1 / 37

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

uma-garza
Download Presentation

ECE & TCOM 590 Microwave Transmission for Telecommunications

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related