What is an advantage of a 5/8-wavelength whip antenna for VHF or UHF mobile service compared to a 1/4-wave antenna?
Why A 5/8-wavelength vertical is longer than a quarter-wave, so its current distribution squeezes the radiation pattern down toward the horizon instead of spreading it upward. That concentration of energy at low elevation angles shows up as gain, typically a few dB over a quarter-wave whip, which is exactly what you want for mobile work over the horizon. The tradeoff is that a 5/8-wave whip is not naturally resonant, so it needs a loading coil at the base to match 50 ohms.
Watch out The claim about a higher radiation angle is the opposite of the truth: the whole point of the 5/8-wave length is a lower takeoff angle. Its feedpoint impedance is not inherently lower or better matched either, which is why the matching coil is required.
Longer whip, flatter pattern: 5/8 wave pushes RF at the horizon, which means gain.