Nirod K. Das

Full-wave spectral-domain computation of material, radiation, and guided wave losses in infinite multilayered printed transmission lines

A unified solution for full-wave computation of losses in a general multilayered planar transmission line is presented. It includes material losses (dielectric and conductor losses), losses due to radiation leakage, and losses caused by leakage of power to source-free characteristic modes (surface-wave or waveguide modes, for example) of the multilayered geometry. A spectral-domain moment method is used with the Galerkin testing procedure. Significant modification of the conventional spectral-domain analysis of planar transmission lines is necessary in enforcing proper boundary conditions in the Galerkin testing procedure and, more importantly, in accounting for poles and branch cuts in the complex Fourier transform domain in order to rigorously account for the different loss mechanisms discussed. Results for a few representative geometries, namely, strip and/or material loss in a microstrip line and a slotline, surface parallel plate mode leakage loss in a conductor-backed slotline and a two-layer stripline, and radiation loss in a single and a coupled stripline at the interface between two infinite mediums, are presented to demonstrate these various loss effects. >

Methods of suppression or avoidance of parallel-plate power leakage from conductor-backed transmission lines

Four useful methods are presented to suppress and/or avoid parallel-plate leakage from conductor-backed printed transmission lines. These include: 1) the use of shorting-pins; 2) the use of a dielectric-guide-coupled configuration; 3) using a two-layered conductor-backing configuration; and 4) dielectric loading on top. New analyses to model the leakage suppression due to the shorting-strips and the dielectric-guide-coupled geometries are presented, with selected demonstrative results and critical discussions. It is concluded that the unwanted leakage in many printed transmission lines, that are otherwise attractive for integrated circuits and phased array applications, can be successfully avoided and/or significantly suppressed using the proposed techniques.

Multiport scattering analysis of general multilayered printed antennas fed by multiple feed ports. I. Theory

A general solution is given for a class of printed antenna geometries composed of multiple dielectric layers or ground planes, radiating patches, dipoles, or slots, and an arbitrary configuration of multiple transmission lines proximity-coupled or aperture-coupled to the radiating elements. The solution uses a full-wave spectral-domain moment method approach, and a new generalized multiport scattering formulation to model the excitation from the multiple feed lines. This method treats infinite phased arrays as well as isolated elements. The general theory using the new multiport scattering formulation is elaborated, with details of the key analytical and numerical aspects. Considering the unified nature of the multiport scattering analysis, and its simplicity, this analysis is appropriate for computer simulation of a large variety of multilayered microstrip antennas involving radome layers, dual polarized feeds, proximity-coupled or aperture-coupled elements, multifeed stacked or parasitic patches, and several related configurations for integrated phased array applications. >

Multiport scattering analysis of general multilayered printed antennas fed by multiple feed ports. II. Applications

For Part I, see ibid., vol.40, no.5, p.469-481 (1992). The general analysis of part I is applied to several practical geometries of multilayer/multifeed printed antennas. These examples include a dual-feed circularly polarized geometry; a stacked patch geometry; a stripline-aperture coupled geometry with a radome; an open-end proximity-coupled patch; and dipole and slot geometries inclined or perpendicularly coupled to different feedlines. Features of the selected geometries cover many practical aspects of multilayer integrated phased arrays. Experimental results for several geometries are compared with the analytical results to demonstrate the accuracy and versatility of the analysis used. Various design considerations for the use of these multilayered printed antenna geometries in integrated phase array applications are discussed. >

Whispering gallery modes of microspheres in the presence of a changing surrounding medium: A new ray-tracing analysis and sensor experiment

A simple plane wave, ray-tracing approach was used to derive approximate equations for the dielectric microsphere whispering gallery mode (WGM) resonant wavenumber and quality factor, as dependent on the surrounding medium’s refractive index. These equations are then used to determine the feasibility of a micro-optical sensor for species concentration. Results indicate that the WGMs are not sensitive enough to refractive index changes in the case of gas media. However, they can be sufficiently sensitive for measurements in liquids. Experiments were carried out to validate the analysis and to provide an assessment of this sensor concept.

