Abstract: The present invention relates to antennas of a planar profile coupled to waveguides, and particularly to completely planar antennas, applicable in mobile telephony, radars and space communications, which base their operating on the transmission of electromagnetic waves, mainly in the range of microwaves and millimetric waves, through a thin opening of a height that is less than the wavelength, having corrugations around said opening such that maximized wave transmission as well as the collimation thereof in a defined direction towards leaky waves by means of a resonant coupling mechanism are obtained.

Abstract: The cement comprises a belite clinker (A) and a second component (B) made up of particles of at least one ceramic material. Preferably this second component has a particle size under 100 nm, and is present in a ratio between 0.2% and 15% by weight of the belite component (A). This cement has the advantages of conventional belite cement and also has better mechanical properties. The process for obtaining a building cement comprises the steps of: (a) producing a belite cement (A) clinker from low lime content fly ash by adding lime (CaO) to the clinker until reaching a CaO/SiO2 molar ratio greater or equal to 2 and hydrothermally treating the mixture; (b) grinding the obtained clinker; and (c) adding to the clinker a second component (B) made up of at least one ceramic material with a particle size under 100 nm.