NASA to be unable to contact Voyager 2 for almost a year

NASA announced that Voyager 2 will stop receiving commands due to upgrades on the DSS43 radio antenna in Australia. This antenna, part of the Deep Space Network, is undergoing critical upgrades over 11 months. During this time, Voyager 2, traveling in a downward direction relative to Earth's orbital plane, will be out of command reach but will continue sending scientific data. The upgrades are necessary as the antenna's components are 40 years old and increasingly unreliable.

Why are the radio antennas and transmitters being replaced?

What is the role of the DSS43 antenna in the US Space Agency's operations?