using delay line whose phase difference equals to the mechanical angle between two antennae,and phasing in +ve or -ve  depends on direction of radiation

how to design the phase delay line for particular freq. i am designing planar antennas.

Built delay lines with pieces of transmission line, you can use microstrip technology . Please read the book of D.M. Pozar - Microwave Engineering. Read the chapters about transmission lines.

Either a micro strip line or coaxial cable line, it has its velocity factor. Using velocity factor, calculate length per electrical degree. Use line length from source to antenna feed point length L1 and L2 either physically equal, if it is not possible, use relation   L1 = 2*n*pie*L2, where n is integer (choose n such that you have convenient length).

Let, you have selected L2 as convenient length, calculate L1 and vice varsa