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International Journal of Emerging Trends in Science and Technology
Low Cost Radar For Target Movement And Heartbeat
Measurement
Allton Shibhu .J1 and Sudha .S2
1 Easwari engineering college and [email protected]
2 Easwari engineering college and [email protected]
ABSTRACT
The main aim of this project is to build low cost radar with simple circuit blocks. It is used to measure
target movement and heart beat measurement. Costs are reduced in the project by choosing a simple
FMCW architecture, using coffee cans for antenna. I verified the block using minicircuit components ,
designed two cantennas for transmitting and receiving purposes and designed a video amplifier along
with a filter for Radar. The amplifier output and transmit synchronization pulses were fed into the right
and left audio inputs of a mono stereo pin and given as input to laptop computer for digitization. The
radar operates at ISM band centered at 2.4 GHz. The radar operates in ranging. Ramp is used to
measure heart beat by varying amplitude. To record data .wav recorder program (for example, ’VLC’) is
used in the computer. MATLAB scripts read the .wav data, process, and then form the appropriate plots.
Key Words: : Frequency Modulated Continuous Wave(Fmcw), Inverse Discrete Fourier Transform(Idft), Radio
Frequency(Rf), Cantenna.
1. INTRODUCTION
Radar is an acronym for “radio detection
and ranging.”A radar system usually operates in
the ultra-high-frequency(UHF) or microwave part
of the radio-frequency(RF) spectrum, and is used
to detect the position and/or movements of
objects. Radar can track storm systems, because
precipitation reflects electromagnetic fields at
certain frequencies. Radar can also render precise
maps. Radar systems are widely used in air-traffic
control, aircraft navigation, and marine
navigation. High-power radar, using large dish
antennas, has been used to measure distances to
the moon, other planets, asteroids, and artificial
satellites. From unnamed space probes, aradar has
been used to map Venus, whose surface is
obscured at visible wave lengths by a thick layer
of clouds. Radar has been employed by NASA
(the U.S. National Aeronautics and Space
Administration) to make highly detailed
topographical maps of the earth’s surface as well.
Un-modulated CW radars have the
disadvantage that they cannot measure range,
because run time measurements is not possible
(and necessary) in un-modulated CW-radars. This
is achieved in modulated CW radars using the
Allton Shibhu .J
frequency shifting method. In this method, a
signal that constantly changes in frequency around
a fixed reference is used to detect stationary
objects. Frequency is swept repeatedly between f1
and f2. On examining the received reflected
frequencies (and with the knowledge of the
transmitted frequency), range calculation can be
done. If the target is moving, there is additional
Doppler frequency shift which can be used to find
if target is approaching or receding. FrequencyModulated Continuous Wave radars (FMCWs) are
used in the project.
The industrial, scientific, and medical
radio band (ISM band) refers to a group of radio
bands or parts of the radio spectrum that are
internationally reserved for the use of radio
frequency (RF) energy intended for scientific,
medical and industrial requirements rather than
for communications. ISM bands are generally
open frequency bands, which vary according to
different regions and permits. The 2.54 GHz ISM
band is a commonly accepted band for worldwide
operations. Microwave ovens, cordless phones,
medical diathermy machines, military radars and
industrial heaters are just some of the equipment
that makes use of this ISM band.ISM bands are
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also called unlicensed bands. So we are using ISM
band in the project.
It is an FMCW radar centered at 2.4 GHz
with less than 20mW of transmit power. To
reduce cost, the antennas (transmit and receive)
were made from coffee cans in an open ended
circular waveguide configuration. The video
output and transmit synchronization pulses were
fed into the right and left audio inputs of a laptop
computer for digitization. The radar operates in
ranging. To record data we use a .wav recorder
program (for example, ’VLC’) in the computer.
MATLAB scripts read the .wav data, process, and
then form the appropriate plots.
The outline of the paper is as follows:
Section II describes the proposed method which
uses the FMCM and also estimates accuracy,
sensitivity, specificity and further clutter removal
through correct percentage of IDFT classification.
