Microstrip Mitred Bend Calculator

When laying out microstrip transmission lines an abrupt bend of 90° can cause a significant portion of the signal on the strip to be reflected back towards its source. This results in only a portion of the signal passing through and causes un-necessary reflections in the system which degrades performance. Mitering the bend is one of the ways in which the reflections can be reduced. A 90 degree bend in a transmission line adds a small amount of capacitance to the transmission line, which causes a mismatch. A Mitered bend reduces some of that capacitance, restoring the line back to it's original characteristic impedance. This calculator below helps calculate the dimension of the mitre bend.

Result

• D
mil
• X
mil
• A
mil
Formula for Microstrip Mitred Bend Calculator

Where,

W = Width of the the line

h = Height of the substrate

D = The diagonal of a square miter

A = Compensated length for optimal bend

What is a Mitered Bend?

A mitered bend is a bend that is made by cutting the curved ends of transmission lines at an angle to minimize the VSWR, insertion and/or return loss that otherwise becomes a major problem in the transmission line bends.

When a transmission line is bent at 90˚ (approximately), small amounts of positive and negative charges build up on the bent surfaces of the transmission lines thereby causing capacitance to develop across the line. This results in a change in the impedance of the transmission line, which causes a mismatch at the load. This mismatch causes a fraction of the signal on the line to be reflected back towards its source which reduces the overall system performance.

Therefore, it is necessary to remove this unwanted capacitance created when a transmission line is bent. Mitering is a process that is used to cut a portion of the line at a predetermined angle to minimize the capacitance at the bend.

Mitering can be performed at any angle from 30˚ to 120˚. When the mitering is done at 45˚, the resulting line will look like what is shown in there figure above.. Here, the cut portion occurs at two corners of the line and the tilted section acts like a reflector that directs the incoming EM signal in a direction perpendicular to the incoming direction i.e. the signal will flow in the vertical direction along negative y-axis. However, other angles such as 22.5˚ can also be chosen to cut the line three times along the bend.

So while a curved transmission line might look better, mitering is important as it reduces the losses in the transmission line bends.