If you go thinner than ½ ounce copper its “skin depth” at 2.4GHz will exceed its thickness and will start to become lossy. As the material gets thicker the impedance will shift down very slightly. A change of 4.2 times is not little and would impact performance in a bad way.Īt ½ ounce copper and up there is little impact of performance. Above I wrote the line impedance is fairly insensitive to small changes (+/- 15%) in width or the Er of the material. This is to maintain the W/H ratio and the designed impedance. 35mm layer 1 to 2 thickness and you switch to a single layer board that is 1.5mm thick the transmission line must get 1.5/.35 or 4.2 times wider. If the W/H is 1.9 (for 50 ohms on FR4) on a 4 layer design with a. When using a reference design it is important to maintain the W/H of the transmission line. Note it does not matter how many additional layers there are or the total thickness of the board. That is from the top trace to the ground plane which is layer 2 on a 4 layer design. The impedance of a transmission line is set by its Width over the dielectric thickness (Height). Whether the line is 50 or 65 ohms you will see little difference in the performance. A 0.5cm transmission line is only 8% of a wavelength at 2.4GHz and 3% at 1GHz. A wave length in air at 2.4GHz is 12.5 cm, for microstrip it is scaled by 1/(sqrt Er) which is 6 cm for a Er of 4.3. The majority of the matching is done in lumped elements (Ls and Cs) which may benefit from the lower stray shunt capacitance resulting from a thicker substrate or the Rogers material with a lower Er (3.66). If you were designing a narrow notch filter or resonant element for an oscillator with transmission lines the Er of the material would be very critical, but you are not. ![]() The "core" is between layer 2 / 3, it is the same basic material as the pre-preg but purchased as sheet stock to have a solid material to build the layers up on.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |