Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 121

Sometimes, the conversion of one kind of network parameter to another kind is needed for the analysis of a circuit. For instance, if several circuit blocks comprising of the lumped elements and the transmission line sections are cascaded, each circuit block could be expressed by its [ABCD] matrix. It helps to get an overall [ABCD] matrix of the cascaded network. However, the final [ABCD] matrix, describing the cascaded network is further converted to the [S] matrix. Similarly, the [S] matrix of each building block of the cascaded network has to be converted to the [ABCD] matrix to get the overall [ABCD] matrix of the cascaded network. Finally, the overall [ABCD] matrix is converted to the [S] matrix of the cascaded network. The S‐parameters are measurable quantities. The performance of a network is measured in the [S] matrix using a VNA.

On several occasions, the S‐parameters of a line section or a network are known either from the simulations or from the measurements. The S‐parameters are used to get the characteristic impedance and the propagation constant of a line, or a network. However, the true S‐parameters of a network are needed for this purpose. The true S‐parameters are normally embedded in the measured or the simulated S‐parameters at the ports of measurement, or the ports of simulation. The true S‐parameters of a line or a network are extracted, i.e. de‐embedded, from the measured, or simulated, S‐parameters at the ports. This is known as the de‐embedding process [B.10]. The EM‐Simulators have provision to de‐embed the true S‐parameters from the S‐parameters obtained at the measurement or simulation ports.

This section presents the conversion of matrix parameters, de‐embedding of the S‐parameters, and extraction of the propagation characteristics.