Planar antenna, planar array antenna, multi-axis array antenna, and wireless communication module

A planar antenna includes a planar radiation conductor 11, a common ground conductor 32, a first strip conductor 21 located between the planar radiation conductor 11 and the common ground conductor 32 and extending in a direction in parallel to a first axis in a first right rectangular coordinate system including first, second, and third axes, a second strip conductor 22 located between the planar radiation conductor and the common ground conductor and extending in a direction orthogonal to a direction of extension of the first strip conductor, and at least one pair of passive conductors 12 to 15 each including a side at an angle of 45±3° or −45±3° with respect to the first axis and opposed to the planar radiation conductor.