Sputnik 1 was filled with nitrogen to detect damages by micrometeroites causing a leak and a pressure loss. Therefore electrical vacuum feedthroughs were needed to connect the antennas to the transmitters.
Sputnik’s antennas consisted of four whips attached to the aluminum
enclosure through insulators that were spaced symmetrically around the
circumference of the spherical casing. These elements extending at a
70 degree angle to each other and gave the satellite its iconic shape.
The antenna configuration was a compromise between simplicity, the
space constraints of the launch vehicle and function. During launch,
the antenna elements were compressed against the side of the rocket at
an angle of 45 degrees and were held in place by clips and a conical
shroud that protected the satellite. Only part of the antenna was
covered by the shroud, leaving a significant portion of the element
exposed during its trip to orbit. When the satellite reached orbital
altitude and velocity it was separated from the launch vehicle and the
elements were freed to assume their 70 degree angle of separation
The antennas are described as matched pairs, one 2.4 meters and the
other 2.9 meters in length. The available literature gives no
information on the electrical characteristics of the antenna system
but it is probably safe to assume that they were some variation of a
center-fed dipole with the longer pair radiating the 20 MHz (14 meter)
signal and the shorter pair set up for 40 MHz or 7.5 meters.
Source: Sputnik and Amateur Radio
A flexible mount of the antennas was needed for the 45 ° angle during launch and the 70 ° angle after separation.
To emit as much as possible of the transmitter power by the antennas probably a matching network of inductors and capacitors was used. An unmatched antenna would waste too much of the precious transmitter power of only 1 watt.