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Integrated Framework for Radar Design

Parent Category: 2014 HFE

By Dr. Gent Paparisto

Introduction

As modern radar systems become more complex, they depend heavily on advanced signal processing algorithms to improve detection performance, making their design and implementation more challenging and expensive. At the same time, the radio front end must meet specifications that are often a combination of available devices, implementation technologies, regulatory constraints, requirements from the system, and signal processing. 

To overcome these challenges, digital and RF/microwave engineers are increasingly cooperating such that the overall system performance metrics are jointly optimized across the two disparate domains. This paper demonstrates how this can be done using the NI AWR Design Environment™ combined with NI LabVIEW and PXI instruments to design, validate, and prototype a radar system. The NI-AWR integrated framework provides a unique avenue for digital, RF, and system engineers, to all collaborate on a complex radar system.

EDA tools offer a unique value in this process: they help to accelerate the design process and reduce the cost of system implementation and testing. While computers are becoming cheaper and more powerful every day, the simulation complexity associated with radar systems is also growing. Hence, innovative solutions are needed to facilitate and shorten the design cycle.

Another challenge unique to radar systems is the wide variety of signal sources and signal processing algorithms used by different types of radar and/or manufacturers. Due to the nature of this field, there is little standardization and most manufacturers rely heavily on proprietary designs for their products. This makes it difficult for any EDA tool to provide a comprehensive library.  

NI AWR has taken the approach of providing a number of radar signal sources and signal processing capabilities that are well documented in the technical literature, along with a set of tools that make it easy for users to implement and test their own proprietary signals, designs, and algorithms.

The AWR simulation tools and hardware offered by NI provide a framework that can be indispensable for engineers working at the system, sub-system, and hardware level. They enable various engineering groups to work on the same platform while developing and testing their particular elements at different levels of the design process. One advantage of this approach is that all groups involved in the design process employ the same IP throughout the phases of product development and testing, reducing risks associated with potential inconsistencies between offerings from different tools and/or manufacturers.

Radar System Modeling

The radar signal design has evolved significantly over the last decades and a wide variety of radar signals and detection techniques have been developed for different applications [1]. While simple continuous wave (CW) radar signals are still used to estimate target velocity, many systems employ various versions of pulsed linear FM, also known as Chirp- or Pulsed-Doppler radar. Such signals allow users to achieve both range detection and relative velocity measurements [2]. 

A simple block diagram of a radar system is shown in Figure 1.

1408 HFE radar fig01

Figure 1 • Simple block diagram of a radar system.

 

The NI AWR Visual System Simulator™ (VSS) Radar Library offers a wide range of capabilities for antennae, propagation and target models. System designers can simulate various propagation environments using the TX and RX antenna models, allowing definition of antenna patterns and different angles of arrivals for different reflections of the signal of interest and/or interferers and clutter. Specific models are also provided for jammers, RF clutter, etc.  The target is modeled using its radar cross section (RCS), which can be calculated based on its geometry or defined by the user based on measurements. Furthermore, target dynamics may be defined, either theoretically or generated using third-party tools.

The signal processing at the receiver contains several well-defined algorithms, including a second-order moving target indicator (MTI), a moving target detector (MTD) and a constant false alarm rate (CFAR) calculator. While users may have their own proprietary designs for such functionality, the NI AWR Design Environment™ makes it easy to add such custom implementations to the overall radar system simulation.  Furthermore, customers are able to take advantage of the VSS framework to test and verify their implementations of their proprietary algorithms. 

System and Algorithm Design

In order to define the architecture and requirements for each of the blocks in this diagram, computer simulations using various EDA tools are always the first step in the design process. Such tools enable system engineers to define requirements for radar system components at the system level, which are then passed on to the sub-system and hardware designers. Realistic models for the signals, RF links and the environment are crucial for achieving reliable results during this process.

The signal generation and signal processing stages always require careful consideration during the various development phases, from design to implementation, prototyping, manufacturing, testing, and verification. A unique approach of the NI AWR framework is that it enables the use of the same IP from the initial design phase all the way to manufacturing, testing, and verification. This eliminates potential inconsistencies between signal sources and/or detection signal processing implementations used during different phases of the design process and reduces the amount of time spent on transitioning between them.

To take advantage of this approach, the VSS platform is used as the main framework for simulations of the radar system. Various blocks of the diagram above can be implemented in VSS, LabVIEW, or any other third-party tool that can seamlessly co-simulate with VSS. The advantage of implementing some of the blocks in LabVIEW is that it provides a clear path towards hardware-in-loop (HIL) simulations or a fast implementation in various FPGA boards offered by NI. This would provide an accelerated path toward prototyping and testing with real hardware.

System and algorithm design

Circuit engineers working on components for radar systems are tasked with providing RF components or complete transmitter/receiver RF links that comply with the requirements defined by system designers. Traditionally, these two groups have worked separately and have relied on a set of hardware requirements for designing and testing the components and/or RF links. The NI AWR Design Environment provides a unique solution where design and testing of the RF components/links can be accomplished in much tighter collaboration with the systems engineers. Microwave Office® provides seamless co-simulation with the VSS system tool, hence circuit designers are able to verify the performance of their components using system-level simulations and measurements. This approach shortens the time required for collaboration between systems and circuit designers and avoids the need for over-specification or over-design of components in order to ensure proper performance of the circuit designs as part of the overall system.

