Real time implemantion of stc and ftc radar system based on fpga

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 02 Issue: 09 | Sep-2013, Available @ http://www.ijret.org 89
REAL TIME IMPLEMANTION OF STC AND FTC RADAR SYSTEM
BASED ON FPGA
Vipul patel1
, Prabat pandey2
and Sanjay patel3
1, 2
Department of ECE, Acropolis institute of technology & research, Indore, M.P,India, Vipulpatel.1988@gmail.com
3
Department of ECE, JIET College, Jodhpur, R. J,India,patelsanju29@yahoo.co.in
Abstract
In this paper we are explosively the fundamental theory of radar system modules STC (sensitivity time control) or sea clutter and FTC
(fast time constant) or rain clutter. The STC and FTC are commonly used to some clutter. The radar signal is widely used for weather
forecast, air port traffic control, military and fire control. The system implements radar processing procedures in real time mode in
FPGA (field programmable gate array). The FPGA device providing good performance of cheap platform for research and
development. The compact structure of STC and FTC can Implementations of Xilinx FPGA using the generated VHDL code.
Index Terms: FPGA, FTC, STC, LUT.
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1. INTRODUCTION
Real time is correctness of system depend not only logical
result of computation but also on which result are produced.
Real time is over all correctness of the system depending upon
both function correctness and timing correctness. Real time
system command and process control system and multimedia
and high speed communication system. Real time system is
creating additional requirement. The radar is required to have
a very good detection capability. Detection and track of small
targets in harsh weather condition can help authorities in
efficient monitoring of illegal activities. The radar device
which is used to detection and ranging of contacts independent
of time and weather condition, was one of the most important
scientific discovery and technology. The radar signal
processing is an excellent tool for weather prediction, civil
aviation and many other applications including its military
uses. The sensitivity time control and fast time constant are
basic modules for radar signal processing that pretend to filter
the echo‟s signal to decrease the effect of the mentioned
clutters. The target recovering from the echo signal is not a
trivial task since rain, snow, hail, or dust clutter affect radar‟s
reading, resulting in poor or false target detection of the signal
during time and space. In this paper we propose real time field
programmable gate array implementations of STC and FTC
radar modules.
2. MODULES
2.1 STC (Sensitivity Time Control)
Land -based radar have permanents echoes. Marine radar has
sea clutter. Permanent echoes are the reflections form nearby
objects: an air craft hanger, a building, a microwave tower,
summit, etc. Except on the sophisticated commercial and
military radar, there is nothing one can do with them except
become familiar with these patterns. A high mounted antenna
will shown “sea return” noise over a greater range, but the
strength of this is quite weak. A low mounted antenna shows
the interface over a smaller range; close in, but with strong
echoes. The sea clutter control uses a special circuit to alter
the receiver gain close to the ship, in such manner that the
intensity of the clutter is reduced. This is makes it possible to
work through the sea clutter ;however as the overall effect is
to reduce the sensitivity of radar receiver close to the vessel
,weak returns from legitimate objects are likely to be
weakened or completely suppressed. This control should be
set to the least (brightest) total that can be tolerated. Always
remember to zero the sea clutter control when the need for it
has passed. Picking out small targets in sea clutter is what we
want most from our radar. Large vessel sit well above the
waves and have a good radar return in about all conditions.
But smaller vessels are often lost in the radar clutter reflected
back from waves. And, there is a tradeoff here between using
tuning controls to reduce sea clutter and losing those small
boat targets we really want to see. There are various controls
on the 2117 which allow us to refine the image surrounding us
in rough water. These include Rain and Sea Clutter, target
averaging, and pulse length. In radar receivers, the wide
distinction in return signal amplitudes make adjustment of the
gain difficult. The adjustment of receiver gain for best
visibility of nearby target return signals is not the best
adjustment for distant target return signals. Circuits used to
adjust amplifier gain with time, during a single pulse
repetition period are called STC circuits, or “swept gain
attenuator”.
Local clutter levels dictate the magnitude of swept gain and
conflicting requirements for swept gain are presented as the

