High-resolution Direction-of-Arrival (DOA) estimation techniques for antenna arrays have been widely desired in many applications such as smart antennas, RF position location, and RFID system. To realize high-resolution capability of the techniques, precise array calibration is necessary. For an array of single-mode elements, a calibration matrix derived by the open-circuit method is the simplest one. Unfortunately, calibration performance of the method is not enough for the high-reslution DOA estimation techniques. In this paper, we consider problems of the calibration matrix derived by the method, and show that errors in the matrix can be effectively removed by an optimal diagonal weight coefficient. In the proposed compensation technique, the number of newly introduced parameters, or unknowns, is only one for an array of the identical elements. Performance of the simple compensation technique is verified numerically and experimentally.

Antenna array is essential factor for multiple- input multiple-output (MIMO) wireless systems. Since the antenna array is composed of closely spaced elements, the mutual coupling among the elements cannot be ignored for the best performance of the array. Mutual coupling affects the MIMO channel, so the performance of a MIMO system, including channel capacity and diversity, varies with the degree of mutual coupling. The effect of mutual coupling is a function of the antenna load impedance. Therefore, designing an optimal element-matched array for a MIMO system requires consideration of the optimal matching condition for the array elements, the one that maximizes the channel capacity. We evaluated the effects of mutual coupling with various matching conditions in dipole arrays, and investigated their effects on the path correlation and channel capacity of MIMO systems. Simulation showed that the conventional conjugate matching of each element is still suitable for closely spaced elements except when the separation is about less than 0.1λ. Theoretical consideration of the received power of a closely-spaced-element array is also provided to show the effects of mutual coupling.

This letter presents mutual coupling reduction in an E-plane arranged microstrip patch array fed by a triplate waveguide. Five mushroom-like electromagnetic band-gap (EBG) elements arranged in one column are embedded both between two radiating patches and between the feeding lines for suppression of the surface wave and the parallel plate mode, respectively. Validity of the proposed EBG elements is confirmed by the measurement.

We propose a wave analysis method for probe-fed Radial Line Planar Antennas (RLPAs) which yields an approximate solution for the aperture field distribution and scattering by loaded probes. Damping of electric power in the radial line due to radiation by antenna elements is included. The method can accommodate the effect of all conductors, including the terminating wall, by introducing the concept of equivalent posts. We have found good correspondence between the measured and calculated values of the aperture field distribution. The proposed method is effective for general geometries of probe-fed RLPAs.

A compensation method of the array element pattern is proposed to measure EM field distribution on an observation plane located several wavelengths away from electronic devices in a short time. Numerical and experimental data of the 3 and 5 element collinear dipole array sensors are presented to demonstrate the validity of the proposed method.

MBF (Microwave Beam Forming) antennas are beam forming antennas that perform pattern control in RF, for a low-cost design suitable for mobile terminals. An MBF antenna has only a single output port, since this antenna consists of an array antenna, microwave phase shifters, and a power combiner. Because of this simple configuration, MBF antennas cannot adopt conventional beam forming algorithms that require both phase and amplitude control, and signal observation of each antenna element. In this paper, mutual coupling matrix estimation and null forming methods are presented for MBF antennas. It is shown that the mutual coupling matrix can be estimated by changing the antenna weight instead of signal observation of each antenna element. It is also shown that phase-only null forming, including mutual coupling effect, can be done by the optimum phase perturbations. Numerical and experimental results show the performance of these algorithms.

This paper describes the choke-loaded patch array antenna for use in the IMT-2000 repeater systems. The choke structure of the 4-element array is designed by means of an electromagnetic analysis. A high front-to-back (FB) ratio is required for suppressing mutual coupling in order to stop the oscillation caused by the interference waves between a transmitting and receiving antenna. The suppression of the FB ratio by a choke is limited in the case of the 16-element array because its side lobe level is large. In this paper, we examine the effect of suppressing the mutual coupling using a binomial array.

This paper presents a framework for the analysis of multi-antenna communication systems with mutually-coupled elements. The approach uses a network model that includes the coupled antennas, the propagation channel, the receiver matching network, a realistic noise model for the receive amplifiers, and externally generated interference. The general scheme is applied to diversity receivers, multiple-input multiple-output, and adaptive array architectures. Application of the formulation to coupled dipole antennas illustrates the impact of both mutual coupling and receiver matching on the performance of several representative multi-antenna applications.

Simple approximate formulas are obtained for the mutual impedance and admittance by using a product of radiation patterns of antennas. The formulas come from a stationary expression of the reaction integral between two antennas where far-field approximations are employed. The theory deals with antennas in free space as well as under the presence of a wedge. Two applications are given for microstrip antennas with experimental verifications.

This paper discusses a method to evaluate mutual couplings of cavity-backed slot antennas using the FDTD technique. The antenna fed by the short-ended probe is considered, which is investigated as an element of the power transmission antenna, Spacetenna, for the solar power satellite SPS2000. It is found from the FDTD computation on E-plane two- and four-element array antennas that the size of the problem space should be larger for the evaluation of the mutual coupling than for the estimation of the input impedance. Since enlarging the size of the problem space requires a large amount of computer storage, it is not practical for computer simulations. In order to carry out accurate estimations of the mutual coupling with relatively small amount of computer memory, the problem space is extended only in the broadside of the array antenna and in the other directions there are ten cells between the antenna surface and the outer boundary. Computer simulations demonstrate that there are no differences between the results of the proposed problem space geometry and the problem space extended in each direction of the axis coordinate by the same number of cells. Furthermore comparisons of computed and experimental results demonstrate the effectiveness of the approach after discussing how large the size of the problem space is required to estimate the mutual coupling.

In the design of a large slotted waveguide array, evaluation of mutual couplings between the slots is time consuming. This paper proposes an effective approximation analysis of the external mutual couplings using periodic boundary condition. Simple design procedure is verified for two-dimensional slot array.

In this paper, mutual coupling S21 between RMSA (ring-shaped microstrip antenna) elements was estimated by the EMF method based on the cavity model. Then, the validity of the proposed method was tested by experiments. The experiments confirmed satisfactory agreement between the computed and experimental data for S21 in both E- and H-plane arrangements. In addition, a circularly polarized planar array composed of R-MSA elements was designed on the basis of the data of S21. The experimental results of such a planar array demonstrated high performance in radiation pattern as well as axial ratio property. Furthermore, the active reflection coefficient Γ in the R-MSA array was also investigated in both equilateral and square arrangements. The computed results of active reflection coefficient in the array demonstrated high performance in both arrangements.

This paper theoretically and experimentally investigates the mutual coupling between two ports of dual slot-coupled circular microstrip antennas. Presented are the effects of feed configuration, slot length, slot offset from the circular disk center, circular disk radius and the dielectric constant of the feed substrate on the mutual coupling. Based on these results, the antenna with low mutual coupling was designed. The mutual coupling of under -35dB at the resonant frequency was obtained.

We analyze the mutual coupling between two microstrip antennas (MSAs) with the finite-difference time-domain (FDTD) method. It is suitable for substrates which have a complex configuration or include feed line structures. The mutual coupling between two MSAs on discontinuous orthogonal substrates is successfully calculated.