hi everyone in this lecture we are going to study about BMW so beam width is one of the most important parameter that is associated with antenna and wave propagation so the beam width is defined as the pressure angle from where most of the power is being radiated since we all know that the antenna will radiate only in the direction of maximum directivity and Beam with somehow says that the a pressure angle from which most of the power is being radiated so directivity and beam width is somehow connected with each other if we talk about the types of the beam it then basically there are two types of beam width that is hpbw and fnbw hpbw stands for half power beam width whereas on the other hand the second type that is fnbw stands for first null beam width now let's discuss about these two types separately so let me first discuss about this HP BW oh so it stands for half power beam width foreign as an angular separation in bit the magnitude of the radiation pattern is -3 DB from the peak of main beam so it is defined as angular separation in which the magnitude of radiation pattern is minus 3 DB from the peak of main beam so this is the definition for the half power beam width if we talk about the representation for the half power beam width then the half hour beam width will be equals to 70 Lambda over d so here Lambda represents the wavelength and if we talk about this D then it represents diameter only so D represents diameter so this is all about the first type of a beam width that is half power beam width now let us have a look at the second type of beam build that is f and BW so fnbw stands for first null beam width it stands for first null beam width now if we talk about its definition then it is defined as angular separation between the first null of radiation pattern so it is defined as angular separation between the first nulls of radiation pattern now if we talk about its representation for the first null beam width then it is represented as F and b w that will be equals to twice of hpvw that is first half power beam width so first null beam width is equals to the twice of hpbw and since we know that hpbw is nothing but equals to 70 Lambda over capital D so replacing its value we get 2 in multiplication with 70 Lambda over capital D so the final expression for the first one beam width comes out to be equals to 140 Lambda over d so this is the representation for first null beam width now let's discuss about the radiation pattern of the half power beam width and first null beam width so this is the representation for the radiation pattern of an antenna this is the major lobe and if you talk about these two then these two are the side lobes and this one is the back lobe similarly these two are the side lobes now let talk about the first null beam width since it is defined as an angular separation between the first null of a radiation pattern so here are the first null of the radiation pattern from the major lobe so here is the first null and here is a personal from this side and it is the angular separation between the first nulls so here is a angular separation so we can say that it is represented by F and b w so it is F and BW that is personal beam width now let's consider this point as a 0 DB and this point will comes out to be 3 DB or we can say that minus 3 DB now if you talk about the half power beam width then according to its definition it is defined as an angular separation in which the magnitude of radiation pattern is -3 DB from the peak of the main beam so here is the peak of the main Beam at the 0 DB and here is -3 DB and according to its definition it is an angular separation from the magnitude of the radiation pattern from minus 3 DB so we can say that this point is nothing but HP BW so these are the radiation pattern for the hpbw and fnbw if you like my content then do subscribe my channel and please hit the like button thank you