Prosiding Seminar Radar Nasional 2008., Jakarta, 30 April 2008., ISSN : 1979-2921.
with vertical axis are linear proportional to the target radial speed v
r
. In fig. 4 we can see
ω-v curves for various R parameter R = 51, R = 307 and R = 461. It is shown
that the parameter R determines the slope of the curve the larger R the larger slope.
Fig. 5:
ω-v ratio curve for various range scales.
ω-v ratio curves for various range scales are shown in fig. 5. The horizontal axis is the cell number which in
turn proportional to the range R. Here we can see the linear relationship between the normalized
ωv and the range R or cell number for various range scales.
50 100
150 200
250 300
350 400
450 500
0.88 0.9
0.92 0.94
0.96 0.98
1
Time M
agni tude
50 100
150 200
250 300
350 400
450 500
-1 -0.5
0.5 1
Time P
has e
[ rad]
Fig. 6: Curve of time-varying magnitudes top and phase bottom of a series of range-FFT conducted at a certain cell
in which a target is detected.
Fig. 6 shows time-varying magnitudes top and phase bottom curve of a series of range-FFT at a certain
cell where a target is detected. The radial speed of a target at this cell can be determined by calculating the
rate of change of its phase. This rate of change of phase was obtained by computing the curve’s slope.
Positive slope of the phase curve indicates that the target is moving away from the origin of radar.
Fig. 7: The same result from fig. 6 can be represented as a pair of two dimensional A-t and
ϕ-t image for time-varying magnitudes left, and phases right respectively, of a series
of range FFT.
The same result from fig. 6 can also be represented as a pair of two dimensional A-t and
ϕ-t image for time- varying magnitudes, and phases respectively, of a
series of range FFT fig. 7. The horizontal axis represents the range R or cell number and the
vertical axis represents the time scale. The values of magnitudes and phases are shown in false colors.
1 2
3 4
x 10
-4
-1 -0.5
0.5 1
time [s] y
t 0.1
0.2 0.3
0.4 0.5
0.2 0.4
0.6 0.8
1
f f s
| Y f
|
0.2 0.4
0.6 0.8
1 0.2
0.4 0.6
0.8 1
R R max
| Y th
re s
h o
ld |
100 200
300 400
500 0.2
0.4 0.6
0.8 1
Range cell | Y
av g
|
Fig. 8: Result of a simulation in the case of three targets detected at range cells 100, 200 and 400.
Based on the same principles we can extend the computer experiments for multiple targets. The result
of a simulation in the case of three targets detected at range cells 100, 200 and 400 is presented in fig. 8.
Starting from this range-FFT we can determine the radial speed of each target using the same method
shown in the previous discussion.
200 400
0.98 0.985
0.99 0.995
1
Time M
agni tude
200 400
-1.5 -1
-0.5 0.5
Time P
has e [
rad] 200
400 0.7
0.75 0.8
0.85 0.9
0.95 1
Time M
agni tude
200 400
-2.5 -2
-1.5
Time P
has e [
rad] 200
400 0.22
0.24 0.26
0.28 0.3
0.32
Time M
ag ni
tude
200 400
-1.5 -1
-0.5 0.5
1
Time P
has e [
rad]
Fig. 9: Time-varying magnitude top and phase bottom of three targets at cells 100, 200 and 400.
27
Prosiding Seminar Radar Nasional 2008., Jakarta, 30 April 2008., ISSN : 1979-2921.
4. CONCLUSION
The time-varying magnitude and phase plots of three targets resulted from the previous simulation is shown
in fig. 9. The horizontal axes represent the number of repetition of the performed range-FFT. Based on the
slopes of phase plots we can see that the first targets were approaching whereas the last target was moving
away from the origin of the radar. In this paper a relative simple method to determine the
radial speed of a target from FMCW radar signal is presented. This method was implemented by
extending and repeating the range FFT many times conducted at a certain azimuth angle in which a target
has been detected. Then the radial speed of target is derived from the phase data of a series of this range
FFT. From previous discussion it is shown that most calculations needed in the processing stages are linear
operations. Furthermore, since the FFT operation is performed only once per sweep the processing time
can be significantly reduced.
Fig. 10: A pair of two-dimensional A-t left and
ϕ-t right images resulted from fig. 9.
REFERENCE [1]
M. I. Skolnik: Introduction to Radar Systems, McGraw-Hill, Auckland, 1980.
If we represent the result as a pair of 2D A-t and ϕ-t
images then we will get similar results fig. 10. In this representation mode three targets are recognized as
three quasi vertical bright lines at the A-t image, which in turn consistent with the result shown in fig. 7.
[2] F. E. Nathanson, J. P. Reilly, M. N. Cohen:
Radar Design Principles: Signal Processing and the Environment 2e, McGraw-Hill, Mendham,
1991.
[3] www.met.rdg.ac.ukradarcloudnetinstrumentsd
ocumentsTara.pdf accessed on March 20, 2008 In comparison to the Doppler-FFT method, we need to
complete the Fourier transform only once per sweep time. Due to this fact the determination of radial speed
of target using this method is more time efficient. [4]
S, de Waele, P.M.T. Broersen: Modeling Radar Data with Time Series Models, Eusipco 2000,
Proc. 10th European Signal Processing Conf., Tampere, Finland, p 1-4, 2000.
