James J. Rosenberg

A 100-element HBT grid amplifier

A 100-element 10-GHz grid amplifier has been developed. The active devices in the grid are chips with heterojunction-bipolar-transistor (HBT) differential pairs. The metal grid pattern was empirically designed to provide effective coupling between the HBTs and free space. Two independent measurements, one with focusing lenses and the other without, were used to characterize the grid. In each case, the peak gain was 10 dB at 10 GHz with a 3-dB bandwidth of 1 GHz. The input and output return losses were better than 15 dB at 10 GHz. The maximum output power was 450 mW, and the minimum noise figure was 7 dB. By varying the bias, a signal could be amplitude modulated with a modulation index as large as 0.65. Tests show that the grid was quite tolerant of failures-the output power dropped by only 1 dB when 10% of the inputs were detuned. The grid amplifier is a multimode device that amplifies beams of different shapes and angles. Beams with incidence angles up to 30 degrees were amplified with less than a 3-dB drop in gain. >

Modeling and performance of a 100-element pHEMT grid amplifier

A 100-element hybrid grid amplifier has been fabricated, The active devices in the grid are custom-made pseudomorphic high electron mobility transistor (pHEMT) differential-pair chips. We present a model for gain analysis and compare measurements with theory. The grid includes stabilizing resistors in the gate. Measurements show the grid has a peak gain of 10 db when tuned for 10 GHz and a gain of 12 dB when tuned for 9 GHz. The maximum 3-dB bandwidth is 15% at 9 GHz. The minimum noise figure is 3 dB. The maximum saturated output power is 3.7 W, with a peak power-added efficiency of 12%. These results area significant improvement over previous grid amplifiers based on heterojunction bipolar transistors (HBTs).

Gain and stability models for HBT grid amplifiers

A 16-element heterojunction bipolar transistor (HBT) grid amplifier has been fabricated with a peak gain of 11 dB at 9.9 GHz with a 3-dB bandwidth of 350 MHz. We report a gain analysis model for the grid and give a comparison of the measurement and theory. The measured patterns show the evidence of a common-mode oscillation. A stability model for the common-mode oscillation is developed. Based on the stability model, a lumped capacitor gives suitable phase shift of the circular function, thus stabilizing the grid. A second 18-element grid was fabricated, using this theory, with improved stability.

A 16-element tunnel diode grid oscillator

A 16-channel tunnel diode grid oscillator has been fabricated. The grid oscillates at 1.86 GHz with an effective radiated power (ERP) of 1.3 mW. Frequency components were observed at multiples of one-third of the main frequency, but at power levels at least 16 dB lower. The average single-sideband (SSB) noise level was measured to be -76 dBc/Hz at an offset of 100 kHz from the carrier.

A single chip two-stage W-band grid amplifier

The first monolithic grid amplifier using a cascade differential-pair amplifier unit cell has been designed and measured. The grid is packaged using reflection architecture with waveguide input and output. The measured gain at 82 GHz is 5.5 dB. The measured output power is 110 mW with 2.5 dB residual gain. The size of the amplifier module is 20 mm/spl times/10 mm/spl times/10 mm.

A 1 watt, 38 GHz monolithic grid oscillator

We have demonstrated a monolithic grid oscillator that shows 1 watt of effective transmitter power at 38 GHz. Use of a wire twist reflector as an external feedback element added to a successful monolithic grid amplifier allows a tuning range from 37.5 GHz to 41 GHz. Impedance matching is accomplished by a double-slug tuner and the movable back-short of the twist reflector.

A 100-element MODFET grid amplifier

A 100-element quasi-optical amplifier is presented. The active devices are custom-fabricated modulation-doped field-effect transistors (MODFETs). Common-mode oscillations were suppressed using resistors in the input gate leads. The grid has 9 dB of gain at 10.1 GHz. The 3-dB bandwidth is 1.2 GHz. We present a model for the gain of the grid versus frequency and compare measurement with theory.

Efficient spatially combined amplifiers for compact Ku-band satellite communication terminals

Spatially combined amplifiers offer advantages in size and efficiency that are unmatched using traditional solid-state combining approaches. We present measured data from a spatially combined Ku-band deck amplifiertrade for use in the 13.75-14.5 GHz satellite uplink band. This amplifier module generates over 45 dBm (31.6 W) of saturated power by spatially combining the outputs of six commercial MMICs with nearly ideal combining efficiency. The power amplifier module occupies less than 12 cubic inches and draws 165 W DC power while delivering 25 W output. We present linearity and spectral regrowth data for this module and demonstrate the flexibility of the deck amplifier architecture with data for a range of module output powers. The high efficiency of these deck amplifier modules enables creation of very compact, lightweight SSPAs and block upconverters capable of being mounted directly on the feed for small aperture satcom applications such as on-the-move and flyaway

Ka-Band Quasi-Optical Measurements Using Focused Gaussian Beams

This paper describes the use of focused Gaussian beams in making quasi-optical measurements at Ka-band. Measurement results for a known standard are presented to validate the measurement technique. Measurement are presented both for the case in which the beam waist is smaller than the quasi-optical array under test and in which the beam waist is slightly larger than the array. The measurements are compared with simulations of infinite arrays illuminated by plane waves. Good agreement can be found between measurement and simulation, provided appropriate calibrations are performed and certain precautions observed. This paper describes a newly developed calibration technique that can be applied when the size of the array under test is comparable to or slightly smaller than the beam waist.

Stimulating appropriate uses of simulation in design

This article addresses the issue of educating undergraduate engineering students in the appropriate use of computer simulation in the design process. The premise that poorly designed assignments involving simulation can actually impair understanding is addressed. A set of goals for simulation-based exercises is suggested, and some tactics for meeting these goals are introduced. Finally, a specific example of a half-term assignment that is used to meet these goals is provided for illustration.