Analysis and design of series-fed arrays of printed-dipoles proximity-coupled to a perpendicular microstripline

An analysis of a printed dipole element and a generalized configuration of a series-fed array of such elements, electromagnetically coupled to a covered microstripline running perpendicularly under it in a substrate-superstrate configuration, is presented. The solution is based on the principle of reciprocity and is formulated using a rigorous method of moments and full-wave spectral-domain Greens functions for multilayer dielectric substrates. The dipole excitation is characterized by an equivalent impedance, and can be controlled by suitably selecting the offset of the dipole from the feed line. Mutual coupling between dipoles is included. Using the results of the element analysis, a series-fed array prototype has been successfully designed, built, and tested in a standing-wave configuration; the design details are described, and measured performances are evaluated using the results of the array analysis. Mutual coupling effects are found to be not detrimental for this configuration, but can be severe for other nonstanding-wave configurations. >

Generalized multiport reciprocity analysis of surface-to-surface transitions between multiple printed transmission lines

A method of analysis of surface-to-surface transitions between arbitrary combinations of multilayered printed transmission lines using a general multiport reciprocity formulation is presented. The scattering parameter at a given port of the transition is computed by directly relating it to simple reactions of the known eigenfields of the particular port on various induced strip currents or slot electric fields of other transmission lines. With simplifying practical assumptions, and by use of an efficient singularity extraction technique, equivalent circuit models for particular cases are extracted with simple closed-form expressions for the equivalent circuit parameters. The multiport scattering matrix of the transition completely describes the coupling characteristics of the transition, and via standard network analysis can be conveniently used for design optimization for any port terminations and/or matching circuits. Detailed case studies illustrating the application of the general analysis method are presented. >

Excitation of a parallel-plate dielectric waveguide using a coaxial probe-basic characteristics and experiments

In this paper, we study the basic characteristics of a probe excitation to a parallel-plate dielectric waveguide (PPDW), and present design data and experimental results. A coaxial probe has been used in microstrip lines and rectangular waveguides. The present study shows that it is also an effective method to excite/couple a PPDW, thus facilitating the introduction of a new class of PPDW technology in microwave/millimeter-wave integrated circuits. We use here a spectral-domain analysis for analytical modeling of the probe transition, where the probe is approximated by a current strip of an equivalent width. Applying the method of image, the structure is transformed to an infinite-long thin strip inside a dielectric slab, which reduces the transition analysis into a simpler planar geometry. Basic characteristics of the probe excitation, and a complete design data for the radiation loss, excitation efficiency, and input impedance for various transition parameters are computed. Prototype design experiments were conducted, which show that quite efficient excitation can be achieved using; the probe, with insertion loss as low as 0.1 dB. This is contrary to some misconceptions that a probe transition to the fundamental PPDW mode is quite inefficient due to parallel-plate mode radiation.

A generalized CAD model for printed antennas and arrays with arbitrary multilayer geometries

Abstract A general full-wave solution to arbitrary multilayer geometries of printed antennas and arrays coupled to multiple printed feed lines has been developed. It uses spectral-domain Greens functions for multilayer substrates to account for the substrate layering of the printed antenna, and a newly developed generalized multiport reciprocity analysis to treat the coupling of the transmission feed lines to the antenna elements. The analysis is completely rigorous, including all surface wave or other non-radiating modal effects. The solution has been developed for both isolated elements as well as infinite arrays. The theoretical formulation of the generalized multiport reciprocity analysis is described in details and results for several practical examples are presented to demonstrate the accuracy and versatility of the analysis used. Considering the rigor and versatility of the analysis, it should find useful for full-wave simulation and computer aided design of a variety of multilayered printed phased-array configurations.

Infinite array of printed dipoles integrated with a printed strip grating for suppression of cross-polar radiation. I. Rigorous analysis

A rigorous analysis of an infinite array of printed dipoles integrated with a covering layer of printed strip grating is presented. Such designs can be useful to achieve low to ultra-low levels of cross-polar radiation from printed antennas, which is otherwise difficult to obtain from standard printed antenna designs. The analysis rigorously accounts for coupling between the grating strips and the dipole array in a general multilayered environment. Various demonstrative and design results showing loading effects of the grating on scan and impedance characteristics of the array are presented. Some interesting fundamental effects of the grating on the cross-polarization level and scan-blindness behavior are discussed.