Congratulations to the ROG Blog team on their 50th post! This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal.

This ROG Blog series on printed-circuit-board (PCB) materials has reached the half-century mark, already covering a wide range of topics on circuit materials with this, the 50th ROG Blog. For example, this series has recommended materials for amplifiers, for antennas, for filters, and for different types of transmission lines. It has even detailed the effects of different PCB material thicknesses on circuit performance, and described the influence of conductor roughness on circuit performance.

While it would be difficult to pick out the top 10 Blogs from the first 49 Blogs appearing since August 2010, at least 10 of these ROG Blogs deserve mention for how they have attempted to help readers with their different uses of PCB materials.

From the very first ROG Blog, in August 2010, which compared low-cost FR-4 circuit substrates with higher-frequency PCB materials such as the Rogers substrates, to the latest ROG Blogs, which examine circuit material requirements for emerging millimeter-wave wireless applications through 300 GHz and higher, the ROG Blogs have attempted to provide clear and honest information on the use of circuit materials. The next 50 ROG Blogs will pursue the same ambitious goals, in hopes of providing readers with greater benefits for their uses of high-performance circuit materials.

While it would be difficult to name the “Top Ten” ROG Blogs from the series so far (see the list below), it is not surprising to find that one of the most popular (in terms of viewers/readers) would be one that also refers to something for free: the January 2011 ROG Blog on Rogers’ free transmission-line modeling tool, the MWI-2010 Microwave Impedance Calculator. This easy-to-use modeling tool, which has also been reviewed in many of the leading RF/microwave trade publications, calculates key parameters for most common microwave transmission lines, including microstrip, stripline, and coplanar-waveguide transmission lines. The executable (.exe) file is available for free download from the Rogers’ website and runs on Windows-based personal computers (PCs), including those with Windows XP, Windows Vista, and Windows 7 operating systems. The free software is even backed by a 22-page operator’s manual in PDF file format, also available for free from the Rogers website.

In many ways, the ROG Blog series is like a book on circuit materials, unfolding online before its readers, with each Blog adding a new chapter to the book. Each chapter shares what Rogers’ engineers have learned over the years about making and using circuit materials, and this first set of 50 Blogs has covered some areas of interest to a large number of readers. In line with the ROG Blog on free software, the ROG Blog “Comparing RF Circuit Material Processing Costs & Performance” also offers advice meant to help readers save money without sacrificing their performance goals. Although first appearing on “April Fool’s Day” (April 1) in 2011, this ROG Blog takes a serious look at the total costs of circuit materials, and how some circuit materials may have lower material costs than other materials, but pay for it later with higher processing costs and lower yields. It also explains how some performance parameters, such as passive intermodulation (PIM) in wireless circuits and signal integrity in digital circuits, require a careful consideration of tradeoffs in material and processing costs when choosing a circuit material.

These first 50 ROG Blogs have drawn readers for familiar themes as well as for some not-so-familiar topics. For example, the ROG Blog appearing on November 19, 2010, “What Is Outgassing and When Does It Matter,” addresses a subject that may be unknown to some readers but quite significant to others. Outgassing, which refers to the release of gas inside a solid such as a circuit material, especially when it is placed in a vacuum, can greatly impact the performance of circuits used in satellite-communications systems in space, or in medical electronics systems. This ROG Blog introduced many readers to a material term known as total mass loss (TML), and how the parameter could be used to help guide the selection of a circuit material for space-based or other applications where outgassing was a critical concern.

On the other hand, some of the more popular ROG Blogs covered the roles that circuit materials play in the design of some basic RF/microwave components, such as amplifiers, couplers, and filters, and how the choice of a circuit material can affect transmission-line losses in high-frequency circuits. One of the more popular ROG Blogs, “When Digital Signals Reach Microwave Frequencies,” covered an area of  interest to many microwave circuit designers, how to deal with digital circuits operating at microwave frequencies. This ROG Blog, appearing on February 23, 2011, reviews some of the important concerns for selecting a circuit material when circuits cross over from the digital area into the microwave realm. These high-speed digital signals will behave much like analog microwave signals, affected by PCB loss and even conductor surface roughness. To guide those in need of circuit materials for high-speed digital designs or even multilayer circuits that may combine fast digital and microwave circuits, this ROG Blog points out how different circuit material characteristics, such as dielectric constant and even coefficient of thermal expansion (CTE), can impact high-speed digital circuit performance.

