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Common types of monopole antenna are the whip, rubber ducky, umbrella, inverted-L and T-antenna, inverted-F, folded unipole antenna, mast radiator, and ground plane antennas. The monopole is usually used as a resonant antenna; the rod functions as an open resonator for radio waves, oscillating with standing waves of voltage and current along ...
Counterpoises are typically used in antenna systems for radio transmitters where a good earth ground connection cannot be constructed.. Monopole antennas used at low frequencies, below 3 MHz, such as the mast radiator antennas used for AM broadcasting, require the radio transmitter to be electrically connected to the Earth under the antenna; this is called a ground (or earth).
The ground rods create a ground plane under the antenna which increases the gain. The ground rods may extend horizontally from the base, but in antennas fed by coaxial cable as shown here they are usually sloped downward to increase the radiation resistance of the antenna from the 36 ohms of a quarter wave monopole closer to 50 ohms, so the ...
It is shaped like the Greek letter Π or an upside-down capital letter U, and is the loop antenna analog of a ground-mounted monopole antenna. Similar to how a vertical monopole uses its ground system to produce a "phantom" image of the rest of a dipole, the missing lower half of the half-loop is replaced by its image in the ground-plane. If ...
A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver or transmitter. A whip antenna is a form of monopole antenna. The antenna is designed to be flexible so that it does not break easily, and the name is derived from the whip-like motion that it exhibits when ...
Putting an antenna indoors significantly decreases its performance due to lower elevation above ground level and intervening walls; however, in strong signal areas, reception may be satisfactory. [20] One layer of asphalt shingles, roof felt, and a plywood roof deck is considered to attenuate the signal to about half. [25]
The North Tower of the original World Trade Center also had a 110-metre (360 ft) telecommunications antenna atop its roof, constructed in 1978–1979, and began transmission in 1980. When the buildings collapsed, several local TV and radio stations were knocked off the air until backup transmitters could be put into service. [ 13 ]
So at low frequencies, even a 'T'-antenna can have very low radiation resistance, often less than 1 ohm, [5] [11] so the efficiency is limited by other resistances in the antenna and the ground system. The input power is divided between the radiation resistance and the 'ohmic' resistances of the antenna+ground circuit, chiefly the coil and the ...