Phase noise is a measurement in the frequency domain. It is used to quantify the frequency...

# Why Is Low Phase Noise Critical for Radar Systems?

Phase noise can significantly affect the performance of today’s radar systems. In this blog post, discover why radar requires extremely low phase noise levels as well as effective phase noise measurement solutions.

### Phase Noise Overview

An ideal, mathematically calculated carrier signal is free of distortions with respect to time. In the frequency domain, it appears as a clean carrier signal at a specific power level.

Real-world carrier signals have random fluctuations in amplitude and phase over time, which results in spectrum spreading. Instead of a narrow carrier frequency, unwanted sidebands develop on both sides of the carrier. Phase noise measurements are used to analyze these random frequency instabilities.

For a concise refresher on the basics of phase noise, read our blog post – “What is Phase Noise & How Is It Optimally Measured?”

### Radar Systems & Phase Noise

Typically, radar systems transmit radio waves toward a specific target and capture the reflected signal for analysis.

The level of returned energy and the elapsed time interval can be used to determine valuable information about the target, such as size and distance.

Doppler radar systems reveal additional data, namely the speed a target is moving toward, or away from your radar antenna. Evident by its name, Doppler radar makes use of the Doppler effect, which involves the way waves behave when emitted from a moving object with respect to a stationary spectator. Signals compress (move higher in frequency) when traveling toward the observer and elongate or stretch (move lower in frequency) in the opposite direction. As Doppler radar systems detect the change in frequency from the initial radio pulse, both speed and direction of motion can be determined.

Phase noise limits the ability of a radar receiver to process Doppler information. For example, slow moving targets with a low frequency doppler shift or "close-in" to the carrier can be hidden by excessive phase noise. Additionally, if the signal of interest has a low reflected power it can also be hidden by excessive phase noise. In the image below, phase noise (orange) masks this type of radar return (purple).A cross-correlation phase noise analyzer is a fast, highly accurate option to measure phase noise, especially for today’s Doppler radar systems. In some cases, local oscillator (LO) substitution may be needed to make phase noise measurements. Poor LO performance within a radar system can increase the severity of distortions, completely obscuring radar returns close to the initial transmit frequency. In this case, a high-performance synthesizer/signal generator can be used in place of the LO. Substituting the system LO with a cleaner signal puts the LO's performance to the test, enabling engineers to determine its phase noise impact.

Is your signal generator agile enough for radar system testing? Uncover the answer in an interesting Boonton white paper, featured on Microwave Journal.

### Must-watch Webinar on Phase Noise Fundamentals

Beyond radar systems, low phase noise performance is also important for the latest communications systems. Want to learn why? Watch the on-demand webinar, “Low Phase Noise is Critical for Communications and Radar. Do You Have What It Takes?” Presented by Bob Muro, Applications Group Manager at Holzworth, viewers will learn phase noise basics, phase noise's critical nature for radar and communications applications, phase noise measurement tools for your system’s LOs, and the availability of low phase noise LO substitutes.

Sharpen your phase noise fundamentals and watch the webinar today.