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.

Dielectric Concerns For Directional Couplers

Directional couplers are vital components for sampling signal power in an RF/microwave system without necessarily disturbing the signal path. Such couplers come in many forms, including in metal housings with coaxial connectors. A typical coaxial directional coupler has four connectors, for input, output, coupled, and isolated ports. The coupled port provides a small amount of power taken from the input port, defined by the coupling factor, such as a 20-dB coupler. This blog posts covers the advantages of using high quality PCB materials for directional couplers.
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Make Waveguide In Planar PCB Form

Forming resonant cavities on microwave printed-circuit boards (PCBs) is a good first step to the design of high-frequency oscillators and filters. Another approach is the use of substrate-integrated-waveguide (SIW) technology, which is not only suitable for oscillators and filters, but can be formed into extremely compact antennas, and can support signals well into the millimeter-wave range. SIW technology structures are versatile design elements for integrating active and passive circuits together with radiating elements, such as antennas, onto compact circuits using popular PCB laminate materials. As the last blog showed, creating resonant cavities in different circuit materials can lead to high-performance microwave oscillators and filters. As this blog will reveal, SIW structures can also serve as resonators in planar, multilayer PCBs, helping to create compact, high-performance filters, oscillators, and other resonator-based circuits.
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Creating Effective Cavity Resonators

The resonant frequency or frequencies of a cavity depend on several factors, including the dimensions of the cavity, the materials that form the cavity, and how energy is launched and/or extracted from the cavity. A resonant cavity is sometimes referred to as a form of in-circuit waveguide, short-circuited at both ends of the waveguide structure so that EM energy builds within the cavity at a designed frequency or band of frequencies. The size of a cavity resonator, for example, is a function of the desired resonant frequency and the characteristics of the PCB materials used for the resonator. PCB materials with higher dielectric constants will support smaller cavity resonators for a given frequency than circuit substrate materials with lower dielectric constants.
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Picking PCB Material For A Patch Antenna

A patch antenna, which is also known as a microstrip antenna, can be fabricated with standard printed-circuit-board (PCB) processes using high-frequency laminate materials. An antenna can be as simple as a rectangular patch above a ground plane or as elegant as a complex array of patches, customized for a specific radiation pattern. As with other printed circuits, the choice of circuit material can greatly impact the performance possible from the final antenna design. That choice should be guided by a clear understanding of how a circuit material’s electrical and mechanical properties relate to the performance of a patch antenna.
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Charting Conductor Profile Effects On Stripline

Microwave circuits are generally susceptible to the effects of copper conductor surface roughness, some less than others. As circuit designers learned in the last blog, microstrip designs that must minimize loss can benefit from the use of circuit materials with low-profile copper conductors, such as RO4000® LoPro™ series circuit laminates from Rogers Corp. As the last blog pointed out, CPW and conductor-backed CPW (CBCPW) circuits will not benefit at higher frequencies from the use of laminates with low-profile conductors to the same degree as microstrip circuits. But is this also the case with high-frequency or high-speed stripline circuits? Just how does conductor surface roughness influence high-frequency stripline circuit performance?

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CPW Can Minimize Conductor Profile Effects

Conductor surfaces on a printed-circuit board (PCB) can vary widely, from a “smooth-as-glass” finish to a more typically rough profile. As detailed in an earlier ROG Blog, a conductor surface profile can impact the performance of a sufficiently high frequency circuit, increasing insertion loss and dispersion and even causing propagation delays and changes in the effective dielectric constant of the circuit. But are all RF/microwave transmission-line technologies affected by conductor surface profiles in the same way? What about designs based on coplanar-waveguide (CPW) transmission lines, or stripline? Do they require circuit materials with low-profile conductors, or are they less affected than microstrip by conductor surface roughness?
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Celebrating ROG Award Contest Winners at IMS 2012

The ROG Award Contest kicked off in November 2011. We invited customers to enter the contest by telling us about their applications using Rogers?materials. For the next several months, customers shared stories about their Best Digital Application, Most Challenging Board Build, Most Unique and Creative Use of Material, Most Innovative Design, Longest Product Life, and Most Extreme Conditions, all accomplished together with Rogers?materials. One winning application was chosen for each category.
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Picking Prepregs For Multilayer Microwave PCBs

Multilayer microwave PCBs can pack much circuitry into a small volume. But creating a multilayer microwave circuit is more than just stacking layers. It takes planning and knowledge of the multilayer fabrication process. In particular, an understanding of how prepreg materials are used in multilayer circuits can be helpful.
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Minimize Microstrip Radiation Effects

Radiation loss can be a concern in microstrip circuits at higher microwave frequencies. Fortunately, its effect can be minimized by reducing the number of discontinuities in a circuit design, and by carefully weighing the choice of circuit substrate material in terms of thickness and dielectric constant, where thinner materials and higher dielectric constants can both contribute to lower radiation losses.
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Low-Loss PCBs Enable MM-Wave Auto Electronics

Evolution of the electronic systems in automobiles and other vehicles is exciting to watch, and many technologies once associated with the military, such as radar systems, are becoming available to average drivers. As highlighted in the previous ROG blog, 24-GHz short-range-radar (SRR) systems are being offered more and more in car models around the world. But vehicle designers and manufacturers are also looking ahead to the greater resolution possible with 77- and 79-GHz automotive radar systems. And for that evolution in automotive electronic systems to truly take place, printed-circuit-board (PCB) materials are important building blocks that will enable the potentially much safer automobiles of the future.
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