At times, readers of the ROG Blog series shared their areas of interest and applications for circuit materials, and these applications are many and diverse, from lower-frequency analog and power circuits to high-speed digital and even microwave/millimeter-wave circuits. The ROG Blog series is written to serve its readers with new information on circuit materials as that information is needed, much like new chapters to an on-going, online book about circuit materials. Do you have a suggestion for future ROG blogs? We’d love to get your input. Let us know what you are interested in reading about.

Top 10 Popular ROG Blogs (based on reader feedback)

  1. Transmission-Line Modeling Tool: Free Downloadable Software” (1/27/11)
  2. What Is Outgassing And When Does It Matter” (11/19/10)
  3. Comparing RF Circuit Material Processing Costs & Performance” (4/1/11)
  4. Controlling Conductor Losses In Coplanar Transmission Lines” (3/14/11)
  5. When Digital Signals Reach Microwave Frequencies” (2/23/11)
  6. Do You Have An Award Winning Application?” (11/11/11)
  7. The Role of PCB Materials In Impedance Matching” (12/3/12)
  8. Choose Circuit Materials For Bandpass Filters” (1/16/13)
  9. Make Waveguide In Planar PCB Form” (10/18/12)
  10. Celebrating ROG Award Contest Winners at IMS 2012” (7/17/12)

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal. You can view Bandpass Filters, Part 1 here.

Bandpass filters make many of our modern electronic systems possible, from dependable cellular telephones to secretive military surveillance and radar systems. The last blog – Part 1 of this two-part series on bandpass filters – highlighted the versatility of one circuit material from Rogers Corporation, RT/duroid® 6010.2LM laminate, for fabricating RF/microwave bandpass filters. But not all circuit materials are the same and there may be some advantages to designing bandpass filters on other materials, such as Rogers RO4000® family of printed-circuit-board (PCB) materials. This blog will examine different grades of these and other circuit materials and the impact they have on the design and fabrication of high-frequency bandpass filters, especially compared to filters formed on filled-PTFE-based circuit materials.

The first installment of this two-part blog on bandpass filters described different bandpass filter responses, including Chebyshev, Bessel, and Butterworth filters, and reviewed a number of the performance parameters for comparing bandpass filters, such as center frequency, passband, passband insertion loss, and stopband responses. As was noted in that first part, the choice of PCB material for a bandpass filter usually starts with the material’s dielectric constant (Dk). Materials with higher values of Dk, such as 10.2, have long been favored for RF/microwave filters because of the relationship of the Dk value to the size of the filter. Quite simply, higher Dk values result in shorter wavelengths and higher frequencies, enabling filter designers to occupy less PCB area for a given filter structure.

Circuit materials with a Dk of 10.2 are typically based on polytetrafluoroethylene (PTFE), which provides excellent electrical characteristics but tends to be more expensive than other circuit materials. As pointed out in the first part of this blog, circuit materials based on PTFE with some form of filler are also susceptible to moisture absorption, which can result in shifts in their Dk values in high-humidity environments. As that earlier blog suggested, a lower-cost material such as RT/duroid 6010.2LM laminate, which is a composite of PTFE and ceramic materials, can also provide the high Dk value without the concern for moisture absorption.

But are there benefits to designing and fabricating bandpass filters on materials with lower values of Dk? Rogers RO4000 circuit materials are widely favored by amplifier designers for their mechanical and electrical stability, but they are also excellent starting points for bandpass filters. The materials are based on reinforced hydrocarbon/ceramic laminates, not PTFE. RO4360™ laminates, for example, have a Dk value of 6.15 in the z-axis at 10 GHz, held to an impressive tolerance of ±0.15. The material is based on a ceramic-filled, thermoset-resin system reinforced by glass fiber for excellent mechanical stability. These lead-free-process-capable laminates exhibit dissipation factor (loss) of 0.0030 at 2.5 GHz and 0.0038 at 10 GHz, both in the material’s z-axis.

