vector network analyzer &its application for rcs akm

8/2/2019 Vector Network Analyzer &Its Application for Rcs Akm

1/36

VECTOR NETWORK ANALYZER &ITS

APPLICATION FOR RCS MEASUREMENT ATMICROWAVE FREQUENCY RANGE(3 TO 8

GHZ)


2/36

STEALTH TECHNOLOGY: It is a sub disiciple of military tactics which cover a range of

techniques used with aircrafts, submarines, ships & missiles to makethem less visible to radar,infrared sonar & other detection methods.

It is a technology used in radar cross section reduction.

Its attempt is to greatly reduce the distance at which a person orvechile can be detected.

Stealth aircraft:


3/36


4/36

EM waves are made by the viberations of electric & magnetic waves. These fields are perpendicular to one another in the direction of the wave is

travelling.

The energy carried by an EM wave is proportional to the frequency of thewave.

The wavelength & frequency of the wave are connected via the speed of

light. C=f , where c= speed of light , f= frequency & = wavelength.


5/36

ELECTROMAGNETIC SPECTRUM: EM waves are split into different categories based on their frequency.

Visible light ranges from violet to red.

Violet light has a wavelength of 400 nm.

Red light has a wavelength of 700 nm.

Any wavelength between these extremes can be seen by humans.


6/36

Microwaves are electromagnetic waves with frequency ranging between 300MHz (0.3 GHz) & 300 GHz.

MICROWAVE SOURCES: VACCUM TUBES: These operate on the ballistic motion of electrons in a

vaccum under controlling action of electric & magnetic fields.

TUNNEL DIODE, GUNN DIODE & IMPATT: These are low power microwave

sources.

MICROWAVE WAVEGUIDE:

The waveguide is a linear structure that conveys electromagneticwaves between its end points.

These are metallic transmission lines that are used at microwavefrequencies.


7/36

TE MODES (Transverse electric) TM MODES (Transverse magnetic)

TEM MODES (Transverse electromagnetic)

Microwave frequency bands Letter Designation

Frequency range

L band

1 to 2 GHz

S band 2 to 4 GHz

C band

4 to 8 GHz

X band

8 to 12 GHz

Ku band

12 to 18 GHz

K band

18 to 26.5 GHz

Ka band 26.5 to 40 GHz

Q band

33 to 50 GHz

U band

40 to 60 GHz
http://en.wikipedia.org/wiki/L_bandhttp://en.wikipedia.org/wiki/S_bandhttp://en.wikipedia.org/wiki/C_bandhttp://en.wikipedia.org/wiki/X_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/K_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Q_bandhttp://en.wikipedia.org/w/index.php?title=U_band&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=U_band&action=edit&redlink=1http://en.wikipedia.org/wiki/Q_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/K_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/X_bandhttp://en.wikipedia.org/wiki/C_bandhttp://en.wikipedia.org/wiki/S_bandhttp://en.wikipedia.org/wiki/L_band


8/36

Radar uses microwave radiation to detect the range, speed, & othercharacteristics of remote objects.

Development of radar was accelerated during World War 2 due to its greatmilitary utility.

Now it is widely used for a no. of applications such as:

Air traffic control

Weather forecasting

Navigation of ships

Speed limit enforcement


9/36

What is a network? A network is a group of interconnected components.

An electrical network is a group of electrical components such as resistors,capacitors, transmission lines, voltage & current sources.

NETWORK ANALYZER:

It is an instrument which measures the network parameters of electricalnetworks.

PRINCIPLE OF NETWORK ANALYZER:


10/36

Scalar Network Analyzer: It measures the amplitude properties only. Vector Network Analyzer: It measures both amplitude phase properties. A VNA may also be called as Gain Phase Meter or an Automatic Network

Analyzer.

ZVA40 vector network analyzer from Rohde & Schwarz


11/36

The basic architecture involves a signal generator, a test set, & one or morereceivers.

SIGNAL GENERATER: It provides a signal to the VNA. High performance network analyzers have two built in sources.

TEST SET: The test set takes the signal generater output & routes it to thedevice under test, & it routes the signal to be measured to the receivers.

It often splits off a reference channel for the incident wave.

The test set may also contain directional couplers to measure reflectedwaves.

RECEIVER: A network analyzer have one or more receivers connected to itstest ports.

The reference test port is usually labeled as R & the primary test ports as A,

B, & C.

For a VNA, the receiver measures both the magnitude & phase of the signal.

It needs a reference channel R to measure phase so a VNA needs atleast tworeceivers.


12/36

It involves measurement of known standards & using those standards tocompensate for systematic errors.

After making these measurements, it can compute some correction values toproduce an expected answer.

NETWORK ANALYSIS TERMINOLOGY:

S PAPAMETERS:

The scattering parameters describes the electrical properties of networks.

They are mostly used for networks operating at radio & microwavefrequencies.

2 PORT S PARAMETER:


13/36

The relationship between the incident & reflected waves is:

If port 2 is terminated in a load identical to the system impedance (z) then bwill be totally absorbed making a=0.

Similarly if port 1 terminated in system impedance , then a becomes 0.

S= Input port voltage reflection coefficient, S= Output port reflectioncoefficient

s= Reverse voltage gain, S= Forward voltage gain


14/36

A) COMPLEX LINEAR GAIN: The complex linear gain G is given by: G = S B) SCALAR LINEAR GAIN: It is given by: G=S

C) SCALAR LOGARITHMIC GAIN: The scalar logarithmic gain ( decibels or dB)expression is given by:

g= 20 logS dB.

D) INSERTION LOSS: I.L.=-20 logS

E) INPUT RETURN LOSS: RL=20 logS dB.

