Changes

=== Many passive RF devices such as directional couplers, hybrids and some filter designs involve segments of parallel coupled [[Transmission Lines|transmission lines]]. According to the coupled mode theory, one can define even and odd mode impedances (Z0e and Z0o) for such [[Transmission Lines|transmission lines]]. The Generic Coupled Tresulting RF structure can be modeled as a four-Lines ===port network device as shown in the opposite figure. Note that the four-port device has eight pins. Ports 1 and 2 correspond to the input and output of the first transmission line segment, while Ports 3 and 4 correspond to the input and output of the second (coupled) line segment. It is very important to connect and ground the negative pins at the input and output of the two transmission line segments.

Many passive RF devices such as directional couplers, hybrids and some filter designs involve segments of parallel coupled [[Transmission Lines|transmission linesRF.Spice A/D]]. According to the provides three coupled mode theoryline devices, one can define even and odd mode impedances for such all of which assumes lossless [[Transmission Lines|transmission lines]]. The resulting RF structure can be modeled as a four:  # Generic Coupled T-port network device as shown in the opposite figure. Note that the four-port device has eight pins. Ports 1 and 2 correspond to the input and output of the first transmission line segment, while Ports 3 and 4 correspond to the input and output of the second (coupled) line segment. It is very important to connect and ground the negative pins at the input and output of the two transmission line segments. Lines # Coupled Microstrips# Coupled Striplines

This model assumes lossless [[Transmission Lines|transmission lines]].  === Analyzing and Designing Physical Coupled Lines ===  In the case of The coupled microstrips and coupled striplinesstripline devices are characterized by their strip width, it is the even strip spacing and odd mode characteristic impedances (Z0e and Z0o) that really mattersubstrate properties. The Coupled Microstrips Calculator and Coupled Striplines Calculator find these two the even and odd mode impedances for the given strip width and strip spacing. They also calculate the even and odd mode effective permittivities, which are typically different. The system characteristic impedance of the coupled line is calculated from the formula: Z_0s = √( Z_0e . Z_0o ). To calculate the guide wavelength, the average of the two effective permittivities is used. In addition, the coupling coefficient of the coupled line is calculated in dB from the formula: C = ( Z_0e - Z_0o ) / ( Z_0e + Z_0o ).  The Coupled Microstrips Designer and Coupled Striplines Designer, on the other hand, find the values of the strip width and strip spacing for given values of the even and odd mode characteristic impedances.