There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Substrate-integrated waveguide (SIW) technology represents an emerging and very promising candidate for the development of circuits and components operating in the microwave and millimetre-wave region. SIW structures are generally fabricated by using two rows of conducting cylinders or slots embedded in a dielectric substrate that connects two parallel metal plates, and permit the implementation of classical rectangular waveguide components in planar form, along with printed circuitry, active devices and antennas. This study aims to provide an overview of the recent advances in the modelling, design and technological implementation of SIW structures and components.

Review of substrate-integrated waveguide circuits and antennas

This paper provides a systematic review of the mutual coupling in multiple-input multiple-output (MIMO) systems, including the effects on performances of MIMO systems and various decoupling techniques. The mutual coupling changes the antenna characteristics in an array, and therefore, degrades the system performance of the MIMO system and causes the spectral regrowth. Although the system performance can be partially improved by calibrating out the mutual coupling in the digital domain, it is more effective to use decoupling techniques (from the antenna point) to overcome the mutual coupling effects. Some popular decoupling techniques for MIMO systems (especially for massive MIMO base station antennas) are also presented.

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A Review of Mutual Coupling in MIMO Systems

Owing to the excessive demand on signal processing and space constraint, a full digital implementation of a large adaptive antenna array at millimeter wave frequencies is very challenging. Targeted at long range high data rate point-to-point link in the 70/80 GHz bands, a novel hybrid adaptive antenna array which consists of analogue subarrays followed by a digital beamformer is presented in this paper to overcome the digital implementation difficulty. Two subarray configurations, the interleaved subarray and the side-by-side subarray, are proposed, and two Doppler resilient adaptive angle-of-arrival estimation and beamforming algorithms, the differential beam tracking (DBT) and the differential beam search (DBS), are developed. Simulation results on the DBT and DBS performance are provided using a 64 element hybrid planar array of four 4 by 4 element subarrays with the two subarray configurations, respectively. Recursive mean square error (MSE) bounds of the developed algorithms are also analyzed and compared with simulated MSEs.

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A hybrid adaptive antenna array

Wireless Sensor Networks (WSN), an element of pervasive computing, are presently being used on a large scale to monitor real-time environmental status. However these sensors operate under extreme energy constraints and are designed by keeping an application in mind. Designing a new wireless sensor node is extremely challenging task and involves assessing a number of different parameters required by the target application, which includes range, antenna type, target technology, components, memory, storage, power, life time, security, computational capability, communication technology, power, size, programming interface and applications. This paper analyses commercially (and research prototypes) available wireless sensor nodes based on these parameters and outlines research directions in this area.

Wireless Sensor Networks: A Survey

The so called universal steering vector (USV) whose locus is equivalent to the array element pattern is applied to the direction of arrival (DOA) estimation by multiple signal classification (MUSIC) algorithm. It is shown that if the USV which includes the effect of the mutual coupling between the array elements is used, the compensation for the received voltage to remove the effect of the mutual coupling is not required any more. The USV for array antennas with arbitrary geometry is derived and evaluated efficiently by using the method of moments (MoM) so that the DOA estimation can be performed accurately by using the array antenna with arbitrary geometry. Numerical examples of the DOA estimation by a dipole array antenna, and an antenna array composed of a monopole antenna and a planar inverted-F antenna (PIFA) mounted on a mobile handset are presented to demonstrate the effectiveness of the proposed method.

Accurate DOA estimation using array antenna with arbitrary geometry

A fundamental study was focused on the investigation of wireless power transmission by near-field coupling from the view point of the antennas. Two types of antennas - dipole and loop antennas - were used as the transmitting antenna and the receiving antenna for electrical near-field coupling and for magnetic near-field coupling, respectively. The relationships among the power-transmission efficiency and the antennas' geometries, the antennas' electrical sizes, the impedance matching of the antennas, and the ohmic losses in the antennas and the impedance-matching circuits were clarified. Several observations were obtained, demonstrating the influence on the power-transmission efficiency of the impedance matching and ohmic losses in the wireless power-transmission system associated with near-field coupling.

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Antenna Characterization for Wireless Power-Transmission System Using Near-Field Coupling

The effect of the mutual coupling between the array elements on the performance of the adaptive array antennas (AAA) is investigated when the actual received voltages which include the mutual coupling are directly used to estimate the weight vector based on the adaptive algorithm. The output signal-to-interference-noise ratio (SINR), the convergence of the adaptive algorithm and the synthesized pattern are evaluated to study the effect due to the existence of the mutual coupling. It is found that the mutual coupling affects the antenna adaptive gain, but does not affect the adaptive processing. It is also found that the mutual coupling does not always degrade the iterative convergence of the adaptive algorithm. It is proved that any invertible matrix for compensating the mutual coupling cannot improve the output SINR. It is also indicated that the radiation pattern can be correctly synthesized in the presence of the mutual coupling by introducing the universal steering vector (USV) whose element corresponds to the array element pattern.

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Performance of adaptive array antenna with arbitrary geometry in the presence of mutual coupling

A novel passive RFID tag for a long reading range composed of a divided microstrip antenna and a rectifying circuit boosting the DC voltage is proposed. Experimental study of fabricated passive tag using varactor diodes, in which 30 m range response can be achieved at 860-950 MHz band, is described. Passive tags for temperature-monitoring system at 2.45 GHz band is also fabricated to demonstrate validity of proposed tags for a range longer than 9 m. The tags have sizes of 90×60×4 mm and 60×25×4 mm for 900 MHz and 2.45 GHz bands, respectively. Keywords-passive RFID; sensor networks; long range transponder; microstrip antenna; multiplying rectifier

Long range passive RFID-tag for sensor networks

The present invention aims to overcome the drawback with conventional RFID tag devices having a short communication range, and expand the communication range to several times or more that in the conventional scheme. The conventional scheme is based on equilibrium feeding/equilibrium modulation (a two-terminal circuit for antenna operation), whereas the present invention is based on disequilibrium feeding/equilibrium modulation (a three-terminal circuit for antenna operation). The conventional scheme is based on simple rectification of received RF signals, whereas the present invention employs a circuit based on a combination of a stub resonance-based, impedance transformation boosting scheme and a ladder boosting scheme. The conventional scheme is based on ASK or BPSK modulation, whereas the present invention is based on passive modulation, but can employ a QPSK modulation circuit.

Kunio Sawaya

Papers

Accurate DOA estimation using array antenna with arbitrary geometry

Antenna Characterization for Wireless Power-Transmission System Using Near-Field Coupling

Performance of adaptive array antenna with arbitrary geometry in the presence of mutual coupling

Long range passive RFID-tag for sensor networks

RF ID tag device