Measurements of all complex permeability tensor components and theeffective line widths of microwave ferrites using dielectric ringresonators

A method of measuring all the complex permeability tensor components of microwave ferrites using a single cylindrical ferrite sample is described. Two dielectric ring resonators having the same height and internal diameter but different external diameters, operating on HE₁₁₁^± and H₀₁₁ modes respectively, are applied for these measurements. Permeability tensor components are computed from the measured resonant frequencies and Q factors of these resonators with and without the ferrite sample. Computations are based on the exact eigenvalue equations for these modes. Measurements of all permeability tensor components versus static magnetic field intensity, performed for different ferrite materials, generally confirm results obtained by earlier researchers, but they also contain certain aspects concerning relations between particular permeability tensor components below saturation     

Field theoretical treatment of E-plane waveguide junctionswith anisotropic medium

E-plane waveguide junctions containing an anisotropic medium are analyzed. The analysis is based on the equivalence principle and on cavity field expansions. Using the equivalence principle, magnetic surface currents are introduced at the imaginary boundaries chosen between the central region of the junction and the waveguides. The electric displacement D in the junction is expressed in terms of a solenoidal set and an irrotational set. Matching the tangential magnetic field at the imaginary boundaries leads to a matrix equation, the unknown of which are the amplitudes of the scattered waveguide modes. Using this method, the performance of E-plane waveguide junctions with full-height and partial-height ferrite post is analyzed. The influence of the completeness terms G_oq on the numerical results of an empty E-plane Y-junction is shown. The numerical results are compared with previously published experimental and theoretical results     

Field theoretical treatment of H-plane waveguide junctionswith anisotropic medium

A method based on the equivalence principle and cavity field expansions is used to analyze an H-plane waveguide junction containing an anisotropic (ferrite or composite ferrite) post. Using the equivalence principle, magnetic surface currents are introduced at the imaginary boundaries chosen between the central region of the junction and the waveguides. The electric displacement in the junction can be completely expressed in terms of a solenoidal set. On the other hand, the magnetic induction in the junction must be expressed in terms of a solenoidal set and an irrotational set. Continuing the tangential magnetic field at the imaginary boundaries leads to a matrix equation, the unknowns of which are the amplitudes of the scattered waveguide modes. Using this method, H-plane waveguide junctions with ferrite and composite ferrite posts are considered. The numerical results show excellent agreement with previously published experimental and theoretical results     

Modeling ferrimagnetic resonators

The impedance matrix for an arbitrary n-port ferrimagnetic resonator is derived by applying Poynting's theorem to a region of space surrounding the resonator. Simplifications to the impedance matrix for low-loss (Q>≈100) ferrite material make it possible to obtain an equivalent circuit model for the resonator, which can be used with most computer-based circuit simulation programs. The circuit model for the general-case polymodal ferrimagnetic resonator consists of a network of single-pole resonators, each of which has a possible non-frequency-dependent, nonreciprocal phase shift. The components of the circuit model are described in terms of the properties of the ferrite material, and the coupling strength of the microwave circuit to the magnetostatic modes of the ferrimagnet. The method is demonstrated in three simple examples, including a one- and two-port loop coupled filter, and a ferrimagnet in a waveguide     

Tunable microwave and millimeter-wave band-pass filters

The authors present an overview of tunable microwave and millimeter-wave bandpass filters realized in different technologies. Some general design principles are described. Recent progress in the performance of various tunable filters is reported. The authors survey magnetically tunable filters (ferrimagnetic resonance filters, magnetostatic-wave filters, evanescent waveguide filters, E-plane printed circuit filters), electronically tunable filters, and mechanically tunable filters. The typical performance parameters are summarized. This comparison shown that none of these devices can simultaneously satisfy all requirements for perfect tunable filters. For microwave systems where multioctave tuning is essential, a YIG filter is an obvious choice. In systems where the requirement of high power handling capability combined with low insertion loss, predominates, mechanically tunable filters and magnetically tunable E-plane filters are recommended. If the tuning speed is a crucial requirement, varactor-tuned filters or E-plane filters with ferrite toroids are devices of choice. For millimeter-wave design, the most promising structures are ferrimagnetic resonance filters utilizing hexagonal ferrite resonators or, up to 60 GHz, magnetically tunable E-plane printed circuit filters     

A variational analysis of anisotropic, inhomogeneous dielectricwaveguides

The authors derive a variational formulation for anisotropic, dielectric waveguides using only the (E_x, E _y) or (H_x, H_y) components of the electromagnetic field. They show that the (E _x, E_y) formulation is completely equivalent to the (H_x, H_y) formulation. In fact, they are the transpose problems of each other. Given the variational formulation, one can derive the finite-element solution quite easily. The authors also show how to derive a variational expression where the natural boundary conditions are incorporated as an optimal solution of the variational expression. The theory is illustrated with a simple implementation of a finite-element solution. The solutions agree with previous results, and there is no occurrence of spurious modes     

