One radio frequency identification (RFID) antenna in my cat’s chip.Three near-field communication (NFC) antennas in my credit and debit cards.Almost the same number of antennas in my smartwatch.So, this looks like 130-year-old technology invented by Heinrich Hertz in 1886 The metal sleeve is also ¼ wavelength long.
It is essentially a dipole antenna, in which the inner exposed conductor is ¼ wavelength long. This vertically polarized 360° omnidirectional antenna is used for the wireless router. The effect of the antenna wire thickness is taken into account by the factor k in the following formula, which is used in our calculator:Ģ.4 GHz 2 dBi Wi-Fi rubber ducky antenna design left - the assembled antenna, middle and right - the disassembled antenna. The thicker the dipole wire, the shorter must be the antenna for a given frequency. However, if an antenna is made of a tube, especially on very high frequencies, the antenna length depends on the ratio of the length of the thin dipole to its diameter. Where c = 299,792,458 m/s is the speed of light and f is the frequency in Hz. The classic formula for calculation of the length of a half-wavelength dipole in meters for a very thin antenna wire is These kinds of dipoles can work in the frequency range of two octaves! For example, the pictured dipole antennas of the Ukrainian (built in the USSR) radio telescope UTR-2 have an operating frequency range of 8–33 MHz. These dipole antennas were invented in 1937 by a Soviet engineer Sergey Nadenenko and are manufactured both in the form of a rigid cage made of rods or pipes and from flexible copper or steel antenna wires. Not surprisingly that such antennas are called cage antennas. Instead of increasing the thickness of dipole wires, they can be made in the form of a cage made of galvanized steel rods or tubes, galvanized steel cable, or copper antenna wire. However, if we increase the thickness of dipole wires, the antenna can become usable over a larger bandwidth without re-tuning. For example, a 5/4-wave dipole antenna has a gain about 3 dB higher than that of a half-way dipole and therefore it is often used in various applications.ĭipole antennas are resonant, which means they can be used only on a single frequency. The most common dipole length is half the wavelength. Any dipole antenna consists of two identical elements in the form of metal rods with the feedline between them. Dipole antennas are used alone and as parts of dipole arrays. The dipole antenna is the simplest and most widely used in radio communications since the beginning of the RF technique. The photo was taken in 1973, four years after the radio telescope was put into operation. This photograph shows the broadband cage dipoles (or Nadenenko dipoles) of the Ukrainian radio telescope UTR-2, which was built in the USSR.