I. Wolff

CAD models of lumped elements on GaAs up to 18 GHz

Lumped elements are considered as very attractive structures for the realisation of MMICs with respect to considerable size-reduction. Improved models for integrable lumped-element straight-line, single-loop, and spiral inductors, as well as for interdigitated and MIM capacitors, have been derived using numerical solutions of the inductance integral, basic microstrip theory, and network analysis. The broad experimental verification shows good agreement between models and experiments, with deviations of 5-10% up to 18 GHz. Besides the practical values and frequency range, losses of the lumped elements are presented. >

Fast, accurate and simple approximate analytic formulas for calculating the parameters of supported coplanar waveguides for (M)MIC's

Fast, accurate, and simple approximate analytic formulas are presented for calculating the quasi-static-TEM parameters of supported coplanar waveguide structures (SCPWs). These include, the open, covered as well as dielec- tric over-layed SCPWs. These formulas have been designed for use in (M)MICs-CAD programs and are only valid when- ever the supporting material is of lower permittivity. Compre- hensive comparisons have been made by using a rigorous spec- tral-domain hybrid mode analysis. Accuracy is found to be better than 1 percent for most of the operating range of phys- ical dimensions and available dielectric materials (E, = 1 to 20). Numerical results are also presented in order to investigate the properties of different SCPW structures

Equivalent capacitances of coplanar waveguide discontinuities and interdigitated capacitors using a three-dimensional finite difference method

Equivalent capacitances of coplanar waveguide discontinuities on multilayered substrates are calculated using a three-dimensional finite-different method. The application of the method is demonstrated for open ends and gaps in microstrip and coplanar waveguides, as well as for more complicated structures such as interdigitated capacitors. The main advantage of the method is its flexibility in treating multilayered substrates and different conductor configurations. It can therefore be applied to more complicated structures such as interdigitated capacitors, air bridges, and waveguide transitions. The effect of conductor metallization thickness and shielding walls is also taken into account. Good agreement between the calculated data and measurements up to 25 GHz in the case of coplanar structures indicates the validity of the static analysis even for high frequencies. >

A Method for Calculating the Frequency-Dependent Properties of Microstrip Discontinuities

A method is described for calculating the dynamical (frequency-dependent) properties of various microstrip discontinuities such as unsymmetrical crossings, T junctions, right-angle bends, impedance steps, and filter elements. The method is applied to an unsymmetrical T junction with three different linewidths. Using a waveguide model with frequency-dependent parameters, a field matching method proposed by Kuhn is employed to compute the scattering matrix of the structures. The elements of the scattering matrix calculated in this way differ from those derived from static methods by a higher frequency dependence, especially for frequencies near the cutoff frequencies of the higher order modes on the microstrip lines. The theoretical results are compared with measurements, and theory and experiment are found to correspond closely.

Analysis of 3-D metallization structures by a full-wave spectral-domain technique

A full-wave method for the investigation of microstrip and coplanar structures including 3-D metallization structures is presented. The spectral-domain analysis method is used to calculate the S-parameters of unshielded microwave components containing bond-wires and air-bridges. The general formulation and the implementation procedure of the method are described. The application of the theory is given by a comparison of measured and calculated results for a spiral inductor, including an air-bridge. >

A rigorous dispersive characterization of microstrip cross and T junctions

A full-wave spectral-domain analysis is applied to the characterization of multiport microstrip discontinuities. This approach uses the moment method to find the currents in the microstrip circuits and, subsequently, the scattering parameters of the junctions. In this approach, all the physical effects are considered, including radiation and surface waves. The numerical results for a tee and a cross junction are presented and agree well with the quasi-static values at low frequencies. The S-parameters of a tee junction are further compared with the measured results with excellent agreement. The utilization of a shaped T-junction as a broadband equal-power divider is also discussed. >

General design equations, small-sized impedance transformers, and their application to small-sized three-port 3-dB power dividers

In this paper, design equations for three-port power dividers have been derived. These design equations are available for both arbitrary power divisions and arbitrary termination impedances, and many sets of design equations are possible. Therefore, the design equations may be called general design equations and an arbitrary design impedance A is introduced to describe them. On the basis of the derived general design equations, a coplanar three-port power divider with a power split ratio (3 dB) terminated by 50, 60, and 70 /spl Omega/ is designed with A=33.33 /spl Omega/, so that a commercially available resistor 100 /spl Omega/ can be used for the isolation resistance. Additionally, to reduce the size of transmission-line impedance transformers, two types of small-sized impedance transformers are designed, named a constant VSWR-type transmission-line impedance transformer (CVT) and a constant conductance-type transmission-line impedance transformer (CCT) and compared with conventional reduced-sized impedance transformers. These impedance transformers are designed in the low-Q region on the Smith chart. Therefore, they show wide-band properties. To make sure that the derived design equations of CVTs and CCTs are reasonable, four 1;6:1 impedance transformers, CVT 20/spl deg/, CVT 30/spl deg/, CCT 15/spl deg/, and CCT 20/spl deg/ have been fabricated in microstrip technology and measured. The measured results show the expected tendency. Based on the CVTs and CCTs, small-sized three-port 3-dB power dividers are constructed and named a constant VSWR-type three-port 3-dB power divider (CVT3PD) and a constant conductance-type three-port 3-dB power divider (CCT3PD). For the CVT3PD and CCT3PD, perfect isolation conditions are derived, and it is shown that the perfect isolation circuit (I.C) must be composed of resistance combined with capacitance or inductance in the case that the length of transmission lines is not /spl lambda//4. These I.Cs are quite different from conventional ones composed of only resistance. Finally, on the basis of the derived perfect isolation impedance, CVT3PD and CCT3PD are designed and simulated, giving the possibility that a CCT3PD can be realized with the electrical length 15.30/spl deg/ of the transmission lines.

The Skin-Effect at High Frequencies

During the last years, monolithic integrated circuits have been used more and more in microwave techniques. As a result, the metallization thickness of the planar circuits became of the order of the skin depth even at very high frequencies, so that the approximate methods for loss calculations used until recently must be revised. In this paper, a variational formulation of the skin-effect problem for calculating the losses as well as the inner inductances of components in such circuits will be described, and the first numerical results of the method will be discussed.

A new miniature magnetic field probe for measuring three-dimensional fields in planar high-frequency circuits

A new noncontacting miniature magnetic field probe for measuring the surface current distribution on high-frequency planar circuits in x-, y-, z-directions in the 1-20 GHz band has been designed, fabricated and tested. The field probes have very small dimensions and do not need any connection to the operating circuit under test, therefore there is almost no perturbation of the circuit properties. This simple and practical magnetic field probes can be used to assist the design of microwave circuits, antenna diagnostics and to test products in industry. This paper describes the production procedure of the magnetic field probes, a scanning diagnostic system, measurement examples and comparisons between measurements and calculations. The measurement results agree very well with theoretically expected field distributions.

Miniature electric near-field probes for measuring 3-D fields in planar microwave circuits

Three-dimensional (3-D) electric near-field probes applicable to the 0.05-20-GHz band have been developed, which can measure both the magnitude and the phase of the microwave field inside radio-frequency (RF) and microwave circuits. The field probes have very small dimensions and do not need to be connected to the operating device-under-test (DUT), therefore, the circuit properties are nearly not disturbed by the probe, Investigations on different circuits (e.g., antenna, meander lines, filters, and power amplifiers) show that such near-field probes can be applied not only to simple passive circuits, but also to measure the fields inside complex active circuits. These simple, stable, and cheap field probes are very useful for assisting the design of microwave circuits, antenna diagnostics, and testing products in industry.