I am not an expert in electronics. Hence, I am looking for a broad conceptual answer.

Is it possible to a directional Bandpass/Bandstop filter i.e. Bandpass in one port and Bandstop in another.

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    \$\begingroup\$ I don't think that is possible with discrete inductors, capacitors and resistors. But in RF there is a circulator. There is also something called a duplexer or diplexer. Neither is exactly what you are saying but it is similar. You may be able to accomplish something similar with amplifiers if that is allowed. Not really an answer. Just a few terms to google. \$\endgroup\$ – mkeith Oct 16 '19 at 6:10
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    \$\begingroup\$ I agree that at low frequencies, this isn't possible. At RF, high frequencies, where the size of the components approaches the wavelength of the signal, more is possible. In theory the same is possible at low frequencies as well but the filter and its components would need to be enormous in size (think size of an office building) so that's impractical. \$\endgroup\$ – Bimpelrekkie Oct 16 '19 at 6:21
  • \$\begingroup\$ Thanks for the comments, the image shared in this question seems to be the circuit I may be interested in. electronics.stackexchange.com/questions/293610/… Now I also will be thankful if you could answer if I call this as a "Diode". I am working on Optics and there are a lot of misnomers being thrown around. Realization of an "Optical diode" is yet to be discovered. \$\endgroup\$ – Chetan Waghela Oct 16 '19 at 6:24
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    \$\begingroup\$ You want an optical filter? When using a color enlarger I noticed that the dichroic filters reflected the complementary color to what they transmitted - IOW they transmitted a band pass, and reflected a band stop. Perhaps that property could be used to do what you desire? en.wikipedia.org/wiki/Dichroic_filter \$\endgroup\$ – Bruce Abbott Oct 16 '19 at 7:05
  • \$\begingroup\$ the circuit that you linked in your comment is not what you described in your question ... there is one input feeding a voltage divider ... the voltage across the top 1/2 of the voltage divider is complementary to the bottom 1/2 \$\endgroup\$ – jsotola Oct 16 '19 at 7:26

2-wire telephony circuits handle signals travelling simultaneously in opposite directions and "figure out" which is the one they are interested in processing. They achieve this by using Wheatstone bridge circuits where the balancing impedance is the known and controlled impedance of the telephone wire. This is why when blowing into a handset microphone you don't get deafened by the noise coming from the earpiece. Tried and tested technology.

An extension of this principle is splitting the simultaneously occurring send and receive signals into forward and return channels. The circuit that does this is called a "hybrid" and they are used in 2 to 4 wire converters: -

enter image description here

The above circuit (from RF World) uses two hybrids to split forward and receive signals into simpler unidirectional channels so that conventional amplifiers can be applied and this, of course, makes a 2-wire, bidirectional line amplifier.

Is there a configuration where a circuit acts as Bandpass filter in one direction and Bandstop in other?

Using the idea above, put filter A in the forward channel and filter B in the return channel.

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