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Now you can download the microwave circuits presentations discussed during John Coonrod’s Microwave Journal webinars. Log into our Advanced Circuit Materials Tech Support Hub.

October: High Frequency Materials and Characterization up to Millimeter Wave Frequencies

November: Essential Thermal Mechanical Concepts Needed in Today’s Microwave Circuit Designs

Our thanks to Microwave Journal for hosting.

Coonrod_webinars

 

Visit Rogers Corporation’s Advanced Circuit Materials at DesignCon, January 28-29, 2015. We’re in booth 749 at the Santa Clara Convention Center.

We’ll be featuring our new ULTRALAM® 3850HT laminates. This is a higher temperature LCP material for more robust high temperature, multi-layer PCB designs. The higher melt temperature also provides improved dimensional stability.

Don’t miss our own John Coonrod on the DesignCon panel, “Isn’t GBPS Design Complex Enough? Now High Speed Circuit Boards Act Like Microwave Components!” January 27th, 4:45 – 6:00pm.

DesignCon_2015

 

 

This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal.

Ferromagnetic materials come in many forms and can serve RF/microwave applications in many ways. These materials are often recruited for high-frequency circuits for their resonant qualities as building blocks for such components as filters and oscillators. Ferromagnetic materials are so named because they have magnetic properties and can be made into magnets; they are materials that will exhibit spontaneous magnetism and remain magnetized when exposed to an external magnetic field and the field is then removed. These materials are typically used with printed-circuit-board (PCB) materials to add inductance and resonance and enable the fabrication of resonant circuits at specific frequencies.

PrintAs an example, most engineers working with higher-frequency instruments and military systems will be familiar with yttrium-indium-garnet (YIG) substrates, a ferromagnetic material which has long served as a building block for tunable RF/microwave filters and oscillators. Components formed of these materials can be varied in frequency according to applied current, often over a considerably wide bandwidth.

Ferromagnetic materials are based on magnetic elements, such as cobalt, iron, and nickel, and have been formulated as ceramic-based materials with the high magnetic permeability needed to store magnetic fields. These materials possess many unpaired electrons, which will align under the effects of an applied electromagnetic (EM) field to form a magnetic field. Commercial ferromagnetic materials are available as soft, formable ferrite materials and harder, machinable materials, such as ceramic-based materials commonly found in magnetically based microwave components, such as circulators and isolators. Typically, a small disk of ferromagnetic material is machined as a main component in a circulator or isolator circuit, with that material contributing a great deal to the electrical performance of the circulator or isolation, including isolation and insertion loss.

These materials have grown more popular in recent years not only for fabricating some of the high-frequency components noted but for such additions to PCBs as planar electromagnetic bandgap (EBG) structures that can add electromagnetic-interference (EMI) shielding to critical segments of a PCB. When used in this way, ferromagnetic materials are extremely useful in mixed-signal (analog and digital) circuits to isolate RF/microwave transmission lines from the noise that can be produced from the digital portions of the circuit.

Ferromagnetic materials will remain magnetized to some extent after being subjected to an external magnetic field. In fact, different types of magnetic materials will maintain more or less of an applied magnetic field. Hysteresis refers to the capabilities of a material to “remember” the applied magnetic field, and the material’s remanence is the amount of magnetism that is retained when the applied magnetic field has been removed, which is a critical parameter for fabricating permanent magnets.

Ferromagnetic materials are one of several types of magnetic materials used in electronic circuits, with other materials, such as diamagnetic and paramagnetic materials, offering somewhat different magnetic properties. These three types of materials, for example, are categorized by their bulk magnetic susceptibility, which is a measure of how much magnetism a material will retain when exposed to a magnetic field. Ferromagnetic materials feature positive susceptibility, reproducing a healthy portion of an applied magnetic field even when that field has been removed. Paramagnetic materials, such as aluminum and manganese, also have a positive susceptibility, but retaining a much smaller amount of magnetism from the applied field, and failing to keep the magnetism once the field has been removed. Diamagnetic materials, such as copper and silver, have a small and negative susceptibility, resisting magnetism from an applied magnetic field. Yet another form of magnetic material, ferromagnetic materials such as garnet, are somewhat less magnetic than ferromagnetic materials.

