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The Rog Blog is contributed by John Coonrod and various other experts from Rogers Corporation, providing technical advice and information about RF/microwave materials.

Picking PCB Materials for Power Amplifiers

Designing a high frequency power amplifier takes more than just finding the right power transistor. It involves the design of input and output impedance-matching circuits for maximum power transfer and well regulated power-supply circuits. It also requires choosing a printed-circuit-board (PCB) material that will deliver the right combination of performance and reliability for the cost. The right choice of PCB material for an amplifier design can improve gain, gain flatness, gain stability, and output power.
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Understanding the true meaning of dielectric constant

Dielectric constant (Dk or relative permittivity) is a parameter that design engineers use constantly, often without fully understanding it. Every material has a dielectric constant, even air (slightly more than unity). And the parameter is commonly used by circuit designers to compare different printed-circuit-board (PCB) materials, typically by referring to a fixed value for a given frequency, found on a product data sheet. However, the number can vary for most PCB materials, regardless of material quality. Variations in the Dk value actually have less to do with quality and more to do with how the material is used and tested.
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FR-4 Versus High Frequency Laminates

Epoxy-based FR-4 circuit-board materials are popular for a wide range of electronics applications, and for good reason. These glass-reinforced substrates are reliable, low in cost, with well understood mechanical and electrical characteristics. They are used in everything from audio circuits through microwave designs. But they are not the answer for every circuit, especially for a wide range of high frequency designs, and for several reasons.
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