Ioan E. Lager

Sunflower Array Antenna with Adjustable Density Taper

A deterministic procedure to design a nonperiodic planar array radiating a rotationally symmetric pencil beam pattern with an adjustable sidelobe level is proposed. The elements positions are derived by modifying the peculiar locations of the sunflower seeds in such a way that the corresponding spatial density fits a Taylor amplitude tapering law which guarantees the pattern requirements in terms of beamwidth and sidelobe level. Different configurations, based on a Voronoi cell spatial tessellation of the radiative aperture, are presented, having as a benchmark the requirements for a typical multibeam satellite antenna.

The design of shared aperture antennas consisting of differently sized elements

A consistent strategy for the design of finite array antennas consisting of differently sized radiating elements is discussed. In view of increasing the total bandwidth of the antenna system, while maintaining a low mutual coupling between the elementary radiators, sparse subarrays, operating at adjacent frequency ranges, are interleaved on a common (shared) aperture. The sparse architectures are designed using a combinatorial method that ensures an acceptable behavior in the side-lobes region in conjunction with a narrow beamwidth. The effect of the mutual coupling between identical and differently sized elements is accurately evaluated and is accounted for in predicting the performance of each individual radiator. The concept is illustrated by designing a shared aperture antenna consisting of two interwoven subarrays that jointly cover a fractional bandwidth of 14% in the X-band. Cavity-backed, stacked-patches antennas with coaxial feeding are used as elementary radiators.

Interleaved Array Antennas for FMCW Radar Applications

An effective and robust strategy for concurrently designing the transmit and receive antennas of a frequency-modulated, continuos-wave radar is discussed. The aperture architecture is based on the use of non-periodic, interleaved sub-arrays. Deterministic element placement is employed for ensuring design efficiency. The procedure yields controllable sub-array radiation patterns and two-way side-lobe levels below - 30 dB, that are also stable over a wide frequency range.

Design considerations in sparse array antennas

The design aspects concerning the sparse array antennas are discussed. Commonly, the beamwidth, the side-lobes level and the gain are the relevant features in antenna design procedures. These parameters are evaluated for different sparse topologies and generalised design relations are provided. The capabilities of sparse architectures are evaluated by comparison with uniform arrays for a similar level of performance

The Pulsed-Field Multiport Antenna System Reciprocity Relation and Its Applications—A Time-Domain Approach

A novel time-domain approach to the derivation of the pulsed electromagnetic field multiport antenna system reciprocity theorem is presented. The theorem interrelates the field and system properties in two states: the transmitting state and the receiving state. General time-domain Thevenin (voltage-source, impedance-based) and Norton (electric-current source, admittance-based) type equivalent circuits are constructed for antenna systems whose local properties are described in terms of multiport Kirchhoff circuits. Applications to an indoor wireless communication performance analysis and the analysis of cosmic microwave background radiation measurement are briefly indicated. Numerical results are provided for the pulsed-field transfer between two wire loops, a configuration that is representative for the operation of wireless telecommunication systems and for the pulsed-field EM interference analysis in nano-electronic integrated circuit devices.

Finite formulation and domain-integrated field relations in electromagnetics - a synthesis

Complementary formulations of the integral type have established themselves as the most adequate approach to computational electromagnetics. This paper proposes a computational strategy that benefits from the advantages offered by the finite formulation of the electromagnetic (EM) field, employing integral field quantities and dual meshes, and by the domain-integrated field relations approach to EM field computation.

On the Causes of Spurious Solutions in Electromagnetics

The problem of spurious solutions in finite-element methods for electromagnetics is discussed with the explicit aim to re-open the discussion on this much debated subject. First, an overview is given of existing ideas about the causes of spurious solutions together with the solutions that are proposed. Subsequently it is concluded that the cause of spurious solutions may differ from what is usually suggested or claimed, and an alternative cause for spurious solutions is proposed. Finally, suggestions are given about how a finite-element method should be designed that is free of spurious solutions.

A Novel CPW-fed Optimized UWB Printed Antenna

An optimized coplanar waveguide (CPW)-fed, ultra-wideband (UWB) printed radiator is presented. Balanced shapes are incorporated to the radiating section so that the impedance is matched in a balanced manner over the intended bandwidth. Both the CPW-feed and the antenna sections are realized on one single layer of standard RT5870 high frequency laminate. The radiator possesses good UWB-characteristics in the designed spectrum (4.2 to 14.2 GHz). These include nearly perfectly symmetrical patterns, no side-lobes, no cross-polar components in the symmetrical axial plane and low cross-polar components in all other planes, balanced impedance bandwidth, and almost 4 octaves impedance bandwidth.

Model Pulses for Performance Prediction of Digital Microelectronic Systems

Pulse-shape models are presented that furnish the tools for analyzing a number of aspects of the performance of microelectronic circuits. Model pulse shapes are provided and their properties are analyzed in detail. Applications that are covered include the replication of measured pulses that are of relevance for inter- and intra-chip interconnects and, concurrently, examples of passive circuits that generate them. The pulses are appropriate as input to time-domain electromagnetic simulation. They are also instrumental to microelectronic performance prediction protocols and measurement equipment-aspects that are of crucial importance to integrated circuit packaging.

Pulsed Electromagnetic Field Radiation From a Wide Slot Antenna With a Dielectric Layer

Analytic time-domain expressions are derived for the pulsed electromagnetic field radiated by a wide slot antenna with a dielectric layer in a two-dimensional model configuration. In any finite time window of observation, exact pulse shapes for the propagated, reflected and refracted wave constituents are constructed with the aid of the modified Cagniard method (the Cagniard-DeHoop method). Numerical results are presented for field pulse shapes at the dielectric/free-space interface, the pulse time widths of the excitation being chosen such that the separate arrivals from the two edges of the slot can be distinguished. Applications are found in any system whose operation is based on pulsed electromagnetic field transfer and where digital signals are detected and interpreted in dependence on their pulse shapes.