MICROWAVE DEVICES AND ENGINEERING Lecture No 3& 4 Review & Microstrip Transmission Line, Striplines, Coaxial Cables & Waveguides Ref Material: Microwave Engineering by Pozar (2nd Ed) Chapter 3, and Gonzalez Chapter 1. Instructor: Irfan Ahmed Avionics Engineering Department

This lecture will cover : Block Diagram of Microwave System Review of dB scale Review of Transmission Line Concepts Review of Microstrip Transmission Lines Waveguides / Coaxial cable / Stripline

deciBels Ratio of two Quantities Benefits : Nonlinear to Linear scale Large numbers can be represented easily

Microwave Power, dB & dBm 0 dBm 1 mW 10 dBm 10 mW 30 dBm 1 W -10 dBm .1 mW -30 dBm .001 mW

Microwave Communication System

Microwave Communication System

Transmission Line Concepts Diff b/w Circuit Theory and Transmission Line Theory is electrical size. Transmission Line often represented as a two-wire line.

Two Wire Parallel Transmission Lines

Coaxial Cables

Coaxial Cables Wide bandwidth. No lower cutoff frequency. Low loss. High isolation. Supports TEM mode. Cutoff frequency.

Coaxial Cables

Waveguides

Waveguides

Waveguides Metallic transmission lines used at microwave frequencies. Negligible loss. Excellent shielding. Extremely high peak power. High cost. Large size, especially at lower frequencies. Lower cutoff frequency. (Depends upon mode) TE and TM modes will propagate No propagation below cutoff frequency

Planar Transmission Lines

Microstrip Transmission Line

Microstrip Transmission Line

Microstrip Transmission Line Developed by ITT laboratories as a competitor to stripline (1952). All active components can be mounted on top of PCB. Most popular microwave transmission line.

Microstrip Transmission Line

Microstrip Transmission Line

Stripline

Stripline Invented by R. Barrett in 1950s. Conductor sandwiched by delectric between a pair of groundplanes. TEM transmission line media. Non-dispersive nature. Much harder to fabricate. Requires comparatively thicker boards and narrower strips.

Stripline t

Waveguides

Quarter Wave Transformer Impedance match only at a particular frequency Will see more interesting phenomena in an assignment or in lab

Quote of the day Failures are often the results of timidity and fears; disappointments are the results of bashfulness; hours of leisure pass away like summer-clouds, therefore, do not waste opportunity of doing good.