Magnetic tuning of cylindrical H01δ-modedielectric resonators

The theory of magnetic tuning of cylindrical H_01δ dielectric resonators is developed. It is based on rigorous solutions to the dielectric resonator systems containing microwave ferrites. It is shown that the most effective magnetic tuning of H_01δ dielectric resonators can be accomplished by inserting a thin ferrite rod through an axial hole in the resonator. This kind of tuning utilizes the dependence of the parallel permeability tensor component μ_z on the magnetic field applied. Experiments have been performed which show that a 4% tuning range can be attained with a Q-factor of the resonant system of the order of 2000 at X -band. Using an appropriate DC magnetic field circuit, a 120 MHz tuning bandwidth has been obtained with a consumption of tuning power of about 75 mW     

Ferromagnetic tridisk-coupled resonator and magnetically tunablestripline Y circulator

A ferromagnetic tri-disk-coupled (TDC) resonator is constructed by placing three YIG ferrite disks mutually attached on the circular center conductor. The EM fields in one of the disks is described in terms of expanded circular harmonics with an approximated transformation of derivative, and the EM fields in a TDC resonator is synthesized from the respective constituent fields of the disks, by sum-transformation, regarding three eigenjunctures of the TEC resonator. The synthesized fields include coefficients A, B, and D, which are described as functions of the radis ratio r₀ /r and azimuthal angle φ. The special case in which A=D=0 is treated. Two conditional equations of perfect Y circulation are calculated. Magnetically tunable operation is theoretically analyzed using the conditional curves, and the magnetically tunable operation is examined experimentally with theoretical analysis     

Optimal `series-parallel' networks of 3-state devices

A 3-state component is one which can fall in two different modes: an open mode and a shorted mode. Systems built from such components can also experience either of these two failure modes. For a given number of s-identical s-independent components, a pure `series' or pure `parallel' configuration would be most reliable if only one of the two failure modes were possible. This paper treats the problem of designing the most reliable configuration of a given number of s-identical components that can experience both failure modes. Two simple algorithms for designing an optimal configuration are presented, and by analysis of 6, 8, and 20-component systems they illustrate the extent to which other configurations can be more reliable than `series-parallel' or `parallel-series' arrays     

Analysis of N×N passive optical starcoupler based on the normal modes of N input waveguides

An integrated passive N×N optical star coupler on silicon wafer is described. Antiresonant reflecting optical waveguides (ARROWs) are analyzed and utilized as the input and output waveguides of the N×N coupler. Combining the exact solutions of the slab ARROW waveguide with the effective index method, a 5×5 coupler is analyzed. In the slab waveguide analysis, the input waveguides are coupled to their neighbors. The interaction of the waveguides is described in terms of the normal modes of propagation. The resultant field distribution is then diffracted into the free space region which separates the input and output sections. The radiation illuminates the receiving aperture from which the receiving N waveguides branch out, each output element obtaining equal power levels. Different types of loss such as spillover loss and mismatch loss were analyzed and estimated for N=5. A 5×5 star coupler with a transmission efficiency of 56% at a wavelength of 1.3 μm is achievable     

Millimeter-wave three-port finline circulator using distributedcoupling effect

The design and experimental results for a novel three-port finline circulator are presented for the frequency range 26-40 GHz. The circulator consists of a T^E-junction cascaded with the section of ferrite coupled slot finlines magnetized in the propagation direction. The T^E-junction structure refers to a transition from a unilateral single slot finline taper to a coplanar line region via a tapered center conductor. The design procedure for the structure is described and confirmed by experimental results. The proposed structure belongs to the family of the distributed coupled ferrite line nonreciprocal devices suitable for application in the millimeter-wave range     

Recursive solution technique in a multi-server bi-level queueingsystem with server breakdowns

The authors present a multiserver, first-come first-served queuing system that alternates between two modes of system operation. In one mode, all s servers are available, and in the other mode, only s-1 servers are available for serving the customers. This is due to breakdown of one of the servers. The random variables representing the system with s servers and s-1 servers have exponential distributions. In such a system, the steady-state birth/death equations are coupled because of the two modes of operation. A recursive solution is presented for computing the steady-state probabilities of such a system. Once these probabilities are known, the performance measures of interest can be easily obtained. Two practical examples validate the results and show the utility of this method. A distinct advantage of the recursive technique is that it is much faster and requires much less memory than the existing nonrecursive techniques. In a bilevel situation, the system performance measures are always bounded by two independent queuing systems with s and s-1 servers. A procedure has been outlined for extension to multiple modes of system operation     

