Reflector antenna diagnosis from phaseless data

The problem of determining the surface profile or a reflector antenna from only amplitude measurements arises whenever the phase cannot be accurately detected. We apply the quadratic approach to solve this “holography” problem by looking directly for the aperture field function from measurements of field intensities at the feed location under different defocusing conditions, which can be easily achieved in testing radioastronomical antennas. A suitable finite-dimensional approximation of the unknown function and two sets of square amplitude data are employed. The solution procedure consists of minimizing a nonquadratic functional and can be critically affected by the existence of local minima. This crucial problem is discussed and solved and the procedure is applied to both simulated and experimental data. The reliability of the whole algorithm is confirmed by the fact that results are obtained starting from completely random initial guesses. A viable and simple way to determine the positions of the individual panels making up large radioastronomical antennas is also employed     

Reflector antenna profile measurement using ultrasound

A method for the measurement of reflector antenna surface profiles requiring no mechanical contact is described. The technique consists of placing an ultrasonic transmitter at the reflector focus and measuring the phase over the whole of the reflector aperture. Profile errors of order ±0.1 mm have been measured.     

The exact kernel for cylindrical antenna

In the numerical calculation for a cylindrical antenna, the thin-wire kernel is widely used as a convenient approximation to the exact kernel of the electric-field equation. However, this thin-wire approximation is valid only if the radius of wire is much less than its length and the wavelength; furthermore, arbitrarily using this approximation may not obtain the convergent outcomes. The expression of the exact kernel for the cylindrical antenna, which would be useful in the numerical work, is presented     

Reflector antenna radiation pattern analysis by equivalent edge currents

Equivalent edge currents, derived from the edge diffraction theory for a half-plane, are used to obtain the radiation patterns of a parabeloidal reflector antenna when illuminated by a source at the focus. Cylindrical wave diffraction coefficients are used. The method avoids infinities at caustics and shadow boundaries thus giving solutions which are finite everywhere. A slope-wave equivalent current correction term is applied when the illumination is tapered towards the edge of the reflector. Comparisons are given with the physical optics approach and experimental results.     

Reflector antenna power pattern synthesis: a general and efficientapproach

A general and computationally efficient procedure is developed for synthesizing the primary illumination of a focusing reflector antenna, in order to obtain the best fit (in the mean square sense) to a given far-field amplitude pattern. The mathematical framework of the synthesis problem is discussed in some detail in order to reveal the difficulties related to its ill-posedness and to the nonuniqueness of the solutions. The advantage of a two-step procedure is then shown, and the corresponding algorithms are developed. The effectiveness and flexibility of the procedure are discussed and illustrated with examples     

A new approach to active antenna design

Design considerations for wide-band active antenna circuits for frequencies up to 30 MHz are presented. High performance is obtained by using unusual amplifier types having a virtually grounded input electrode of the input active device, and a large amount of negative feedback over several stages. The realized antennas with a physical length of 0.5 m have a flat frequency response from 5 kHz to 30 MHz and extremely low distortion (second-order intercept >+70 dBm, third-order intercept > +50 dBm). The antennas are thoroughly protected against statics; without sacrificing the high dynamic range. Output power levels up to +28 dBm can be handled. The electric field strength may exceed 10 V/m. The equivalent input noise field strength amounts to about 25 nV/msqrt{Hz}.     

Hybrid approach for sub-arrayed monopulse antenna synthesis

A computationally effective hybrid approach to define the 'optimal' compromise between sum and difference patterns in monopulse arrays is presented. First, the partitioning into sub-arrays is performed by exploiting the knowledge of independently optimal sum and difference excitations. Then, the sub-array gains are computed by means of a gradient-based procedure, which takes advantage from the convexity of the problem at hand. Selected results are shown and compared with those from state-of-the-art methods in dealing with representative test cases.     

A cross-layer approach to transmit antenna selection

In this paper, we investigate a cross-layer approach to transmit antenna selection capable of adapting the number of active antennas to varying channel conditions. We address a cross-layer methodology in the sense that the criterion for the selection of antenna subsets is the maximization of link layer throughput which takes into account characteristics both at the physical and link layers. In order to enhance system performance, adaptive modulation is included to jointly perform antenna selection and rate adaptation. Performance assessment is conducted in terms of link layer throughput and transmission delay.     

Reflector arrays

A method for the theoretical investigation of an arbitrary reflector array of the Van Atta type is described. The analysis is carried out for a reflector consisting of dipoles. Each pair of antenna elements is represented by an equivalent circuit. Mutual impedances and scattering by the dipoles are taken into account. The theory is illustrated by a numerical example of a linear reflector consisting of four half-wave dipoles. The result shows that the simple explanation of the action of a Van Atta reflector is not sufficient.     

