attenuators and phase shifters in microwave engineering

attenuators importance and phase shifters

1. Attenuators and phase shifters 1

2. Attenuat o rs 2 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.

3. Cont’d 3 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.

4. Fixed type of attenuator 4 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.

5. 5

6. Cont’d 6 The performance characteristics of a fixed attenuator are: Input and output impedances Flatness with frequency Average and peak power handling capability Temperature dependence

7. Variable Attenuators 7 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.

8. Flap attenuator 8 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.

9. Co n t’d 9 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.

10. Movable vane attenuator 10 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 11 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

12. Co n t’d 12 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 𝑐𝑜𝑠 2 𝜃 , which has the same

13. APPLIC A TIONS 13 Used in a variety of communication and radar systems microwave instrumentation and measurement systems In industrial applications.