Mode orthogonality in chirowaveguides

The orthogonality relations for modes supported by a general cylindrical chirowaveguide are derived. These waveguiding structures are cylindrical waveguides containing chiral materials. It is pointed out that one of these relations is valid for lossless waveguides, whereas the other holds for the lossy as well as the lossless case. It is demonstrated that the orthogonality relations can be used to express an arbitrary electric or magnetic field within a chirowaveguide in terms of the mode functions. As in conventional waveguides, the orthogonality relations reported can be used to expand an arbitrary E or H field within a chirowaveguide in terms of a complete set of mutually orthogonal modes in the waveguide     

Optimal design of parallel-series systems with competing failuremodes

The problem of achieving optimal subsystem size for parallel-series systems, assuming that components and systems are subject to two types of failure modes, open and short, is addressed. Components are statistically independent and identically distributed; the costs of the two modes of system failures need not be the same. The number of subsystems (m), for a given number of components in each subsystem (n), is optimized so that: the mean system profit is maximized showing how m depends on system parameters and showing that there does not exist a pair (m,n) maximizing the mean system-profit, and the mean system cost is minimized. The results are illustrated by several numerical examples     

Focused codes for channels with skewed errors

Consider a channel with inputs and outputs in the field F _q(q>2). It is said that the channel is skewed on a set B⊂F_q* if the additive noise generated by the channel is likely to lie in B, i.e. B is a set of common errors. The concern is the construction of focused codes that are appropriate for such channels. It is said that a code is (t₁,t₂)-focused on B if it can correct up to t₁+t₂ errors provided at most t₁ of those errors lie outside of B; the strategy is to offer different levels of protection against common and uncommon errors and so provide novel tradeoffs between performance and rate. Techniques for constructing focused codes and bounds on their rates are described     

Short-channel pMOSTs in a high-resistivity silicon substrate. II.Noise performance

For pt.I, see ibid., vol.39, no.10, p.2268-77 (1992). The noise performance, important for the use of p-channel transistors on high-resistivity silicon in analog applications, is investigated. This is done for the two operation modes: bulk (|V_gs|<|V_T|) and surface (| V_gs|>|V_T|). For the studied transistors, both modes are characterized by a 1/f noise spectrum extending to frequencies of up to ≈100 Hz, and followed by a white-noise spectrum, determined by the substrate resistance     

Diffusion and noise in GaAs material and devices

The variation of the diffusion coefficient D(E) versus the electric field strength E is determined at 300 K in n-type GaAs (N_D=3×10^-17 cm^-3 ), using pulsed high-frequency noise measurements. D(E) is found to increase slightly at low field, then to decrease down to one tenth of its ohmic value near the threshold field. Long (⩾4 μm) real n⁺-n-n⁺ Gunn diodes, with an arbitrary doping profile, can be modeled. Comparisons are made, and excellent agreement is found, between experimental and theoretical characteristics of two real diodes, with notch and with gradual doping profiles. The doping profile N_D(x ) is shown to have a considerable influence on the diode behavior, in regard to the electric field profile as well as the noise characteristics. Using the impedance field method, the noise current is modeled and found to by very sensitive in the D(E) variation law, in particular in the range of 2.5-4 kV/cm. The agreement between the experimental noise and the computed noise of real diodes is quite satisfactory when using the D(E) determined     

A unified theory of thin material wires [EM scattering]

The author presents an integral equation and method of moments (MM) solution to the problem of scattering by a thin material wire of circular cross section. In general the material wire has permittivity and permeability different from those of free space. The wire of radius a must be sufficiently thin so that k₀a ≪1, where k₀ is the free space wavenumber. However, there is no restriction on |k|a, where k is the wavenumber in the material wire. The method is referred to as unified in that it applies to thin material wires of arbitrary complex permittivity and permeability. Thus, a single or unified formulation applies to a low-density dielectric/ferrite wire or to a highly conducting metallic wire     

Current gain collapse in microwave multifinger heterojunctionbipolar transistors operated at very high power densities

The rapid development of heterojunction bipolar transistor (HBT) technologies has led to the demonstration of high power single-chip microwave amplifiers. Because HBTs are operated at high power densities, the ultimate limits on the performance of HBTs are imposed by thermal considerations. The authors address a thermal phenomenon observed when a multifinger power HBT is operating at high power densities. This phenomenon, referred to as the collapse (of current gain), occurs when suddenly one finger of the HBT draws most of the collector current, leading to an abrupt decrease of current gain. A quantitative model and the condition separating the normal operation region and the collapse are presented. Critical difference of the collapse in the constant l _b and constant V_be modes of operation is discussed for the common-emitter l-V characteristics. The collapse in the common-base l-V characteristics and its relationship with avalanche breakdown are also described. A solution to eliminate the collapse is experimentally verified