This post authored by John Coonrod, Technical Marketing Manager, and team originally appeared on the ROG Blog hosted by Microwave Journal.

Millimeter-wave frequency bands hold valuable spectrum for what lies ahead: fifth-generation (5G) wireless communications and automotive collision-avoidance radar systems. Signals at 60 GHz and higher might have once been thought too high to transmit and receive with affordable circuits. But semiconductor devices and circuit technologies have improved in recent years and millimeter-wave circuits are becoming standard electronic equipment in many car models. Millimeter-wave signals are also expected to play major roles in 5G networks in transferring high-speed data over short distances. For that to happen, low-loss laminates must be available for circuits operating from 60 through 77 GHz, without performance limitations placed by the glass weave effect at those high frequencies. Just what is the “glass weave” effect and what does it have to do with millimeter-wave circuits? It’s all about the wavelengths.

Glass and fiberglass fabrics are commonly used to fortify resin-based circuit laminates. Many PCB materials for higher-frequency use are formed from different woven glass fabrics bound together with epoxy resins. The glass fabrics actually follow precise patterns through the PCB material, with a warp yarn running the length of the material and a fill yarn running the width of the material. The relative permittivity (Dk) values of these different material components are different, so the combination of glass fabrics and epoxy resins form a non-homogeneous medium for signals propagating through transmission lines formed on that medium.

Although such non-homogeneity is less of a concern at lower, RF signals, for millimeter-wave signals with extremely small wavelengths, differences in Dk throughout a propagation medium can result in differences in the characteristic impedance of transmission lines fabricated on that medium. The epoxy resin typically has a lower Dk value than the glass fabric, and the density of the glass fabric will change throughout a PCB as a function of the glass weave pattern. Quite simply, where there is more glass, there is a higher Dk value. Depending upon a particular glass weave, glass bundles can form, resulting in a rise in the Dk value at that location of the PCB material.

In terms of example values, the Dk of a typical resin system may range from 2.0 to 3.0 while the Dk of the glass bundles formed by the glass weave running through the material can be equal to 6.0 or higher. In the open areas of the PCB between glass bundles, the Dk of the laminate will be much lower in value than in those areas around the glass bundles. For lower-frequency signals with relatively large wavelengths, a certain amount of averaging of the effective Dk values of these different sites will take place, resulting in fairly predictable signal propagation behavior that can be accurately analyzed with a computer-aided-engineering (CAE) software simulation program. But at higher, millimeter-wave frequencies, where the signal wavelengths are smaller, the differences in Dk across the PCB due to the glass weave effect can result in transmission-line impedance differences that cause phase shifts at millimeter-wave frequencies.

The types of transmission line used in a high-frequency circuit can also play a part in how significant the role of the glass weave effect plays on the performance of a millimeter-wave circuit. In a multilayer microstrip circuit, for example, due to the randomness of the glass fabric patterns from layer to layer, it is likely that a certain amount of averaging  in the Dk will occur across the circuit board and more consistent performance will be achieved in a multilayer circuit construction. Any type of circuit construction in which two or more layers with glass weave are used will benefit from the averaging effects of the multiple layers.

High-speed digital signals such as differential lines operating at data rates beyond 10 Gb/s can be affected by the increased concentrations of glass bundles within PCB material, since the differential lines depend upon tightly maintained phase relationships for their signal information. As with millimeter-wave signals, high-speed differential lines rely upon circuit materials with low conductor and dielectric losses; minimizing signal phase variations as a result of the glass weave effect is a positive circuit material trait for both millimeter-wave and high-speed-digital signal propagation.

Admittedly, the glass and fiberglass fabrics that are combined with the resin systems to form high-performance circuit materials provide a great deal of mechanical strength to the circuit material, although the non-homogeneity that they can introduce to the material at higher frequencies can be an unwanted side-effect at millimeter-wave and high-speed-digital signals. Automotive radar systems, for example, rely upon the reception of reflected pulses at 77 GHz to determine the position of other vehicles in traffic as well as pedestrians. Phase variations resulting from transmission-line skew in a PCB can effectively shift the position of vehicles being detected in traffic.

Fortunately, the benefits of glass material reinforcement can be added to high-frequency circuit laminates without suffering the negative impact of the glass weave effect. Newer circuit materials such as RO4830™ circuit laminates from Rogers Corp. combine glass and resin materials with a type of glass known as “spread glass.” Rather than using a bundled configuration with a tendency to produce uneven distribution of the glass content throughout the laminate, the glass material is spread evenly throughout the epoxy resin, with no openings between the glass bundles. In this way, the layer of glass fabric in the laminate appears very much like a plane of glass, minimizing or eliminating any variations in Dk throughout the laminate.

