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Dielectric material basics

This page describes dielectric material basics and specifications. It includes dielectric substrate material duroid, PTFE-woven glass fiber, epoxy glass and Alumina.It covers properties of various microwave substrates.

dielectric material cross section
Figure shows cross section of a typical dielectric material. Following are some of the very popular dielectric materials available . This materials are very useful for RF and microwave high frequency circuit design.

Dielectric Material Permittivity(Epsilon) T, Thickness of pattern (50 Ohm Line) W, Width of 50 Ohm line
RT/Duroid 2.3 0.015" 0.044"
PTFE-woven Glass fibre 2.55 0.010",0.031",0.062" 0.25",0.079",0.158"
Epoxy-Glass 4.8 0.062" 0.108"
Alumina 10.0 0.025",0.050" 0.025",0.048"

Above mentioned dielectric materials are used for RF and Microwave circuit design based on need. Line width is the major criteria for selecting the dielectric material for various RF/Microwave frequencies.

The dielectric material is used as PCB for fabricating the RF circuit layout as per design of various RF/microwave systems.

The dielectric substrate selection plays very vital role in size reduction and impedance matching. To obtain specific characteristic impedance transmission line requires appropriate width (W) of the line. This W depends on dielectric constant and thickness of the dielectric substrate.

The higher dielectric constant substrates help achieve lower size line(width) on the dielectric substrate. The low dielectric constant substrates are used for broadband low loss circuit designs.

Properties of Microwave Dielectric Substrates

dielectric Substrate Dielectric constant tan δ measured at 10GHz Thermal Conductivity(W/cm-degreeC)
Si 11.7-12 40-150 0.9
GaAs 12.8-13 16 0.3
InP 12.5-14 NA 0.68
Alumina 9.6-9.9 1-2 0.2 - 0.3
Beryllia 6.6-6.8 3 2.5
Fused silica 3.8 <1 0.013
Sapphire 9.3-11.7 <1 0.38-0.46
Woven PTFF/glass,Non-woven 2.2 9 0.0026
PTFE/glass,Ceramic filled 2.1 4.5 Approx.0.003
PTFE/glass 10.5 15 0.004
Polyolefin 2.3 1 0.001
Ferrite/granite 1316 2 0.03


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