A moment method solution to the problem of radiation or scattering from geometries consisting of open or closed surfaces, wires, and wire/surface junctions is presented. The method is based on the sinusoidal reaction formulation. Several examples of input impedance calculations illustrate the versatility, accuracy, and computational efficiency of the method.

Electromagnetic modeling of composite wire and surface geometries

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

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 new method of increasing the bandwidth of normal-mode helical antennas (NMHA) is proposed. The antenna has length of around 0.1 of the target wavelength, and consists of a helix constructed with two flat wire strips. The method exploits the two current modes of the two-wire design to obtain wideband response. Based on an analysis of the equivalent circuits of the two modes and subsequent optimization of design parameters, a final two-strip NMHA design is proposed that is demonstrated to have a bandwidth of 12% in the 760-MHz band at a voltage standing wave ratio of less than 2.

A compact broad-band helical antenna with two-wire helix

In this paper, we describe a directional borehole radar comprising a dipole antenna array with an optical modulator capable of determining the position of targets in three dimensions (3-D). Optical modulators using a Mach-Zehnder interferometer are used to transform electrical signals into optical signals at the feeding points of the dipole antennas. The advantages of using these modulators are that we can easily arrange the dipole antennas in a borehole, and that we can expect a good agreement between the experimental data and a theoretical model representing the array. We have made a prototype borehole radar system with five dipole antennas for the reception. In order to model the antennas, we used the method of moment (MoM), utilizing a modified Green's function for dipole antennas in multiple cylindrical layers. The Green's function is evaluated analytically by numerical integration. Cross-hole and single-hole measurements were carried out in granite at the Kamaishi mine (Iwate, Japan), and we obtained good agreement between the experimental data and the MoM results. After applying superresolution techniques to the data received by the array, we estimated the 3-D scattering position of a geological interface in granite. The results were in fairly good agreement with borehole scanner images.

Directional borehole radar with dipole antenna array using optical modulators

The mutual impedance of nonplanar-skew sinusoidal dipoles is presented rigorously as a summation of several exponential integrals with complex arguments.

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N. Geary

Papers

Mutual impedance of nonplanar-skew sinusoidal dipoles