In terms of bandpass filter size, the lower Dk value of 6.15 for RO4360 laminates  compared to a Dk of 10 or higher for filled PTFE circuit materials translates into somewhat larger filter structures, with wider conductor widths. The higher loss of RO4360 laminates compared to filled-PTFE-based materials typically means somewhat higher passband insertion loss, but the differences in loss between filters formed on the two materials may not be so significant when factoring in RO4360 laminate’s wider conductors. RO4360 laminates offer lower material costs than filled-PTFE-based substrates, and circuits are easier and lower in cost to fabricate compared to filled PTFE. RO4360 laminates provide improved mechanical stability and consistency compared to filled-PTFE-based materials, especially in environments with high humidity. Essentially, the tradeoffs between the two materials involve cost versus the levels of performance required for a particular application, as well as the somewhat smaller size possible for high-frequency bandpass filters fabricated on materials with higher Dk values.

Larger filter dimensions may not always be a design goal but at times can be a benefit, especially for applications that involve higher power levels. When designing and fabricating filters on higher-Dk materials, transmission-line conductor widths must be reduced compared to lower-Dk circuit materials to maintain the typical 50-Ω impedance of higher-frequency designs. But those thinner conductor widths, along with the circuit material’s thermal properties such as its thermal conductivity, will serve as a limit for a filter’s power-handling capabilities on that particular material. Also, the thinner conductor widths can result in penalties in terms of production yields.

RO4360 circuit materials provide better thermal conductivity than many substrates based on filled PTFE, although with somewhat higher loss that can in part offset the enhanced thermal conductivity. RO4360 laminates provide typical thermal conductivity of 0.8 W/m/K, enabling it to dissipate heat produced by circuits handling high power levels. In addition, RO4360 laminates have coefficients of thermal expansion (CTE) of 16.6 and 14.6 ppm/°C, respectively, in the x and y directions, very closely matched to copper in support of good circuit reliability at higher power levels.

For some small sacrifice in passband insertion-loss performance compared to filled-PTFE-based materials, RO4360 circuit materials can deliver RF/microwave filters without complicated production processes. The thermoset material can be handled in much the same way as low-cost, epoxy-based FR-4 circuit materials, and even readily combined with these lower-cost materials as part of a multilayer circuit structure. Often, a circuit design is “segmented” by material type in a multilayer design, with higher-frequency circuits, such as RF/microwave bandpass filters, fabricated on materials such as RO4360 laminates and less-critical circuits, such as power supplies, formed on lower-cost circuit materials such as FR-4.

Compatibility in processing the different materials not only simplifies production, but also ensures reliability of the plated through holes (PTHs) used to electrically connect the different circuit layers in a multilayer circuit construction. The reliability of those PTHs in multilayer circuits with RO4360 laminates is also aided by the materials excellent CTE in the z-axis (30 PPM/ºC), also closely matched to that of copper to minimize stress of connections and circuitry across a range of operating temperatures.

In contrast to filled-PTFE-based materials, which require special processing measures, RO4360 laminates are compatible with standard PCB processing methods, as used with FR-4 materials. They boast a high glass transition temperature (Tg) of greater than +280ºC as assurance of handling high process temperatures. In addition to electrical and mechanical characteristics that make them attractive for fabricating RF/microwave bandpass filters, they are environmental friendly and RoHS compliant. For those bandpass-filter applications that can afford slightly higher passband loss and slightly larger circuit dimensions (than some filled-PTFE materials), RO4360 circuit materials offer a high-performance alternative that can cut both material and processing costs.

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

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

Resonant circuits are critical for the generation and selection of desired RF/microwave frequencies. For any transmission line, including stripline, microstrip, or waveguide, a suitable length can be used as a resonator, with dimensions for the resonant structure that correspond to the desired wavelength. When that resonant structure is in the form of a cavity, it is simply called a cavity resonator. High-frequency cavity resonators, for example, serve as excellent starting points for RF/microwave oscillators capable of generating low-noise signals and for filters used to select signals at specific frequencies. For example, cavity resonators can be embedded within a multilayer circuit substrate, to achieve a high-quality resonance without a larger metal cavity or tuning screw. Excellent performance is available from such multilayer cavity resonators, given available high-frequency circuit laminates and the pre-impregnated glass fabric (prepreg) materials.

