Multi-target Detection in FMCW Radar based on Six-Port ... - IEEE Xplore

Multi-target Detection in FMCW Radar based on Six-Port Technology YANG Jian LIU Fa-Lin Dept. Electronic Engineering and Information Science, Univ. of Science and Technology of China Hefei, Anhui 230027, China E-mail: liufl@ustc.edu.cn Abstract: The traditional FMCW radar has its own

traditional heterodyne receiver. While FMCW radar

limitation in multi-target detection. Six-port radar is

based on six-port technology can suppress the false

proposed as a new way to solve this problem because of

alarm easily.

its phase measurement capability. The structure of six-port radar is given and the operating principle of

I. CONVENTIONAL FMCW RADAR AND MULTIPLE

the six-port as direct conversion receiver in FMCW

TARGETS’ FALSE ALARM

radar is discussed. How six-port radar suppresses false

f

alarm is analyzed in this paper. Computer simulations f0

practical.

∆f

Key words: six-port radar technology; direct conversion receiver;

fr

ft

prove that the analysis is correct and the method is

frequency modulated

continuous

wave;

∆f

+

∆f

−

F

2T

T

t

0

multi-target; false alarm.

t

Fig. 1 Frequency Modulated Continuous Wave

Fig.1 shows frequency modulated continuous The six-port network is made up basically of

wave modulated by a triangular signal. f t is the

couplers and diode detectors. It is mostly used to develop reflectometers and network analyzers [1, 2].

frequency of emitted signal whose center frequency

The applications of six-port technology in smart

is f 0 . Modulated cycle of triangular signal is T and

antenna systems [3], for direct millimeter-wave receivers [4] and in position sensing [5] have also

modulated bandwidth is F . f r is the frequency of

been reported. Its most important feature is the capability to perform accurate phase measurements through

simple

scalar

measurements.

the received signal. ∆f

Phase

+

and ∆f

−

represent the

difference between two RF signals is determined

difference frequency of emitted signal and received

from four power measurements. The circuit has no

signal in the rising part and declining part of a

active device, so it can be miniaturized in MMIC

triangular modulated cycle, respectively.

technology [6], which renders it suitable for low cost

The FMCW radar obtains a target’s range R and relative speed v through the measurement of the

and compact size applications. Frequency modulated continuous wave (FMCW)

difference frequency ∆f + and ∆f

is widely used in range/relative speed radar because

−

. If there are

of its simple generation and easy signal processing.

multiple targets, however, the received signals are

However, there is the problem of false alarm in

sum of each target’s received signal; and the

multi-target detection for FMCW radar based on

difference frequencies may result from different

1

0-7803-9433-X/05/$20.00 ©2005 IEEE.

APMC2005 Proceedings

targets. So, it is impossible to get the unique corresponding relation of ∆f + and ∆f

−

modulated by a triangular signal. A part of the emitted signal is coupled to one input port of the

for every

six-port as a reference signal. The received signal is

target. Considering all the possible combinations of n

injected to another input port after low noise

2

targets, we will obtain n pairs of ranges and relative speeds and they contain n 2 − n false targets. Fig. 2 shows two targets condition. In

amplification. Output signals are connected to power

addition to two real targets generated by the rising

to obtain the relative speed and range of the target.

and declining modulated frequency line 1 and 1′ , 2and 2' , we also get two false targets generated by 1and 2 ′ , 2 and1′ .

Or four output signals can go to the analog-to-digital

detectors to get square law detection and then amplified by video amplifiers. Then an ASP is used

(A/D) converter to have digital signal process, also can obtain same results. The frequency counter is used to guarantee a perfect linearity.

V

1

o

•

2

•

o

III.

TARGETS

R

2′

1′

SIX-PORT RADAR CAN DETECT MULTIPLE

Six-port radar transmits signals as fig.1 shows.

Fig. 2 Multi-target detection by FMCW

For six-port’s ability of accurate phase measurement, we can not ignore phase information of the received II. PRINCIPLE OF SIX-PORT RADAR

signal.

According to six-port’s measurement principle, through

power

measurement,

the

phase

In the first half of modulated cycle, the emitted

and

signal can be written as

amplitude of the reflection coefficient can be

s (t ) = sin(2πf 0 t + π

obtained which is defined as the ratio of the received

F 2 t + ϕ0 ) T /2

(1)

After a propagation time ∆t = 2(R − vt ) , the

signal to emitted signal. Six-port as a direct

c

conversion receiver replacing conventional mixer can achieve direct conversion measurement and high

phase difference of received signal and emitted

measurement accuracy. Fig.3 shows the block

signal will be

diagram of the FMCW radar based on six-port

2 f0 R 2 f 0v 8 FR 8 FR 2 − 2π + t +π t −π c c Tc Tc 2 16 FRv 8 Fv 2 8 Fv 2 2 π − π − π t t t Tc Tc 2 Tc 2 ∆θ + = 2π

discriminator [7, 8]. PA

f0

Then difference frequency and difference phase

LNA

Frequency measurement

VCO control

2 f v 4 FR 8 Fv 1 d∆θ + ⋅ =− 0 + − t 2π dt c Tc Tc 8 FRv 8 Fv 2 + − t Tc 2 Tc 2

∆f

R

Sixport

ASP

v

f0 VCO

control

Frequency measurement

Sixport

form of (2) and (3) as follow

DSP

R v

∆f

Fig.3 System block diagram of six-port radar

oscillator

(2)

2 f0R 8 FR 2 (3) −π c Tc 2 Where v