dipole antenna
The dipole is the 'hello world' of antennas: two straight rods pointing in opposite directions, fed from the gap in the middle, like a drinking straw snapped in two and reconnected through a battery. It is the building block from which most antennas are understood. The TV rabbit-ears on an old set were a pair of dipoles.
The famous half-wave dipole is cut so each arm is a quarter-wavelength, giving a total length of λ/2. At that length the current forms a neat standing wave — maximum in the centre, zero at the tips — and the antenna's input impedance settles near a friendly 73 ohms, easy to match to common feed lines. Its radiation pattern is a doughnut: it radiates strongly broadside (out to the sides) and nothing straight off the ends, which is why you rotate rabbit-ears to find a station.
73 + j42.5 ohms is the textbook impedance of an ideal half-wave dipole; in practice it is trimmed slightly shorter (about 95% of λ/2) to cancel that reactive +j part and become purely resistive at the operating frequency.