Attenuators and phase shifters

1. Attenuators and phase
shifters
MR. HIMANSHU DIWAKAR
Assistant Professor
JETGI
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2. 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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3. 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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4. 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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6. Cont’d
• The performance characteristics of a fixed attenuator are:
1) Input and output impedances
2) Flatness with frequency
3) Average and peak power handling capability
4) Temperature dependence
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7. 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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8. 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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9. 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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10. 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.

11. Cont’d
• A resistive rotary vane attenuator provides precision attenuation with
an energy of ±2.1% 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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12. 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 𝜃, the E
sin𝜃 sin𝜃 component is attenuated and E cos𝜃 component is present at
the output of vane 2 and the final output of attenuator becomes
E 𝑐𝑜𝑠2 𝜃, which has the same
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13. Phase Shifters
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14. Contents
1. Introduction
2. Types Of Phase Shifter.
3. Applications.
4. Conclusion.
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15. •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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17. Classification Of Analog Phase Shifters
Analog Phase Shifters
SemiconductorFerrite
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18. 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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19. 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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20. Specification of Digital Phase Shifter
Frequency 0.5 to 2.0 GHz
Phase Accuracy +/- 10
Amplitude Balance +/- 1.0 dB
V.S.W.R 1.7:1
Noise Figure 7 dB
Input power
0 dBm CW ~ +2- dBm
Max
Size 4.95 x 3.38 x 1.0 inch
Switching Speed 500 nSec
Digital Phase Shifter
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21. Basic terms connected to antenna array :
1.Insertion phase - It is the phase delay experienced by the RF signal between
its input and outputs ports.
2. Input VSWR - The input voltage standing wave ratio is defined as
VSWR =
1 + | S11 |
1 − | S11 |
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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22. APPLICATIONS
• Used in a variety of communication and radar systems
• microwave instrumentation and measurement systems
• In industrial applications.
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23. 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.
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