Shigeki Obote

Design and analysis of transmitting and receiving characteristics of a small MIMO array antenna with a matched load

A new design formulas for a N×N matching network for an array antenna with mutual coupling is presented. Using matching conditions, decoupling between excitation ports and beam orthogonality have been explicitly verified. Numerical results of the antenna pattern in the vertical plane suggest that the received power of a two elements array is two times larger than a single dipole. A method for enhancing frequency characteristics and a new definition of a receiving antenna efficiency are also proposed.

An array antenna for MIMO systems with a decoupling network using bridge susceptances

Decoupling and matching feeding networks are considerably interested in small wireless terminals to enhance their abilities for MIMO systems. In various proposals of DMFNs, the feeding networks composed of bridge susceptances and transmission lines are simple. However, this DMFN has only been applied to the limited array with special characteristics. This paper presents general design formulas of the DMFN for the two elements and three elements arrays and fundamental numerical data are presented to assure the validity of the design formulas.

Bandwidth Enhancement of a Low-Profile Microstrip Antenna Electromagnetically coupled with a Folded Inverted L-shaped Probe

A microstrip antenna (MSA) has a number of useful properties. However, its narrow bandwidth characteristic is disadvantage in applying to practical wireless systems. Some of the conventional techniques for widening bandwidth for the MSA are using thick structures, adding parasitic patches or using electromagnetically coupled feed. In this paper, we proposed a folded inverted L-shaped probe (FILP) to widen the bandwidth of a low-profile MSA by electromagnetically coupled feed. We showed that the FILP which is placed under the patch can increase the value of the input impedance compared to the L-probe, and that the wide bandwidth characteristics of the low-profile MSA is achieved.

Radiation and reception properties of a MIMO antenna system with a decoupling and matching feeding network

We discussed the radiation and reception properties of an array antenna with a decoupling and matching feeding network. When the feeding network is designed and constructed to satisfy the matching condition of the array antenna, each port pattern exhibits orthogonal property and eigen mode patterns when the orthonormal matrix, which constitue the sub matrix of the feeding network, is an unit matrix. When the spacings of the array are small compared to the wavelength, the radiated power of each antenna element considerably deviates and the reactive energy stored around the array increases. To show this quantitatively, we proposed Q factor of the array and showed numerical result. As for the reception properties of the array, we presented the total received power when the plane wave is incident. Averaged gain in the horizontal plane for the four elements array is also presented and it is shown that this can be larger by four times than that of a single dipole. The reason of this phenomena comes from the narrower beam width in the vertical plane as well as in the horizontal plane.

A design methodology of a tapped delay line adaptive array antenna

Unlike the basic adaptive array antenna (AAA) , a tapped delay line adaptive array antenna (TDL-AAA) is effective in mitigating interference from user signals or multipath waves which impinge on the array close to the direct wave. This is also useful for reducing the number of antenna elements under a multipath propagation environment. Furthermore, this adaptive antenna system is also effective for multi-input multi-output (MIMO) spatial multiplexing techniques under frequency selective fading channels. However, a method of designing the required number of antenna elements or tap stages has not been studied. We propose a design equation for TDL-AAA when a number of users and maximum delay time are given. We assume that multipath waves impinge on the array successively with symbol period interval and individual waves have a different direction of arrival (DoA). The influence of the roll-off factor of a cosine roll-off filter is also studied by computer simulation. Simulation results show that the proposed design equation is applicable in case of a roll-off factor of 1.0. On the other hand, simulation results of a roll-off factor of 0.5 show that one can determine the number of antenna elements.

Computational complexity reduced MMSE adaptive array antenna with space-temporal joint equalization

A tapped-delay-line adaptive array antenna (TDL-AAA) is proposed for the method of space and temporal (frequency) equalization. However, this method has a drawback that requires many variable taps (AAA elements /spl times/ LE (linear equalizer) taps) and many multiplications. In this paper, in order to reduce the computational complexity, we propose the cascade connection of one adaptive array antenna and one linear equalizer with space and temporal joint equalization. The LE mitigates multipath waves close to the direct wave. The AAA removes only interference users waves. The effectiveness of the proposed method is confirmed by theoretical consideration and computer simulation.

Design of a broadband low-profile microstrip antenna with multi-layer substrates

We have proposed the bandwidth enhancement technique of the MSA with an electromagnetically coupled feed by the offset located FILP. It has been shown that the maximum bandwidth is about 6.0% which is 2.7 times wider than that of the coaxial fed MSA, and that it is slightly effective in bandwidth enhancement compared with the original model of the FILP fed MSA when the patch height is 0.03λ0 and the permittivity is one. In addition, the offset model can design the height of the FILP without restrictions of the configuration to fabricate, and can widen the bandwidth using substrates with the same thickness.

Pattern synthesis of an array antenna with maximum directivity and nulls at specified directions

In order to solve a problem of maximizing a directivity of a transmitting array antenna with nulls at specified directions, we intended to utilize an adaptive antenna algorithm which enables the SNR to be maximum under the incidence of interferences. However, we encountered the discrepancy between transmitting antenna patterns and receiving ones. We investigated why this discrepancy arises, although a reciprocity theorem is effective between the transmitting pattern and the receiving one. Through these investigations, we derived the equation which determines the matched load impedances of the array elements and solved it numerically up to five elements. We also derived an equation to evaluate output voltages which are summed up into an output of the array and confirmed the coincidence between the transmitting pattern and the receiving one.

A study on frame synchronization method for adaptive array antenna

This paper proposes a reference signal synchronization method for improving the performance of the maximum likelihood type synchronization method under the realistic environment accompanying frequency offset. In the proposed method, the search of correlation was carried out to not only the timing direction but also frequency offset direction. In this way, correlations were computed for time and frequency direction and two dimensional maximum correlation search has been done. In this way the reference signal synchronization has been achieved. Furthermore, a increase ratio of the computational complexity for the conventional method has been shown. We have made it clear that the increase is relatively small and this ratio decreases with increasing the number of antenna elements

Study on the reciprocity for the maximum directive gains of a transmitting array and a receiving array

This paper describes the reciprocity of a transmitting array and a receiving array when they have maximum directivities. This study may be useful and applicable to an optimum design of the transmitting array or the receiving array with interference incidence. To achieve the same maximum directivity in the receiving array as that in the transmitting array, each element of the receiving array should be terminated by the matched load impedance and the currents through the loads, instead of the voltages across the loads should be summed into the array output. The reason for these procedures are theoretically investigated and discussed.