In this area, by far the greatest effort has been focused on arrays, particularly phased arrays; the results have been summarized in three books [Hansen, 1966; King et al., 1968] and two special journal issues [Radio Science, 1968; IEEE, 1968]. Complete design formulas for scannable Baklanov-Chebyshev arrays [Tseng and Cheng, 1968] and new approximations for long Dolph-Chebyshev arrays [Drane, 1968] were developed. Infinite array models dominated in numerous studies of large phased arrays. Grating lobe effects were investigated by the induced emf method [Stark, 1966] and by use of impedance craters [Wheeler, 1966] Important and unexpected element pattern nulls not attributable to grating lobes have been observed and explained as coupling accumulation [Lechtreck, 1968] and as external resonances in dielectric sheets [Knittel et al., 1968; Wu and Galindo, 1968]. They have also been observed as mismatches in array simulators [Hannan, 1967a]. Proof of the possibility of impedance matching for all scan angles has been offered [Hannan, 1967b] and contested [Varon and Zysman, 1968] Limited control of coupling for wide angle impedance matching has been achieved by means of dielectric sheets [Magill and Wheeler, 1966], hole coupling of waveguides [Amitay, 1966], multiple modes in waveguides [Tang and Wong, 1968], and parasitic chokes [Dufort, 1968], and the form of asymptotic decay of coupling with distance has been established [Galindo and Wu, 1968]. Systematic procedures for the design of phased array elements have appeared [Wheeler, 1968; Amitay et al., 1968], as have methods of analysis of waveguide phased arrays without [Farrell and Kuhn, 1968], and/or with [Borgiotti, 1968a] dielectric sheets. Finally, there was developed an important geometrical description of phased array behavior, based on the fundamental principle of planar apertures, that unifies much of the existing knowledge of infinite arrays [Diamond, 1968]. A thorough application of this development to arrays of rectangular waveguides shows clearly the individual roles of the lattice and the elements [Ehlenberger et al., 1968]. The same principle was used to compute mutual admittances between slots [Borgiotti, 1968b], and formulas for observable stored energies of planar apertures have been derived from it [Rhodes, 1966] and contested [Borgiotti, 1967; Collin, 1967].