Abstract: A microwave directional coupler comprises a coupler dielectric board which is mounted substantially perpendicular to the surface of a parent circuit board. Upper interdigital elements are disposed on opposing surfaces of the coupler dielectric board. The coupling between the upper interdigital elements determines the odd mode impedance Z.sub.oo of the microwave directional coupler. Lower interdigital elements are also disposed on opposing surfaces of the coupler dielectric board. The lower interdigital elements are connected to ground and are arranged so that coupling between the lower interdigital elements and the upper interdigital elements determines the even mode impedance Z.sub.oe of the microwave directional coupler.

Abstract: A method of sorting comprising viewing objects to be sorted to determine whether any of them, at least in part, reflects, transmits or emits light in a predetermined part or parts of the spectrum to an undesired extent or in an undesired ratio, the objects being viewed while passing across a background which is also viewed and whose reflectance, transmission or emission of light in the said part or parts of the spectrum has a predetermined relationship with that of the average of the objects, effecting relative separation between any undesired objects which have been viewed and the remaining objects, periodically effecting an examination as to whether the said predetermined relationship exists and, if it does not, effecting an adjustment of the reflectance, transmission or emission of light by the background and/or adjusting the incident radiation onto the objects in the said part or parts of the spectrum so as to tend to restore the said predetermined relationship.