Development of linear phase modulator for spacecraft transponding modem

Abstract

A new Spacecraft Transponding Modem (STM) is being developed for deep space communication applications. The STM receives an X-band (7.17 GHz) uplink signal and generates an X-band (8.4 GHz) and a Ka-band (32.0 GHz) coherent or noncoherent downlink signals. The STM architecture incorporates two miniature linear phase modulators. These modulators are used to modulate the X-band and Ka-band downlink frequencies with the downlink telemetry, turnaround ranging, or regenerative PN-ranging signals. The linear phase modulators are designed with custom developed MMIC chips. The phase modulator MMICs, the amplifiers, and driver circuits are laid out on drop-in alumina substrates. These modulator designs meet the following requirements: phase deviation range of /spl plusmn/140 degrees at X-band and Ka-band downlink carrier frequencies, phase linearity of less than 8%, phase modulation input bandwidth of greater than 100 MHz, and differential input with sinewave or squarewave modulating format.