Mark D. Prouty

Hybrid couplers in bilevel microstrip

Hybrid couplers can be built using a bilevel microstrip structure in which two strips are positioned broadside, one above the other. This simple geometry provides large coupling factors without the need for rigorous manufacturing tolerances. Remarkably, if the dielectric constant of one of the layers can be freely chosen, ideal hybrid coupler performance is achievable. Even when the choice of dielectric constant is constrained, good results can be obtained. A technique for achieving optimal design has been developed, and design curves are shown. Experiments confirm design predictions. The reentrant coupler may be analyzed as an interconnection of two bilevel couplers of the kind described here. This provides a simpler analysis than methods used earlier, and in some cases yields more accurate results. >

Solving microstrip discontinuities by the measured equation of invariance

The measured equation of invariance (MEI) is a newly developed computational method which allows finite-difference (FD) or finite-element (FE) mesh to be terminated very closely to objects of interest. In this paper, the authors show how the MEI method may be applied to microstrip antennas and discontinuity problems. The authors demonstrate its use in general full-wave three-dimensional (3-D) microstrip problems, and give results for open-ended microstrip lines and microstrip bends.

A new approach to quasi-static analysis with application to microstrip

The measured equation of invariance (MEI), a new, rapid technique for electromagnetic field analysis, is applied to planar circuit problems. Variations of the technique applicable to microstrip geometry are described. As a demonstration, it is then applied to electrostatic analysis of structures held at different potentials, using novel umbilical meshes. The MEI technique offers the possibility of order-of-magnitude increases in computational speed for typical problems of microwave CAD.<<ETX>>

Optical Imaging With Phase Shift Masks

The imaging characteristics of masks which have arbitrary phase shifts between adjacent regions has been investigated. The process simulation program SAMPLE was extended to compute images of masks with an arbitrary number of regions of varying amplitude and phase transmission. In order to do this, the code was modified to calculate the imaginary, in addition to the real, part of the transmission cross-coefficient and perform complex multiplications within the image intensity summation. The disadvantage of phase shift masks lies in the high printability of defects. Phase shifts of 180° cause defects twice as small to print. This printability is phase shift dependent, and may be considerably reduced with smaller phase shifts. A second disadvantage is that phase shifts occurring in the middle of large clear areas produce such a deep dip in the image intensity that these clear field transitions are impractical. The advantage of phase shift masks lies in reducing proximity effects between adjacent features. The best measure of this reduction is the improvement in image con-trast for periodic arrays of lines. A significant improvement can be obtained, especially at low sigma. This improved contrast enables a smaller linewidth to be used. At a sigma of 0.3 the size of periodic features may be reduced from 1.2 μm to 0.5 μm, still maintaining a contrast of 0.85. Not only is the contrast improved, but its sensitivity to defocus is actually reduced, thereby increasing the useful depth of focus. Phase shifts less than 180° give similar results although the improvement decreases rapidly for phase shifts less than 120°. The image of isolated features may be improved 30 percent by using unprintable phase shifted proximity features. By proper defect control and elimination of clear field transitions, very significant improvements in aerial image quality are possible with phase masks.

Application of the measured equation of invariance to radiation and scattering by flat surfaces

Because on flat surfaces the electric currents are confined to two dimensions, a simple vector potential formulation can be used. The problem of radiation and scattering by rectangular strip dipoles is solved, including the transversal variation of the current across the dipole width. Also of interest are the currents induced on antennas with step variations in width, and with bends and T-junctions.<<ETX>>

Application of the measured equation of invariance to transmission lines and discontinuities

The MEI (measured equation of invariance) method can easily be applied to static analyses of uniform transmission lines, such as single and coupled microstrip lines. Laplaces equation is solved for the static electric potential, and the total charges on the metal structures are found. Solving the problem with the correct permittivity values for the dielectrics yields the capacitance of the structures, while solving the problem with all permittivities equal to the free-space value yields the inductances. The quasi-static impedance values may then be obtained. Planar microstrip-type structures, where currents are confined to two dimensions are also considered. Results are presented for cases where no dielectric is present. This simplifies the Greens function calculation for the present purposes, but the method may be applied to more general cases.<<ETX>>

A comparison of backscattered electron and optical images for submicron defect detection

A rapid and automated inspection system is a necessity for the detection of defects in x ray and optical lithography masks. Monte Carlo techniques and optical simulation are used to examine the relative qualities of backscattered electron signals and transmitted optical images for use in a mask inspection system. The backscattered electron signals from one and two dimensional submicron structures are examined for different take‐off angle ranges and beam sizes and compared to the corresponding optical images for different wavelengths and numerical apertures. It is shown that signal quality in electron‐beam inspection systems can improve as defect size decreases while the optical images tend to degrade. An examination of shot noise signal‐noise ratio characteristics shows that shot noise alone should not be a fundamental limit in a well designed inspection system.

Microstrip antennas and discontinuities using the measured equation of invariance

The recently invented MEI technique is applied to the 3-dimensional full-wave analysis of discontinuities in microstrip. Results for a microstrip dipole antenna, open end, and right-angle bend are in good agreement with earlier work. The MEI technique is faster and more powerful than previous methods. Its advantage increases with the size and complexity of the problem.<<ETX>>

Further insight into the measured equation of invariance EM theory

The measured equation of invariance (MEI) is a concept in field computation which leads to the generation of local linear equations in lieu of absorption conditions to terminate finite difference or finite element equations. The advantage of the method is that the equations are not limited to replacing absorbing conditions, but can be used where there are both outgoing and incoming waves. In fact, they can be used in closed or semiclosed environments such as cavities or waveguides. Yet unlike the integral equation or boundary element method, which results in global matrices, MEI gives local equations and sparse matrices. The savings in storage and computing time by MEI over conventional methods are very substantial.<<ETX>>

Radiation from planar resonators

Power radiated from microstrip-based resonators is calculated by integration of a Greens function with assumed currents, a method that is convenient and is thought to be more accurate than previous methods used in calculations of radiation Q. Resonators consisting of two coupled microstrips excited in the odd mode are found to radiate much less than conventional single-microstrip resonators or U-shaped hairpin resonators. However, when the resonator is loaded by a semiconductor device, as in an oscillator, radiation increases. Asymmetries in the resonators, arising from output coupling or fabrication errors, introduce even-symmetric currents which radiate much more strongly than odd-mode currents. The effects of such asymmetries on radiated power are estimated. On the basis of these findings, a convenient geometry for high-power planar oscillators with low radiation is proposed. >