This routine designs a band-pass filter, that has a constant input impedance
of Zo at all frequencies, both in the pass-band and in the stop-band. At the
edges of the passband, the impedance is not too good, but its perfect at DC,
centre and infinity.

---------------L1-----------------C1------------
	 |                              |
	 |                              |
	 |------Zo-----------------Zo---|
			|
			|
	  -------------------------------|
	 |                               |
	 |                               |
	 L2                              C2
	 |                               |
	 |                               |
------------------------------------------------

