thumb|300px|right|a horizontal three-wire rhombic antenna. this example is terminated with a lossy transmission line instead of a resistor. frame|rhombic antenna signal-gathering action compared to other end-fire, backfire and traveling-wave types. a rhombic antenna is a broadband directional wire antenna co-invented by edmond bruceus patent no. 2285565a, edmond bruce, directive antenna, filed february 3, 1931; granted june 9, 1942 and harald friis,us patent no. 2041600a, harald t. friis, radio system, filed april 5, 1934; granted may 19, 1936harald t. friis at ieee ghn.org http://www.ieeeghn.org/wiki/index.php/harald_t._friis in 1931, mostly commonly used in the high frequency (hf) or shortwave band. == description == it consists of one to three parallel wires suspended above the ground in a "rhombic" (diamond) shape, supported by poles or towers at each vertex to which the wires are attached by insulators. each of the four sides are the same length, typically at least one wavelength (Î») or longer. a horizontal rhombic antenna (picture, top right) radiates horizontally polarised waves. its principal advantages over other types of antenna are its simplicity, high forward gain and the ability to operate over a wide range of frequencies. it is typically fed at one of the two acute (sharper angle) vertices through a balanced transmission line. less commonly, it can be fed with coaxial cable through a balun transformer. the end of the wires meeting at the opposite vertex is either left open (unconnected), or terminated with a non-inductive resistor. when resistor-terminated, the radiation pattern is unidirectional, with the main lobe off the terminated end, so this end of the antenna is oriented toward the target country or geographical region. when unterminated the rhombic is bidirectional, with two opposite lobes off the two acute ends, but is not perfectly bi-directional. this is because of energy losses caused by radiation, conductor resistance, and coupling to the lossy soil below the antenna. the rhombic antenna, like other horizontal antennas, can radiate at elevation angles close to the horizon or at higher angles depending on its height above ground relative to the operating frequency and its physical construction. likewise, its beamwidth can be narrow or broad, depending primarily on its length. the shallow radiation angle makes it useful for skywave ("skip") propagation, the dominant mode at shortwave frequencie
Radio_frequency_antenna_types