Networks

 Reciprocal networks

A network is said to be reciprocal if the voltage appearing at port 2 due to
a current applied at port 1 is the same as the voltage appearing at port 1 
when the same current is applied to port 2. Exchanging voltage and current 
results in an equivalent definition of reciprocity. A network that consists 
entirely of linear passive components (that is, resistors, capacitors and 
inductors) is usually reciprocal, a notable exception being passive 
circulators and isolators that contain magnetized materials. In general, it 
will not be reciprocal if it contains active components such as generators 
or transistors.
Reciprocity in electrical networks is a property of a circuit that relates 
voltages and currents at two points. The reciprocity theorem states that the 
current at one point in a circuit due to a voltage at a second point is the 
same as the current at the second point due to the same voltage at the first. 
The reciprocity theorem is valid for almost all passive netwonetworks.

Symmetrical networks

A network is symmetrical if its input impedance is equal to its output impedance. Most often, but not necessarily, 

symmetrical networks are also physically symmetrical. Sometimes also antimetrical networks are of interest. These 

are networks where the input and output impedances are the duals of each othnetwork

Lossless network

A lossless network is one, that contains no resistors or other dissipative elements.