Tod A. Boyd

Theoretical and Experimental Study of a New Class of Reflectionless Filter

A design methodology and equations are described for lumped-element filter prototypes having low-pass, high-pass, bandpass, or bandstop characteristics with theoretically perfect input- and output-match at all frequencies. Such filters are a useful building block in a wide variety of systems in which the highly reactive out-of-band termination presented by a conventional filter is undesirable. The filter topology is first derived from basic principles. The relative merits of several implementations and tunings are then compared via simulation. Finally, measured data on low-pass and bandpass filter examples are presented, which illustrate the practical advantages, as well as showing excellent agreement between measurement and theory.

A millimeter-wave diode-MMIC chipset for local oscillator generation in the ALMA telescope

A set of MMIC frequency multipliers and balanced mixers have been designed for the local oscillator system of the Atacama large millimeter array (ALMA). These millimeter-wave elements form a critical link in the active multiplier chains between the relatively low frequency microwave oscillators and the very high frequency submillimeter-wave, cooled multipliers of the LO subsystem. A complete chipset for four frequency bands is described, along with preliminary results on prototypes for two additional bands.

Development of electronically tuned local oscillators for ALMA

We report on the local oscillator (LO) development for the ALMA 64-antenna sub-millimeter wave telescope array. Measurements of output power and AM noise are presented for four wideband electronically-tuned MMIC-based LOs up to 710 GHz.

Medium power amplifiers covering 90-130 GHz for the ALMA telescope local oscillators

This paper describes a set of power amplifier (PA) modules containing InP high electron mobility transistor (HEMT) monolithic millimeter-wave integrated circuit (MMIC) chips. The chips were designed and optimized for local oscillator sources in the 90-130 GHz band for the Atacama large millimeter array telescope. The modules feature 20-45 mW of output power, to date the highest power from solid state HEMT MMIC modules above 110 GHz.

Non-Reflective Transmission-Line Filters for Gain Slope Equalization

In this paper we present several topologies of simple non-reflective filters using transmission lines and resistive elements. These filters are well-matched at all frequencies, making them especially suitable for gain slope equalizers without the need for external attenuators or isolators. The application of these filters to a 2-4 GHz, plusmn15 dB selectable-slope equalizer for the expanded very large array is described with measured results that are in good agreement with theory.

Compact Orthomode Transducers Using Digital Polarization Synthesis

In this paper we present a novel class of compact orthomode transducers which use digital calibration to synthesize the desired polarization vectors while maintaining high isolation and minimizing mass and volume. These digital orthomode transducers consist of an arbitrary number of planar probes in a circular waveguide, each of which is connected to an independent receiver chain designed for stability of complex gain. The outputs of each receiver chain are then digitized and combined numerically with calibrated, complex coefficients. Measurements on two prototype digital orthomode transducers, one with three probes and one with four, show better than 50 dB polarization isolation over a 10°C temperature range with a single calibration.

Reflectionless Filter Structures

This paper expands on the previously described reflectionless filters-i.e., filters having, in principle, identically zero reflection coefficient at all frequencies-by introducing a wide variety of new reflectionless structures that were not part of the original publication. In addition to extending the lumped-element derivation to include transmission line filters, this is achieved by the introduction of a novel method wherein the left- and right-hand-side stopband terminations are coupled to each other using a two-port sub-network. Specific examples of the sub-network are given, which increase the stopband attenuation per filter cell and steepen the cutoff response without disrupting the reflectionless property or increasing the insertion loss in the passband. It is noteworthy that a common feature of all the structures derived by these methods is that most, if not all, of the reactive elements are of equal normalized value. This greatly simplifies the tuning requirements, and has facilitated their implementation as monolithic microwave integrated circuits (MMICs). A number of examples of MMIC reflectionless filters constructed in this way are presented and their results compared to the theory.

A 10–100-GHz Double-Ridged Horn Antenna and Coax Launcher

The design, fabrication, and measurement of a coax to double-ridged waveguide launcher and horn antenna is presented. The novel launcher design employs two symmetric field probes across the ridge gap to minimize spreading inductance in the transition, and achieves better than 15 dB return loss over a 10:1 bandwidth. The aperture-matched horn uses a half-cosine transition into a linear taper for the outer waveguide dimensions and ridge width, and a power-law scaled gap to realize monotonically varying cutoff frequencies, thus avoiding the appearance of trapped mode resonances. It achieves a nearly constant beamwidth in both E- and H-planes for an overall directivity of about 16.5 dB from 10-100 GHz.

Performance of a Highly Sensitive, 19-element, Dual-polarization, Cryogenic L-band Phased-array Feed on the Green Bank Telescope

A new 1.4 GHz 19-element, dual-polarization, cryogenic phased array feed (PAF) radio astronomy receiver has been developed for the Robert C. Byrd Green Bank Telescope (GBT) as part of FLAG (Focal L-band Array for the GBT) project. Commissioning observations of calibrator radio sources show that this receiver has the lowest reported beamformed system temperature (

Compact cm-Wave and mm-Wave integrated receivers

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