Abstract—Worldwide, fuel is stored and the measurements

Abstract—Worldwide, there is an average demand of nearly 96
million barrels of oil and liquid fuels per day. It is thus necessary that its
measurement and handling is done with great care as the major losses take place
when the fuel is stored and the measurements are taken. The fuel tanks are
majorly 40m in height as well as 40m in radius. In such large fuel tanks, even
an error of a small millimeter can cause a large loss. Thus it is really important
to design a system which is highly accurate in measuring fuel levels. The
current measuring devices available in the market are having an accuracy of
3mm-10mm. Using FMCW (Frequency Modulated Continuous Wave) RADAR at a very high
frequency (of 24GHz) is what we aim, so as to lessen the error up-to 1mm. By
doing this we can save upto 4000$ dollar behind every fuel tank. The system
works in two stages, the transmission and the reception stage. The high
frequency continuous wave is generated, modulated and transmitted. On the basis
of the discrepancies at the receiving end, level gauging of the order of 1mm
accuracy is obtained.

Keywords-FMCW, high frequency, 24GHz, VCO, Signal processing,
microstrip coplanar coupler, accuracy, beat frequency,  Advanced Design System.


In recent times, FMCW (Frequency Modulation Continuous
Wave)are being widely used for the measurement of distance/range in a variety
of industrial applications like automotive safety, level gauges, defense
seekers, security etc. It is popular in most of the modern industrial plant for
the measurement of bulk materials since the digital approach is more flexible
and program updates are very easy1. Here, our aim is to use a High frequency
of 24-24.3 GHz FMCW radar so as to obtain a much better and accurate results.
The current systems that have been deployed in the industries have been using a
technology that gives a precision of about 2mm-3mm. The main focus of this
project is to reduce that error of 2mm-3mm to about 0.05mm. The work for this
project has been effectively carried out and the software simulation has been
done and tested successfully. The hardware part for the same is being done and
the work is speeding up smoothly so as to get the desired results and accuracy.
Once this system is deployed it will give much accurate results and the losses
faced by the industries for the same can be minimized.


Block digram of the proposed system

Fig. 1: Block
diagram for FMCW radar (Transmitter                Section)

In the transmitter system our main task is to design a VCO  which can be modulated between 24 and 24.3 GHz
using triangular or sawtooth waveform.

We have various alternatives like Magnetron, Klystron,
Dielectric resonator, 24 GHz VCO module etc.

Different types of couplers can be used to segregate
the signal.

We will design and implement the system in a simulation

Compare the output of the simulation with the desired

Implement the entire system in hardware.

We will test the system.

B.    Working

A high-frequency signal of 24GHz is first emitted using a
radar in the proposed system. This signal after hitting the target gets
reflected and the reflected frequency is captured by the system. A difference
between the transmitted and the reflected frequency(?f) is calculated and is
transformed using Fourier transformation (FFT) for further calculations. The
distance calculation is done on the basis of this difference a much accurate
result is obtained2.


Fig 2: Graphical representation of Transmitted wave


150 MHz=40metres


 m                ……..1mm=Max Resolution

x=3.75 kHz …..Beat frequency(Fb)

For Modulating Frequency:

R =

R= 1mm   i.e. Minimum Distance

C= 3 X


Bsweep = 300 MHz

Fb = 3.75 kHz

Therefore ,

Ts =


Therefore ,    Ts = 5.33 X

 sec .

Therefore ,Fs =
1/Ts = 1.875 MHz .

Coupling Factor (C) =



Z0= 50 ?

2.4GHz Bi-directional Quadrature Coupler:


24 GHz 6 dB Coplanar Coupler:

Coupling Factor (C) =

= 0.5011


= 86.73 ?


= 28.83?


24 GHz 9 dB Coplanar Coupler:  

Coupling Factor (C) =

= 0.31622


69.37 ?


36.03 ?



Hardware Components Required

The hardware being employed for such high-frequency
circuit implementation are:

RT/duroid 5880Laminates:.

RT/duroid 5880 laminates are made by reinforcing PTFE
composites and microfibers of glass. It has good dielectric constant and works
in high frequencies.

The reason it is preferred is that it has low dielectric
constant. This makes it useful for high frequency applications. It can also be
used in high moisture areas as it has low water absorption characteristics.

RT/duroid 5880 laminates are malleable and hence can be
made into any shape with little effort. It offers resistance to solvents and
reagents which are used during the process of etching printed circuits. It also
has uniform electric properties.

Rogers RT/duroid 5880 high frequency laminates are used in:

1. commercial airline broadband antennas

2. microstrip and stripline circuits

3. millimeter wave applications

4. military radar systems

5. missile guidance systems

6. point-to-point digital radio antennas


D.    High-frequency
SMA End Launch Connectors:

RF high frequency SMA end launch connectors offer excellent
VSWR performance up to 26.5 GHz.

These connectors feature an optimized end launch design with
either through-hole legs or traditional slide-on mounting legs that make them
an ideal PCB connector solution for high frequency applications.

High frequency connectors are precision connectors used for
test and measurement or for sensitive low loss, phase stable, high frequency
microwave applications up to 67 GHz. They are made of high grade materials in
order to allow for longer life cycle and higher durability. 
Thanks to their high mechanical stability and screw-on design, high frequency
connectors provide best electrical performance with superior repeatability and
excellent reliability.


