**Reciprocal Network**- is defined as having identical transmission characteristics from port one to port two or from port one to port two. This implies that the S-parameter matrix is equal to its transpose, . In case of a two-port network, .
**Lossless Network**- does not dissipate any power. The power incident on the network must be equal to power reflected or . This implies that the S-parameter matrix is unitary, or . In case of a two-port network, .
**Lossy Network**- implies the net reflected power is less than the net incident power, or
is positive definite.