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Multidiode broadband microwave signal modulators based on 4H-SiC p-i-n diodes were fabricated and fully characterized for the first time. The diodes used for the modulator fabrication exhibited a blocking voltage of 1100 V, a 100-mA differential resistance of 1-3 [ohm], a punch-through voltage (100 V) capacitance below 0.5 pF, and a carrier effective lifetime of 15 ns. The three-diode modulators are characterized by a transmission loss of 1-2 dB and isolation of 27-34 dB in the 2-7-GHz frequency range, while their switching speed is as low as 30 ns. Two-diode modulators were specially designed for high-temperature operation. These modulators are characterized by a transmission loss of 1.1-2.6 dB and isolation of 33-44.5 dB in the 2-7-GHz frequency range at temperatures up to 300[degrees] C. Index Terms--Insertion loss, isolation, microwave modulators, p-i-n diode, silicon carbide, switches.

The analysis and systematic design procedure for multiconductor coupled-line Marchand baluns are presented in this paper. A simple two-conductor coupled-line model is used to analyze the Marchand balun and simplify the analysis significantly. Two monolithic balanced frequency doublers with miniature Marchand baluns are implemented to verify the design procedure. Both the chips achieve the smallest chip sizes at their operating frequencies with comparable performance. Index Terms--Balun, diode, frequency doubler, Marchand balun, monolithic microwave integrated circuit (MMIC).

A new digital-to-analog converter (DAC) structure employing Schottky diode samplers has been developed for very high-speed operation. Instead of switching used for conventional DACs, sampling of a digital bit stream is employed to retrieve the analog signals based on sampling theory. The sampled signals are added using an R-2R resistive ladder network. The samplers are designed to provide impedance matching for reflected signals. The DAC was fabricated as a hybrid circuit, and it achieved 1 Gs/s. Due to its transmission-line architecture, our design is scalable for use at much higher frequencies, as well as higher resolutions. Index Terms--Digital-analog conversion, digtial-to-analog converter (DAC), sampler, Schottky diode.

The monolithic integration of tunneling diodes (TDs) with other semiconductor devices such as high electron-mobility transistors (HEMTs) or HBTs, creates novel quantum functional nonlinear devices and circuits with unique properties: the negative differential resistance and the extremely low dc power consumption. In this paper, we present a family of InP-HEMT-TD-based voltage-controlled oscillators operating in the 4-6-GHz band suitable for wireless applications, along with an effective analytical treatment of the stability issues. Prototypes having different circuit topologies of HEMT-TD devices have been designed and fabricated. The circuits generated an output power in the range of -11 to -18 dBm when operated at a bias current of 1.75 mA at 500 mV. Phase noise characteristics and tuning capability of the circuit configuration have been experimentally determined. The maximum tuning range of 150 MHz and the maximum single sideband-to-carrier ratio of -97 dBc/Hz at 200 kHz have been achieved. Index Terms--Microwave voltage-controlled oscillator (VC), monolithic microwave integrated circuit (IC), quantum-well device.

Solid-state devices have had a major impact on the development of microwave and millimeter-wave systems. Starting with development work dating back to the 1940s, a variety of two- and three-terminal device structures have been proposed, fabricated, and found their way into commercial and military applications. These devices have resulted in the realization of numerous systems that would not otherwise be possible. The device development effort has been closely linked to advances in semiconductor materials growth and processing technology. Many of the advanced device concepts can only be implemented with the advent of advanced materials growth technology, such as molecular-beam epitaxy, and fine-line lithography techniques, such as electron-beam lithography. Advanced materials technology has also provided the ability to fabricate heterostructures that permit the advantages of multiple material layers to be optimized for device applications. High-performance diodes and transistors are now available for use from UHF into the millimeter-wave spectrum, approaching terahertz frequencies. The development, operating principles, and state-of-the-art of various diode and transistor structures are reviewed. Index Terms--Active device, diode, electron beam, heterostructure, lithography, MBE, microwave, molecular-beam epitaxy, semiconductor, solid-state device, transistor.

A novel initiation scheme, utilizing the new pulsed IMPATT to generate millimeter-wave oscillations in a series-integrated quantum-well resonant tunneling diode (RTD), is proposed and theoretically investigated for the first time. To facilitate transient analysis, a generalized impedance is defined and adopted in this work. The detailed investigation of a two-RTD oscillator is carried out at 100 GHz. The maximum oscillator output power versus the minimum initial input power required of initiation is about 50%. The duration of only a few RF cycles is needed for such initiation.

The grooved mirror type Fabry-Perot (GFP) oscillator is used for coherent power-combining of multi-elements in millimeter and submillimeter wave region. The admittance of the Gunn diode in oscillation has been measured experimentally in the millimeter wave region for designing the GFP oscillator. The gain characteristics of the diode has been found at the frequencies from 42 to 48 GHz from the measured results. With this Gunn diode in the GFP resonator, the oscillation has been observed. These experimental results indicated that for impedance matching between the diode and the resonant cavity the groove height must be adjusted.

This paper describes the design and operation of a 60-GHz quasi-optical power combining array employing IMPATT diodes in a weakly coupled, hybrid, two by four arrangement. Frequency-locked operation of all eight elements has been achieved for CW operation with a total radiated power in excess of 2 W. Approximately 61 W of DC power was required to drive the array. Pulsed operation was investigated as a means of preventing overheating. In particular, the locking behavior of these pulsed arrays was characterized. The array was pulsed with a 2-microsecond rise time, low duty cycle, 4-kHz bias. Under these conditions, single frequency operation was observed throughout the duration of the pulse, including the turn-on period.

We report on the first demonstration of velocity-matched distributed photodetectors and balanced photodetectors with p-i-n photodetectors. Record-high linear dc photocurrent of 45 mA has been achieved without suffering from thermal damage, thanks to the superior power handling capability of p-i-n photodiodes. A novel fiber alignment technique has been developed to achieve high linear photocurrent. More than 37 dB of common-mode-rejection ratio and 45-dB suppression of laser relative intensity noise over a broad frequency range have been achieved using the distributed balanced photodetectors in an RF fiber-optic link. The frequency response is flat from 1 to 35 GHz. Index Terms--Analog fiber-optic links, balanced photodetectors, high power photodetector, microwave photonics, noise suppression, optical receivers, p-i-n photodetectors, RF photonics.