An approximated Rectangular function with sharp edges on the expense of ripples

As the title says "An approximated Rectangular function with sharp edges on the expense of ripples". This is a simple project and this problem must have been solved before however since it is not in my field I just do not know its solution. The project might seem complicated since I do not know all the terminology as it is not my field and I am communicating with graphs and Mathematics however the problem might be a typical textbook solved example. Few notes that should be considered: There are two domains in the problem theta domain and n-domain. The rectangular function is in the theta domain and the sinc is in the n-domain. Your function will have a rectangular like function and it will allow ripples but have the sharp edge (the jump discontinuity). The ideal function will be rectangular and its transform sinc however since our n=-N:+N and N<40 there will be errors. We could tolerate ripple errors. You may use Maltab programs to prove your point however it should be based on mathematical science. Please read the attached pdf. I am looking for a function preferable continuous and trasformable with its truncated Fourier transform or inverse transform providing the rectangular function with the sharp jumps on the expense of ripples . The project budget is between $10-$50. The project is very simple. It is either you know how to solve it or not.