Some doubts in antenna arrays

I couldn't understand these concepts-

How does a distance of wavelength/4 and phase difference of pi/2 radian provides an unidirectional pattern?

How does end fire send the waves in a direction along the axis of the array?

Thanks in advance.

Hello, iVenky.

For example...

../imgqa/eboard/Antenna/rf-yumxifhouqh.jpg

Here the phase difference is 0 in the direction of the +z-axis, and the phase difference is 180 in the direction of the -z-axis. Therefore, the main lobe is formed in the direction of the +z-axis.

I hope that, I have correctly understood your question.