A Modular MIMO Millimeter-Wave Imaging Radar System for Space Applications and Its Components

This article presents the design and prototyping of components for a modular multiple-input-multiple-output (MIMO) millimeter-wave radar for space applications. A single radar panel consists of 8 transmitters (TX) and 8 receivers (RX), which can be placed several times on the satellite to realize application-specific radar apertures and hence different cross-range resolutions. The radar chirp signals are generated by SiGe:C BiCMOS direct-digital-synthesizers (DDS) in the frequency range of 1 to 10.5GHz with a chirp repetition rate of < 1μs within each TX and RX. The latter allows for easy interfaces in the MHz range in between the TX/RX units and therefore optimized 2-D sparse antenna arrays with rather large distances in between the TX/RX antennas. Furthermore, this allows for ideally linear frequency modulated continuous-waveforms (FMCW) in conjunction with phase-shift-keying (PSK) radar signals and enables simultaneous operation of all TX when code division multiplex (CDMA) modulation schemes are applied. Comparably low complexity of the TX/RX units has been achieved by applying straightforward frequency plans to signal generation and detection but comes with challenging requirements for the individual active and passive components. Tackled by thin film technology on alumina and the recently developed SiGe and InP semiconductor technologies, which have been further optimized in terms of process maturity and space qualification. Upconversion and downconversion to and from 85 to 94.5GHz are performed by double balanced Gilbert mixers realized with InP double heterojunction bipolar transistor technology (DHBT) and 42-GHz local oscillator signals from SiGe:C BiCMOS VCO synthesizer using phase-locked-loops (PLL). InP DHBT power amplifiers and low-noise amplifiers allow for output power levels of 15dBm and > 30dB gain with noise figure values of 9dB, respectively. The MIMO radar utilizes patch antenna arrays on organic multilayer printed circuit boards (PCB) with 18dBi gain and 18^∘ half power beamwidth (HPBW). Generation of power supply and control signals, analog-to-digital conversion (ADC), and radar signal processing are provided centrally to each panel. The radar supports detection and tracking of satellites in distances up to 1000m and image generation up to 20m, which is required to support orbital maneuvers like satellite rendezvous and docking for non-cooperative satellites.