About Cavity Resonators

Cavity resonators are essentially hollow conductors or sections of a printed-circuit board (PCB) which can support electromagnetic (EM) energy at a specific frequency or group of frequencies. An EM wave entering the cavity that is resonant within the cavity will bounce back and forth within the cavity with extremely low loss. As more EM waves enter at that resonant frequency, they reinforce and strengthen the amplitude of the existing resonating EM waves.

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.

Creating a cavity resonator in a PCB

While there are many ways to create a cavity resonator in a PCB, most methods rely on either building up materials around an empty area on the PCB, or removing materials from a PCB structure to form an empty area, such as by means of laser ablation. In forming a window-type resonant cavity in a multilayer circuit assembly, the different layers that create the circuit assembly also form the walls of the resonant cavity. Such circuit-material layers often include a high-performance circuit material, such as RT/duroid® 5880, RO4003C™ LoPro™, or RO4350B™ LoPro laminates, and a compatible prepreg material, such as RO4450F™ prepreg, to bond the circuit layers together.

In the window-type approach to forming cavity resonators, windows are punched into some of the circuit layers used to assemble a multilayer circuit. As the laminate and bonding or prepreg layers are assembled, the layers forming the windows will create the walls of the soon-to-be resonant cavity. The size of this cavity, of course, determines the ultimate frequency or frequencies of the resonant cavity, so manufacturing efforts are usually focused on keeping the dimensions of the resonant cavity tightly controlled.

Prepreg Materials

Ideally, prepreg materials used for bonding the multilayer structure have the flow characteristics required for a multilayer resonant cavity. For example, in a multilayer construction in which voids must be filled, such as in circuits with plated copper, prepregs with “high-flow” characteristics are desired. But when bonding of multilayers is needed, without flow into the resonant cavity formed by those multiple laminate layers, a “low-flow” prepreg is preferred, with a high glass transition temperature (Tg) for good reliability. Because the bonding materials in a multilayer circuit assembly will flow during lamination, designers must be wary of bonding materials that lack good flow control and might flow into the resonant window or cavity area, changing the dimensions of the resonant cavity (and its operating frequency or frequencies). An effective multilayer prepreg should exhibit low loss, good adhesion to commercial PCB laminates, stable dielectric constant with temperature and frequency, and the capability of supporting multiple or sequential laminations if needed.

Ideally, any prepreg in a multilayer circuit assembly with a resonant window should have not only low-flow characteristics, but predictable flow characteristics. The predictability allows for tight control of the circuit manufacturing process. In a circuit with a resonant cavity, a prepreg with predictable flow may alter the size of the cavity because of that flow, but it will be in a manner that can be predicted and even modeled in a commercial EM computer-aided-engineering (CAE) software program such as Ansoft HFSS. However, if the prepreg has low-flow characteristics without predictable flow, the final size of the resonant cavity will vary according to the flow characteristics, as will the resonant frequency or frequencies of the cavity.

As an example, RO4450F prepreg is a low-flow prepreg material with relatively well-controlled flow characteristics. It is compatible with RO4350B or RO4350B LoPro laminates and well suited for forming multilayer cavity resonators with consistent and predictable characteristics. In contrast, our 2929 Bondply is also a durable prepreg material, but with greater flow than RO4450F material. Although both are candidates for a multilayer cavity resonator design, the fabrication and lamination conditions will dictate which prepreg provides a greater level of consistency in a final production run.

RO4450F and the RO4400™ family of prepreg materials are based on the RO4000® core materials and readily compatible with those laminates in multilayer constructions, such as in cavity resonator designs. The prepregs feature a number of key attributes that contribute to reliable performance in multilayer constructions, including a high post-cure glass transition temperature (Tg) of greater than +280°C, an indication that the prepregs are capable of handling multiple lamination cycles. The RO4400 prepregs also support FR-4-like bonding process conditions (+177°C), enabling the use of standard lamination equipment.

