Alejandro Garcia-Lamperez

Analytical synthesis of microwave multiport networks

An analytical, exact method for the synthesis of multiport microwave networks formed by coupled resonators is proposed. The method is based on the definition of a novel class of coupling matrix with non-resonant nodes and an arbitrary number of input/output ports. The use of this coupling matrix allows a synthesis procedure analogous to the one used for filters. Some applications of the presented technique are the design of power dividers, multiplexers and diplexers. A synthesis example of a diplexer formed by two box-section filters with one transmission zero at a specified frequency for each one is included.

Dual-Band Recursive Active Filters With Composite Right/Left-Handed Transmission Lines

Unique properties exhibited by metamaterial transmission lines have been previously used to design a large number of dual-band microwave passive devices, but not active ones. In this paper, a novel dual-band active filter scheme based on composite right/left-handed transmission lines is proposed. The inclusion of these types of lines as feedback sections in a first-order recursive topology can be used to generate a filtering response with two arbitrary passbands. Additionally, dual-band couplers are also required. These may be implemented by means of stub-loaded branch-line structures. As an added advantage, these elements produce a strong rejection level at the central stopband that improves the overall response. Theoretical analysis and design procedures are verified by means of manufacturing and measurement of a prototype containing a distributed amplifier.

Single-Band to Multiband Frequency Transformation for Multiband Filters

A method for the design of bandpass filters with multiple pass bands is presented. The key point of this method is a frequency map between single-band resonators and multiple-band networks formed by those resonators with additional resonators coupled to them. The mapping problem is a non-linear one and the mathematical treatment, based on mapping the cut-off frequencies, is not simple. However, the resulting method is quite straightforward: first, synthesize a single-band equivalent filter; then, couple to each resonator a set of as many resonators as pass bands minus one, being the sets identical between them. The method is illustrated by designing several microstrip prototypes with one to three bands. They consist of conventional parallel-coupled half-wavelength resonator filters with additional hairpin or meandered resonators.

Compact multiplexer formed by coupled resonators with distributed coupling

Conventionally, the design of microwave multiplexer networks is performed in two steps: first, the filters for each channel are independently synthesized. Second, a power divider or manifold network is designed so that the responses of the isolated filters are minimally affected when integrated into the whole device. Usually this network is formed by lengths of transmission lines that introduce phase shifts to each channel. An additional optimization step of the complete network is carried out in order to further improve the response of each channel. We have followed a different approach. The complete network is formed exclusively by coupled microwave resonators, just like filters but with an arbitrary number of ports. The network is described by means of a generalized coupling matrix, suitable for the increased number of ports. The signal combination is obtained through distributed couplings between the resonators of each channel. As a result, the placement of the non-complete transmission zeros due to the interaction between channels can be controlled and used to increase the selectivity of the multiplexer.

An Improved Marching-on-in-Degree Method Using a New Temporal Basis

The marching-on-in-degree (MOD) method has been presented earlier for solving time domain electric field integral equations in a stable fashion. This is accomplished by expanding the transient responses by a complete set of orthogonal entire domain associated Laguerre functions, which helps one to analytically integrate out the time variable from the final computations in a Galerkin methodology. So, the final computations are carried out using only the spatial variables. However, the existing MOD method suffers from low computational efficiency over a marching-on-in-time (MOT) method. The two main causes of the computational inefficiency in the previous MOD method are now addressed using a new form of the temporal basis functions and through a different computational arrangement for the Greens function. In this paper, it is shown that incorporating these two new concepts can speed up the computational process and make it comparable to a MOT algorithm. Sample numerical results are presented to illustrate the validity of these claims in solution of large problems using the MOD method.

A novel Ku-band dielectric resonator triplexer based on generalized multiplexer theory

The synthesis, design, manufacturing and measurement of a Ku Band dielectric resonator triplexer is presented. In contrast to classical multiplexer configurations, where channels are disposed either in manifold or connected by means of bifurcations, this new design avoids extra elements, and only resonators and coupling elements are needed to achieve the required transfer function. Coupling matrices obtained by the optimization algorithm are simplified in order to converge towards feasible topologies. For verification purpose, a three 36 MHz-channel multiplexer has been manufactured and measured.

SIW compact diplexer

A compact diplexer fabricated on substrate-integrated waveguide (SIW) technology is presented. The diplexer is a coupled-resonator network with no additional elements such as power dividers, composed exclusively of six SIW resonators coupled through inductive irises, with one transmission zero at each channel that improves the selectivity. The close physical proximity of the resonators and the leakage associated to via-hole walls characteristic of the SIW technology are the main challenge of this design. However, this effect can be taken into account, as proved by a fabricated prototype with pass bands around 8 GHz.

A Critical Look at the Principles of Electromagnetic Time Reversal and its Consequences

A plethora of papers can be found in the scientific literature talking about time reversal. The term time reversal exists in the publications in a variety of different fields, such as ultrasonics, acoustics, wireless communications, electromagnetics, antennas and propagation, optics, physics, and philosophy. The term time reversal by itself sounds very interesting, and can provide many interpretations that are fascinating. However, due to a loose use of this term, it may in many cases lead to fallacious interpretations and conclusions if it is not interpreted in strict scientific terms. The main goal of this paper is to explain the appropriate definition of the term time reversal in electrical engineering in general, and in electromagnetics for wireless communications, to be specific. However, the motivation of the work presented in this paper is not to raise a controversy about time reversal and its related research. Rather, the aim of this work is to highlight the basic electrical engineering fundamentals that are necessary to study time reversal and to correctly define it, and to then accordingly interpret the results. Hence, the true and fallacious benefits of electromagnetic time reversal will be exposed. To serve this purpose, the paper is divided into two parts. First, a detailed literature review is presented. The true history of the term time reversal in electrical engineering is traced. In this part, most of the reported definitions of time reversal and its claimed capabilities are summarized. Some problems with the application of time reversal in electromagnetics are discussed, both theoretically and practically. All of the time-reversal papers talk about reciprocal networks, so the fact of the non-reciprocity of a single-antenna system in the time domain (the way we generally interpret it) is presented, to prove theoretically that there is a problem with how we interpret time reversal in electromagnetics. Finally, practical examples are shown, where time reversal is used in a wireless system and in an acoustic de-reverberation problem. The exact capabilities of time reversal in electrical engineering are exposed in those experiments.

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.

Comparison of the Performance Between a Parasitically Coupled and a Direct Coupled Feed for a Microstrip Antenna Array

This communication presents an alternate methodology- parasitically coupled feed-for exciting a four element microstrip array radiating primarily in the broadside direction. Typically, a four element microstrip array is fed directly through a corporate feed network using T-junctions and quarter wave transformers. The proposed parasitically coupled feeding of the array simplifies the geometry and results in a smaller size for the array. In this study, the matching of the microstrip array and the radiation characteristics of the two different feeding mechanisms are simulated using an electromagnetic analysis code and then implemented in hardware for comparison of the performance of each mechanism. The microstrip line based array feed and the parasitically coupled feed both have similar bandwidth characteristics and radiate in the broadside direction with similar gains. The simulated efficiency of the proposed parasitically fed broadside array antenna is around 85% to 90% over majority of the bandwidth and compares well with the conventional direct feed structure.