Why are short connections used at microwave frequencies?

At microwave frequencies, the wavelengths of the radio signals are incredibly short. Because of this, a physical connection wire of just a few centimeters can represent a significant fraction of a full wavelength. When an RF signal travels along a wire, its phase changes continuously across the length of the conductor. If a connection is long relative to the signal's wavelength, the signal will experience a significant phase shift from one end to the other, which can ruin circuit timing, cause unwanted resonances, or result in severe impedance mismatches. Keeping connections as short as possible ensures the phase shift along the physical wire is minimized, maintaining the expected timing, stability, and impedance of the microwave circuit.