ROG Blog

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

Suppressing Spurious Modes in Microwave PCBs

Spurious modes can occur in printed circuit boards (PCBs) in spite of the best-laid plans. These modes support extra, unwanted signals, in addition to the intended signals, that can wreak havoc on a PCB and its application, causing interference and degradation of the intended signals. Although minimizing spurious modes in PCBs is largely a result of careful design practices, the choice of PCB material can have some bearing on the final spurious mode behavior, especially at higher frequencies.

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Survey Multilayer Circuit Possibilities With Stripline

Stripline is one of the transmission-line options facing high-frequency circuit designers, especially for circuits where minimal electromagnetic (EM) radiation is important. Stripline can be thought of as a flat conductor suspended between two ground planes, with dielectric material separating the conductor from the ground planes. The choice of printed-circuit-board (PCB) material can contribute a great deal to the success of a single-layer or multilayer stripline circuit assembly.

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Effectively Launch Signals Onto PCBs

 High-frequency signals must survive many transitions in an RF/microwave system, with one of the more challenging being the point at which signals are “launched” from a coaxial connector to a printed-circuit board (PCB). Following some general guidelines can help improve the effectiveness of an RF/microwave signal launch in double-copper-layer and multilayer PCBs, even when they contain different types of transmission-line formats, such as microstrip, stripline, and coplanar-waveguide (CPW) transmission lines. 

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Match Circuit Materials to Power Dividers and Couplers

 Power dividers/combiners may be among the most popular and most used of high-frequency components. And couplers, such as directional couplers, are not far behind. When designing and fabricating power dividers/combiners and couplers, it can be helpful to better understand how different PCB material properties relate to the final performance possible with these components, to help set limits on a number of different performance parameters, such as frequency coverage, operating bandwidth, and power-handling capability. 

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Making Microstrip Coupled Features Work

 The printed-circuit-board (PCB) material plays a major role in how microstrip transmission lines perform their duties in RF and microwave circuits, and it can be helpful to understand how certain PCB material characteristics contribute to the ways that microstrip transmission lines and their coupled features perform in these different high-frequency components. 

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Taming Discontinuities in Microwave Circuits

 Designing high-frequency microwave circuits and, with increasing frequency, millimeter-wave frequencies require for the most part laying out carefully conceived transmission lines to carry those high-frequency signals across a printed-circuit board (PCB). Of course, if the task of fabricating the PCB was simply a matter of adding circuit elements, such as resistors, capacitors, and inductors, to create the necessary frequency-domain/time-domain response for the PCB, it might go somewhat easier. But every PCB with high-frequency transmission lines must also manage any number of circuit discontinuities and junctions. Since these and similar discontinuities can be found on all but the simplest of RF/microwave circuits, the question is “How can the effects of these discontinuities be minimized through the thoughtful choice of PCB material?” 

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Probing Microwave PCB Heating Patterns

Learn more about this topic at IMS 2014

RF/microwave power applied to a printed-circuit board (PCB) will generate heat. A key to designing a practical circuit on a given PCB material is to understand how different circuit material properties can impact the heating patterns on an RF/microwave PCB, and to work within the limits of a high-frequency circuit material.

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Sorting Circuit Materials For Low-Noise Amplifiers

Low-noise amplifiers (LNAs) are essential in many high-frequency receivers, delivering gain where needed while keeping noise levels to a minimum. Designing an effective LNA circuit often comes down to a critical choice of active device, such as a transistor or integrated circuit (IC). But selecting the right printed-circuit-board (PCB) material can also have a lot to do with achieving LNA performance goals, since circuit laminates can contribute a great deal to final amplifier noise-figure performance. It can help to know what to look for when selecting PCB materials for RF/microwave LNAs.

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Comparing Differential and Single-Ended Transmission Lines

Circuit designers often channel RF/microwave signals by means of a variety of different transmission-line technologies, such as microstrip or stripline transmission lines. They may also choose between single-ended and differential (also known as balanced) circuit configurations for certain applications, such as when the benefit of differential transmission lines may be necessary to suppress the influence of outside noise or signal sources. How do these types of transmission lines and circuit configurations differ, and how do they impact the choice of circuit material? Each circuit approach has positive and negative aspects, and the choice of printed-circuit-board (PCB) materials can play a role in the level of performance possible with each circuit configuration.
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Ring Resonators Help Characterize PCB Materials

Circuit designers often reach for a particular printed-circuit-board (PCB) material based on what they know of its essential material properties, such as dielectric constant (Dk) and dissipation factor (Df). At lower frequencies, having accurate material parameters may be helpful but not crucial whereas, at higher frequencies, knowing such circuit-material parameters as Dk and Df can be critical to the success of a circuit design. For those who need to know, fortunately, a number of different methods have been developed over the years for measuring and calculating a PCB material’s Dk at different frequencies, perhaps other than what is provided on the data sheets by a circuit-material’s manufacturer. One of the most reliable methods for determining a PCB material’s Dk and Df values is through the use of microstrip ring resonator circuit elements, due to the relationship of the resonant frequency of these circuit elements to the permittivity of the PCB material.
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