What kind of diagram is used to show the phase relationship between impedances at a given frequency?
Why A phasor diagram plots impedances (or voltages and currents) as vectors on a complex plane, with the horizontal axis for resistance (real part) and the vertical axis for reactance (imaginary part). The length of each arrow is the magnitude and the angle from the real axis is the phase, so you can see at a glance how much a reactive element leads or lags at one specific frequency. Adding impedances becomes simple vector addition on that diagram.
Watch out Near field and far field diagrams describe antenna radiation patterns at different distances, and a Venn diagram shows overlap between sets, none of which involve phase angle.
Phase relationship = phasor. The word is right there in the answer.