Michael R. Lyons

Design of low-cost 4W & 6W MMIC high power amplifiers for Ka-band modules

Two Ka-band power amplifier MMICs, 4W and 6W, with high power density and gain are presented. Each amplifier was designed using a 5-stage topology to demonstrate over 30dB of gain. The 4W design exhibited a peak saturated output power of 37.2dBm and a chip output power density of 532 mW/mm/sup 2/. This is the highest recorded power density for a Ka-band power amplifier design to date. The high gain and power density make them ideal for low-cost Ka-band transmit systems.

A two-dimensional finite element formulation of the perfectly matched layer

A perfectly matched layer (PML) is implemented using the finite element method (FEM) to successfully terminate the output port of a parallel-plate waveguide operating over a wide range of frequencies. The PML layer is modeled as a nonphysical anisotropic lossy material backed with a perfect electric conductor (PEC). Numerical results showing the reflection coefficient as a function of frequency, for both TEM and TM/sub 1/ propagation modes, demonstrate the effectiveness and accuracy of the PML concept as applied in the context of the FEM.

Finite element analysis of MMIC waveguide structures with anisotropic substrates

This paper presents an extended finite element formulation for a full-wave analysis of biaxial and transverse plane electric and magnetic anisotropic materials with application to monolithic microwave integrated circuits (MMICs). A convenient formulation of the characteristic impedance based on a power-voltage definition is developed using vector-based finite elements. The resultant generalized eigenvalue problem is solved using a numerically efficient algorithm based on a forward iteration, taking full advantage of the sparsity of the involved matrices. Numerical results are compared and agree well with existing published data for various MMIC configurations. Two specific coplanar waveguide structures, one with a conventional and the other with a suspended substrate, are examined using four common anisotropic materials. Principal axis rotations of the anisotropic substrates are also considered to improve dominant mode dispersion characteristics and minimize higher order mode interactions.

Enhanced dominant mode operation of a shielded multilayer coplanar waveguide via substrate compensation

The cutoff frequency of the first higher-order even mode in a shielded multilayer coplanar waveguide (CPW) is studied using the spectral domain approach (SDA). The effective dielectric constant for the dominant odd and first higher-order even mode in a shielded multilayer CPW is computed and compared to other published numerical results. Dielectric constant and substrate height are varied with respect to even mode cutoff frequency and plotted for several CPW structures. Different combinations of internal substrates are shown to produce even mode cutoff frequency maximization for increased odd mode operation bandwidth. >

Transient coupling reduction and design considerations in edge-coupled coplanar waveguide couplers

Edge-coupled coplanar waveguide (CPW) forward directional couplers are studied using an even/odd mode analysis. Specific height combinations of multilayer substrates are found which equalize the phase velocities of the even and odd modes. These modal velocity equalization points are seen to be relatively constant over a wide band of frequencies. Results of simulated pulse distortion are presented in a multilayer compensated structure showing a dramatic reduction in transient signal coupling and overall distortion. Design considerations for practical circuit designs are also discussed.

Analysis of arbitrary shaped cavity-backed patch antennas using a hybridization of the finite element and spectral domain methods

A hybridization of the finite element method (FEM) [Jin, 1993] and the spectral domain method of moments (MoM) [Zavosh and Aberle, 1994; Aberle and Zavosh 1994] is utilized in the analysis of cavity-backed patch antennas mounted on an infinite ground plane. The spectral domain MoM models the fields in the external region of the cavity through the use of the half-space Greens function whereas the FEM models the fields inside the cavity using linear edge-based tetrahedral elements. The two regions are coupled through the continuity of the fields in the aperture. The MoM formulation can be completely decoupled from the FEM formulation with the use of the physical equivalence principle after a surface magnetic current is introduced just above and below the aperture plane. The use of edge-based tetrahedral elements inside the cavity volume results in a triangular discretization of both the aperture and patch surfaces. The spectral domain implementation of the Rao, Wilton and Glisson [1982] basis functions with triangular support is one of the most appropriate choices in our case, if indeed arbitrary shaped apertures and/or patches are to be considered in the analysis.

Dispersive effects of a thin metal-insulating layer in MMIC structures

A full-wave finite element analysis is used to examine the dispersive effects of a thin metal-insulating layer in CPW and microstrip MMICs. This layer is often encountered in the MMIC manufacturing process residing on top of a semiconducting substrate. The effects of metallization thickness are also examined.

On the accuracy of perfectly matched layers using a finite element formulation

A Perfectly Matched Layer (PML) is applied to a three-dimensional edge-based finite element formulation to calculate the S-parameters of waveguide structures. The PML region is implemented in the finite element code as a non-physical uniaxial anisotropic lossy material. Numerical results demonstrate the accuracy and future potential of such an absorber.

Transient coupling reduction in edge-coupled coplanar waveguide forward directional couplers

Picosecond pulse propagation is studied in symmetric, edge-coupled, coplanar waveguide (CPW) forward directional couplers. Frequency dependent even-and odd-mode effective dielectric constants are found that exactly equalize for specific multi-layer substrate height configurations at a given frequency. Results of transient coupling reduction are presented in a multi-layer compensated structure.<<ETX>>

Enhanced dominant mode operation of shielded multilayer coplanar waveguide

The effects of substrate height and dielectric constant on the propagation characteristics of a multilayer shielded symmetrical coplanar waveguide (CPW) are examined using a full-wave spectral-domain analysis (SDA). It was found that the effective dielectric constant of the shielded CPWs displayed a cutoff frequency for the even mode which can be controlled by varying the height and dielectric constant of the substrate, especially those directly below the coplanar slots. The highest cutoff frequencies found in three-layer CPW configurations utilized air as the lower substrate dielectric. In certain multilayer CPW combinations, when the lower substrate was not air, a bandwidth maximization effect was demonstrated using internal substrates.<<ETX>>