is confirmed. The results derived are applicable to the design of the coaxial collinear antennas of any configuration. >

AM-FM-cellular mobile telephone tri-band antenna with double sleeves

An AM-FM cellular mobile telephone (MT) triband antenna with double sleeves has been designed and measured. The radiation patterns and the VSWR (voltage standing wave ratio) of the triband antenna were good at the transmitting frequency of the MT. At the receiving frequency of the MT, the radiation patterns were similar to those for a lambda /4 monopole antenna, and the VSWR was good (2.0 or less) in the 883-890 MHz range. The antenna has such a length as to make the radiation efficiency sufficient. As a sleeve can be made precisely, the antenna with sleeves is suitable for mass production. A sleeve can be used to realize a triband antenna effectively.<<ETX>>

Consideration on the measurement of current distribution on bent wire antennas

As part of the measurement of the current distribution on a bent wire antenna with a shielded loop, the electromotive force (EMF) induced on the loop is theoretically formulated, and the relation between the current distribution and the measured values is investigated. The EMF is expressed as a summation of terms involving the current and the derivative of the current with coefficients depending on the measurement point. The calculated EMF agrees well with the measured value. At points away from the antenna ends and bend, the EMF is proportional to the current, but near the ends and bend the difference between EMF and current increases. It is shown that the current distribution is easily estimated from the measured data. The authors also present the measurement of charge distribution using a small dipole. The expression for the open-circuit voltage of the dipole is formulated and compared with measured values. >

Stacked circular polarized microstrip antenna with wide band and high gain

The characteristics of a stacked microstrip antenna which radiates circularly polarized waves have been investigated experimentally. A top element of this stacked antenna increases gain, and a first parasitic element, which is near a radiator, widens the bandwidth of the axial ratio as well as the impedance bandwidth. A stacked circularly polarized microstrip antenna with high gain and wide band is obtained.<<ETX>>

Determination method of the loading impedances of beam tilting antenna with passive loads

For the base station antenna of cellular mobile telephone systems, a beam tilting antenna, which achieves down-beam tilting of the main beam with smaller cell size, is desired. Such a beam tilting is realized easily by a wire antenna with loads. If we can obtain the loading impedances from the desired tilt angle in the design it is practically useful. In this paper, a determination method of the impedances loaded on the antenna for a desired beam tilting is described.

Determination method of the loading impedances of loaded antenna. Realizing desired beam tilting and low sidelobe level

The determination of the loading impedances loaded on a straight wire antenna in order to realize the desired beam tilting and low sidelobe level is discussed. We obtained the loading impedances from the desired characteristics in a straightforward manner. Moreover, we obtained the desired characteristics using a reactive load which is easy to realize.

Representation of a stepped-radius antenna by a loaded antenna

Presents a new method to represent a stepped-radius antenna by a uniradius loaded antenna with lumped impedances. The stepped-radius antenna can be analyzed by applying the moment method to the integral equation of a loaded antenna with lumped impedances. The authors investigate the validity of this method by numerical results. The numerical examples of the current distributions and the input impedances for these antennas, are presented and discussed. Furthermore, as an application of this method, an improvement of the input impedance characteristic of a stepped-radius antenna is presented.<<ETX>>