It also explains the cantenna design calculations
Section III, describes the experimental results and
simulation outputs and finally Section IV, the
paper is concluded.
2. METHODOLOGY USED
2016
2.2. FMCW
Modular RF components were used
because of ease of fabrication (making each
module from scratch is time prohibitive) and
understanding. When looking at the completed
radar kit it is apparent how the radar system
works. FMCW radar architecture was chosen
because of its simplicity. It is not difficult to
generate slow 20ms wideband linear FM chirps
using a voltage controlled oscillator (VCO) and a
ramp generator, and then de-chirp down to audio
frequency range which can be digitized
inexpensively using the audio input port of a
laptop computer. The centre frequency is 2.4 GHz
with a chirp bandwidth adjustable up to 330MHz.
An equivalent short pulse radar system would
require a significantly more complicated (and
expensive) wide-band digitization system.
2.3. Cantenna
To reduce the transmit-to-receive mutual
coupling, separate transmit and receive antennas
are used. For the laptop radar application, a simple
metal coffee can acting as an open ended circular
waveguide antenna is attractive, due to its low
cost and good performance in terms of reflection
coefficient, gain, and beam width.
Fig 1: Experimental Block Diagram
Fig 2: Basic Cantenna
2.1. Description
The main aim of this experiment is to
build low cost radar with simple circuit blocks.
Costs are reduced in the kit by choosing a simple
FMCW architecture, using coffee cans for
antenna. The complete experimental block is
shown in Figure3.2. In Phase 1 I verified the block
using minicircuit components, designed two
cantennas for transmitting and receiving purposes
and designed a video amplifier with filter for
Radar.
Allton Shibhu .J
A typical metal coffee can with diameter
approximately 10 cm has the dominant TE11
circular waveguide mode cut off wavelength of
approximately 17 cm corresponding to a cut-off
frequency of 1.8 GHz, which allows good
performance for the laptop radar operation at 2.4
GHz. At 2.4 GHz, the free space wavelength is
12.5 cm, and to excite the TE11 mode a onequarter
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Relative power coupled between two
antennas (transmits and receive)
Pr( θ , ϕ )/Pt = Gt( θ , ϕ ) Gr( θ , ϕ )
λ2 / (4 π r )2 (4)
Radiated power density Pd at a distance r
from the transmit aperture is given by
Fig 3: Cantenna with SMA
wavelength monopole thin wire probe with
length 3.125 cm (as measured from the tip of the
probe to the inside metal surface of the coffee can)
is used. The monopole wire probe is conveniently
installed within the coffee can by extending the
centre pin of a SMA bulkhead receptacle jack. At
2.4 GHz, the coffee can has a guide wavelength of
18.5 cm and, to provide a good impedance match,
the monopole wire probe is spaced one quarter of
the guide wavelength (4.6 cm) from the back wall
of the waveguide. A plastic cover, which is
typically used to seal the coffee can after it is
opened, also serves as a microwave transparent
material.
2.4. Design Equations
The gain G(relative to an isotropic
radiator) of an antenna aperture of arbitrary shape
is given by the following expression:
G= 4π Ae /λ2
(1)
Where Ae is the antenna effective aperture
area and λ is the wavelength.
Pd ( θ , ϕ )= EIRP/ 4 π r2 = PtGt( θ , ϕ ) /
4 π r2
(5)
Wavelength λ of electromagnetic wave in
free space
λ = c/ f
(6)
where cis the speed of light, f is the
frequency
TE11 mode cutoff wavelength λc in
circular waveguide
λc = c/ fc
λc = 1.705 D
(7)
(8)
where D is the diameter of the circular
waveguide
Dominant TE11 mode will not propagate
below corresponding cutoff frequency.
Guide wavelength λg – Wavelength is
longer in waveguide compared to wavelength in
free space.