Scalar green function method for microstrip antenna analysis based on the exact image theory

Exact image theory, applicable to the analysis of plane-stratified structures, is reviewed in general form and expressions corresponding to the microstrip geometry are given. It is seen that essential in this method is the calculation of two scalar Green functions, responsible for the effect of the geometry for the field. Exact expressions for these Green functions are found for the microstrip in terms of integrals of special functions. The Green functions are needed in the formulation of electric field integral equations for the surface currents of the microstrip. The Green functions are shown to possess the same type of singularity as the free-space Green function and also a similar limit when the distance grows larger, with the exception of a waveguide-mode term, which can be easily evaluated separately. Simple approximate expressions for the Green functions are evaluated, suitable for practical analysis of microstrip structures.     

Novel approach to exact design of digital LDI allpass networks

A novel approach is proposed for the direct z-domain design and synthesis of arbitrary-order digital LDI allpass networks. This leads to the development of two LDI allpass network structures, one of which is completely new whereas the other has recently been derived indirectly by using the bilinear LDI design technique. Both structures lend themselves to fast two-cycle operation independent of the order of the corresponding transfer function. In addition, they are minimal in the number of digital multipliers and require only one unit-delay more than the minimum number possible.<>     

Transmit antenna selection in linear receivers: geometrical approach

Transmit antenna subset selection in spatial multiplexing systems is considered. In particular, selection algorithms aiming to minimise the error rate when linear detectors are used at the receiver are proposed. Previous work on antenna selection has considered capacity and post-processing SNR selection criteria. However, a geometrical interpretation of the decoding process which also permits development of a suboptimal algorithm that yields a considerable complexity reduction with only a small loss in performance, is considered.     

A separation of the logarithmic singularity in the exact kernel of the cylindrical antenna integral equation

The well-known logarithmic behavior of the singular "exact" kernel of cylindrical antenna integral equations is explicitly separated. The elliptic integral partitioning of the kernel by Schelkunoff is the point of departure in the development. The result is an expression for the kernel comprising the logarithmic term and a well-behaved economically computable residual term. This result is readily amenable to numerical solutions of integral equations of cylindrical geometries. Numerical results obtained from method-of-moments solutions to cylindrical antennas are given to verify the result.     

Reflector plasma array antennas

A reflector plasma array antenna is investigated. A plasma array with a controlled pattern is created with the help of a discharge creeping over a dielectric surface. The scattering microwave radiation pattern is calculated for the vertical and horizontal polarizations of the radiation incident on the plasma array.     

A new approach to the optimization of robust antenna arrayprocessors

The authors present a method for solving a class of optimization problems with nonsmooth constraints. In particular, they apply the method to the design of narrowband minimum-power antenna array processors which are robust in the presence of errors such as array element placement, look direction misalignment, and frequency offset. They first show that the constrained minimum power problem has a unique global minimum provided that the constraint set is nonempty. Then it is shown how the design problem derived directly from considerations of the sensitivity of the antenna array processor to errors can be transformed into a quadratic programming problem with linear inequality constraints which can be solved efficiently by the standard active set strategy. They also present numerical results for two types of nonsmooth constraints developed to provided robustness. These results confirm the effectiveness of the method     

Fast mimo transmit antenna selection algorithms: a geometric approach

Motivated by matrix determinant properties, this letter develops a fast transmit antenna selection algorithm for MIMO systems: the G-circles method. This novel scheme is shown to achieve many advantages over other existing algorithms     

Power-azimuth-spectrum modeling for antenna array systems: a geometric-based approach

In this paper, we propose the geometric-based channel modeling technique as a means to establish innovative models for the power azimuth spectrum (PAS). When the geometry of the environment is matched to that of the TSUNAMI II project, the PAS model we achieve (referred to as the secant-square model) may be compared to the Laplacian model introduced previously in the literature. In this case, we observe that our model is a better fit to the TSUNAMI II project measurements. Specifically, our model has a simple mathematical representation and demonstrates a lower squared error when compared to measurement data, and considers effects ignored in the earlier modeling (e.g., the nonzero values at the edge of the PAS). Moreover, the proposed geometric-based channel modeling technique extends to other environments with different topologies, whereas the earlier Laplacian model is limited to the TSUNAMI II measurement environment.     

Small-size CPW silicon resonating antenna based on transmission-line meta-material approach

A small-size zeroth-order resonating antenna based on a composite right/left-handed transmission line (CRLH TL) fabricated on high resistivity silicon substrate using coplanar waveguides (CPW) is proposed. The CRLH TL consists of a series of CPW interdigital capacitors and parallel short-ended CPWs. The predicted and experimental results for return loss, gain and radiation pattern are in very good agreement.