Dear Student,
Magnetic field is maximum at the centre of the current carrying circular loop. The magnetic field lines of force due to circular coil of current are perpendicular to the plane of circular loop and is in the form of concentric circles around every part of the periphery of the conductor. The circles are small near the wire and becomes large as we move away from the wire. At the centre of the loop, the arcs of these circles appear as straight lines because of very large radius of the circle.
Regards