Ahmed I. Khalil

Global modeling of spatially distributed microwave and millimeter-wave systems

Microwave and millimeter-wave systems have generally been developed from a circuit perspective with the effect of the electromagnetic (EM) environment modeled using lumped elements or N-port scattering parameters. The recent development of the local reference node concept coupled with steady-state and transient analyses using state variables allows the incorporation of unrestrained EM modeling of microwave structures in a circuit simulator. A strategy implementing global modeling of electrically large microwave systems using the circuit abstraction is presented. This is applied to the modeling of a quasi-optical power-combining amplifier.

The generalized scattering matrix of closely spaced strip and slot layers in waveguide

In this paper, a method-of-moments integral-equation formulation of a generalized scattering matrix (GSM) is presented for the full-wave analysis of interactive planar electric and magnetic discontinuities in waveguide. This was developed to efficiently handle a variety of waveguide-based strip-to-slot transitions, especially on thin substrates. This single matrix formulation replaces the problematic procedure of cascading individual GSMs of an electric (strip) layer, a thin substrate, and a magnetic (slot) layer.

Efficient method-of-moments formulation for the modeling of planar conductive layers in a shielded guided-wave structure

An electric-field integral-equation formulation discretized via the method of moments (MoM) is proposed for the analysis of arbitrarily shaped planar conductive layers in a shielded guided-wave structure. The method results in a generalized scattering matrix (GSM) for the planar structure and can be used with other GSMs, derived using this or other techniques, to model cascaded structures in waveguide. The Kummer transformation is applied to accelerate slowly converging double series expansions of impedance matrix elements obtained in the MoM solution. In this transformation, the quasi-static part associated with a singularity of the electric-type Greens function in the region of a conductive layer is extracted and evaluated in terms of modified Bessel functions, resulting in a dramatic reduction of terms in a double series summation. The proposed technique permits the modeling of a variety of conductive frequency-selective surfaces, including quasi-optical grids and patch arrays for application to spatial power combining.

A generalized scattering matrix method using the method of moments for electromagnetic analysis of multilayered structures in waveguide

The method of moments (MoM) in conjunction with the generalized scattering matrix (GSM) approach is proposed to analyze transverse multilayered structures in a metal waveguide. The formulation incorporates ports as an integral part of the GSM formulation, thus, the resulting model can be integrated with circuit analysis. The proposed technique permits the modeling of interactive discontinuities due to the consideration of a large number of modes in the cascade. The GSM-MoM method can be successfully applied to the investigation of a variety of shielded multilayered structures, iris coupled filters, determining the input impedance of probe excited waveguides, and of waveguide-based spatial power combiners.

Circuit theory for spatially distributed microwave circuits

A spatially distributed radio-frequency (RF) circuit, microwave, or millimeter-wave circuit does not have a global reference node as required in conventional nodal analysis. Instead, local reference nodes associated with ports are required. This paper adapts modified nodal analysis to accommodate spatially distributed circuits, allowing conventional harmonic balance and transient simulators to be used.

An integrated electromagnetic and nonlinear circuit simulation environment for spatial power combining systems

An integrated electromagnetic and circuit simulation environment is developed for the simulation of spatial power combining systems. The analysis incorporates surface modes, nonuniform excitation and full nonlinear effects. The simulation tools are used to predict the performance of a 2 by 2 quasi-optical grid amplifier.

A low-power high performance 4GHz SiGe HBT VCO

This paper reports the lowest VCO phase noise achieved using SiGe HBT process at 4GHz. Te SiGE HBT devices have an f/sub T/ of 47GHz. The differential LC-tuned VCO operates over the voltage range 2.7 to 3.3 supply voltage. It has a 4.2GHz center frequency, 13% tuning range, -106 dBc/Hz at 100KHz offset and -128 dBc/Hz at 1MHz offset. The core power dissipation is 26mW from a 3.3 V supply. A high figure of merit (-186.35) is also achieved. The die area, including buffers and bond pads, is 1 mm/sup 2/.

Integrated electromagnetic and circuit modeling of large microwave and millimeter-wave structures

A strategy integrating electromagnetic, nonlinear circuit and thermal analysis is presented for the modeling of large microwave and millimeter-wave systems. The work is applied to the modeling of a spatial power combining amplifier.

Efficient MOM-based generalized scattering matrix method for the integrated circuit and multilayered structures in waveguide

The generalized scattering matrix (GSM) approach is proposed to analyze transverse multilayered structures with circuit ports in a metal waveguide. The Kummer transformation is applied to accelerate slowly converging double series expansions of Greens functions that occur in evaluating the impedance matrix elements. In this transformation the quasi-static part is extracted and evaluated to speed up the solution process resulting in a dramatic reduction of terms in a double series summation. The formulation incorporates electrical ports as an integral part of the GSM formulation and so that the resulting model can be integrated with circuit analysis.

Modeling of waveguide-based spatial power combining systems

A modeling scheme is proposed and tested for the analysis of waveguide-based quasi-optical systems. The system is partitioned into blocks, each block is characterized by its generalized scattering matrix (GSM) which in turn are cascaded to obtain the model of the complete system. Blocks with active devices are accounted for in the GSM by means of circuit ports. The calculated and measured results for a Ka-band double layer patch array is presented. A good agreement between theory and measurement is obtained.