Sheng Cheng

A deterministic approach for designing conditionally stable amplifiers

Microwave devices with the Rollet parameter (k) less than one can always be made stable by resistive loading. In cases where noise figure or output power is at a premium, the performance of an amplifier can often be enhanced by using a design where k is less than unity thereby avoiding resistive loading. While a simultaneous conjugate match is impossible for such conditionally stable designs, single-sided matching can be achieved. Low-noise and power designs are examples where single-sided matching considerations naturally occur. With single-sided matching and 0 >

MESSENGER mission: first electronically steered antenna for deep space communications

The MESSENGER mission to orbit the planet Mercury poses significant design challenges for its deep space communication system. These challenges include a wide pointing range, tight packaging, and a high temperature environment. To meet these challenges, the spacecraft incorporates the first steerable phased array antenna flown for deep space communications. The invention of a method for achieving circular polarization in a high-temperature (+300/spl deg/C) environment has doubled the science return of the mission relative to its initially proposed implementation. Cross-strapping between the phased array antennas and solid state power amplifiers (SSPAs) enables both amplifiers to be turned on when sufficient power is available, enhancing the scientific return at the planet. A science return of 25 Gbits/year is achieved using only one SSPA in Mercury orbit. The science return increases to 100 Gbits/year if both SSPAs are used in the orbital phase.

Phased-array antenna system for the MESSENGER deep space mission

MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) is the latest NASA Discovery mission managed by The Johns Hopkins University Applied Physics Laboratory. MESSENGER is a mission to orbit the least explored terrestrial planet, Mercury. MESSENGERs high-data-rate downlink will use the first electronically scanned phased-array antenna for a deep-space telecommunication application. Measured results for the lightweight phased-array antenna and the high-efficiency solid state power amplifiers (SSPAs) are presented. Two functional amplifiers within the X-band SSPAs provide output power that is scalable from 11 to 15 watts without major design changes. Five different hybrid microcircuits, including high-efficiency HFET amplifiers and MMIC phase shifters have been developed for use within the SSPAs. A highly efficient packaging approach enables the integration of a large number of hybrid circuits into a SSPA with a mass less than 450 g. The hybrids and the hermetic package are generic and are suitable for a wide range of space applications beyond the MESSENGER program.

TEM equivalent circuits for quasi-TEM couplers

Equivalent circuits for quasi-TEM (transverse electromagnetic) coupled lines have been developed for symmetric lines (C/sub 1/=C/sub 2/) and for asymmetric lines having a congruent LC matrix. It is shown that the congruence assumption is very general. The error is insignificant provided the line width is narrower than the substrate thickness, a condition generally met in practical circuits. These equivalent circuits are easy to implement using a computer-aided engineering (CAE) system such as TOUCHSTONE, which accepts and correctly calculates ideal transmission line performance even for negative characteristic impedances.<<ETX>>

Comments on "A deterministic approach for designing conditionally stable amplifiers"

For original paper see M.L. Edwards et al., ibid., vol.43, no.7, pp.1567-75 (July 1995). In the above paper, the authors presented a careful analysis of single-sided matched conditionally stable amplifiers. In particular, they determined a maximum single-sided matched gain G/sub msm/ which is reached for passive jointly stable source (load) terminations G/sub msm/=2 kG/sub ms/ where k is the Rolletts stability factor and G/sub ms/=|S/sub 21//S/sub 12/| is the maximum stable gain of device. However, at least some of the results presented in the above paper can be found in other literature. In this paper, I would like to outline the formerly published papers treating conditionally stable amplifiers in terms of the scattering parameters. A reply by the original authors is included.

A low cost amplifier design technique for wireless applications

Conditionally stable amplifiers can be an attractive design option for wireless applications where the potential for enhanced gain can translate into reduced cost of RF parts. Such an approach is illustrated for a 2.4 GHz wireless local area network (WLAN) application where device cost is reduced an order of magnitude.

Advances in Microwave Technology for the MESSENGER Mission to Mercury

The MESSENGER spacecraft, designed to orbit the planet Mercury, uses the first electronically scanned phased-array antenna for a deep-space telecommunication application. Two lightweight phased arrays, mounted on opposite sides of the spacecraft, provide the high-gain downlink coverage. Medium-gain antennas are used for uplink and downlink during cruise phase. The invention of a method for achieving circular polarization in a high-temperature (+300degC) environment has doubled the science return of the mission relative to the inherent linear polarization from a slotted waveguide array. Monolithic microwave integrated circuits and discrete heterostructure field effect transistors are integrated to provide the high-efficiency X-band solid-state power amplifier.

Conditionally stable amplifier design using constant /spl mu/-contours

Conditionally stable amplifiers can be an attractive design option for commercial applications where increased gain can be achieved by accepting a measured risk of instability. A procedure is presented for designing amplifier input and output matching networks which permits an a-priori, quantitative trade-off between gain and the stability parameter, /spl mu/.