Achieving Optimum Performance

Optimum performance from any multilayer cavity-resonator-based design, whether for generating or filtering signals, requires careful consideration of the type of feed structure used with the cavity resonator, especially at higher frequencies. A number of approaches provide good results through millimeter-wave frequencies, including slot and probe excitation techniques. Using a slot is fairly straightforward and requires very simple fabrication while probe excitation, which can be somewhat more demanding in terms of fabrication, can yield extremely wideband results. Some cavity-resonator filters, for example, have used feed approaches as simple as a microstrip line through a coupled slot in the ground plane. In the case of either slot or probe feed in a multilayer cavity-resonator construction, high-quality prepreg materials help ensure minimal loss and stable performance.

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

curamik® electronics, which is part of Rogers’ Power Electronics business, will be presenting at the eCarTech Conference in Munich on October 23-25,
2012.  This conference takes place during  the 4th International Fair for Electric- and Hybrid-Mobility for electric vehicles. curamik recently released a new silicon nitride (Si3N4) ceramic substrate that can significantly extend the life span of power electronic modules, and will be presenting this product at the conference.

Manfred Götz, Product Marketing Manager from curamik will be giving a presentation about this new ceramic substrate on Thursday, October 25th at 3:00 PM:

“How silicon substrate can increase the duration of power modules”

“In test cycles we have conducted so far, ranging from -55 °C to 150°C , curamik® silicon nitride substrates have shown more than a 10X improvement over substrates typically used in the Automotive segment, especially HEV/EV. From this data, we can expect to see a longer life span for modules using these substrates,” reports Manfred

 About curamik’s New Ceramic Substrate 

Until now, the reliability of copper-bonded ceramic substrates used in power modules has been limited by the lower flexural strength of the ceramic that can result in reduced thermal cycling resistance. For applications combining extreme thermal and mechanical stress, such as hybrid and electric vehicles (HEV/EV), the current commonly used ceramic substrates are not optimal. The significant difference in thermal expansion coefficients of the substrate (ceramics) and the conductor (copper) exert stress on the bonding zone during thermal cycling, threatening reliability. Rogers Corporation introduced a new silicon nitride ( Si3N4) ceramic substrate under its curamik® ceramic substrates brand. Due to the higher mechanical robustness of silicon nitride relative to other ceramics, the new curamik® substrate is intended to help designers achieve critical, long-life performance under the demanding operating environments and conditions of HEV/EV renewable energy applications and other high reliability applications.

With the growth of HEV/EV and renewable energy applications, designers have struggled to find new ways to ensure reliability of the electronics required to power these new, challenging technologies. With an increase in operating life span of potentially ten times or more relative to other ceramics used in power electronics, silicon nitride substrates provide the mechanical robustness critical to achieving the necessary reliability requirements. The life span of ceramic substrates is measured by the number of repetitions of thermal cycles the substrates can survive without delamination or other failure modes that compromise the function and safety of the circuit. This testing is typically done by cycling the samples from – 55° C to 125°C or 150°C.

Download the data sheet.

The entire event will cover these topics:

  • Electric Vehicles
  • Drive and Motor Technique
  • Energy Storage Technology
  • Engineering and subcontracting
  • Reparation and spare parts
  • Connected Car – sMove360°
  • MATERIALICA – Lightweight Design for New Mobility
  • Finance
  • eCarLiveDrive – Test Area

For More information:

curamik electronics GmbH
A division of Rogers
Am Stadtwald 2
92676 Eschenbach, Germany
phone: +49964592220
fax:+499645922222
e-mail: info@curamik.com
www.curamik.com

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

About Patch Antennas

Patch antennas are a mainstay of many wireless applications, including in Global Positioning System (GPS) receivers and in wireless local area network (WLAN) routers. They feature the low profile that allows them to be mounted unobtrusively to a flat surface and they are relatively simple to fabricate. They can be as simple as a rectangular conductive patch that is one-half wavelength long at a center frequency of interest, mounted above a slightly larger ground plane, with dielectric material in between. Of course, the type of dielectric material can play a strong hand in the performance of 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.

Considering Different Circuit Materials for a Patch Antenna

A laminate’s relative dielectric constant, denoted as εor Dk, is a good starting point when considering different circuit materials for a patch antenna. Since the dielectric material in a circuit laminate isolates the circuit traces from the ground plane, it is usually specified in terms of Dk value in the thickness or z direction, with z-axis values from about 2 to 10 commonly used in RF/microwave circuits. Laminates with the lowest Dk values are typically used for patch antennas. These lower Dk values typically support circuits, such as patch antennas, with higher center frequencies, enabling effective RF/microwave operation. But other material characteristics, such as thickness, can affect final performance.

