Magdalena Salazar Palma

Adaptive processing using a single snapshot for a nonuniformly spaced array in the presence of mutual coupling and near-field scatterers

This paper presents an adaptive technique to extract the signal of interest (SOI) arriving from a known direction in the presence of strong interferers using a single snapshot of data. The antenna elements in this method can be nonuniformly spaced and there can be mutual coupling between them. In addition, near-field scatterers can also be present. First, the voltages induced in the antenna elements of the array due to interferers, mutual coupling between the elements, and near-field scatterers is preprocessed by applying a transformation matrix to these voltages through a rigorous electromagnetic analysis tool. This electromagnetic preprocessing technique transforms the voltages that are induced in a nonuniformly spaced array containing real antenna elements to a set of voltages that will be produced in a uniform linear virtual array (ULVA) containing omnidirectional isotropic point radiators. In the transformation matrix we would like to include various electromagnetic effects like mutual coupling between the antenna elements, presence of near-field scatterers and the platform effects on which the antenna array is mounted. This transformation matrix when applied to the actual measured voltages yields an equivalent set of voltages that will be induced in the ULVA. A direct data domain least squares adaptive algorithm is then applied to the processed voltages to extract the SOI in the presence of interferers. Limited numerical examples are presented to illustrate the novelty of the proposed method.

Generation of accurate rational models of lossy systems using the Cauchy method

A method to generate an accurate rational model of lossy systems from either measurements or an electromagnetic analysis is presented. The Cauchy method has been used to achieve this goal. This formulation is valid either for lossless or lossy system responses. Thus, it provides an improvement over the conventional Cauchy method and takes into account the relationship between the transmission and reflection coefficients of the system which in our case is a filter. The resulting model can be used to extract the coupling structure of the filter. Two examples have been presented. One deals with measured data and the other one uses numerical simulation data from an electromagnetic analysis.

Dual band filter with split-ring resonators

This work proposes the use of split ring resonators (SRRs) as basic blocks for planar filters with dual-band band-pass frequency response. This application requires some geometrical modifications on the original SRRs used for metamaterial synthesis. The resonance frequencies and their dependence on the dimensions are analytically derived, and the field distribution on each SRR is studied in order to design the coupling and tuning mechanisms. The measurements of a manufactured prototype show the validity and potential of the proposed elements

Filter Model Generation from Scattering Parameters using the Cauchy Method

A method to obtain an accurate band-pass filter model from numerically computed or measured data is presented. A modified new version of the Cauchy technique that uses simultaneously both transmission (S21(f)) and reflection (S11(f)) parameters is applied in order to find a rational polynomial characterization of the filter. From this rational model the coupling structure can be extracted, revealing the differences with the designed one. An application example of a narrow-band and a wide-band model of a microstrip filter is presented.

DOA estimation utilizing directive elements on a conformal surface

In this paper we present a methodology on how to use directive elements in an adaptive array methodology. Typically one uses isotropic elements having practically no gain then the signal level is increased by putting hundreds and thousands of these elements together. In this paper we demonstrate a methodology where the elements can be arbitrarily spaced and may even be non-planar. In addition it is shown how to deal with nonuniformly spaced and non-planar arrays. We illustrate these principles in a direction of arrival (DOA) estimation utilizing directive elements.

Analysis of electromagnetic systems irradiated by ultra-short ultra-wideband pulse

The objective of this paper is to present a methodology for the analysis of electromagnetic systems irradiated by an ultra-short ultra-wideband electromagnetic pulse. This is accomplished through the use of a hybrid method that involves simultaneous generation of early time and low frequency information. These two data sets, namely early time and low frequency, in the original and transform domains are not only easy to generate, but also contain all the necessary mutually complementary information to electromagnetically characterize the system. This assumes that a sufficient record length is available in both domains. A criterion is provided to assess whether the record lengths are sufficiently long. Utilizing orthogonal associate Hermite functions, a time domain signal representing the electromagnetic quantity of interest (be it current or the scattered electromagnetic fields) can be expressed as a weighted sum of these quantities in an efficient way. The associate Hermite functions are orthonormal and are expressed through the Hermite polynomials. The frequency domain response can also be characterized by the same set of functions weighted by the same sets of coefficients, as the Hermite polynomials are the eigenfunctions of the Fourier transform operator. The available data in both domains are then simultaneously used to solve for the unknown weights. Once these coefficients are known the data can be simultaneously extrapolated in both the time and frequency domains. Computational load for the electromagnetic analysis for this method is quite modest compared to solving the electromagnetic analysis problem exclusively in either domain. Numerical examples are presented to illustrate the application of this hybrid methodology.

