Radar systems are employed in far more applications than “just” on the battlefield. Modern weather forecasts, for example, are based on commercial weather radar systems, while many modern automotive collision-avoidance systems are now based on millimeter-wave radar systems. Implementing such systems in practical and affordable solutions, however, has long proven challenging for high-frequency system engineers; the size and costs of components required to achieve the wideband in-phase/quadrature (I/Q) modulation in such systems are prohibitive. Fortunately, researchers at Caltech, involved in design work for NASA’s Jet Propulsion Laboratory (JPL), developed a novel modulation scheme for a Ka-band precipitation profiling radar system. This approach makes it possible to significantly shrink the size of the system compared to conventional designs.
The modulation scheme uses pulse compression and direct I/Q upconversion to overcome some of the classic problems of I/Q mixers, both in terms of gain and phase imbalances between channels, and leakage of the local oscillator (LO) signals required for frequency upconversion from baseband modulated signals. By adopting a direct-conversion architecture, the new approach reduces the total number of components required in the radar system. Through optimum selection of transmit signals and digital signal processing (DSP), the system minimizes sensitivity to LO leakage and image generation. The system is capable of achieving high-purity signals with exceptional sidelobe suppression. See “Offset IQ Modulation Technique for Miniaturized Radar Electronics,” NASA Tech Briefs, April 2016, p. 36.
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