An example of typical analysis performed during the design of a transmitter RF link is in Figure 2 [3].  A two-stage up-converter architecture is employed, and a monolithic microwave integrated circuit (MMIC) power amplifier (PA) designed in Microwave Office is used as part of this link. VSS is used to perform a number of cascaded budget measurements.

1408 HFE radar fig02

Figure 2 • An example of a typical analysis performed during the design of a transmitter RF link.

 

The measurements shown in Figures 3 and 4 include the cascaded noise figure (NF) and available gain at each point of the RF link.  Other measurements can be easily obtained using the same system diagram, but they are not shown here due to space restrictions.

1408 HFE radar fig03

Figure 3 • Cascaded noise figure measurement at each point of the RF link.

 

1408 HFE radar fig04

Figure 4 • Available gain at each point of the RF link.

 

 

Another type of analysis that is performed in VSS is spur heritage analysis, which enables designers to track down the heritage of each spur observed at various point of the RF link. Understanding the heritage of the spur helps in modifying the link design to reduce and/or eliminate such spurs.

Hardware Simulations and Prototyping

This phase of the design process consists of testing various components and/or RF links developed for a radar system.  An important component for achieving this is the NI PXI platform [4]. PXI is a rugged PC-based platform for measurement and automation systems.  Because it is both a high-performance and low-cost deployment platform, it is ideal for applications such as manufacturing test, military and aerospace, and industrial test.  PXI can host various controllers, modules, and software, making it ideal for development and rapid prototyping efforts.

Some of the PXI modules employed in this process are vector signal generators (VSG) and vector signal analyzers (VSA). They can be used for generating radar signals based on the VSS models, driving the RF components under test, and capturing the signal, which is then sent back to the VSS receiver signal processing unit.  This configuration enables testing of RF components with realistic signals and evaluating them using system-level measurements.

1408 HFE radar fig05

Figure 5 • Another type of analysis that is performed in VSS is spur heritage analysis.

 

A recent offering from NI is the vector signal transceiver (VST) [5], which combines a VSG and a VSA with FPGA-based real-time signal processing and control. The advantage of this module is that it enables users to implement part of their receiver in FPGA to be used as a hardware accelerator for the computationally-intensive signal processing algorithms, such as the MTD and CFAR. The latter blocks usually consist of proprietary algorithms and implementations and require extensive testing using controlled target dynamics and environment conditions.  To achieve this, a test bench was developed using a combination of NI AWR EDA software and NI hardware. This test bench uses VSS to model the radar signal, transmitter RF link, propagation environment, target dynamics, and receiver front end and stores the signal at the input of the receiver baseband section for various configurations of the target dynamics and propagation environment. These signals are then used by the PXI to drive the MTD and CFAR algorithms implemented in a hardware platform, such as FPGA boards, resulting in much faster simulation and testing of such algorithms. The benefit of such an approach is that the signal used for testing of the baseband algorithms contains all the effects of hardware implementation and controlled target dynamics and propagation environment, and it takes advantage of hardware acceleration, providing much faster results.

As an example of such a methodology, the signal at the output of the MTD processor is shown in Figure 6, when a single target is present. The results show measurements of the target range and Doppler offset estimated by the signal processing algorithms.

1408 HFE radar fig06

Figure 6 • The signal at the output of the MTD processor when a single target is present.

 

Conclusion

This paper has presented a framework that can be used for the design, development, and testing of modern radar systems.  This framework takes advantage of the extensive RF design and measurement capabilities of NI AWR VSS and the flexibility of the NI PXI hardware, offering a unique platform that enables designers to use the same IP from design/simulation all the way to the implementation/testing phase. Such an approach accelerates the design process, yields better components and reduces the need for lengthy validation periods when moving between different phases of the product cycle, driving faster time to market.

About the Author:

Dr. Gent Paparisto serves as Senior Systems Engineer, AWR Group, National Instruments.

References

[1] G. Eason, B. Noble, and I. N. Sneddon, “On certain integrals of Lipschitz-Hankel type involving products of Bessel functions,” Phil. Trans. Roy. Soc. London, vol. A247, pp. 529–551, April 1955. (references)

[2] J. Clerk Maxwell, A Treatise on Electricity and Magnetism, 3rd ed., vol. 2. Oxford: Clarendon, 1892, pp.68–73.

[3] I. S. Jacobs and C. P. Bean, “Fine particles, thin films and exchange anisotropy,” in Magnetism, vol. III, G. T. Rado and H. Suhl, Eds. New York: Academic, 1963, pp. 271–350.

[4] K. Elissa, “Title of paper if known,” unpublished.

[5] R. Nicole, “Title of paper with only first word capitalized,” J. Name Stand. Abbrev., in press.

[6] Y. Yorozu, M. Hirano, K. Oka, and Y. Tagawa, “Electron spectroscopy studies on magneto-optical media and plastic substrate interface,” IEEE Transl. J. Magn. Japan, vol. 2, pp. 740–741, August 1987 [Digests 9th Annual Conf. Magnetics Japan, p. 301, 1982].

[7] M. Young, The Technical Writer’s Handbook. Mill Valley, CA: University Science, 1989.

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