Integrated Cryogenic Satellite Communications Cross-Link Receiver Experiment

An experiment has been devised which will validate, in space, a miniature, high-performance receiver. The receiver blends three complementary technologies: high temperature superconductivity (HTS), pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuits (MMIC), and a miniature pulse tube cryogenic cooler. Specifically, an HTS band pass filter, InP MMIC low noise amplifier, HTS-sapphire resonator stabilized local oscillator (LO), and a miniature pulse tube cooler will be integrated into a complete 20 GHz receiver downconverter. This cooled downconverter will be interfaced with customized signal processing electronics and integrated onto the space shuttle’s “HitchHiker” carrier. A pseudorandom data sequence will be transmitted to the receiver, which is in low Earth orbit (LEO), via the Advanced Communication Technology Satellite (ACTS) on a 20 GHz carrier. The modulation format is QPSK and the data rate is 1.024 Mbps. The bit error rate (BER) will be measured in situ. The receiver is also equipped with a radiometer mode so that experiment success is not totally contingent upon the BER measurement. In this mode, the receiver uses the Earth and deep space as a hot and cold calibration source, respectively. The experiment closely simulates an actual cross-link scenario. Since the receiver performance depends on channel conditions, its true characteristics would be masked in a terrestrial measurement by atmospheric absorption and background radiation. Furthermore, the receiver’s performance depends on its physical temperature, which is a sensitive function of platform environment, thermal design, and cryocooler performance. This empirical data is important for building confidence in the technology. Introduction The benefit of cryogenic cooling to low noise receiver front-ends has been well established. For example, the noise temperature of a Ka-band PHEMT amplifier can be reduced an order of magnitude by lowering the physical temperature of the device from 300 K to 20 K.1,2 The satellite communications community has generally recoiled from serious consideration of this technology because onboard cooling appeared unrealistic. For example, to provide one Watt of cooling at 77 K, about 1600 kg of liquid nitrogen would be necessary to support a ten year mission life. At the communications subsystem level, passive cooling cannot supply the required lift at the desired operating temperature. However, recent advances in mechanical refrigerators cause us to reevaluate this issue. Single-stage, closed-cycle coolers are available that: provide ample cooling capacity in the neighborhood of 77 K; offer a mean time between failures (MTBF) of order 10 years; and consume only about 30 W of prime power. Coupled with the late discovery of high temperature superconductors (HTS), and the emergence of PHEMT MMIC, cooled front ends become practical and enticing. The surge in wireless communications including voice, video, and data creates a tremendous demand for channel bandwidth and drives transceiver systems to frequencies beyond 20 GHz. In some cases, terrestrial wireless networks are challenging the satellite industry for precious frequency spectrum allocation. Bandwidth will necessarily be rationed. Terrestrial and space-based systems will exact the final measure of performance from state-of-the-art technologies to be competitive and provide the desired quantity and quality of services. So, it is not too speculative to presume that these pressures will encourage the