Ferromagnetic materials intended for use for their resonant properties are often doped with different materials and different doping concentrations to achieve a target resonant frequency or ferromagnetic resonance (FMR) frequency. YIG films, for example, are doped with different materials, including aluminum, to achieve different magnetization responses. Ferromagnetic films can be doped in different ways to respond with different resonant frequencies when exposed to a magnetic field.

Evaluating and comparing different ferromagnetic materials is a matter of understanding some of the essential properties of these materials and what those properties mean for different applications. For example, every ferromagnetic material has a specific temperature, known as the Curie temperature, above which they no longer exhibit magnetic behavior. Data sheets for ferromagnetic materials usually list a maximum temperature along with a recommended operating temperature range. The operating temperature range is usually considerably lower than the Curie temperature for any magnetic material, but the Curie temperature can be an important parameter to consult when reviewing any material-processing steps for ferromagnetic materials. Bonding ferromagnetic materials to PCBs and other materials can require high temperature and pressure, and the electrical and mechanical characteristics of these materials can be impacted by extremely high temperatures. As with many other electronic materials, for example, ferromagnetic materials exhibit a coefficient of thermal expansion (CTE) with mechanical/dimensional changes that occur as a result of temperature and which can play a role in performance and reliability.

Some of the other properties of ferromagnetic materials that can be compared and contrasted include permeability, resistivity, quality factor (Q), magnetic loss, and magnetic anisotropy. For example, the inductance of an inductor formed with a particular ferromagnetic film depends not only on the configuration of the inductor but on the permeability of the material, with higher permeability to be preferred. Since the effective permeability of a ferromagnetic material will decrease with increasing frequency, the inductance of a given inductor formed on that material will decrease with frequency as well. Using a ferromagnetic film or material with a higher value of effective permeability can help reduce the size of inductors and transformers for any applicable frequency.

Ferromagnetic materials with high electrical resistance or resistivity (measured in Ohms-cm) will exhibit low eddy current loss. This characteristic makes these materials suitable for inductors, transformers, and electromagnetic, but also for applications such as radar absorption and for in-circuit control of EMI. Saturation (measured in Gauss or Tesla) is a point in a ferromagnetic material in which an increase in current or in magnetic field strength no longer results in an increase in magnetic flux in the material or inductor formed from the material. A ferromagnetic material that reaches its saturation point will also exhibit a decrease in the inductance of the material or inductors formed from the material, as the material can no longer increase its level of magnetism with any increase in magnetic field or current. Magnetic materials can usually be compared in terms of their saturation behavior by a parameter known as saturation flux density, with higher numbers indicating greater potential to achieve larger magnetic fields for a given material. If a ferromagnetic material is approaching saturation for a particular application, it may be beneficial to specify a magnetic material with lower permeability or to run the selected material/application at a lower current level to avoid saturation.

Ferromagnetic materials are a large part of electronic designs across a wide range of frequencies, from audio through higher microwave frequencies. Research continues to advance these materials, including in US government laboratories, on the development of multiferroic composite materials that are formed from a blend of ferrite and other materials. These multiferroic materials bring the benefits of voltage-tunable frequency response to magnetic circuits and components, allowing adjustments to the FMR frequency of a multiferroic magnetic material. For such components as tunable antennas, circulators/isolators, and filters, these materials offer tremendous potential for improving the performance and reliability of such systems as RF/microwave radios and radars.

ROG Mobile App

Download the ROG Mobile appto 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.

 

by Jared Rouleau, Go-To-Market Manager, Rogers Corp.

In today’s fast paced world, getting your designs off the drawing board and into reality is essential. Unfortunately, we’ve all known those great ideas that simply couldn’t get off the block. Getting to that first prototype quickly and being able to see and test how the product will perform are key to market success.

The ability to help a customer design, prototype, and test their designs is an important function of the XRD® Impact Institute. It’s here where we work with our customers to find the right XRD solution for their unique impact protection design. Part of this process involves helping to provide a protective padding prototype which is as close to the final product as possible.