Analysis of Information and Power Transfer in Wireless Communications

An analysis of wireless information compared to power transfer over the same channel, consisting of a transmitting and receiving antenna system, is discussed. This frequency-selective additive-white-Gaussian-noise channel displays a fundamental tradeoff between the rate at which energy and the rate at which reliable information can be transmitted over the same channel, as in an RFID system, a power-line communication system, or for an energy-harvesting system. The optimal tradeoffs between power transferred and the channel capacity due to Shannon (which is additive-white-Gaussian-noise limited), Gabor (which is interference limited), and Tuller (which is defined in terms of the signal and noise amplitudes, and not power) are compared, and the differences are discussed. The appropriate use of each of the channel-capacity formulations for a frequency-selective transmitting/receiving antenna system in wireless communication is then computed as an illustrative example, to describe the tradeoff between wireless power transfer and wireless information transfer over a transmitting/receiving antenna system.

Dyson conical quad-spiral array as ultrawideband feed system

VLBI2010 requires a feed that simultaneously has high efficiency over the full 2-14 GHz frequency range. The simultaneity requirement implies that the feed must operate at high efficiency over the full frequency range without the need to adjust its focal position to account for frequency dependent phase center variations. Two feeds meet this specification with some lacks to be fulfilled [1]: The Eleven Feed developed at Chalmers University and the Quadruple Ridged Flared Horn (QRFH) developed at the California Institute of Technology. In this frame, Universidad Carlos III de Madrid has developed a new topology for complete covering the requirements of the VLBI2010, including two new pretty attractive characteristics: dual circular polarization (versus the dual lineal solutions present in the state of the art) and constant input impedance of the antenna due to its self-complementary geometry, what is highly interesting for the LNA design. This manuscript is divided as follows: first, results of the complete system using an ideal Gaussian feed are summarized. Then, the new topology proposed is presented and analyzed both, isolated and integrated in the radiotelescope. Finally, a closed solution for covering all the requirements has been manufactured and results from full wave electromagnetic simulations together with measurements are presented. Conclusions and future lines are presented at the end of the present manuscript.

Wireless power transfer versus wireless information transfer

Currently, there is not only a great need for power harvesting but also in many cases it is necessary to send information along with power over the same channel like in a RFID scenario. The goal of this paper is to illustrate that these objectives of simultaneous power transfer and information transfer are contradictory and a balance must be reached for the optimum operation. A simple example of a set of dipole antennas as transmit and receive case is used to illustrate how one can optimize simultaneously the power transfer along with information transfer over the same channel. It is important to note that the meaning of information in the colloquial language is quite different from the implication of information in information transfer. We start with the expression for the Shannon Channel capacity and illustrate how the dual goal of power and information transfer can be achieved. It is demonstrated that an optimization need to be performed for simultaneous transmission of information and power as one is carried out at the expense of the other.

Problems associated with the choice of the proper S-parameters in characterizing antennas and how to rectify it

The purpose of this paper is to demonstrate that the conventionally used S-parameters are not suitable for characterizing antennas, particularly relating their radiation efficiency with the input scattering parameters. In particular, the classical S-parameters do not work when the load is conjugately matched as it produces nonphysical artifacts. These artifacts are not real and do not exist when a different form of the S-parameters are used. Thus, the first objective of this paper is to introduce the two different types of S-parameters generally used to characterize microwave circuits with lossy characteristic impedance. The first one is called the pseudo wave, an extension of the conventional travelling wave concepts, and is useful when it is necessary to discuss the properties of a microwave network junction irrespective of the impedances connected to the terminals. However, one has to be extremely careful in providing a physical interpretation of the mathematical expressions as in this case the reflection coefficient can be greater than one, even for a passive load impedance with a conjugately matched transmission line. Also, the power balance cannot be obtained simply from the powers associated with the incident and reflected waves. The second type of S-parameters is called the power wave scattering parameters. They are useful when one is interested in the power relation between microwave circuits connected through a junction. In this case, the magnitude of the reflection coefficient cannot exceed unity and the power delivered to the load is directly given by the difference between the powers associated with the incident and the reflected waves. Since this methodology deals with the reciprocal relations between powers from various devices this may be quite suitable for dealing with a pair of transmitting and receiving antennas where power reciprocity holds. This methodology is also applicable in network theory where the scattering matrix of a two port (or a multiport) can be defined using complex reference impedances at each of the ports without any transmission line being present, so that the characteristic impedances become irrelevant. Such a situation is typical in small signal microwave transistor amplifiers, where the analysis necessitates the use of complex reference impedances in order to study simultaneous matching and stability. However, for both the definition for the S-parameters, when the characteristic impedance or the reference impedance is complex, the scattering matrix does not need to be symmetric even if the network in question is reciprocal. The second objective is to illustrate that when the characteristic impedance of the line or the reference impedances in question is real and positive, then both of the pseudo-wave and the power-wave scattering parameters provide the same results. Finally, a general methodology with examples will be presented to illustrate how the S-parameters can be computed for an arbitrary network without any a priori knowledge of its characteristic impedance.