F) OUTPUT RETURN LOSS:

G) REVERSE GAIN & REVERSE ISOLATION:


15/36

H) VOLTAGE STANDING WAVE RATIO: It is the ratio of the standing wavemaximum voltage to the standing wave minimum voltage.

At the input port the VSWR is given by :

At the output port the VSWR is given by:


16/36

Measuring both magnitude & phase areimportant for several reasons.

Both measurements are required to fullycharacterize a linear network for distortionfree transmission.

In computer aided engineering techniques,programs requires magnitude & phase data

for accurate models. Time domain characterization requires

magnitude & phase information to obtaininverse fourier transform.


17/36


18/36


19/36


20/36

RADAR CROSS SECTIONDefinition

Radar cross section(RCS) is ameasurement of how detectable an objectis with radar. A larger RCS indicates that

an object is more easily detected.An object reflects a limited amount of

radar energy. A number of different

factors determine how muchelectromagnetic energy returns to thesource such as: material of which the target is made. absolute size of the target.


21/36

relative size of the target. the incident angle.

reflected angle. distance between emitter-target-receiver.

Typical RCS diagram


22/36

Factors that affect RCS1. SizeThe larger an object, the stronger its Radar

reflection and thus the greater its RCS.2.MaterialMaterials such as metal are strongly radar

reflective and tend to produce strong signals.Some materials are: wood & cloth, plastic &fiberglass, chaff etc.

3.Radar absorbent paintThis consisted of small metallic balls. Radar

energy is converteted.td to heat rather thanbeing reflected.


23/36

4.Shape, directivity and orientation.The surfaces of the F-117A are designed to

be flat & very angled. The edges are sharp to

prevent there being rounded surface. Theplane will have stronger signal from the sidethan front called orientation.

5.Smooth surfacesThe relief of the surface could containindentations that act as corner reflectors whichwould increase RCS from many orientations.

This could arise from open bomb-bays, engineintakes, ordnance pylons, joints betweenconstructed sections etc. Also, it can beimpractical to coat these surfaces with radar-

absorbent materials.


24/36

Measurement of RCSMeasurement of a targets RCS is performed at

a radar reflectivity range or scattering range. Therange includes outdoor type.

Near Field And Far Field Measurement1. Near Field

These techniques have been developed toincrease accuracy, throughput, lower costs, and

provide antenna diagnostics. The most commonlyused techniques are: Planer Spherical

Cylindrical


25/36

The reactive near field region isthe region close to the antennaand up to about 11 away from

any radiating surfaces. Near Field test system measures

the energy in the radiatingnear-field region & converts

those measurements by a Fouriertransform into the far-field result.

2. Far FieldThis technique is used for determining the

amplitude and phase characteristics of an AUT.

Low gain antennas operating below 1GHz, and


26/36

where partial radiation characteristics arerequired, are candidates for far- fieldmeasurements.

Far Field Distance DeterminationR > 2D2 /

D=aperture of antenna under test

=measured wavelength


27/36

RANGE CONSIDERATIONS

The aim in designing a Far-Field range is to

simulate the operating environment of the testantenna as closely as possible. Far-fieldmeasurements can be performed on indoor andoutdoor ranges.

The selection of range is depended on:

Availability, access & cost of real estate. Weather. Budget. Security considerations. Test frequency n aperture size.

Antenna handling requirements.


28/36

CalculationsQuantitatively, RCS is calculated in three-dimension:

Where = RCS , = incident power densitymeasured at target, Ss = scattered power density.

In electromagnetic analysis

Where Es & Ei are far-field scattered & incidentelectric field intensities respectively.

We use computer to predict what the RCS will

look like before fabricating an actual object.

Si


29/36

METHODS OF RCS REDUCTION(A)Purpose shaping

In this, the shape of the targets reflectingsurfaces is designed such that they reflect energyfrom the source. The aim is usually to create

cone of silence about the targets direction ofmotion. Due to the energy reflection, this methodis defeated by using Passive(multi-static) radars.

(B)Active cancellationWith this, the target generates a radar signal

equal in intensity but opposite in phase to the

predicted


30/36

reflection of an incident radar signal.

(C)Passive cancellationIt refers to RCS reduction by introducing a

secondary scattering to cancel with thereflection of primary target.

(D) Radar absorbent materialWith RAM, it can be used in the originalconstruction, or as an addition to highly

reflective surfaces. There are three types ofRAM.


31/36

RESULTS OF RCS MEASUREMENT1) SPHERE

Fig 1: Comparison of theoretical and experimental RCS ofsphere (dia: 25.25 cm)


32/36

RCS COMPARISON BETWEEN SPHERES OFDIFFERENT DIAMETER

Fig 2: Response of RCS v/s frequency of spheresof different diameter


33/36

METAL PLATE

Fig 3: Comparison of theoretical and experimentalRCS of metal plate (15 cm x 15 cm)

RCS COMPARISON BETWEEN METAL


34/36

RCS COMPARISON BETWEEN METALPLATES OF DIFFERENT DIMENSIONS

Fig 4: Response of RCS v/s frequency of metal plateof different dimensions


35/36

CYLINDERCylinder length=15 cm and Diameter= 2.4 cm.

Fig 5: Comparison of theoretical and experimental RCS ofcylinder(dia: 2.4cm; length 15 cm)

CONCLUSION


36/36

CONCLUSION

We have studied Vector Network Analyzer andIts application for measurement of Radar CrossSection (RCS). The RCS of different objects likesphere, metal plate and cylinder were measured.

RCS measurements of various targets likesphere, metal plate and cylinder were carried outin Anechoic Chamber facility. It has been

observed that for sphere RCS is constant overfrequency while it increases with frequency formetal plate and cylinders.

vector network analyzer &its application for rcs akm

Documents