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Significant advances in digital and RF/microwave technologies are leading to more diverse radar applications as well as greater commercialization. This article discusses some of the fundamental research and development challenges in both the digital and RF/millimeter-wave domains, as well as current and future directions in design, system integration, and test.

Figure 4. High-level block diagram of a radar front-end transmit and receive unit.
The HPA performs the critical function of amplifying the illumination signal to the highest power permitted without adding distortion, while having high enough efficiency to maintain power consumption within specified limits. Depending on the application, transmit power levels can range from milliwatts to kilowatts. Linearity of the power amplifier is of great importance since nonlinearity can cause pulse degradation and introduce spurs that violate spectral mask requirements or corrupt the receive signal. In recent years, field plate technology has allowed GaAs HPAs to be operated at higher voltages. Field plate technology and air-bridges increase the breakdown voltages of high electron mobility transistors (HEMT). Increased power density, however, introduces heat dissipation issues. Field plate technology has been used with devices that already support higher voltages and power densities, such as gallium nitride (GaN) on silicon carbide (SiC) substrates. PA designers are faced with a multitude of problems in trading off devices, component count, thermal management, and miniaturization, all while satisfying the amplification and spurious emission requirements.

Figure 5. Link budget analysis using the National Instruments AWR Visual System Simulator.
While LNA design is relatively mature, its performance is crucial to achieving front-end sensitivity and overall radar performance goals. Link budget and noise figure analyses have historically been performed with simple hand calculations or spreadsheets; however, use of a graphical tool like the NI AWR Visual System Simulator (VSS) or similar, greatly enhances the designer’s ability to close in on the specification and spot problem areas (Figure 5).

Integration: Putting it All Together

Figure 6. An example of an integrated tool chain by the National Instruments AWR Visual System Simulator.
The radar system architect has the enormous task of understanding various tradeoffs in the digital domain as well as in the RF/microwave domain, and putting it all together. Many years ago, radar systems might have been designed and integrated by a small team of hardware engineers, but today’s radar systems are becoming increasingly complex with domain experts from several areas contributing to the development of one system. How can an algorithmic tradeoff be adequately balanced with microwave circuit requirements and cost? There is clearly a greater need for mixed digital and RF/microwave design, simulation, and a prototype framework so that the corresponding domain experts can communicate with each other to address this complex design problem. One approach is to consider a well-integrated tool chain that supports microwave design, digital signal processing, hardware-in-the-loop (either hardware-based processing such as on FPGAs or measurements), and the corresponding hardware capability to support rapid prototyping of designs (Figure 6). Various systems software packages allow multiple designers to easily create and evaluate subsystem architectures, bringing their designs from concept to simulation and, ultimately, to physical implementation in a single system within a single framework.

Conclusion

Today’s radar systems are as complex as they are diverse. What is common, however, is that they each contain a digital signal processing section and RF/microwave front end. In this article, we looked at a few key elements in both of these areas with examples for pulse compression radar and discussed several technology challenges as well. While radar systems previously were developed by a few hardware engineers, today’s systems often rely on the design contributions of multiple domain experts. Various software tools simplify the complexity of the design process and allow engineers to think across the traditional boundaries.

This article was written by Dr. Takao Inoue, Senior RF Platform Engineer, and Phyllis Cosentino, Senior Product Marketing Manager, at National Instruments in Austin, TX. For more information, Click Here.

References

  1. M. Grossi, A. Fiorello and S. Pagliai, “Advances in Radar Systems by SELEX Sistemi Integrati: Today and Towards the Future,” European Radar Conference Proceedings, September-October 2009, pp. 310-317.
  2. J. Hasch, E. Topak, R. Schnabel, T. Zwick, R. Weigel and C. Waldschmidt, “Milli meter-Wave Technology for Auto motive Radar Sensors in the 77 GHz Frequency Band,” IEEE Transactions on Microwave Theory and Techniques, Vol. 60, No. 3, March 2012, pp. 845, 860.
  3. C. Li, J. Cummings, J. Lam, E. Graves and W. Wu, “Radar Remote Monitoring of Vital Signs,” IEEE Microwave Magazine, Vol. 10, No. 1, February 2009, pp. 47-56. C. Gentner, E. Munoz, M. Khider, E. Staudinger, S. Sand and A. Dammann, “Particle Filter Based Positioning With 3GPP-LTE in Indoor Environments,” IEEE/ION Position Location and Navigation Symposium Proceedings, April 2012, pp. 301, 308