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Metamaterials for antenna applications

Metamaterials for antenna applications

Some applications of metamaterial superstrates for directivity enhancement of printed antennas were researched. Three different types of superstrates viz, multilayer dielectric slabs, electromagnetic band gap (EBG) materials, and frequency selective surfaces (FSSs) were suggested. The first design is a multilayer dielectric slab which consist of high and low permittivity dielectric layers and air-gap tuners for suppressing the grating lobes of patch array antennas. Next, a dielectric-rod EBG type superstrate with two defect frequencies is proposed for dual-band directivity enhancement of a patch antenna at a boresight. With this design we can increase the degrees of freedom that adjust the level of directivity enhancement and operating frequency location, relative to those of the multilayer dielectric slab type. Finally, an FSS superstrate consisting of two-layered FSS screens for dual-band directivity enhancement is introduced as an alternative to an EBG type of dielectric superstrate to reduce its height and facilitate the fabrication process. Now we are not only researching on directivity enhancement antennas but also small antennas using metamaterial concepts.

Small antennas for mobile devices

A lot of integrated antennas for mobile communication devices are based on the planar inverted-F antenna (PIFA) or the integrated inverted-F antenna (I-IFA) - sometimes called printed inverted-F antenna, since these antenna types are compact and have a sufficient bandwidth for most applications. So far in mobile phones PIFA-based concepts are mostly deployed for GSM standards, because there is not enough space available on the printed circuit board (PCB) for a printed multi-band antenna. On the other hand, in cell phones with the Bluetooth feature a printed IFA at the side or bottom edge of the multi-layer substrate is used as BT antenna, operating in the 2.4 GHz ISM band. Several types of small antennas were researched for mobile devices.

Measurement of dielectric constant

Measurement of dielectric constant

The transmission and reflection method is performed by measuring transmitted and/or reflected electromagnetic power from the sample under test. If the material of the sample is isotropic then determination of the complex permittivity and the complex permeability is possible from two measured parameters: the complex reflection (S11) and the complex transmission (S21) coefficients. For nonmagnetic materials the complex permittivity can be derived only from one measured complex parameter (either S11 or S21). Transmission and reflection measurements can be performed employing closed measurement cells, open-ended probes but can also be undertaken in a free-space environment. The transmission and reflection method based on the coaxial air line was constructed and it is available in our laboratory.

Beam forming array antennas

Beam forming array antennas

A switched-beam system consists of a fixed beam-forming network, an RF switch, and an antenna array. This system can be used to increase the channel capacity limited by the presence of interference. By using narrow beams available from this system, it can be possible to increase the gain to the desired signal direction and to reduce the gain to the interference directions. In other words, it can be possible to increase the gain to the desired signal direction and to reduce the gain to the interference directions. Various structures of multiple-beam networks (beam-formers) have been proposed, such as the Blass matrix, the Nolen matrix, the Rotman lens, and the Butler matrix. The most important beam-forming networks used for multiple beams with a linear array are based on the Butler matrix. Our laboratory researching on various beam-forming antenna types and feed-networks.

Metamaterial small antennas for mobile phones

Using metamaterial zeroth or minus modes, we can make small antennas. However, most of the metamaterial antennas do not have sufficient bandwidths for mobile applications. We are researching on bandwidth enhancement of metamaterial-concept antennas for mobile phones.

Crosstalk analysis between transmission lines

Crosstalk analysis between transmission lines_img1Crosstalk analysis between transmission lines_img2

Twisted-pair cables are widely used in high-speed LAN systems because they have less magnetic coupling between transmission lines. There are many important specifications, and near end cross-talk (NEXT) is a most important parameter. Sometimes inferior goods which does not satisfy the NEXT characteristics can be made during manufacturing. We are researching into the analysis of the crosstalk between transmission lines so that we can predict the NEXT characteristics.

Design of frequency selective filters

Frequency selective filters are widely used for various applications. It can pass or reject waves in free space or transmission lines. It should have sharp cutoff characteristics over a wide range of elevation (azimuth) angle. We are researching on filters in free space.