RO3003™ circuit laminates from Rogers Corp. are low-loss, ceramic-filled, PTFE-based laminates engineered for circuits to 77 GHz and beyond. This laminate does not have woven-glass fabric and therefore has no concern with the glass-weave effect. The laminate features a Dk of 3.00 ± 0.04 across the board for extremely consistent and predictable performance even at millimeter-wave frequencies. These materials have additional characteristics that make them a good fit for millimeter-wave circuits, including very low moisture absorption, nearly ideal thermal coefficient of Dk (TCDk) at 3 ppm/ºC, and a coefficient of thermal expansion (CTE) of 17 ppm/ºC that is closely matched to copper in the x and y axes and equal to 24 ppm/ºC in the z-axis for highly reliable plated through-holes.

For any concerns related to the glass weave effect, RO4830 materials are produced by means of the spread glass approach, thus avoiding the potential for glass bundles from the glass weave effect. RO4830 and RO3003 materials provide the mechanical stability with temperature to maintain consistent low-loss performance even in rigorous automotive operating environments and, as expected, for an emerging number of 5G millimeter-wave data link applications.

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The Rogers team is passionate about helping the world’s leading innovators solve their toughest material challenges. As we do so, we believe that how we conduct our business is just as important as what we achieve. The Rogers Corp. Corporate Responsibility hub and our updated Code of Business Ethics reflect our commitment to corporate responsibility.

At Rogers, our actions are governed by our Cultural Behaviors and work performance.

“We believe that how we conduct our business is just as important as what we achieve. We strive for ‘Results, but Results in the Right Way,’” states Bruce Hoechner, President & CEO of Rogers. “This means making choices that are based on what is ethically sound and not just what is easy or expedient.”

Our Code of Business Ethics describes how our Cultural Behaviors are to be translated into concrete actions. It explains what is expected of each of us as we work to achieve our business goals. It is the cornerstone of our ethical culture that we reaffirm daily in our business activities.

What is Workplace Conduct?

Workplace conduct concerns how employees communicate, behave, interact, and treat each other. Improper workplace conduct may involve any communication or display of inappropriate material, offensive behavior, and verbal, physical and all other forms of harassment.

We take that a step further, ensuring that Rogers’ employees conduct themselves with courtesy, consideration, and respect towards each other and towards people who deal with the company. We do not allow harassment in workplace conduct. We prohibit retaliatory treatment against employees that make or assist in making a good-faith claim of improper workplace conduct.

The Rogers Code of Business Ethics describes how our cultural behaviors are to be translated into concrete actions. It is organized around the following policies:

The Rogers Corporate Responsibility hub provides an inside look at the conscience of our company and how we operate around the world. Updating our Code of Business Ethics is the next step in an evolving commitment to demonstrate what we believe in at Rogers Corp. Stay tuned for more.

If you have questions, please contact the Rogers Legal and Compliance Department or Ben Buckley, Associate General Counsel & Director of Global Compliance and Integrity, at ben.buckley@rogerscorporation.com.

Selected quotes from our recent earnings call. Read the corporate financials news release: Rogers Corporation Reports Third Quarter 2017 Results

In Q3 2017, Rogers achieved all-time record net sales and record third quarter earnings. Net sales were $207 million, an increase of 25% over Q3 2016. Our results confirm that we have implemented a winning approach and we are clearly benefiting from our solid execution.

Over the past several years, Rogers has greatly expanded, diversified and improved the performance of our business portfolio through new product innovation; thoughtfully identified, well-integrated acquisitions; increased geographic penetration; and enhanced operational execution. Today, our products play a vital role in many exciting advanced mobility and advanced connectivity applications, such as Advanced Driver Assistance Systems or ADAS, electric and hybrid electric vehicles or EV/HEV, and the latest generation of high-performance wireless networks. These rapidly emerging markets play well to Rogers’ strengths, putting us in a great position to capitalize on the significant growth opportunity.

Bruce Hoechner, CEO, on Innovation Leadership & Growth Drivers

Our focus on market-driven innovation is helping us advance our position in a number of rapidly growing areas. One example is our Power Electronics Solutions (PES) business, where we are seeing continued adoption of our silicon nitride substrates for wide bandgap semiconductors. These products offer high thermal connectivity and reliability, which are essential for EV/HEV applications.