PORON_XRD_ChevronDecision makers don’t want to imagine what a product “would look like;” they demand more finished products they can use. For this, we’ve developed a new line of XRD molded parts call the XRD 810 Series. The XRD 810 Series includes 5 unique tessellation patterns, each with varying functions and features:

  • XRD 810 Hex
  • XRD 810 Mini Hex
  • XRD 810 Cones
  • XRD 810 Delta
  • XRD 810 Tear Drop

Each pattern offers designers and product developers the ability to easily die cut their unique shape from the 8” x 10” pad (hence the name 810) and quickly incorporate and test their PORON_XRD_8protective padding design. We’ll dedicate our next few blogs to telling you more about the various XRD 810 Series patterns, their features and how you can benefit from using each design. If you have immediate questions or sample needs, please contact us for additional information. XRD 810 Hex The XRD 810 Hex size and thickness (about 7.1 mm)  offers good coverage for larger zones requiring impact protection. Yet, the hex pattern still provides good movement and flexibility while being durable and abrasive resistant. The Hex pattern is a popular choice for designers of protective apparel and equipment.   The convenient tessellation pattern allows for various protective padding designs for rib, chest, thigh and other areas.  For example, our partners at Cliff Keen Athletic have used the XRD Hex design in their popular Xtreme Impact™ Kneepad.

The XRD 810 Hex is easy to work with, simply:

  • Use scissors to cut a desired shape from your XRD 810 Hex sample.. For your use, a PDF pattern of the XRD 810 Hex can be downloaded for testing your initial shape ideas before you test them on physical samples.
  • Arrange the XRD shapes on your application.
  • Apply the XRD shapes using an acrylic or polyurethane adhesive, fusible web adhesive or insert it into a pocket. (Note: We have found that Pellon’s Heavy Duty Wonder Under paper backed fusible web tends to work well when bonding to apparel)
  • Test, trial and wear your prototype. Make updates and cut new design ideas as they work for your project.
  • If you are satisfied with your XRD Hex shape, you may order this directly from Rogers (we’ll die cut the final part for you) or work with the XRD Team to develop a custom XRD molded part based from your prototype.

The XRD 810 Hex dimensions (length x width x thickness): 10” x 8” x 0.280” (254 mm x 203 mm x 7.1 mm). It is available in two different densities: 12 lb/f³ (192 kg/m³) and 20 lb/f³ (kg/m³) and comes in the XRD Vivid Yellow color. Please contact us for additional PORON formulation requests.

 

This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal.

High-frequency circuit designers have a number of different circuit types from which to provide solutions from radio frequency (RF) through millimeter-wave frequencies. Coplanar waveguide (CPW) might be an approach to consider as an option to popular microstrip techniques. Traditional CPW circuitry consists of a conductor separated by a pair of ground planes, on the same plane on top of a dielectric material. A variation on that circuit approach is grounded coplanar waveguide (GCPW), also known as conductor-backed coplanar waveguide (CBCPW). It adds a ground plane to the bottom of the basic CPW circuit structure, with plated through holes (PTHs) connecting the top and bottom ground planes.

PrintThe absence of PTH ground connections in CPW results in less radiation at discontinuities than GCPW, although both circuit types feature superb isolation of adjacent signal channels, resulting in low crosstalk for densely packed circuits. The placement of PTHs in GCPW circuits can be critical for achieving impedance and loss goals, but the use of these grounding PTHs can allow the use of a much thicker dielectric material for a given higher frequency than when using microstrip circuits. The added ground plane in GCPW circuits provides additional mechanical stability compared to CPW circuits, with improved thermal management for higher-power circuits and devices. Microstrip circuits typically suffer increased surface-wave leakage and radiation losses compared to GCPW circuits when using the same circuit materials and at higher microwave and millimeter-wave frequencies.

Both CPW and GCPW circuits are fairly straightforward to fabricate and provide consistent performance through millimeter-wave frequencies. The electromagnetic (EM) energy through the transmission lines, especially for GCPW, remains largely concentrated within the PCB’s dielectric material. Both CPW and GCPW circuits can suffer higher conductor losses than microstrip circuits, but the loss characteristics of CPW and GCPW circuits follow a constant slope with frequency, whereas microstrip undergoes loss transitions at the upper microwave frequencies associated with radiation losses. Such losses can be minimized in CPW and GCPW designs through proper spacing of PTHs and other circuit dimensions.

At higher frequencies, such as millimeter-wave frequencies, circuit dimensions become smaller and more critical as the lengths of circuits begin to approach the dimensions of the wavelengths of the signals propagating through those circuits. Selecting a suitable circuit technology can be critical at higher frequencies, as reflections and radiation losses can increase for microstrip and even stripline circuits at higher frequencies. When treated properly, CPW and especially GCPW can provide excellent results at higher frequencies, and are often even combined with microstrip. In many cases, GCPW provides practical, high-performance interfaces at connector interfaces before making a transition to microstrip transmission lines for the remainder of a high-frequency design.

