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Attenuators and phase shifters

MR. HIMANSHU DIWAKARAssistant Professor

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Attenuators

• An attenuator is an electronic device that reduces the power of a signal without appreciably distorting its waveform.

• An attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, an attenuator provides loss, or gain less than 1.

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Cont’d

• Attenuators are usually passive devices made from simple voltage divider networks used to control the amount of microwave power transferred from one point to another point.

• Reflects and absorbs the energy in some of dissipative elements.

• Attenuation is a function of frequency.

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Fixed type of attenuator

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• Fixed attenuators in circuits are used to lower voltage, dissipate power, and to improve impedance matching.

• Fixed type of attenuators are commonly used where a fixed amount of power is to be provided. If such type of attenuator absorbs all the energy entering into it, we call it as waveguide terminator.

• This normally consists of a short section of waveguide with a tapered plug of absorbing material at the end.

• The tapering is done for providing a gradual transition from the wave guide medium to the absorbing medium thus reducing the reflection occurring at the media interface.

• Dielectric used is glass.

• Attenuators are also used to 'match' impedance by lowering apparent SWR.

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Cont’d

• The performance characteristics of a fixed attenuator are:

1) Input and output impedances2) Flatness with frequency3) Average and peak power handling capability4) Temperature dependence

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Variable Attenuators

• Variable attenuators provide continuous or step wise variable attenuation.

• For rectangular waveguides, these attenuators can be flap type or vane type.

• For circular waveguide rotary type is used.

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Flap attenuator• Flap type attenuator

consists of a resistive element or disc inserted into a longitudinal slot cut along the center of the wider dimension of the guide.

• Which is responsible for attenuation.

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Cont’d• Flap is mounted on the hinged arm allowing it to descent into the

center of waveguide.• Degree of attenuation can be determined by depth if assertion.

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Movable vane attenuator

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• The vane positioned at center of guide can be moved laterally from center, where it provides maximum attenuation to the edges where the attenuation is considerably reduced since E lines are always concentrated at the center of waveguide.

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Cont’d• A resistive rotary vane attenuator provides precision attenuation with

an energy of of indicated attenuation over the operating frequency range.• It consists of three vanes. The central vane rotating type placed in the

central section of circular waveguide arrangement tapered at both the ends

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Cont’d• When all the three vanes are aligned their planes at 90 degree to the

direction of E, so no attenuation.

• Vane 1 prevents any horizontal polarization and hence output of vane 1 is vertically polarized.

• Center vane 2 is rotating type and if it is rotated by an angle , the E component is attenuated and component is present at the output of vane 2 and the final output of attenuator becomes , which has the same

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Phase Shifters

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Contents1. Introduction

2. Types Of Phase Shifter.

3. Applications.

4. Conclusion.

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•A Phase Shifter is two-port device whose basic function is to provide a change in the phase of RF signal with practically negligible attenuation.

Introduction

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Classification Of Analog Phase Shifters

Analog Phase Shifters

Semiconductor Ferrite

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Ferrite Phase Shifters

• THEORY• Is the change in the effective permanent of ferrite with the magnetic

field ?

As the permeability increase the effectiveness of the ferrite rod increases since guided wavelength is equal to wavelength in space divided by effectiveness (permeability), hence guide wavelength decreases, which result in a change or RF insertion phase.

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Semiconductor Phase Shifters

Reciprocal Reciprocal Non reciprocalNon reciprocal

P-I-N diode

GaAs FET(Passive)

• Switched line• Hybrid coupled• Loaded line• High-pass low- pass• Switched network

GaAs FET (active switch)

• Switched path

GaAs FET (passive)

GaAs FET (active switch)

• Switched line/loaded line• Hybrid coupled• High-pass low -pass

• Switched path DGFET

Planar/hybrid MIC Monolithic

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Specification of Digital Phase Shifter

Frequency 0.5 to 2.0 GHzPhase Accuracy +/- 10Amplitude Balance +/- 1.0 dBV.S.W.R 1.7:1Noise Figure 7 dB

Input power 0 dBm CW ~ +2- dBm Max

Size 4.95 x 3.38 x 1.0 inchSwitching Speed 500 nSec

Digital Phase Shifter

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Basic terms connected to antenna array :

1.Insertion phase - It is the phase delay experienced by the RF signal betweenits input and outputs ports.

2. Input VSWR - The input voltage standing wave ratio is defined as  VSWR =

3.Directivity - The ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions

D = 4 U / P rad

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APPLICATIONS

• Used in a variety of communication and radar systems

• microwave instrumentation and measurement systems

• In industrial applications. 

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CONCLUSION• Phased array radars are used for inertia less scanning and tracking. They as well can be

used for multi target tracking.  • Phased arrays can also be used for air traffic control at the airports.  • Other than defense applications, phase shifters are finding their place in routine life.  • An American company is working on a project where phased arrays are used for finding the

blind stops on road while driving.  • With such high tech commercial application, driving on road will be safer.  • The phase shifter technology for phased arrays has no limitation either in defence

applications or in our daily life.MR. HIMANSHU DIWAKAR