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Radar Measurements

Application Notes

Table of Contents  

  • Current trends and technologies in radar 
  • Radar basics and the radar range equation
    • The fundamentals of radar operation
  • Radar block diagram and the radar range equation
    • Relating the range equation to the elements of the radar design
  • Radar measurements
    • Power, spectrum, and related measurements
    • Component and subassembly test 
    • Antenna measurements 
    • Radar cross-section 
    • Noise figure 
    • Time sidelobe level 
    • Phase noise, AM noise, and spurs 
  • Summary
  • Related information 
  • References

Introduction

Today, different types of radar systems are used in a variety of applications: avionic, military, automotive, law enforcement, astronomy, mapping, weather, and more. Within this broad range of uses, several radar technologies have emerged to meet specific needs in terms of performance, cost, size, and capability. For example, many police radars use continuous-wave (CW) radar to simply assess Doppler shifts from moving cars; range information is not needed. As a result, low cost and small size are more important than advanced capabilities and features. 

At the other extreme, complex phased-array radars may have thousands of transmit/receive (T/R) modules operating in tandem. In addition, these may rely on a variety of sophisticated techniques to improve performance: sidelobe nulling, staggered pulse repetition interval (PRI), frequency agility, real-time waveform optimization, wideband chirps, and target-recognition capability are a few examples. 

To provide a foundation for the discussion presented here, this application note starts with a brief review of radar basics. After that, the remainder of the note focuses on the fundamentals of measuring basic pulsed radars, which is the basis of most radar systems. Where appropriate, this note will discuss adaptations of certain measurements for more complex or modulated pulsed-radar systems. This note will emphasize the measurement of radar signals for transmitter testing. A separate Keysight application note titled Radar, EW & ELINT Testing: Identifying Common Test Challenges (publication 5990-7036EN) discusses the signal generation and the characterization of radar receivers and electronic countermeasure (ECM) systems.

Current trends and technologies in radar 

Current trends and technologies in radar For engineers and scientists, the names behind the earliest experiments in electromagnetism are part of our everyday conversations: Heinrich Hertz, James Clerk Maxwell, and Nikola Tesla. Fast forward from their work in the late 19th and early 20th centuries to the early 21st Century: the fundamental concept—metallic objects reflect radio waves—has evolved into a host of technologies that are pushed to the extremes in military applications: detecting, ranging, tracking, evading, jamming, and more. 

As is the case in commercial electronics and communications, the evolution from purely analog designs to hybrid analog/digital designs continues to drive advances in radar system capability and performance. Frequencies keep reaching higher and signals are becoming increasingly agile. Signal formats and modulation schemes—pulsed and otherwise—continue to become more complex, and this demands wider bandwidth. Advanced digital signal processing (DSP) techniques are being used to disguise system operation and thereby avoid jamming. Architectures such as active electronically steered array (AESA) rely on advanced materials such as gallium nitride (GaN) to implement phased-array antennas that provide greater performance in beamforming and beam steering. 

Within the operating environment, the range of complexities may include ground clutter, sea clutter, jamming, interference, wireless communication signals, and other forms of electromagnetic noise. It may also include multiple targets, many of which utilize materials and technologies that present a reduced radar cross-section. 

This updated edition of our Radar Measurements application note reflects these realities. Because any document begins to lag behind current reality at the moment of publication, the content included here is a mix of timeless fundamentals—the radar range equation—and emerging ideas such as the time sidelobe level measurement technique. Many of the sidebars highlight products—hardware and software—that include future-ready capabilities that can evolve along with the continuing evolution of radar systems. 

Whether you choose to read this note from cover to cover or selectively sample the sections, we hope you find material—timeless or timely—that will be useful in your day-to-day work, be it on new designs or system upgrades.

Radar basics and the radar range equation 

The fundamentals of radar operation 

The essence of radar is the ability to gather information about a target — location, speed, direction, shape, identity, or simply presence. This is done by processing reflected radio frequency (RF) or microwave signals in the case of primary radars, or from a transmitted response in the case of secondary radars. 

In most implementations, a pulsed-RF or pulsed-microwave signal is generated by the radar system, beamed toward the target in question, and collected by the same antenna that transmitted the signal. This basic process is described by the radar range equation found on page 6. The signal power at the radar receiver is directly proportional to the transmitted power, the antenna gain (or aperture size), and the radar cross-section (RCS) (i.e., the degree to which a target reflects the radar signal). Perhaps more significantly, it is indirectly proportional to the fourth power of the distance to the target. Given the large attenuation that occurs while the signal is traveling to and from the target, having high power is very desirable; however, it is also difficult due to practical problems such as heat, voltage breakdown, dynamic power requirements, system size, and, of course, cost.

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