S. Sekine

A method to improve the correlation coefficient and the mutual coupling for diversity antenna

Wireless LAN systems employ diversity antennas to reduce the effects of multipath fading. When several antennas are provided in close proximity, the radiation patterns becomes similar to one another and the diversity gain decreases. Moreover, the radiation efficiency decreases due to mutual coupling between antennas. In order to increase the diversity gain, a method to improve the correlation coefficient among the antenna elements by mutual coupling between antenna elements has been reported (Sawaya, K. et al., 1982). However, this leaves the problem of a decrease in the radiation efficiency caused by mutual coupling. The paper proposes a new method to improve the correlation and the mutual coupling between antennas simultaneously. A slit is provided on a finite ground plane with antennas. The slit changes the current distribution on the ground plane. This change of current distribution causes differences between antennas in the radiation pattern and a pattern diversity effect is achieved. This diversity effect improves the correlation coefficient without applying mutual coupling. Additionally, by changing the current distribution, the mutual coupling is improved and the radiation efficiency increases under low correlation conditions.

A Study of Wideband Built-in Antenna using RF-MEMS Variable Capacitor for Digital Terrestrial Broadcasting

In this paper, the wideband properties of a proposed antenna with the low-voltage-actuated MEMS variable capacitor is shown by calculation and measurement. First the mechanism of the wideband properties of the proposed antenna due to the use of a dual resonant mode is clarified. Then, applying the MEMS variable capacitor, the properties of the proposed antenna are calculated and measured

Piezoelectric MEMS Variable Capacitor for a UHF Band Tunable Built-in Antenna

A UHF band tunable built-in antenna is realized using piezoelectric MEMS variable capacitors. The variable capacitor, which is driven by a piezoelectric actuator, has a tuning ratio of 11 with control voltage ranging from 0 to 8 V and quality factor of more than 37 at 650 MHz. The built-in antenna, which is an inverted-F antenna, is mounted at the top of an upper PCB board of a clamshell mobile phone, and the antenna element has a meander shape for a built-in structure. In the tunable built-in antenna, the variable capacitor is connected to one point of the meander structure of the built-in antenna. The antenna covers a frequency from 510 to 800 MHz with an efficiency of more than -3.5 dB, or the relative bandwidth of 44% by changing the value of the variable capacitor.

High speed radiation characteristics measurement equipment over the solid angle of a sphere to evaluate antennas attached to an 800 MHz cellular telephone

An improved measurement equipment for the radiation characteristics of a small antenna over the solid angle of a sphere has been developed on the basis of experimental investigations. It has been found from the measured results of directivity for a half-wavelength dipole antenna that a frequency coverage of 900 MHz can be obtained judging from the H-plane ripple of 2 dB. This measurement equipment displays the radiation characteristics over a sphere surrounding the test antenna for a short period of one minute including the measuring time. This equipment has been designed to evaluate an antenna attached to an 800-MHz hand-held cellular telephone.<<ETX>>

Two methods for estimating the diversity characteristics of built-in antennas for mobile communication equipment

In mobile communications, the diversity technique plays a very important role in improving the quality of digital transmissions, and the fading simulator is widely employed to achieve a quasi-fading environment. However, the fading simulator cannot be used to evaluate the effects of the antenna radiation patterns on the diversity characteristics. It is very difficult to predict analytically the radiation characteristics of built-in antennas in portable radio equipment, because they are affected by nearby electrical devices. Therefore, an experimental investigation is important. We proposed two measurement systems for evaluating the radiation characteristics of built-in antennas for hand-held radio equipment. Two methods for estimating the diversity characteristics of mobile communication equipment using these two measurement systems are presented.

The radiation characteristic of a lambda /4-monopole antenna mounted on a conducting body with a notch (portable telephone model)

The authors describe the radiation characteristic and the current distributions of a lambda /4-monopole antenna on the conducting body modeled as an ordinary portable telephone by simulation using the time domain method. The results show that the current on the conducting body has an undesirable influence on the radiation of the antenna. A novel method is proposed to prevent such an undesirable influence by cutting a notch in the conducting body. In terms of the radiation characteristic of the model with such a notch, the results of simulation and an experiment agree and indicate good performance.<<ETX>>

A study on the variable radiation pattern antenna using a parasitic slot

It is advantageous for cellular phones or WLAN-APs (wireless LAN access points) that their antennas have variable radiation patterns in certain cases, such when they are mounted on a wall or for the purpose of avoiding interference. Most conventional antennas, such as reactively controlled directive arrays, are composed of multiple elements of identical shape to resolve the above-mentioned issues. This work proposes a novel variable radiation pattern antenna consisting of an inverted-F antenna and a parasitic slot with an electrical switch, and shows its fundamental characteristics and the appropriateness of its parameter optimization with GA.

A wideband inverted F-type antenna for dual-frequency operation

The subject of this paper is an antenna for automobiles. A wideband IFA for dual-frequency operation is presented in which horizontal elements are added on a vertical element. The matching loss and radiation characteristics are calculated by the NEC2 simulation tool, which uses the moment method. A plate is used as a shorted element of the IFA in order to increase radiation resistance. The plate is modeled by the wire-grid and a ground plane is modeled by an infinite plane in the simulation.

A rod antenna with a meander element for hand-held phone

This paper proposes a rod antenna with a meander element mounted on a hand-held phone. The quarter-wavelength meander element can improve the input impedance of a half-wavelength rod antenna. The reason for the improvement of the input impedance is that the total length of the antenna is three quarter-wavelengths. Also, the proposed antenna can realize a high gain in the horizontal plane. The reason for the high gain in this direction is that the meander element is optimized to radiate in the horizontal direction so as to add to the radiation from the antenna.

Broadband folded notch antenna with a parasitic notch

This paper proposes a new broadband folded notch antenna with a parasitic notch on a rectangular conductive board. The parasitic notch can provide current distribution on a folded notch antenna similar to current distribution on an axially symmetric self-complementary antenna, which has an extremely broadband characteristic. In the simulation, frequency bandwidth of the folded notch antenna is increased by 1.5 times by the use of the parasitic notch.