Question on "The Characteristic Impedance of a Filter&q

In the design of a LC passive filter, the "characteristic impedance"(CI) is one important parameter which decides the final device values.

http://www-users.cs.york.ac.uk/~fisher/lcfilter/
the above link indicates that "CI is the input and output impedance of a filter".

But i have two questions:
***one***
Why this CI is always purely real?
In steady state network analysis, the input/output impedance of a LC network is imaginary.How do CI and input impedance equal?

***two***
Some books say that CI is a circuit parameter for matching.
Does that mean if i design a filter with e.g. 50Ohm CI and match it with networks having 50Ohm output or input resistance, i will get minimum loss?
In other words , will CI affect the measurement result if i connect my filter to a HP Network Analyzer?

Thankyou!

You must search and try : filtry.exe or filter.exe prg.
Sincerely.