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Isn’t designing a microwave filter as simple as loading parameters into a computer-aided-engineering (CAE) program? In truth, many modern CAE software tools are quite good, and can provide accurate predictions of performance when fed sufficient input data. However, most do not account for all variables influencing a high frequency filter, including the effects of anisotropic printed-circuit-board (PCB) materials. When designing RF and microwave filters, it helps to choose your PCB material wisely.

Microstrip or stripline? That choice has been faced by high frequency designers for decades. Both transmission-line technologies are widely used in both active and passive microwave circuits, with excellent results. Is one approach better than the other? Before tackling such a question, it might help to know how each transmission-line technology works and what kind of demands each place on a printed circuit board (PCB) material.

Outgassing is a concern for any electronic equipment intended for use in high-vacuum environments. It refers to the release of gas trapped within a solid, such as a high-frequency circuit-board material. The effects of outgassing can impact a wide range of application areas in electronics, from satellites and space-based equipment to medical systems and equipment. In space-based equipment, released gas can condense on such materials as camera lenses, rendering them inoperative. Hospitals and medical facilities must eliminate materials that can suffer outgassing to maintain a sterile environment.

November 4, 2010 John Coonrod is a Market Development Engineer for Rogers Corporation, Advanced Circuit Materials Division. John has 23 years of experience in the Printed Circuit Board industry. About half of this time was spent in the Flexible Printed Circuit Board industry doing circuit design, applications, processing and materials engineering. The past ten years have been spent supporting circuit fabrication, providing application support and conducting electrical characterization studies of High Frequency Rigid Printed Circuit Board materials made by Rogers. John has a Bachelor of Science, Electrical Engineering degree from Arizona State University. Thinner printed-circuit-board (PCB) materials have some...

Printed-circuit antennas must provide big performance in small packages, especially for modern fixed and mobile wireless devices. In some cases, they must provide high gain, or light weight, or handle high power levels. The choice of circuit-board laminate material plays a key role in the size and performance of a printed-circuit antenna, such as achieving maximum gain at RF and microwave frequencies. When selecting a circuit-board laminate for a printed-circuit antenna, it helps to understand how laminate material parameters relate to antenna performance.

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.

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.

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.