Dipole mutual impedance for design of slot arrays

In the design of waveguide slot arrays it is necessary to include the effects of external mutual coupling between the slots. When the slots are in the broad wall, slot mutual admittance is related to mutual impedance between corresponding strip dipoles through Babinet's Principle, if the slot array is sufficiently large that the slots may be assumed to be in a flat infinite ground plane. The paper presents a computer subroutine in FORTRAN IV for mutual impedance between echelon dipoles of unequal lengths, in which the sine and cosine integrals are compactly and efficiently arranged.