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antenna rotates. Modern systems dynamically measure clutter
levels for a large numeral of cells within the coverage area of
the radar. These measurements are slowly adjusted to take
account of changing clutter levels and used to put the swept
gain attenuator to an appropriate level for the range azimuth
cell currently being processed. In most cases, the values used
are a variation on the normal static law. This is due to abrupt
changes in swept gain law destroying the integrity of the
clutter amplitudes. in addition if long or compressed pulses are
used, amplitude changes can affect the performance.
The STC is really a radar system term. Most modern radar
system have a need to attenuate ,in a controlled Way, the
amplitude of large target returns that may occur close to the
trailing edge of the transmitted pulse. The moments of
reading echo, it has high power due to the nearby and the last
reading usually have a significant power decreasing. The
responsible for correcting this sensitivity time control (STC)
since it is commonly used to decrease the amplitude of nearby
target that could be false target caused by sea clutter. In calm
seas this control is set to its minimum value. STC‟s main task
to detect close target that might be obscured by sea clutter,
but if it is set to its high value trying to remove sea-clutter,
STC could remove small close targets too. The figure 1 shows
the kind of function used by the STC to correct sea clutter.
Figure 1. Echo and STC voltage Vs time (or distance).
This is accomplished through the use of a variable attenuator
which is located someplace in receive channel behind the
receiver protector. In a typical application, the attenuator is set
to maximum attenuation during the period of the transmitter
pulse. At the end of the pulse, the amount of attenuation is
reduced, in a controlled way according to organization
requirements, until it reaches 0 dB. In way, large close-in
target returns are controlled and the effective dynamic range
receiver is increased. The STC is really a programmed
attenuation function.
2.2 FTC (Fast Time Constant)
The shorter wavelength radar is more susceptible to rain or
snow meddling than are its longer wavelength cousins. A
squall within your radar range can blanket the area of heavy
rain with strong returns, twinkling somewhat like grass, but
tending to obscure all other usable data in the vicinity. The
rain clutter control will reduce the effect somewhat, allowing
some ability to see targets within the area, However, like other
clutter reducing circuit, this control also lower the overall
sensitivity of the radar. Rain may be heavy on one azimuth arc
only, and non-existent around the rest of the swept area. If the
squall is not in an area of primary concern, level the clutter
control at its minimum setting. Again, all anti-clutter control
reduces the generally sensitivity of radar. Be in the habit of
turning them off first, then adding back only the least sum
needed to achieve a comfortable display viewing level. In
addition to the rain control, some radar has a separate FTC
control. This adjusts a circuits optimized for the diminution of
precipitation interface at longer ranges. Rain , insects, and
some weather condition like dust could be considered as noise
for the radar signal , for these situations the Fast Time
Constant(FTC) module is used to take away undesired
reading , basically based on a derivative filter and now and
then associated with CFAR (constant false alarm rate) used to
set a constant probability of false echo. FTC sometimes called
Rain clutter Control, Which is a variable FTC, is a
differentiator that detects abrupt changes or fluctuations in
echo‟s signal in order to discriminate constant or almost –
constant echo‟s signal, frequently caused by rain, dust, snow
or other unwanted echoes. It is also known as differential or
anti-rain clutter control. FTC is in fact a high pass strain
whose cost is reduction of maximum exposure range, to avoid
this problem log –FTC could be used for large distances.
When it is used to reduce the rain clutter is also called
weather-fix. The rain clutter is a volumetric phenomenon so
the amount of litter returned back to the radar will be directly
proportional to the volume of the rain illuminated by the radar
beam. Shown in figure2.
Figure 2 The shaped radar beam reduces rain clutter return
and increases radar ranges.

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3. ARCHITECTURE
The architecture of STC & FTC are require to the many
elements like‟s control unit, mixer ,stream data and clock bus
,clock signal, output data bus look up table and ALU
(arithmetic logic unit) etc. Each module the each module
works independently from other two, then we propose a
similar structural design based on stream data processing with
one linear mixer that joins the two output. Show figure 3 is
architecture proposed.
Figure 3. Architecture proposed.
The control unit work is initiate sequences of micro operation.
Perform successively changing from one step to another step.
The control unit receiver the control values for each two
modules. The system arrangement the operation according to
the range used and specifies input to each modules a fix
occupation is used to process the STC those values are
stored in the look up table. The LUT (look up table) is control
the unit value is stored in look up table, but address addition to
read this LUT could not be lineal due to different resolution
and ranges used to radar‟s system. A stream data bus is data
transfer between the personality control units. A clock signal
regulates to flow of logic signal so that system can run
optimum speed. A clock is devices that generate periodic
signal for timing. Mixers are three port active or passive
device are designed to yield both sum and difference
frequency at a signal output port when two distinct input
frequency are inserted into other two ports.
The STC module which elements are LUT (look up table),
ALU (arithmetic logic unit), a counter and a register to store
output data. LUT is used as STC‟s curve storage, the counter
is calculated to configure its increment as function of
resolution and counter„s function is provide the LUT‟s
address. Shows figure 4.
Figure 4 sensitivity time control architecture.
FTC is basically a driver which is built with an adder and two
register, one to store the previous value and other to store
output. The register store temporary result related to the
computation. There are also special purpose register used to
by the control unit. Shown in figure 5.
Figure 5.fast time constant architecture.
4. HARDWARE IMPLIMENTATION
The main objective in this section is to demonstrate a
functioning hard ware for the purposed STC & FTC
architecture. The mat lab is high performance language for
technical computing mat lab is modern programming
language. The hardware realization, a simulation using mat lab
was performed using a synthetic echo is 12 bit integers and
2048 samples. The result of simulating was to validate the
results obtained by hardware once it is implemented and also
to use the same synthetic echo to test the implementation. The
output of the copying of a synthetic echo through the two
mixed modules, the signal with highest and lowest values is
the synthetic echo and the order is the filtered echo (darker
and marked one).shown in figure 6.

