International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 5

Number 3

September 2011

325

1 INTRODUCTION

There are two basic kinds of interferences which de-

crease a performance of FMCW radar. The first

kind are noise and distortion of the own radar, se-

cond one are interferences coming from nearby

buildings, sea clutter and other electronic equipment

working in the same frequency band. There are some

ways to couple with such a problem. Most of them

are based on digital signal processing algorithms

implemented in DSP processor code. Developing of

CFAR (Constant False Alarm Ratio) detector looks

as the best way of suppressing analog interferences.

The radar works in X band. In DPU (Digital Pro-

cessing Unit) 8192 point real FFT was applied as

well as binary integration, correlation and a few

kinds of CFAR including clutter-map. The antenna

and transceiver of FMCW radar are shown in the

figure 1.

Figure 1. FMCW radar

2 INTERNAL INTERFERENCES

Although manufacturers of radars try to achieve per-

fect spectrum performance, there is always small

leakage of interferences coming from the transmitter

and the receiver. Some unwanted products of digital

synthesis and power converters appear in the IF (In-

termediate Frequency) signal. Although the signal

sampled in DPU (Digital Processing Unit) is band

limited, some of the mentioned products remain in

data vector after FFT (Fast Fourier Transform) pro-

cessing. Having a level greater than background

noises, they are detected and displayed as artificial

echoes. Because interferences appear in the fixed

Impact of Internal and External Interferences

on the Performance of a FMCW Radar

P. Paprocki

Telecommunications Research Institute, Gdansk, Poland

ABSTRACT: Although FMCW technology has become by now mature, there are still some unsolved prob-

lems left. First group of them are noise and distortion from own transmitter or receiver. They are usually

caused by DDS (Direct Digital Synthesis) and power converters performance. They appear on radar display as

circles or arcs because of their isotropic properties. Second group are interferences from external world like

beams of pulsed radars working in the same frequency band, reflections from close buildings and installations

or sea clutter. Apart from creating artificial echoes of target they can cause degradation of radar tracking sys-

tem. This paper evaluates influence of internal and external sources of interferences on the FMCW radar per-

formance. DSP (Digital Signal Processing) algorithms which optimize detection of FMCW radar were pre-

sented. Means of suppressing analog interferences by digital techniques were shown as well.