LO 11.1.3 Intro to MW, WG,TE,TEM devices.pptx

electronic components designed to operate at microwave frequencies, typically in the range of 1 GHz to 300 GHz. They are crucial for various applications in telecommunications, radar systems, satellite communication, and more.

1. INTRODUCTION TO MICROWAVES Microwaves - electromagnetic waves with a frequency between 1GHz (wavelength 30cm) and 3GHz (wavelength 1mm) Microwaves frequency are further categorized into frequency bands: L (1-2 GHz), S (2-4 GHz), C (4-8 GHz), X (8-12 GHz) Receivers need an unobstructed view of the sender to successfully receive microwaves Microwaves are ideal when large areas need to be covered and there are no obstacles in the path LO 11.1.3

2. WAVE GUIDES LO 11.1.3

3. USES OF WAVEGUIDES To reduce attenuation loss High frequencies High power Can operate only above certain frequencies Acts as a High-pass filter Normally circular or rectangular We will assume lossless rectangular LO 11.1.3

4. WAVE GUIDE MODES OF PROPOGATION TEM ( E z =H z =0) can’t propagate. TE ( E z =0) transverse electric In TE mode, the electric lines of flux are perpendicular to the axis of the waveguide TM ( H z =0) transverse magnetic, E z exists In TM mode, the magnetic lines of flux are perpendicular to the axis of the waveguide. HE hybrid modes in which all components exists LO 11.1.3

5. TM MODE The m and n represent the mode of propagation and indicates the number of variations of the field in the x and y directions Note that for the TM mode, if n or m is zero, all fields are zero. LO 11.1.3

6. CUT-OFF WAVELENGTH If the free space w/l is incr beyond a limit, wave can no longer propagate for a w/g with a fixed a & m. This is the cut-offf w/l. It is defined as the smallest free space w/l that is just unable to propagate in the w/g under given conditions. At this w/l we will have LO 11.1.3

7. Guide Wavelength λ p = λ /(sin θ ) = λ /(1-cos 2 θ ) ½ = λ /[1-(m λ /2a) 2 ] ½ = λ [1- ( λ / λ o ) 2 ] ½ LO 11.1.3

8. CUT OFF FREQUENCY The cutoff frequency is the frequency below which attenuation occurs and above which propagation takes place. (High Pass) The phase constant becomes LO 11.1.3

9. Group velocity a wave-group, with given whose amplitude is modulated so that it is limited to a restricted region of space at time t = 0. The energy associated with the wave is concentrated in the region where its amplitude is non-zero . At a given time, the maximum value of the wave-group envelope occurs at the point where all component waves have the same phase .. This point travels at the group velocity ; it is the velocity at which energy is transported by the wave. LO 11.1.3

10. Group velocity and Phase velocity The group velocity is the velocity with which the envelope of the wave packet, propagates through space. The phase velocity is the velocity at which the phase of any one frequency component of the wave will propagate. You could pick one particular phase of the wave (for example the crest) and it would appear to travel at the phase velocity. LO 11.1.3

11. The velocity of a wave can be defined in many different ways, partly because there are different kinds of waves, and partly because we can focus on different aspects or components of any given wave. The wave function depends on both time, t, and position, x, i.e.: Where A is the amplitude Group velocity and Phase velocity LO 11.1.3

12. The speed at which a given phase propagates does not coincide with the speed of the envelope. Note that the phase velocity is greater than the group velocity. Group velocity and Phase velocity LO 11.1.3

13. Similarly, at any fixed instant of time, the function varies sinusoidally along the horizontal axis. The wave number , k, of a wave is the number of radians (or cycles) per unit of distance at a fixed time. Group velocity and Phase velocity LO 11.1.3

14. Attenuators Max attenuation when flap is fully inside. Slot for flap is chosen to be at a non-radiating position. Max attenuation when vane is at centre of guide and min at the side-wall. Atten (dB) = 10 log (P i /P o ) = P i (dB)-P o (dB) Resistive Flap Sliding-vane Type Rotary-vane Type P i P o P i P o LO 11.1.3

15. Attenuation in Waveguides Waveguides operating above cutoff frequency have attenuation for any or all of the following reasons:- Reflections due to impedance mismatches Losses due to flow of current in walls Losses in the dielectric filling of waveguides LO 11.1.3

16. Attenuation Factor For waveguides operating below cutoff frequency, attenuation is given by:- A = e α z , where, e - Base of natural Logarithm α = 2 π / λ o – Attenuation factor in Np/m, z - Length of waveguide λ o - Cutoff wavelength A dB = 20 log 10 (e α z ) LO 11.1.3

17. Relation Between Np & dB Attenuation of a wave is a measure of the spatial decay of the wave Attenuation of 1 Np denotes a reduction to e -1 of the original value So, 1 Np = e In terms of dB, 1 Np = 20 log 10 (e) = 20 x 0.434 = 8.686 dB LO 11.1.3