λg = λ / sqrt(1 –(λ/(1.705 D))^2)
(9)
2.5. Design Calculations
Stainless Steel:
1) Diameter=101mm
Probe length=35mm
Frequency=2.4 Ghz
Fig 4: Cantenna Measurements
Bandwidth=200 Mhz
Effective isotropic radiated power (EIRP) is
a function of the transmitted power Pt times the
gain of the transmit antenna
Gt( θ , ϕ ) EIRP( θ , ϕ )= PtGt( θ , ϕ )
2) Diameter=101mm
Probe length=30mm
Frequency=2.5 Ghz
(2)
Transmit Power Density and Receive
Power.
Power received Pr by an aperture is the
product of the incident power density Pdi and the
effective aperture area Ae
Bandwidth=400 Mhz
2.5.1. Model Calculation
Circular waveguide:
1) Diameter=99mm
Frequency=2.4 Ghz
Pr = PdiAe (3)
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Wavelength
λ = c/ f
= 3* 10^8/ 2.4*10^9
=0.125*1000
= 125mm
Circular wavelength, λc = c/ fc
λc = 1.705 D
=1.705*99
=168.79mm
Cutoff Frequency
, fc=c/λc
=3*10^8/168.79
=0.01777356*10^8
=1.77*10^6 Hz
Guided wavelength, λg = λ / sqrt(1 –
(λ/(1.705D))^2)
=125/sqrt(1-(125/(1.705*99))^2)
=125/sqrt(1-(125/(168.79))^2)
=125/sqrt(1-0.54843)
=125/sqrt(0.45157)
=125/0.6719895
=186.0147mm
Height, h=3/4*λg
=3/4*186.0147
=139.511mm
Fig 5: Measured radar coffee can antenna.
2.6. Minicircuit Components
In this project the mixer is used as a
switch, where the pulse generator output is fed to
IF port and the LO port is fed with a high
frequency sine wave from a VCO/signal
Allton Shibhu .J
2016
generator. The RF port gives out the pulse.
In this project we have tested using Mini circuits
ZEM-4300 mixer which has the features of wide
frequency range 300 to 4300 MHz, low
conversion loss 6.65 db.
Power dividers (also power splitters and,
when used in reverse, power combiners) and
directional couplers are passive devices used in
the field of radio technology. They couple a
defined amount of the electromagnetic power in a
transmission line to a port enabling the signal to
be used in another circuit. An essential feature of
directional couplers is that they only couple power
flowing in one direction. Power entering the
output port is coupled to the isolated port but not
to the coupled port. Directional couplers are most
frequently constructed from two coupled
transmission lines set close enough together such
that energy passing through one is coupled to the
other. This technique is favoured at the
microwave frequencies where transmission line
designs are commonly used to implement many
circuit elements. Directional couplers and power
dividers have many applications, these include;
providing a signal sample for measurement or
monitoring, feedback, combining feeds to and
from antennae, antenna beam forming, providing
taps for cable distributed systems such as cable
TV, and separating transmitted and received
signals on telephone lines.
A Low-noise amplifier (LNA) is an
electronic amplifier used to amplify very weak
signals (for example, signals captured by an
antenna). Essentially, an LNA amplifies signals
that are barely recognizable without adding a lot
of noise, as the name implies. An LNA is usually
located close to the signal source in order to
reduce losses in the feed line or minimize
interference. This arrangement is frequently used
in microwave frequency systems such as Global
Positioning Systems (GPS), because coaxial cable
feed-line has a high loss at microwave
frequencies. For example, 10 feet (3.0 m) of RG174 coaxial cable has a loss of 3.2 dB at 1 GHz
the feed line would degrade the signal-to-noise
ratio (SNR) by 3.2 dB (50 percent). A good LNA
has a low NF (e.g. 1 dB), enough gain (e.g. 10 dB)
and should have large enough inter-modulation
and compression point (IP3 andP1dB). Further
criteria areoperating bandwidth, gain flatness,
stability, input, and output voltage standing wave
ratio (VSWR).In this project we use this LNA
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because it havehigh IP3, +42 dB low noise figure
2.5 dB broadband flat gain .