28
Prosiding Seminar Radar Nasional 2008., Jakarta, 30 April 2008., ISSN : 1979-2921.
Aplikasi Radar Pasif untuk Mengisi Celah Kosong Liputan Radar
Syamsu Ismail
Pusat Penelitian Elektronika dan Telekomunikasi - LIPI Kampus LIPI Gd. 20 Lt. 4 Jl. Cisitu 21154D Bandung 40135
Telp : 022-2504660 Fax : 022-2504659 E-mail: ismailppet.lipi.go.id
ABSTRACT
Radar Passive is a system for detecting a targets, such as aircraft, without emitting a signal. Generally speaking, that radar passive only intercepts emitted signals from the target, and, or reflection signal from
another source by the target, processes and analyses, and than displays the image or shows the target data. There are three possibilities form of signal emitted by the aircraft, those are radio, optic, or sonic waves, or
combination of them. In this paper will be discussed radar passive, which intercepts radio wave which is emitted by the aircraft. One of the radar passive’s applications is to fill a blank gap of active radar coverage
area. Some of constellation mode of operation radar passive to intercept targets, such as constellation which is provided by rotary antenna and multilateration, will be discussed. In multilateration mode, there are three or
more receivers which installed apart at a distance in order of ten to twenty kilometers
[2]
. Calculation based on the time different of wave arrival gives accurate information of the target position. Except antenna construction,
both mode of constellation have the same receiver requirement. Receiver for radar passive has a unique local oscillator, very low noise amplifier, and very wide bandwidth, high sensitivity. The oscillator is tuned in a range
of frequency by sweeping frequency or simultaneously multi frequency band. Key words : Radar Passive, Empty Gap, Receiver, Target Emission.
ABSTRAK
Radar Pasif adalah suatu sistem pendeteksi keberadaan target atau objek tanpa harus mengemisikan suatu sinyal. Secara umum dapat dikatakan bahwa radar pasif hanya menangkap sinyal yang diemisikan oleh
target, atau pantulan dari sumber lain oleh target tersebut, memproses dan menganalisis menjadi suatu informasi, kemudian menampilkan citra radar atau data target. Tiga besaran sinyal yang biasa diemisikan oleh
pesawat sebagai target yaitu gelombang radio, suara, atau cahaya, atau gabungan dari ketiga gelombang tersebut. Dalam tulisan ini akan dibahas radar pasif dengan mendeteksi gelombang radio yang diemisikan oleh
target. Salah satu aplikasi radar pasif adalah untuk mengisi celah kososng liputan radar aktif. Beberapa model konstelasi radar pasif untuk mendeteksi target akan dibahas, di antaranya model yang dilengkapi dengan antena
berputar dan multilaterasi. Dalam konstelasi multilaterasi digunakan tiga atau lebih unit penerima yang dipasang terpisah pada jarak antara sepuluh sampai duapuluh kilometer
[2]
. Kalkulasi yang didasarkan pada perbedaan waktu tiba dari gelombang pada ketiga penerima dapat memberikan informasi posisi target lebih
akurat. Kecuali konstruksi antena, semua model konstelasi memerlukan sistem penerima radar yang sama. Sistem penerima radar pasif memiliki keunikan pada osilator lokal yang harus ditala secara kontinyu pada pita
daerah frekuensi tertentu, atau secara simultan mengeluarkan frekuensi pada daerah tersebut. Disamping itu, penguat frekuensi tinggi pada ujung depan harus memiliki tingkat derau sangat rendah dan berpita frekuensi
lebar sehingga mampu menangkap sinyal dari semua kemungkinan daerah kerja dari pesawat target. Kata kunci : Radar Pasif, Celah Kosong, Penerima Radio, Emisi Target.
1. PENDAHULUAN
Suatu negara kesatuan yang mempunyai wilayah lautan dan daratan yang sangat luas, seperti Indonesia,
akan membutuhkan sistem pemantau lalu lintas laut maupun udara yang sangat memadai. Untuk
memantau lalu lintas seluruh wilayah udara dibutuhkan banyak unit radar. Walaupun di seluruh
wilayah Radar aktif sudah banyak digunakan tetapi belum dapat memantau seluruh wilayah, sehingga
masih terdapat celah-celah liputan kosong
[6]
. Penambahan Unit Radar aktif tentu merupakan salah
satu solusi untuk menutupi celah liputan radar pengawas udara. Namun mengingat biaya peralatan
dan pengoperasian suatu unit radar aktif pengawas udara sangat mahal, maka penambahan unit radar
dalam rangka mengisi celah liputan belum tentu merupakan suatu keputusan yang bijaksana. Banyak
radar aktif tersebar di darat dan di lautan, selain radar pertahanan udara dan penerbangan sipil, yang
dioperasikan oleh kapal-kapal laut sipil, angkatan laut, patroli polisi, direktorat bea cukai, dan sebagainya.
Walaupun secara umum di dalam radar aktif akan selalu ada radar pasif penerima radar tetapi dalam
aplikasinya sangat berbeda
[10]
. Perbedaan tersebut terletak bukan saja pada keunikan karakteristik
elemen-elemen radar pasif, seperti multi frekuensi, kepekaan yang tinggi, derau rendah, bidang frekuensi
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