The Dk of a dielectric circuit material has a part in determining the physical dimensions of a patch antenna needed for resonance at a particular wavelength and, thus, frequency. The transmission lines carrying signals to and from the patch antenna, or the feed lines, are also affected by the laminate’s Dk value, with higher Dk values resulting in smaller physical dimensions for a given wavelength or frequency for both the feedlines and the antenna patch. The consistency or Dk tolerance of a circuit material is also important to consider because variability in the Dk value results in variability of the center frequency of a patch antenna formed on that material. In general, a tight Dk tolerance is to be preferred for consistent patch antenna center-frequency performance.

Know the Performance Tradeoffs Before Deciding

But Dk is not the only circuit material parameter to consider when choosing laminates for patch antennas. While it may be possible to shrink an antenna’s dimensions by using a laminate with higher Dk value, other material parameters, such as dissipation factor (Df) and laminate thickness, may point to tradeoffs in performance. A laminate’s Df, which provides an indication of the loss or gain that can be expected from a patch antenna designed on that material, can increase with increasing Dk value. As a result, a microstrip antenna with smaller patch on higher-Dk material will provide less gain and less efficiency than a larger patch antenna on lower-Dk material, with both operating at the same center frequency. So, the savings in size with the higher-Dk material can result in a sacrifice in performance.

Laminate thickness must also be weighed when selecting a circuit material for a patch antenna. The design of any patch antenna is really a compromise between the conflicting requirements of the resonant patch and the microstrip feedlines. The goal for the patch is highly efficient radiation of microwave energy (in transmission), which calls for a thicker circuit substrate. But a thicker substrate will also mean increased radiation loss for the feedline to the antenna patch. Ideally, the feedline would use a thinner laminate with high Dk value for reduced microstrip radiation losses, while the patch would be formed on a thick substrate with low Dk value for high radiation efficiency. While it is possible to address this compromise with a multilayer design using two different circuit materials, any patch antenna with feedlines fabricated on a single circuit material requires a choice in laminate that helps balance the needs of the patch and the feedline.

For patch antenna designers, another laminate parameter to consider is how changes in temperature can affect a circuit material’s Dk value. This parameter, known as the temperature coefficient of dielectric constant, or TcDk, should be carefully considered for any antenna expected to endure a wide range of operating conditions, with smaller values resulting in lower center-frequency variations. An ideal material would exhibit no change in Dk value as a function of temperature, or 0 ppm/°C. Real materials, however, can suffer significant shifts in Dk with temperature, exhibited as unwanted changes in center frequency with changes in temperature.

What are Examples of Real Circuit Materials Engineered for Patch Antennas?

Three examples of high-performance circuit materials include the RO4500™, RO4730™LoPro™, and RT/duroid® 5880LZ laminates.   RO4500 material is an antenna-grade laminate available with Dk values between 3.3 to 3.5 in the z-direction at 10 GHz. These ceramic-filled, glass-reinforced hydrocarbon materials feature excellent dimensional stability. The RO4730 LoPro laminates offer low-profile copper foils with Dk value of 3.0 and Df of only 0.0023 at 2.5 GHz. Both of these RoHS-compatible circuit materials are designed for use with standard FR-4 PCB fabrication methods and high-temperature lead-free processing. RT/duroid 5880LZ laminate is based on PTFE dielectric material with a unique filler, resulting in a low-density, lightweight circuit material ideally suited for portable and airborne antenna applications. It has a very low Dk value of 1.96 at 10 GHz in the z-axis, with low Df of 0.0019, also at 10 GHz. This RoHS-compliant material is usable for antennas to Ku-band frequencies and higher.

These three materials share attributes that make them attractive for patch antennas: low Dk values, low Df and good thermal conductivity for handling relative high power levels when necessary. They are certainly not the only circuit materials suitable for patch antennas, but they illustrate the type of circuit material characteristics that are preferred for antennas.

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

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