In unilateral circuits, the property of circuit changes with the change of direction of supply voltage or current. In other words, unilateral circuit allows the current to flow only in one direction. Diode rectifier is the best example of unilateral circuit because it does not perform the rectification in both direction of supply.
In bilateral circuits, the property of circuit does not change with the change of direction of supply voltage or current. In other words, bilateral circuit allows the current to flow in both directions. Transmission line is the best example of bilateral circuit because, if you give supply from any direction, the circuit properties remain constant
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