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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.

How Is PCB Laminate Dk Determined Anyway?

The dimensions of high-frequency circuit structures, including different types of transmission lines and the spacing between lines for proper isolation and/or coupling, are determined by the circuit material’s dielectric characteristics, and one of the main parameters for understanding those characteristics is Dk. Many designers grow to trust that the Dk value assigned to a given circuit material is truly accurate and consistent from board to board and base their designs on that trust. But how does the material supplier determine a circuit material’s Dk value anyway?


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For Millimeter-Wave Performance, Thinner Materials are Often Better

Thin can be a good thing for high-frequency circuit laminate materials. As this ROG Blog detailed some years ago (see “Thinner Materials Help Target Higher Frequencies,” http://mwexpert.typepad.com/rog_blog/2010/11/thinner-materials-help-target-higher-frequencies.html), thinner printed-circuit-board (PCB) laminates offer many electrical benefits as well as mechanical advantages compared to thicker circuit materials, especially at higher frequencies reaching into millimeter-wave bands.


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Those Holes Are Part of the Circuit

For many circuit designers, plated through holes (PTHs) form pathways, from one circuit plane to another. The key to making PTHs work for the benefit of a circuit design is to understand their effects on electrical performance, especially at higher frequencies. They should be considered as circuit elements, and they can have a great deal to do with a number of analog circuit transmission-line performance parameters, including insertion loss and return loss, and they can also affect high-speed digital circuit performance by degrading signal integrity (SI) and bit-error-rate (BER) performance.


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Shrink Circuits Using Slow-Wave Structures

Microwave circuit dimensions are related to their wavelengths/frequencies and to the dielectric constant (Dk) of their substrates. Quite simply, higher-frequency signals have smaller wavelengths and their electromagnetic (EM) energy of those smaller wavelengths will propagate through circuits with smaller dimensions. Phase velocity is related to wavelength, with slower EM waves having shorter wavelengths which propagate through circuit structures with smaller dimensions than faster waves with their longer wavelengths. 


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Surfing Millimeter Waves with SIW Technology

Millimeter-wave circuits were once considered exotic and only used for specialized applications, typically in the military space. For one thing, frequencies with such small wavelengths, from about 30 to 300 GHz, required special components and circuits scaled to those diminutive wavelengths. But lower-frequency bands are being consumed by a growing number of wireless applications, and millimeter-wave frequency bands are looking more and more attractive for communications systems of the future. Achieving millimeter-wave circuit designs on reliable printed-circuit-board (PCB) materials in a practical manner will be the challenge in making these higher frequencies affordable. Substrate-integrated-waveguide (SIW) circuit technology may just be the solution.


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Finish Makes a Difference In Broadband PCB Loss

 The choice of plated finish can make a real difference in a PCB’s conductive loss, especially for broadband, high-frequency circuits. To better understand the loss performance of different plated finishes, various transmission lines were fabricated on different circuit laminates and different plated finishes applied.  


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Silence Filter Harmonics with Composite Circuit Materials

 Microstrip edge-coupled bandpass filters (BPFs) can help clean the spectrum around a desired center frequency. Fabricated on printed-circuit-board (PCB) materials, these compact filters can be integrated with other circuit functions to provide dependable filtering of communications bands and high-frequency signals for a wide range of applications. 


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Comparing PCBs for Microstrip and Grounded Coplanar Waveguide

Circuit designers must often select a circuit technology, such as microstrip or grounded coplanar waveguide (GCPW) circuitry, with a particular design and circuit material to achieve optimum performance. Circuit technologies, such as microstrip and GCPW, each have their strengths and weaknesses, and it may help to take a closer look at these two circuit technologies in particular to see how they stack up.


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Welcome to ROG Cares

 Here at Rogers Corporation, we help power, protect, and connect our world. On the surface, it means Rogers helps our world with greater reliability, efficiency, and performance, to build a safer, cleaner and more connected world. The materials technologies we create deliver solutions for tomorrow’s breakthroughs.


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