Shigeru Egashira

Stacked microstrip antenna with wide bandwidth and high gain

A stacked microstrip antenna with two parasitic elements, one of which increases the impedance bandwidth and the other which enhances the gain, has been investigated experimentally. The effects of each parasitic element have been clarified as well as the characteristics of the stacked three-element antenna and the design procedure for the stacked microstrip antenna have been described.

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>>

Three-element stacked microstrip antenna with wide-band and high-gain performances

In this paper, the three-element stacked microstrip antenna which is composed of a fed element and two parasitic elements is proposed. It has a wide bandwidth and a high gain. The stacked microstrip antenna is precisely analyzed using the FDTD method, in order to investigate the characteristics and the behavior mechanism of the stacked antenna.

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). >

Sleeve antenna with ground wires

Pocklingtons integral equation for a sleeve antenna with ground wires is formulated. By applying the Galerkin method to this equation, a sleeve antenna, a monopole antenna with ground wires, and a sleeve antenna with ground wires are analyzed, and numerical results for these antennas are compared with measured data. The sleeve antenna features the leakage current on the surface of the coaxial feeder, suppressed by a sperrtopf, but it is mismatched with the 50- Omega feeder. The monopole antenna with inclined ground wires may be adjusted to match the 50- Omega feeder, but the leakage current induced on the feeder cannot be neglected. It is found that the sleeve antenna with ground wires has the advantages of both antennas. >

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>>

On the analysis of the umbrella antennas using the Hallen-type integral equation

Umbrella antennas of heights 0.125\lambda and 0.5141\lambda are numerically and experimentally analyzed, and the effect of the junction on the current distribution is discussed. A simplified Hallen-type integral equation and an integral equation for the scalar potential of the antenna composed of straight wires are formulated and applied to umbrella antennas. The integral terms in these equations are analytically reduced to single integrals, and the extended boundary condition that the electric field vanishes on the axis of the antenna is used.