ECE 563 & TCOM 590 Microwave Engineering Planar Transmission Lines: Striplines and Microstrips October 14, 2004

Planar Transmission Lines

Parallel Plate Waveguide

Surface Waves on a Grounded Dielectric Slab 0r0r 00 x z //////////////////////////////////////

Surface Waves on a Grounded Dielectric Slab

Surface Waves on a Grounded Dielectric Slab – TM Mode

TM mode cutoff frequencies

Surface Waves on a Grounded Dielectric Slab – TE Modes

TE mode cutoff frequencies

Stripline Triplate transmission line

Stripline Advantage (compared to parallel plates) –transverse fields remain in the vicinity of the center conductor between 2 grounded planes –2 conductor line, no lower frequency cutoff: down to f=0, up to cutoff of first TE mode. –Miniaturization

Stripline Compared to coax or waveguide –Advantage if Gunn diodes or mixer diodes to be apart of circuit design. –Advantage, large bandwidth, mini-size –Disadvantage- lack of isolation, lower power handling Dominant mode - TEM

Stripline

Losses

Attenuation due to conductor losses (approximate result)

Planar Transmission Lines

h ////////// t w ////////////////////// Microstrip Lines ­Popular ­fabricated by photolithographic processes ­easily integrated with other passive and active microwave devices ­convenient, economical; therefore, widespread use ­Problem ­radiation and undesired modes by lines at discontinuities

Microstrip w t h

Microstrip Design

Microstrip Design Relationships

Normalized Wavelength vs w/h

Z 0 and W/d approximation

Effects to Dampen Signal Propagation along a Microstrip Signal heats conductor through Ohmic Losses Signal heats substrate which is not lossless Signal leaks away as radiation

Ohmic Losses

Dielectric Losses

Radiation Losses

Quality factor

Microstrip-line Realization

Microstrip Filter Design

Microstrip Line Circuit Elements

Microwave Transmission

Notes on striplines and microstrips ·less bulky than waveguides ·no need for welding and brazing ·planar circuits - 2 dimensional universe ·but high field concentration ·limits power ·breakdown ·heating center condition ·Open structure - radiates

Microwave Advances Considerable Interaction –distribution of analog microwave signals via high speed fiber - optic links –optically controlled microwave devices & circuits Photonics Lightwave Techniques –fiber optics –image processing –high speed High Speed Circiuts MMIC’s - Monolithic Integrated Circuits High speed & high frequency

Microwave Advances Fiber-optic cables to route microwave signals –reduce size and weight –large bandwidth –immunity to interference –crosstalk isolation –potentially smaller transmission losses –applications feeds for phased array antennas delay lines, cable TV signal signal distribution

Millimeter Wave Monolithic Integrated Circuits (MIMIC) Affordable, reliable, reproducible  wave and millimeter wave components frequency –tests up to 40 GHz –pulse power goal S-band (3 GHz) to 75 GHz Materials Research –GaAs –High electron mobility transistors (HEMT’s) –CAD –MHDL-Microwave Hardware Descriptive Language