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.
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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