Removed 'nan' , update the phitarget values

at boundary condition ( 0,2phi) we got 'nan' values at Impulse_responses[1:0] , i wrote the code in which at any target positions the impulse responses has an array. The 'nan' problem is not ignored in SISO,MISO and MIMO cases. 
hence the commit gives you the Impluse_responses with array output.