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Figure 6.Hardware implementation performed with Mat Lab
5. FPGA IMPLEMENTATION
The implementation was performed in a Xilinx Spartan II
FPGA. The FPGA is large array of configuration of logic
block connected via programmable inter connects. The
modern FPGA have very resourceful I/O blocks which make
them easy to interface to other chip. The system was
developed with VHDL Hardware Description Language
coding simulating tool. The VHDL provides a rich of
concurrent statement to module the concurrency in digital
hardware. The VHDL is strongly type talking in the first
stages of design and to generate some of the basic elements; at
figure 7 it is shown the block design at on the go HDL.
Figure 7 Block design in Active-HDL.
The main advantage of proposed structure (the software and
FPGA hard ware) is the facility whereupon we can easily
change the parameters of each block of the system. it is
required in some application to increase the precision of the
system, let us elasticity to adjust the parameter of the system
,and therefore better solutions. VHDL model was synthesize
with Xilinx ISE and targeted for a XC2S50TQ144-5(Spartan
II). ISE core generator was used for the STC LUT creation.
Finally Mat Lab was used for simulation, generating STC
values and its S-Record and plotting the results stored at the
board SDRAM. In order to confirm the hard ware
accomplishment a test bench was implemented. It is basically
a SDRAM driver to read the synthetic echo, stored via S-
record, and also used storing output stream. The drinkable
signal, resulted of the hardware implementation is like the one
replicated with Mat Lab. Some minor difference result from
the limited memory for the LUT that stores STC values
allocated at the BRAMs of the FPGA. The system realization
throughput is one sample per clock cycle. According with
minimum period of 9.787 ns, the maximum frequency is
102.176 MHz.
6. RESULTS
The implementation of STC & FTC on radar system based on
FPGA in real time mode. The trial result measured in the
implemented radar processing model presented the copied
echo signal & filtered signal by the proposed architecture is
shown in figure 7.
Figure 8 Result obtained.
7. DISCUSSION
The proposed parallel architecture implements STC and FTC
modules with some and specialized dedicated hard ware. This
implementation perform the arithmetic operations needed to
process STC and FTC concurrently, has latency of one cycle
and produces an output result on each clock cycle. The
planned architecture process data on stream basis and the
number of samples does not modify the latency. since its
maximum frequency is around 100 MHz and sample is

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processed by cycle, processing 100MSPS (Millions of samples
per second) could be reached, and it is as good as profitable
radar that process between 50 and 100 MSPS. marketable
radar process 4096*4096 sample in 2.5 second which means
6710886.4 samples per second .
CONCLUSIONS
This work presents an efficient implementation of STC and
FTC in real time. The designed architecture for those
controls is based on similar dealing out under dedicated and
specialized hardware that was reached due to bendable and
chip platform provided by FPGA. Therefore this
programmable hardware with its significant improvement in
the processing speed will make it possible to augment the
decision of the radar range cell and open new avenues for
further useful real time application. The presented building is
able to process 100 MSPS (millions of sample per
second).Which is a good metric according with commercial
radars.
REFERENCES
[1] Merrill Ivan skolnik, Introduction to radar systems,
Editorial McGraw-Hill,2000
[2] Ray Andraka, “FPGA as make a radar signal processor on
a chip a reality ”‟ IEEE proceeding of the Asilomar
conference on signals, system and computers, October 1999.
[3] Radar Navigation and Maneuvering Board manual, 2001.
[4] Stefan sjoholm, and Lennart Lindh, VHDL for Designer,
Prentice Hall , First Edition , 1997
[5 ]Andre DeHon, “The Density Advantage of
Reconfigurable computing”, IEEE Computer, Vol .33, No.4,
April 2000, PP.41-49.

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