We view two growth drivers as key priorities: advanced mobility and advanced connectivity. These categories are aligned with the investments we are making in our technology portfolio, marketing and innovation initiatives.

In advanced mobility applications, our growth is driven by mission-critical products for the EV/HEV market as well as ADAS. In advanced connectivity, we expect future growth to come from the 5G infrastructure buildout where industry sources cite new developments on the horizon.

Bruce Hoechner, CEO, on Rogers’ Business Units

Advanced Connectivity Solutions (ACS) achieved third quarter net sales of $73 million, an 11% increase over Q3 2016. Growth was driven by applications for ADAS, aerospace and defense and 4G LTE infrastructure. During Q3, we saw a rebound in demand for both base station power amps and antennas for wireless 4G LTE applications. We are optimistic about the accelerated rollout of 4.5G and 5G, where service providers are reporting that deployments originally scheduled for the 2020 time frame are moving to late 2018 and early 2019. ADAS is another exciting high-growth area for ACS. Our portfolio supports the full spectrum of requirements for short-, mid-, and long-term sensors for features like blind spot detection and adaptive cruise control. We will continue to focus on introducing new innovative technologies to meet customer and market demand.

The Elastomeric Material Solutions (EMS) team delivered all-time record quarterly net sales of $82 million, an increase of 51% over Q3 2016. We saw particular strength in portable electronics and general industrial applications. We continue to broaden our portfolio of solutions with new design wins and applications, such as the flexible flat cable harness for clean room manufacturing equipment. In addition, revenue from portable electronics has improved, driven by a focus on new designs at many global and regional OEMs where our PORON® polyurethane has won new design wins in a wide variety of sealing applications. We are also accelerating growth in EMS by aggressively pursuing general industrial opportunities.

Power Electronics Solutions (PES) achieved third quarter net sales of $46 million, an increase of 17% over Q3 2016. These results were driven by double-digit growth in applications for renewable energy, e-mobility, and laser diode coolers. As we look ahead in PES, we will maintain focus on e-mobility applications, ranging from electric power steering and regenerative braking to EV/HEV. We are looking at significant growth in demand for these applications, and our leading PES technologies have us well positioned to capitalize in the opportunities that lie ahead.

Q3 2017 Earnings Call Full Transcript

Q3 2017 Financials Press Release

Q3 2017 Earnings Call Slides

 

This year marks the 50th Anniversary of Rogers ACS operations in Chandler, AZ, and represents Rogers 50th year as part of the Chandler business community. Join us to celebrate our shared history and success!

The Western history of Advanced Connectivity Solutions (ACS) started back in 1967, when Rogers Corporation opened its plant in Chandler, Arizona to manufacture flexible circuit materials and high-performance PCB laminates.

Today, ACS has manufacturing locations in Rogers, Connecticut; Chandler, Arizona; Bear, Delaware; Gent, Belgium; and Suzhou, China. The products manufactured at these locations are now used in a wide range of markets, including portable communications, communications infrastructure, and aerospace and defense.

As we celebrate the 50th Anniversary and our shared success story, we give special Thank YOUs to all who have made this possible: our employees, customers, and partners!

On October 27, we held an anniversary event with employees, their family and guests to celebrate the occasion with great food and music!

We also would like to extend our gratitude to the Chandler business community – our business and civic partners for their support as we have grown our presence in the region and the Western technology hub in Chandler!

 

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This post authored by John Coonrod, Technical Marketing Manager, and team originally appeared on the ROG Blog hosted by Microwave Journal.

Filter and antenna designers have long appreciated the benefits of designing distributed high-frequency circuits using defected ground structure (DGS) layouts with different types of circuit materials. As the name suggests, a DGS is a circuit in which an intentional defect or interruption has been formed in the ground plane to realize distributed forms of passive circuit elements, such as capacitors and inductors. DGS shapes are often simple resonant u-shaped slots in the ground plane, intended to enhance the coupling of transmission lines or reduce harmonics. The design approach, which can be used with stripline and grounded coplanar waveguide (GCPW) circuits, is most often used with microstrip circuit designs.

DGS circuit telements are useful, for example, as notch resonators to minimize spurious modes in RF/microwave filters. They are supported as design elements in many commercial computer-aided-engineering (CAE) software programs including in electromagnetic (EM) simulators, allowing engineers to import DGS elements to see their effects on otherwise conventional microstrip circuit designs.

