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ECE & TCOM 590 Microwave Transmission for Telecommunications

ECE & TCOM 590 Microwave Transmission for Telecommunications. Introduction to Microwaves January 29, 2004. Microwave Applications. Wireless Applications TV and Radio broadcast Optical Communications Radar Navigation Remote Sensing Domestic and Industrial Applications

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ECE & TCOM 590 Microwave Transmission for Telecommunications

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  1. ECE & TCOM 590Microwave Transmission for Telecommunications Introduction to Microwaves January 29, 2004

  2. Microwave Applications • Wireless Applications • TV and Radio broadcast • Optical Communications • Radar • Navigation • Remote Sensing • Domestic and Industrial Applications • Medical Applications • Surveillance • Astronomy and Space Exploration

  3. Brief Microwave History • Maxwell (1864-73) • integrated electricity and magnetism • set of 4 coherent and self-consistent equations • predicted electromagnetic wave propagation • Hertz (1873-91) • experimentally confirmed Maxwell’s equations • oscillating electric spark to induce similar oscillations in a distant wire loop (=10 cm)

  4. Brief Microwave History • Marconi (early 20th century) • parabolic antenna to demonstrate wireless telegraphic communications • tried to commercialize radio at low frequency • Lord Rayleigh (1897) • showed mathematically that EM wave propagation possible in waveguides • George Southworth (1930) • showed waveguides capable of small bandwidth transmission for high powers

  5. Brief Microwave History • R.H. and S.F. Varian (1937) • development of the klystron • MIT Radiation Laboratory (WWII) • radiation lab series - classic writings • Development of transistor (1950’s) • Development of Microwave Integrated Circuits • microwave circuit on a chip • microstrip lines • Satellites, wireless communications, ...

  6. Ref: text by Pozar

  7. Microwave Engr. Distinctions • 1 - Circuit Lengths: • Low frequency ac or rf circuits • time delay, t, of a signal through a device • t = L/v « T = 1/f where T=period of ac signal • but f=v so 1/f=/v • so L «, I.e. size of circuit is generally much smaller than the wavelength (or propagation times  0) • Microwaves: L  • propagation times not negligible • Optics: L» 

  8. Transit Limitations • Consider an FET • Source to drain spacing roughly 2.5 microns • Apply a 10 GHz signal: • T = 1/f = 10-10 = 0.10 nsec • transit time across S to D is roughly 0.025 nsec or 1/4 of a period so the gate voltage is low and may not permit the S to D current to flow

  9. Microwave Distinctions • 2 - Skin Depth: • degree to which electromagnetic field penetrates a conducting material • microwave currents tend to flow along the surface of conductors • so resistive effect is increased, i.e. • R  RDC a / 2 , where •  = skin depth = 1/ ( f o cond)1/2 • where, RDC = 1 / ( a2 cond) • a = radius of the wire • R waves in Cu >R low freq. in Cu

  10. Microwave Engr. Distinctions • 3 - Measurement Technique • At low frequencies circuit properties measured by voltage and current • But at microwaves frequencies, voltages and currents are not uniquely defined; so impedance and power are measured rather than voltage and current

  11. Circuit Limitations • Simple circuit: 10V, ac driven, copper wire, #18 guage, 1 inch long and 1 mm in diameter: dc resistance is 0.4 m and inductance is 0.027 H • f = 0; XL = 2  f L  0.18 f 10-6 =0 • f = 60 Hz; XL 10-5 = 0.01 m • f = 6 MHz; XL 1  • f = 6 GHz; XL 103 = 1 k  • So, wires and printed circuit boards cannot be used to connect microwave devices; we need transmission lines

  12. High-Frequency Resistors • Inductance and resistance of wire resistors under high-frequency conditions (f  500 MHz): • L/RDC a / (2 ) • R /RDC a / (2 ) • where, RDC = /( a2 cond) {the 2 here accounts for 2 leads} • a = radius of the wire • = length of the leads •  = skin depth = 1/ ( f o cond)1/2

  13. Reference: Ludwig & Bretchko, RF Circuit Design

  14. High Frequency Capacitor • Equivalent circuit consists of parasitic lead conductance L, series resistance Rs describing the losses in the the lead conductors and dielectric loss resistance Re = 1/Ge (in parallel) with the Capacitor. • Ge =  C tan s, where • tan s = (/diel) -1 = loss tangent

  15. Reference: Ludwig & Bretchko, RF Circuit Design

  16. Reference: Ludwig & Bretchko, RF Circuit Design

  17. Reference: Ludwig & Bretchko, RF Circuit Design

  18. Reference: Ludwig & Bretchko, RF Circuit Design

  19. Gauss No Magnetic Poles Faraday’s Laws Ampere’s Circuit Law Maxwell’s Equations

  20. Characteristics of MediumConstitutive Relationships

  21. Fields in a Dielectric Materials

  22. Fields in a Conductive Materials

  23. Wave Equation

  24. General Procedure to Find Fields in a Guided Structure • 1- Use wave equations to find the z component of Ez and/or Hz • note classifications • TEM: Ez =Hz= 0 • TE: Ez =0,Hz  0 • TM: Hz =0,Ez  0 • HE or Hybrid: Ez 0,Hz  0

  25. General Procedure to Find Fields in a Guided Structure • 2- Use boundary conditions to solve for any constraints in our general solution for Ez and/or Hz

  26. Plane Waves in Lossless Medium

  27. Phase Velocity

  28. Wave Impedance

  29. Plane Waves in a Lossy Medium

  30. Wave Impedance in Lossy Medium

  31. Plane Waves in a good Conductor

  32. Energy and Power

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