Compact planar microstrip-slotline symmetrical ring eight-port comparator circuits

It is shown that the common eight-port comparator circuit may be constructed starting from a fully symmetrical eight-port device. The conditions for a lossless symmetrical eight-port circuit to be a symmetrical eight-port comparator are derived. These are used to design several versions of a planar ring microstrip-slotline comparator. Two experimental versions of such an eight-port 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° magic T ring circuit, four of which are frequently used to build a conventional comparator. The bandwidth of these eight-port planar ring circuits can be as much as 30% for a return loss better than 20 dB. A quasi-optic eight-port symmetrical comparator circuit based on a single wire grid is discussed. It has no bandwidth limitation