While DGS elements can provide simple, compact components, including antennas, couplers, and filters, one concern long associated with the design approach is radiated energy from the microstrip circuits. Because different DGS shapes perform as resonant circuit elements, they can also act as unwanted EM radiators within a microstrip circuit construction unless properly controlled. Fortunately, such radiation levels can be minimized through the use of multilayer microstrip circuit constructions. By adding a low-cost prepreg layer with its own metal ground plane to the microstrip circuit construction, the second ground layer acts to suppress any unwanted EM radiation from the DGS circuit elements.

DGS circuit technology is not new but has been in use for several decades, limited however where radiating energy may cause problems with surrounding components or circuitry. By careful selection of DGS shapes and circuit materials, the benefits of the technology are available without the radiation issues. Sufficient suppression is provided by the isolation of the prepreg dielectric layer and the second ground plane, without otherwise impacting the properties of the top-layer microstrip transmission lines or the resonant effects of any added DGS elements. The upper ground plane, which is the primary ground plane for the microstrip signal conductors, must be spaced sufficiently from the signal conductors so as not to act like a coplanar circuit structure.

Even simple DGS shapes can provide useful signal responses without requiring elaborate microstrip transmission-line perturbations. For example, an “H” pattern etched into the metal ground plane of a microstrip circuit board can be used to produce a stopband response at a frequency of interest. Variables such as the size and spacing of the “H” pattern will determine the frequency and depth of the stopband notch.

A simple opening etched in the ground plane, for example, can be sufficient to increase the impedance of a microstrip transmission line. DGS shapes include slots in the metal ground plane, dumbbells, and meander lines. Each shape differs in terms of its ratio of inductance (L) to capacitance (C), thus having a different impact on the properties of the microstrip circuitry.

Radiation can be minimized or eliminated by fabricating DGS microstrip circuits as part of a multilayer circuit construction with three metal layers, with the DGS ground plane buried between two different dielectric layers. The top and the second metal layers of this multilayer construction are as might be found in any standard microstrip circuit, except that the ground plane is not continuous. Beneath that DGS ground plane is a second dielectric layer, followed by the second ground plane.

This type of multilayer circuit design effectively reduces any DGS-caused radiation, but it must be properly constructed to benefit from the effects of the DGS circuit elements. Sufficient conductive paths must be formed between the top conductor layer and the top and bottom ground planes for the DGS circuit elements to function properly as resonant elements.

To demonstrate the design approach, a stepped-impedance lowpass filter was designed and fabricated as a multilayer circuit consisting of two different circuit materials, with different dielectric constants (Dk). The top dielectric layer, with the signal conductors and first ground plane, was 8-mil-thick RO4360G2™ laminate from Rogers Corp., a low-loss, glass-reinforced thermoset material with Dk of 6.15 in the z-axis (thickness) at 10 GHz and design Dk of 6.4. The second dielectric layer, with the bottom ground plane, was 22-mil-thick 2929 prepreg material from Rogers Corp., material with a much lower Dk (design Dk of 2.9 in the z-axis).

The stepped-impedance lowpass filter, with voids etched into the first ground plane as DGS elements, made use of conductor widths and the two different Dk materials to achieve the impedance transitions required for the filter’s frequency response. Narrower conductors can achieve very high impedances with DGS whereas wider conductors are capable of lower impedances on the higher-Dk circuit material. Analysis of the multilayer stepped-impedance lowpass filter with DGS revealed that the use of two different Dk materials and DGS combined to provide a much sharper filter cutoff slope than a conventional microstrip filter design, with good suppression of spurious harmonics and deeper and wider stopband.

This filter is one example of how DGS can be applied to RF/microwave circuit designs. The use of microstrip DGS makes it possible to place transmission zeros in the filter’s forward transmission (S21) response curve. Placement of the transmission zeros can cause the filter’s stopband floor to be lower. But DGS circuits can be used to form delay lines and phase shifters, since shapes such as DGS slots slow even-mode transmissions, with energy propagating around the edges of the slot, changing the effective velocity of the wave and the effective Dk of the circuit.

Note: For more detail on the benefits of DGS in high-frequency microstrip circuits, don’t miss the author’s MicroApps presentation scheduled for European Microwave Week in Nuremberg, Germany at 2 pm on October 11, 2017. 

 ROG Mobile App

Download the ROG Mobile app to access Rogers’ calculators, including the popular Microwave Impedance simulation tool, literature, technical papers, and the ability to order samples of the company’s high performance printed circuit board materials.

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Do you have a design or fabrication question? Rogers Corporation’s experts are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer today.

 
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