A CPW circuit includes a conductor fabricated between two ground planes on the top surface of a dielectric layer, in a ground-signal-ground (GSG) configuration on the top of the circuit material. By using a ground conductor that is coplanar with the signal conductor, CPW circuits use the signal line width and gap between the ground and the conductor to control the impedance. The impedance can be kept constant as the width of the signal conductor is tapered to form a connection with a connector pin.

A GCPW circuit adds a ground plane to the bottom of the dielectric layer and a means of interconnecting the ground areas, such as PTHs. In a CPW circuit, the EM energy is mainly concentrated within the dielectric material. Leakage of CPW and GCPW EM energy into the air can be controlled by maintaining a substrate height that is at least twice the conductor width. The characteristic impedance is established essentially by the width of the center conductor and the spacing between the conductor and the ground planes. For CPW, the characteristic impedance can typically be set between 20 and 250 Ω, compared to about 20 to 120 Ω for microstrip circuits and 35 to 250 Ω for stripline circuits.

Coupling For CPW/GCPW

As with any circuit technology, CPW and GCPW have positive and negative aspects, and tradeoffs that must be weighed for different applications, for both analog and digital circuits. The top-layer ground strips in CPW and GCPW circuits can produce even- and odd-mode current flow that cause mode coupling in those circuits. When tight spacing is maintained between the GSG traces of CPW and GCPW circuits, those circuits deliver tight coupling with excellent mode suppression and low radiation losses at higher frequencies. Loss can be minimized when wider spacings are used between the signal trace and the two top-layer ground strips, especially when a wider signal trace (with lower conductor loss and insertion loss) is used. When the signal conductor is widely spaced from the ground traces, in a loosely coupled configuration, the tradeoff for lower conductor and insertion losses is a possible increase in radiation loss and spurious distortion. Finding the right level of coupling in a CPW or GCPW circuit will provide a balance between low loss and good spurious mode suppression.

In general, thinner circuits are better for minimizing radiation loss than thicker circuits. For millimeter-wave circuits of 30 GHz and higher, radiation losses can become a significant part of a circuit’s total loss. Radiation loss also depends on a PCB material’s Dk value, with circuit materials having higher Dk values suffering less radiation loss than circuit materials with lower Dk values. Since tradeoffs must always be considered, those materials with higher Dk values usually exhibit higher conductor losses than circuit materials with lower Dk values since narrower signal conductors are needed for a given impedance on circuit materials with higher Dk values.

Copper surface roughness affects the electric field and current flow for a PCB. The effective dielectric constant increases as the surface roughness of the copper conductor increases. Copper surface roughness can also impact a PCB’s insertion loss, although with less effect on a GCPW circuit than on a microstrip circuit. On the GCPW circuit, the electric field and current are tightly maintained within the GSG configuration of the PCB whereas on the microstrip circuit, the electric field and current move towards the bottom of the conductive metal, towards the roughness of the metal.

The use of CAE software tools, such as EM simulators, can help find the appropriate values for the various CPW and GCPW circuit parameters, such as conductor width, circuit material thickness, and separation between ground planes, which contribute to circuit performance goals. During a technical presentation at the 2009 Automatic RF Techniques Group (ARFTG) by Sonnet Software’s father and son team of James and Brian Rautio (“High Accuracy Broadband Measurement of Anisotropic Dielectric Constant Using a Shielded Planar Dual Mode Resonator”), methods were detailed for measuring the Dk values of different circuit materials, even for CPW and GCPW circuits across ranges of different key parameters. The presentation included measurements to 10 GHz on the anisotropic RO3010™ circuit material from Rogers Corp. with the capability to separate even- and odd-mode material resonances numerically. The measurements determined two dielectric constant values for a given material: one for the horizontal electric field (parallel to the substrate surface) and one for the vertical electric field. This report shows how different parameters could be analyzed when considering circuit materials for different frequencies and applications and provides valuable guidance for those specifying circuit materials for CPW and GCPW designs as well as for stripline and microstrip configurations.

Screen shot 2014-08-08 at 1.33.54 PMROG Mobile App

Download the ROG Mobile appto 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.

Ask an Engineer

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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