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The phase velocity at which electrical signals travel along a transmission line or other cable depends on the construction of the line. Therefore, the wavelength corresponding to a given frequency varies in different types of lines, thus at a given frequency different conductors of the same physical length can have different electrical lengths.
Twin lead cable is a two-conductor flat cable used as a balanced transmission line to carry radio frequency (RF) signals. It is constructed of two, stranded copper wires, or solid copper-clad steel wires. The wires are held a fixed distance apart by a plastic ribbon that is a good insulator at radio frequencies (usually polyethylene).
A typical T²FD is built as follows, [5] out of two parallel-wire conductors: Span near a half-wavelength of the lowest required frequency. Distance between upper and lower conductors equal to 1 / 100 of the wavelength. This distance is maintained by a number of insulating dowels.
Types of transmission line include parallel line (ladder line, twisted pair), coaxial cable, and planar transmission lines such as stripline and microstrip. [5] [6] The higher the frequency of electromagnetic waves moving through a given cable or medium, the shorter the wavelength of the waves. Transmission lines become necessary when the ...
A Lecher line is a pair of parallel uninsulated wires or rods held a precise distance apart. [9] [1] [10] The separation is not critical but should be a small fraction of the wavelength; it ranges from less than a centimeter to over 10 cm.
A monopole shorter than the fundamental resonance length of a quarter-wavelength at its operating frequency is called electrically short. Electrically short monopoles are widely used since they are more compact, and at long wavelengths construction limitations make it impractical to build an antenna mast a quarter wavelength high.
If the conductor is 1 / 4 of a wavelength long, current from the feed point will undergo 90 degree phase change by the time it reaches the end of the conductor, reflect through 180 degrees, and then another 90 degrees as it travels back. That means it has undergone a total 360 degree phase change, returning it to the original signal.
The gain in any given direction and the impedance at a given frequency are the same when the antenna is used in transmission or in reception. The electric field of an electromagnetic wave induces a small voltage in each small segment in all electric conductors. The induced voltage depends on the electrical field and the conductor length.