Time-frequency toolbox was used mainly
for the analysis.
2.7. Frequency Domain Analysis
3.
EXPERIMENT
DISCUSSION
Frequency domain, or spectral analysis, is
the most popular approach for the diagnosis of
bearing faults. Frequency-domain techniques
convert time-domain vibration signals into
discrete frequency components using a fast
Fourier transform (FFT). Simply stated, FFT
mathematically converts time-domain vibration
signals trace into a series of discrete frequency
components.
The Fast Fourier Transform (FFT) is an
algorithm for calculation of the Desecrate
Fourier Transform first published in 1965.In a
frequency spectrum plot, the X-axis is frequency
and the Y-axis is the amplitude of displacement,
velocity, or acceleration. The main advantage of
frequency-domain analysis over time-domain
analysis is that it has ability to easily detect
the certain frequency components of interest.
James Taylor well explained the sequence of
appearing and disappearing of peaks in the
spectrum.
Xk = ∑ 𝑥𝑛𝑁−1 𝑛=0 𝑒−𝑖2𝜋𝑘𝑛𝑁
(10)
RESULTS
AND
Two experiments can be performed using
the radar kit; Ranging, and Heart beat
measurement as described below.
3.1. Ranging
In this experiment, the radar is directed
toward groups of moving targets. Both the right
and the left audio channels are recorded using a
.wav recorder (Fig. 1). A MATLAB script reads
the .wav and examines the left-channel
synchronization pulses looking for rising edges.
Starting at the time of the rising edge, the script
then computes an inverse discrete Fourier
transform (IDFT) on 20 ms of data from the right
channel. The logarithmic magnitude of the result
is range-to-target. Coherent pulse-topulse
subtraction is used to reject stationary clutter by
about 25 dB allowing the ranging mode to be used
to observe only moving targets. Ranging results
for two walking pedestrians are plotted as a RTI
plot (Fig. 2).
Consider a person, when the person
crosses over this movement produces impulse or
impact of very short duration. The energy of this
impact is distributed at low level over a wide
range of frequencies due to that identification of
movement is difficult to detect by the normal
spectrum. This impact excites the natural
frequency. In FFT, periodic impacts show up as a
peak (with some harmonics) at the characteristics
defect frequency corresponding to the person
movement.
Fig. 1: Range data is triggered
2.8. Software
The software used for recording the .wav
is done by Vlc version 2.1.0. The recorded file is
imported in to matlab as .wav file for FFT.
MATLAB is multi-paradigm numerical
computing environment and fourth generation
programming language. MATLAB 2051a was
used to plot the Fast Fourier Transform of a .wav
signal imported from the Audacity software. A
Allton Shibhu .J
Fig 2: Rti plot
3.2. Heartbeat Measurement
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In this experiment, the radar output is
given as input to the scope and it is combined with
signal generator along with ramp input. By the
change in the amplitude of ramp, we can find the
heartbeat measurement of a person. Fig 3 shows
the variation in amplitude while seeing through
oscilloscope, then this output is combined with
ramp to get clear output of measurement of
heartbeat.
2016
b
Fig 4: a) Rti with clutter b)Rti without
clutter
REFERENCES
Fig 3: Radar output in oscilloscope
3.3. Range-Time Intensity (RTI) Experiment &
Results
According to DTI plots, many inventive
RTI experiments were designed. Figure 4 shows a
number of results from these Ranging
experiments. The first plot, named (a), shows a
person walking first down a hall away from the
radar system operating in ranging mode, then back
again with clutter rejection. Image (b shows a
person walking first down a hall away from the
radar system operating in ranging mode, then back
again without clutter rejection . These images are
more clearer than others, because we use an
improved 2-pulse clutter rejection method which
subtracts the magnitude of the range profiles
rather than using coherent subtraction, which is
not as effective for this radar system because the
rising edge of the left-channel synchronization
pulses are under-sampled at audio frequency
sample rates.
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