Robert G. Harrison

On physical aspects of the Jiles-Atherton hysteresis models

The physical assumptions underlying the static and dynamic Jiles-Atherton (JA) hysteresis models are critically analyzed. It is shown that the energy-balance method used in deriving these models is actually closer to a balance of coenergies, thereby depriving the resulting JA phenomenology of physical meaning. The non-physical basis of its dynamic extension is demonstrated by a sharp contrast between hysteresis loops predicted by the model and those measured for grain-oriented steel under conditions of controlled sinusoidal flux density at frequencies of 50, 100, and 200 Hz.

Nonsquarelaw behavior of diode detectors analyzed by the Ritz-Galerkin method

It is widely believed that diode detectors exhibit true square-law behavior at low power levels, and that at higher power levels there is a gradual change to a linear (peak-detecting) law. This paper demonstrates that this idea is correct only under restrictive conditions, and that slopes corresponding to eighth and higher-order laws can easily be encountered in practical situations. It is shown that these high-order slopes are inherent in conventional diode detector circuits and that the behavior can be predicted by a closed-form solution involving both exponential and modified Bessel functions. The nonlinear theory, which does not depend on a truncated power-series approximation to the diode I-V characteristic, is confirmed by measured data. >

Theory of regenerative frequency dividers using double-balanced mixers

Regenerative frequency halvers using double-balanced mixers are analyzed in terms of modified Bessel functions. Particular attention is given to a regenerative divide using a zero-memory double-balanced Schottky diode mixer. Closed-form solutions predict the threshold of turn on, the steady-state input-output amplitude relationship, and the operational bandwidth. Experimental results are also presented.<<ETX>>

A physical model of spin ferromagnetism

This paper derives a mathematical model for the hysteresis characteristics of spin-ferromagnetic materials on a quantum-mechanical basis. For a given material, the model provides a link between the micromagnetic behavior at the atomic/domain levels and the details of the scalar hysteresis loop at the macroscopic level. Physical input parameters of the model consist of the Curie temperature, the sample temperature, the saturation magnetization, and the intrinsic coercivity. The parameters of the mathematical model are the reduced temperature t, the Weiss coefficient /spl alpha/, a new quantity called the domain coefficient /spl beta/, and a single pinning coefficient /spl gamma/ that defines the anhysteretic magnetization. Quantitative agreement with the measured hysteresis data of a wide range of materials, including temperature dependence, is good. The model is valid for materials with intrinsic coercivities ranging over 6 orders of magnitude.

A compact and selective low-pass filter with reduced spurious responses, based on CPW tapered periodic structures

This paper describes a new low-pass filter topology based on tapered periodic structures. These filters exhibit interesting characteristics in terms of compactness, return loss, insertion loss, selectivity, and the suppression of spurious frequency bands. Hybrid prototypes with a 1-GHz cutoff frequency, based on a coplanar-waveguide technology, and using both low-cost and high-performance substrates, have been fabricated and measured. Spurious frequency bands can be suppressed to below -22 dB at frequencies up to 20 GHz. Passband ripples are negligible, and the return loss is better than 20 dB. A two-section filter has a length of 0.2 lambda and exhibits a -120-dB/dec selectivity, while a six-section filter is 0.51 lambda long and has a -560-dB/dec selectivity. A design procedure has been established. These filters are compatible with monolithic microwave integrated circuit technologies in which the capacitors can be realized as metal-insulator-metal structures

Comparison of fully distributed and periodically loaded nonlinear transmission lines

Two different approaches to realizing nonlinear transmission lines (NLTLs) are investigated in detail. In the first approach, the nonlinearity is continuously distributed along the line; in the second, the line is periodically loaded (PL) with discrete nonlinear elements. Measured heterostructure-barrier varactor (HBV) characteristics are used as the nonlinearities in both pulse-compression and harmonic-generation (20-60-GHz tripler) simulations. We point out that the choice of simulation step size is critical in the case of fully distributed (FD) NLTLs, and should be made sufficiently small that no numerical Bragg cutoff frequency appears. For the frequency tripler considered in this paper, simulations show that with PL (PL) NLTLs, 21% efficiency at 210-mW output power and 30% bandwidth can be obtained, whereas only 4.8% efficiency is possible using FD NLTLs. For pulse compression, we find that when properly matched, the FD NLTLs can deliver pulses that are five times sharper than can be obtained with the PL NLTLs. Measured results for an HBV-based PL NLTL frequency multiplier are reported that agree with our simulations, in particular, the 30% bandwidth. The confirmation of the role of the Bragg cutoff frequency in preventing the generation and propagation of undesired harmonics (this improving the conversion efficiency) is obtained from experimental results carried out from hybrid Schottky diodes NLTL measurements.

Broadband Frequency Dividers Using Microwave Varactors

A novel configuration using GaAs varactors in a balanced circuit incorporating both coplanar waveguide and microstrip elements has permitted the construction of frequency dividers which have near-octave divide-by-two bandwidth and excellent response to pulsed r.f. inputs. The design and performance of such a frequency divider for inputs in the 4 to 8 GHz range is discussed.

Hybrid narrow-band tunable bandpass filter based on varactor loaded electromagnetic-bandgap coplanar waveguides

A varactor-loaded resonator inserted between two Bragg reflectors has been implemented to design high-selectivity tunable bandpass filters. First, a mechanical tuning method is demonstrated. A varactor tunable bandpass filter is then implemented at 9 GHz, yielding good agreement between computational and experimental results. The tuning range reaches 3.5% with a loaded quality factor Q/sub L/=40, a maximum insertion loss of 4.75 dB, and a return loss exceeding 20 dB. The theory is carefully explained, showing the importance of the parameters of the Bragg reflectors and of the resonator, in particular, the effect of diode-case parasitics and varactor position with respect to the resonator. A large-signal experimental analysis is done, showing a maximum allowable input power of a few dBm. Finally, possible filter improvements are discussed, and simulations with a microelectromechanical systems varactor are shown.

A fully distributed heterostructure-barrier varactor nonlinear transmission-line frequency multiplier and pulse sharpener

The discrete symmetric heterostructure-barrier varactor (HBV) was previously developed as an unbiased frequency-tripling device that needed no second-harmonic idler circuit. Other work investigated nonlinear transmission lines (NLTLs) employing discrete varactors attached to linear guiding structures. Fully distributed Schottky-varactor NLTLs were excessively lossy. This paper explores NLTLs based on fully distributed HBV structures. Using both a modified finite-difference time-domain method and numerical integration, it is shown that such NLTLs can provide efficient tripling over a wider input bandwidth than is possible with fixed-tuned triplers. It is also demonstrated that the nonlinearity is strong enough for the NLTL to act as a pulse-sharpening device.

Physical Theory of Ferromagnetic First-Order Return Curves

Based on quantum mechanics and classical physics, a general analytical theory of ferromagnetic first order return curves is developed. No empirical assumptions or approximations are required.