Fr4 dielectric constant vs frequency PCB

Fr4 dielectric constant vs frequency PCB

Properties of FR-4

ER=4.7 (has been reported between 4.35 and 4.8, and is slightly frequency dependent and varies by manufacturer and lot-to-lot) When it comes to delectric constant, FR-4 is an example of an anisotropic material.

tanD=0.018 (which really stinks! and varies by manufacturer and lot-to-lot)

FR-4 is rated to 140C by Underwriter Laboratories.

The "FR" in FR-4 stands for "fire resistant". It has generally replaced the (flammable) board material G-10 because of this property.

Many engineers write "FR4" instead of "FR-4". The correct version is "FR-4", but it's not worth an argument!

It is possible to create low-cost RF circuit cards on FR-4, but the losses will always be much higher than on PTFE-based boards from reputable suppliers. You can expect significant performance variations from one assembly to the next. Because of the high loss tangent, don't try to make any filter structures!

Could someone tell me what value of dielectric constant should I use for FR4 substrate in the 1-2GHz frequency range?
I’ve tried to find out this searching via google and I was surprised by a results!!! Everyone indicate different value for 1 GHz starting from 3.9 and up to 4.9. I have no idea why the difference is so huge!!!
Is it possible to make a precise modeling of FR4 at 1GHz at all? If yes, then which value for dielectric constant should I use?

It is totally dependent on your PCB vendor. I've seen it range from 3.8 to 4.5 depending on who I use for a vendor. I usually do my design at 4.2 and when the final vendor is chosen, do a final tweak on my design before sending it out. I always use FR4 @ 2 GHz and have used it successfully at 5 GHz. When designing consumer products, you just don't have the option of using nice material such as Rogers.

exact value of Dielectric constant can be obtained from the manufacturer at the specified operating frequency.
You may use Rogers RTDuroid at high frequencies , since it is less lossy

A dielectric material conducts minimal electricity, and provides an insulating layer between two conducting copper layers. The most common dielectric material is FR-4, but before selecting it for your board, you must carefully consider its properties.

Here is an overview of the most important properties to consider for any dielectric material:

1. Thermal properties
2. Electrical properties
3. Chemical properties
4. Mechanical properties

High frequency pcb:

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 MHz. It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances. The band is used by international shortwave broadcasting stations (2.310 - 25.820 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.

The maximum usable frequency regularly drops below 10 MHz in darkness during the winter months, while in summer during daylight it can easily surpass 30 MHz. It depends on the angle of incidence of the waves; it is lowest when the waves are directed straight upwards, and is higher with less acute angles. This means that at longer distances, where the waves graze the ionosphere at a very blunt angle, the MUF may be much higher. The lowest usable frequency depends on the absorption in the lower layer of the ionosphere (the D-layer). This absorption is stronger at low frequencies and is also stronger with increased solar activity (for example in daylight); total absorption often occurs at frequencies below 5 MHz during daytime. The result of these two factors is that the usable spectrum shifts towards the lower frequencies and into the Medium Frequency (MF) range during winter nights, while on a day in full summer the higher frequencies tend to be more usable, often into the lower VHF range.

When all factors are at their optimum, worldwide communication is possible on HF. At many other times it is possible to make contact across and between continents or oceans. At worst, when a band is 'dead', no communication beyond the limited groundwave paths is possible no matter what powers, antennas or other technologies are brought to bear. When a transcontinental or worldwide path is open on a particular frequency, digital, SSB and Morse code communication is possible using surprisingly low transmission powers, often of the order of milliwatts, provided suitable antennas are in use at both ends and that there is little or no man-made or natural interference. On such an open band, interference originating over a wide area affects many potential users. These issues are significant to military, safety and amateur radio users of the HF bands.