• Cellular/Broadband Amplifiers

• Microwave Filters

• Wireless Infrastructure

• Remote Sensing and Metering

• GPS Antennas

• Radar Systems

• High Speed Routers and Switches

• Automated Test Equipment





When two unshielded transmission lines are in close proximity,
power can be coupled from one line to the other due to the interaction of the
electromagnetic fields. Such lines are referred to as coupled transmission
lines, and they usually consist of three conductors in close proximity,
although more conductors can be used. Figure 7.26 shows several examples of
coupled transmission lines. Coupled transmission lines are sometimes assumed to
operate in the TEM mode, which is rigorously valid for coaxial line and
stripline structures, but only approximately valid for microstrip line,
coplanar waveguide, or slotline structures. Coupled transmission lines can
support two distinct propagating modes, and this feature can be used to
implement a variety of practical directional couplers, hybrids, and filters.
The coupled lines shown in Figure 7.26 are symmetric, meaning that the two
conducting strips have the same width and position relative to ground; this
simplifies the analysis of their operation. We will first discuss the basic
theory of coupled lines and present some design data for coupled stripline and
coupled microstrip line. We will then analyze the operation of a single-section
coupled line directional coupler and extend these results to multisection
coupled line coupler design.







Bidirectional Quadrature Coupler

hybrids are 3 dB directional couplers with a 90? phase difference in the
outputs of the through and coupled arms. This type of hybrid is often made in
microstrip line or stripline form as shown in Figure 7.21 and is also known as
a branch-line hybrid. Other 3 dB couplers, such as coupled line couplers or
Lange couplers, can also be used as quadrature couplers; these components will
be discussed in later sections. Here we will analyze the operation of the
quadrature hybrid using an even-odd mode decomposition technique similar to
that used for the Wilkinson power divider.

With reference
to Figure ___, the basic operation of the branch-line coupler is as follows.
With all ports matched, power entering port 1 is evenly divided between ports 2
and 3, with a 90? phase shift between these outputs. No power is coupled to
port 4 (the isolated port).






Fig 4:
Bidirectional Quadrature Coupl



Fig 5: Coplanar
Coupler Schematic


Factor (C) =

                                        where a=amount of coupling

50 ?


Z0 *





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. However, lumped component devices are also
possible at lower frequencies, such as the audio frequencies encountered
in telephony.
Also at microwave frequencies, particularly the higher bands, waveguide designs
can be used. Many of these waveguide couplers correspond to one of the
conducting transmission line designs, but there are also types that are unique
to waveguide.

24 GHz VCO


A voltage-controlled oscillator or VCO is
an electronic oscillator whose oscillation frequency is
controlled by a voltage input. The applied input voltage determines the
instantaneousoscillationfrequency.Consequently, modulating signals
applied to control input may cause frequency modulation (FM) or phase
modulation (PM). A VCO is also an integral part of a phase-locked







24 GHz 10 dB Coplanar Coupler:

         Fig. 6: Layout for high frequency
Coplanar coupler


device is been simulated in the ADS software. The entire layout has been
designed using microstrip lines since lumped elements cannot provide the
desired response at such High Frequency. Coplanar coupler is purposely used
since it allows us to change the amount of coupling as per the requirement of
the system. Since maximum power is to be transmitted to the antenna system,we
have specifically designed a 10 dB coupler which splits the power approximately
in the ratio 10:1 .


The response obtained is shown below :

Fig. 7: Response

power :20.41% – 21.37%

power  :87.09% – 84.35%









24 GHz 6 dB Coplanar Coupler:


Fig 8: Coplanar Coupler Schematic(6dB)

Fig. 9: Layout for high frequency Coplanar coupler(6dB)


Coupling Factor (C) =



86.73 ?


 = 28.83 ?


The response obtained is
shown below :

Fig. 10: Response


2.4 GHz 3 dB Bi-directional Coupler:

Fig 11: Bi-directional Coupler Schematic(3dB)

Fig. 12: Layout for high frequency Bi-directional


Coupling Factor (C) =

= 0.707


= 120.91 ?




The response obtained is shown below :


Fig. 13: Response

Future Scope

present study has been made to suggest and develop tools which will eventually
be useful to the governments, industries, owners and/or contractors for timely
and accurate measurements of large infrastructure projects at a reasonable cost
and of a specified quality.




vi.   References

1Dr.Eugin Hyun, Mr.Young-SeokJin andMr. JonghunLeet, “Development
of 24GHz FMCW level measurement radar system”,IEEE conference, Cincinnati, OH,
USA, 23rd of  May, 2014.


2Ali CaferGurbuz, “Homodyne FMCW
Radar Range Resolution Effects with Sinusoidal Nonlinearities in the Frequency
Sweep”, IEEE conference, 1995.


3Y. Musch, “A
high precision 24-GHz FMCW radar based on a fractional-N ramp-PLL”, IEEE























Mario Pauli and Thomas Zwick “FMCW radar system with additional phase
evaluation for high accuracy range detection”, IEEE Conference, 12 December





5Hai chen and yang li, “digital signal processing for a
level measurement system based on fmcw radar”, ieee conference, 1 june 2007.





6David M. Pozar, “Microwave Engineering”,Third
Edition,Wiley Student Edition.