Ramesh K. Gupta

Miniaturized reverse modulation loop of a CQPSK 120 Mbit/s modem for spacecraft applications

The design and performance of a miniaturized reverse modulation loop (RML) for a 120 Mbit/s coherent quadrature phase shift keying (CQPSK) modem for onboard satellite applications are presented. Analysis of time delays within the RML circuit indicates that any differential time-delay errors can adversely affect the associated BER and should be minimized. The RML circuit, consisting of a modulator, demodulator, and comparator circuit, has been fabricated using quasi-monolithic techniques with dimensions of 1.65*4 cm. The relative phase for all four states of the modulator is in close agreement with design values of 90 degrees +or-1 degrees over a 200 MHz bandwidth at 3.95 GHz. The demodulator and comparator circuits of the RML have successfully recovered a 120 Mbit/s bit stream. The RML circuit is capable of recovering higher bit rates because of relatively uniform amplitude and phase performance over the 3.7- to 4.2 GHz communications satellite band. >

Intermodulation Distortion in Microwave MESFET Amplifiers

The third-order intermodulation distortion (IM/sub 3/) of a MESFET amplifier has been analysed using Volterra series representation. A model is described that takes into account the MESFET nonlinearities and their interaction with the surrounding microwave circuit. A theoretical and experimental study of the amplifier intermodulation products has been conducted. Their dependence on the input frequency and power-level of a two-tone test signal is investigated. For power inputs less than -10 dBm, the agreement obtained between measured and predicted IM/sub 3/ is within 3-dB over an amplifier bandwidth of 400 MHz.

Up-Conversion in IMPATT Amplifiers

A simple technique has been presented to determine the up-conversion characteristics of IMPATT-diode amplifiers. The method uses the admittance characteristics of the device and the circuit of the amplifier. Theoretical results are given for a typical example and a comparison is made with experimental results obtained for actual amplifiers. Qualitative agreement is obtained.

Miniaturized reverse modulation loop for a CQPSK 120-Mbit/s modem

The design and performance of a miniaturized reserve modulation loop (RML) for carrier recovery in a 120-Mb/s coherent quadrature phase shift keying (CQPSK) modem for onboard satellite applications are discussed. The RML circuit, consisting of modulator, demodulator, and comparator circuits, has been fabricated using quasi-monolithic techniques with dimensions of 1.65*4 cm. The relative phase for all four states of the modulator is in close agreement with design values of 90 degrees +or-1 degrees over a 200-MHz bandwidth at 3.95 GHz. The demodulator and comparator circuits of the RML have successfully recovered a 120-Mb/s bit stream.<<ETX>>