L. Wilson Pearson

Attaining wide tuning range in quasi-optical voltage-controlled grid oscillators

Previous work in voltage-tuned quasi-optical grid oscillators is reviewed from the point of view of features in designs that limit the tuning range. Fundamentally, the designer is faced with a tradeoff between broad tuneability (low Q) and high power efficiency (high Q). The grid structure influences the Q of the resonator through both. intentional electromagnetic coupling through transmission lines and through inadvertent coupling through parasitic effects, which typically can be modeled as lumped circuit elements. For example, the broader bandwidth of bowtie antenna elements produces a lower-Q/more-broadly-tunable spatial structure than dipole antenna elements when employed as the radiators in a grid oscillator. However, the bowtie elements pose geometric constraints upon the placement of varactor elements so as to weaken their coupling to transistor elements. The lower Q weakens power production, as well. The geometrical constraints are obviated if one employs two-layer fabrication, but the manufacture of the oscillator is complicated when two different layers contain semiconductor devices. We report the performance of a quasi-optical voltage-controlled grid oscillator which integrates the varactor diodes with the MESFET grids on the same side of a Duroid substrate and which operates at a nominal frequency of 5 GHz. The total frequency tuning range of the VCGO reached 12% when the voltage applied to the varactor diodes changes from 0 to ¿20 V with the output power variation of 8 dB. The 3 dB power bandwidth is measured to be 8%.

Phase-locking of grid oscillators

In this paper, we report results of the first successful phase locking, to our knowledge, of a grid oscillator. A voltage controlled grid with a center frequency of 4.7 GHz and with 300 MHz electric tuning range was locked to a frequency synthesizer by way of a phase-locked loop (PLL). The loop was designed with 10 kHz bandwidth and employs three operational amplifiers. Phase noise was improved to match the specification of the synthesizer locking source.

An analysis of coupling between a whispering gallery mode laser in an elliptical microring and the dominant mode in the coaxially oriented elliptical optical fiber

The problem of coupling a whispering gallery mode laser into an optical fiber is considered. The whispering gallery mode laser is generated in a polymer microring formed coaxially on the optical fiber. The focus of this paper is to determine factors that influence the coupling between the laser and the fiber around which it is formed. The coupling mechanism is analyzed and it is found that when the microring and the fiber are of elliptical cross section, there exists controllable coupling between the laser and propagation mode in the fiber. The coupling between laser mode and fiber mode is due to characteristics of Mathieu functions that describe the fields in elliptical waveguides. It is shown that the coupling between the laser and the dominant mode in the fiber can be optimized by the designing the dimension of microring, the eccentricity of the elliptical cross section, and the material contrast between fiber and microring.

Oscillator Locking-Bandwidth Enhancement for Coupled-Oscillator Applications

Coupled-oscillator systems offer a means of phase generation for millimeter wavelength applications. Random phase error in coupled-oscillator systems is controllable by employing oscillator cells with a large (injection) locking bandwidth. Signal quality is maintained in the system through the quality of the externally injected signal that controls the overall coupled oscillator system. In this paper, a new scheme is described for enhancing the locking range of FET and MMIC-based oscillators. This scheme is based on Adlers theoretical result and can be analyzed through the open-loop characterization of an oscillator.

Direct current effects on 1/f noise in patterned Permalloy films

Detailed investigations of 1/f noise were performed in patterned Permalloy films. The gold bridges for the four probe measurement setup were deposited on a quartz substrate. Pattern geometry, bias current, and transverse magnetostatic field effects on the material’s 1/f noise were studied. The normalized Hooge parameter and frequency slope were analyzed in the framework of the empirical Hooge relation. Different dependences of the noise versus bias current generated Oersted field and the magnetostatic field were observed. The normalized Hooge parameter and frequency slope were pattern width and field configuration dependent.

Survey of error-tolerant coupled oscillator array design (1994–2007)

Beginning in 1994, we engaged substantial activity in coupled oscillator array (COA) systems directed specifically toward millimeter-wave applications. Much of our experimentation has been conducted at lower frequencies for simplicity and cost control, but the methods used have always focused on millimeter wave applications.

Array theory via a Fourier-transform operational calculus

The article presents a point of view for array-antenna analysis based on an operational calculus with two-dimensional Fourier transforms. The purpose is to describe the operational calculus, and to employ it in computing the array factor of a finite-extent phased array. Fourier-transform calculus is a very familiar subject to undergraduate electrical engineering students because of its central role in signal analysis, filter analysis and design, and in digital signal processing. The engineering control of the pattern through the parameters of the antenna configuration are particularly clear when the pattern is developed through a two-dimensional Fourier transform operational calculus.

Experimental study of planar finite grid oscillator arrays

Results of an experimental study on finite grid oscillator arrays and the effects of the edge element loading stubs in such arrays are presented. Three finite grid oscillator arrays, based on the same unit cell, with different number of unit were fabricated on RT/Duroid 5870 substrate and tested in terms of the oscillation frequencies, radiated power and radiation patterns. It is observed that the oscillation frequency of a finite grid array differs from the theoretically prediction based on the infinite array assumption and is strongly affected by the edge element loading stubs. The measurement also indicates that mode-jumping and multi-frequency (spurious) oscillation can exist in grid oscillator arrays.

Injection Locked Grid Oscillators

In this paper, we report results of the first successful injection phase locked grid oscillators. The grid oscillator, operate at 4.25 GHz with 150 MHz mechanical tuning range and 32 dBm effective isotropic radiated power, was locked to a frequency synthesizer by way of injection locking. Phase noise was improved to match the specification of the synthesizer reference source.

Frequency Tunable MESFET Active Patch Antenna/Oscillators

An integrated transistor-excited patch antenna/oscillator configuration that provides control of oscillation frequency and E-plane radiation pattern by way of an integral stub transmission line is presented. The configuration has been analyzed experimentally through six different models¿three involving changing patch widths and three involving changing stub length. The latter three are characterized for the case when the stub end is shorted directly to the adjacent patch surface with a capacitor. This modification changes both the oscillating frequency and the radiation pattern of the structure. It is observed that the stub supports both microstrip and coplanar waveguide modes¿a feature that potentially can be exploited because of the additional degree of freedom available.