Satellite television has also changed this making these crude yet useful devices obsolete. This is because the signal could reach people who live near the house and use it to gain internet access without the knowledge of the individuals who purchased the unit.

A cell phone for instance works at frequencies of 950 Mega Hertz which is almost 1 Giga Hertz. Wavelengths get so short at these frequencies that it is not possible anymore to transmit using a pole antenna and transmit in all directions.

Reactance can be eliminated by operating the antenna at its resonant frequency, when its capacitive and inductive reactances are equal and opposite, resulting in a net zero reactive current. The greater the ratio of radiation resistance to ohmic resistance, the more efficient the antenna. When the circuit is much shorter than the wavelength of the signal, the rate at which it radiates energy is proportional to the size of the current, the length of the circuit and the frequency of the alternations. In the case of white noise the amplitude of the exciting signal can be very low and a radio receiver used as the detector.

Side lobes detract from the antenna quality whenever the system is being used to determine the direction of a signal, as in radar systems and reduce gain in the main lobe by distributing the power. The ionosphere changes the polarization of signals unpredictably, so for signals which will be reflected by the ionosphere, polarization is not crucial.

Antennas can be made resonant on harmonic frequencies with lengths that are fractions of the target wavelength. Often a dip is also used as a practical reference as the isotropic source cannot be realised in practice, but it has 2.1 dB gain over an isotropic source.

Antennas with high gain typically show side lobes in the radiation pattern. A conductor by which electromagnetic waves are transmitted or received.

More generally, interferometry allows the combining of signals from several radio receivers or a single moving receiver. The large loop has its strongest signal in the plane of the loop, and nulls in the axis perpendicular to the plane of the loop. There are many variations of , but here are a few common models.