It is shown that the common eight-port (8P) comparator circuit may be constructed starting from a fully symmetrical 8P device. The conditions for a lossless symmetrical 8P circuit to be a symmetrical 8P comparator are derived. These are used to design several versions of a planar ring microstrip-slotline comparator. Two experimental versions of such an 8P circuit have been constructed using a planar microstrip-slotline technique. In the case of the second version, the ring circumference is only a wavelength at midband. This is the same circumference as the common 180-deg magic Upsilon ring circuit, four of which are frequently used to build a conventional comparator. The bandwidth of these 8P planar ring circuits can be as much as 30 percent for a return loss better than 20 dB. A quasi-optic 8P symmetrical comparator circuit based on a single wire grid is discussed. It has no bandwith limitation.