casino payouts best online casino payouts best slots for real money play slot machines for real money online casino american players american online casinos best online blackjack best online blackjack online gambling promotions online casino promotion trusted online casino reputable online casinos

There are a number of test methods to determine the dielectric constant of circuit materials used in the microwave or high frequency industry.

In this video, “Common Test Methods for Measuring Dielectric Constant,” you will learn about the most common test methods like Clamped Stripline Resonator Test, Split Post Dielectric Resonator, Full Sheet Resonance (FSR), and Microstrip Differential Phase Length Method.

For additional information and technical tools, join us at rogerscorp.com/techub

Have you ever looked at a Rogers Corporation data sheet and asked yourself why there are two types of dielectric constants?  What is the difference between Design Dk and Process Dk? If you answered yes to any of the above questions, Coonrod’s CORNER video, “What is Design DK” will help clarify.

After the video, join our Technology Support Hub for more information on Design Dk, free software and other technical assistance.  Still have additional questions or comments? Tweet us at @Rogers_ACM!

 

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

Choosing a high frequency circuit board material often requires weighing several factors, including cost and performance. A key starting point in sorting through printed circuit board (PCB) materials is usually the dielectric constant, or Dk, one of the essential characteristics of a laminate material and one that is subject to much comparison among different suppliers of PCB materials.

ROG_DkApp_finalThe dielectric constant of a laminate refers to a measure of the capacitance or energy between a pair of conductors in the vicinity of the laminate compared to that pair of conductors in a vacuum. The value for a vacuum is 1.0, with all other materials having a value somewhat higher than that. A laminate with higher values of Dk can store more energy than materials with lower Dk values. But at higher Dk values, electromagnetic energy will flow at a slower rate through the conductors (lower frequency).

Several earlier blog posts addressed different approaches available to measure the Dk of PCB materials. These methods involve different test fixtures and circuit configurations, such as the clamped stripline resonator test method and the full sheet resonance (FSR) test. Unfortunately, depending upon the laminate being measured and the frequency, these methods can reveal very different values of Dk for the same material under test.

For that reason, Rogers Corp. has developed alternative sets of dielectric-constant values, Design Dk values, to represent the company’s laminates during design and engineering stages. These are Dk values that can be used reliably and accurately within commercial computer-aided-engineering (CAE) software tools. The Design Dk values are measured by yet other measurement techniques, the differential phase length method. The approach is based on fabricating two microstrip circuits of significantly different length on the same laminate and in close proximity, identical in every way except for length. The test method measures the transmission characteristics of a quasi-transverse-electromagnetic (quasi-TEM) wave propagation and its phase response for a pair of microstrip transmission line circuits. By comparing the expected phase of the lines for a given frequency with the measured results, it can be possible to calculate the Dk for the laminate. In this approach, a large difference in length, such as 1:3, is recommended to simplify the measurements; the shorter circuit will limit the low-frequency accuracy.

But rather than just take Rogers’ word for it, it is also possible to apply the differential phase length method to a laminate of choice to determine its Dk firsthand. For those interested, Rogers Corp. now offers free downloadable software, Rogers’ Microstrip Dk Calculator Software, to determine PCB Dk values. The software works with the aid of associated test equipment, such as a microwave vector network analyzer (VNA). A high-quality test fixture should be used with the same signal launch for both circuits under test. The software can gather data from the measurements and produce a plot of Dk versus frequency, of particular value to designers of broadband circuits wishing to know the relative dielectric constant of the laminate beyond a certain operating frequency range. The range of frequencies across which this method can test depends on the lengths of the circuits, the return loss between the test fixture and the analyzer, and a number of different network analyzer parameters. The accuracy of the measurements depends on these different parameters and the length ratio between the two transmission lines. In addition to the software, an operator’s manual for performing the measurements can also be downloaded for free. The user’s manual provides details about the test method and why it tends to provide reliable results for Dk values.

These Design Dk values are generated for all of Rogers’ commercial laminates, based on this measurement method. The Rogers Microstrip Dk Calculator Software is available online for free download from the Rogers Technology Support Hub, which also includes technical papers and videos and several calculators, including the latest version of the MWI Microwave Impedance and loss calculator, MWI-2013. This free downloadable software tool features an improved grounded coplanar model, added capability to plot insertion loss as a function of frequency, and can compare as many as five models at one frequency or as many as five models over a range of frequencies.

Visitors to the Rogers Technology Support Hub can also download a copy of the ROG Converter software, a web-based application designed for a tablet or smartphone. It can provide simple conversions of dimensions from metric to English units and back, for temperature, for copper thickness, for CTE, and for thermal coefficient of dielectric constant (TCDk). Recently added conversions include for return loss: as VSWR, mismatch loss, and reflection coefficient. Coming soon is a free software tool that will predict minimum bend radius for a PCB without fracturing the copper traces. Based on Rogers’ materials, it can also help when planning multilayer material stackups.

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.

Tagged with:  

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.

If you’re looking for a primer on what Design Dk (dielectric constant) is, then look no further. John Coonrod shares a presentation about Design Dk and what it’s all about.   Circuit design and modeling is a highly complicated process.  There are different test methods and as John notes, each have their pros and cons.  John shares some of the methodology he uses to define a consistent Dk value for Rogers high frequency laminates used in printed circuit boards (PCBs) and other microwave electronics.

The presentation covers:

  • What is meant by Design Dk, Specification Dk and Process Dk
  • Publishing the Design Dk
  • Test methods
  • Design Dk test method defined
  • Supporting documentation

View the presentation:

 

Page 1 of 212