Radiation efficiency of a short cryogenic antenna

Electrically-Small, Superconducting Antennas

“…An actual electrically-small, cryogenic antenna has been reported by More and Travers [18]. The 20 MHz radiation from a 12-inch monopole with loading coil was observed while these elements were cooled to 770 K and then 4.20 K. The radiation efficiency at 77 0 K was 2.5 times that measured at 2900 K. The radiation efficiency increased to 4.3 times the 290 aK value when the elements were cooled tõ 4.20 K.…”

“…This possibility is gained at some cost because reactance and antireactance both are frequency dependent but in inverse ways so that complete cancellation of X takes place only at one frequency; significant cancellation is achieved a only in a relatively narrow frequency interval. A study of expressions (4-21) through tI (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) shows that the latter frequency interval is governed by a deterioration factor Dn = Xat/ r where Xat is the algebraic sum of the antenna reactance and the conjugate reactance.…”

“…to the load. Equating and substituting the expression for loop Ra yields A= (3/8fN) X 2(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) as before for the electric dipole. The conclusion is the same.In consulting the literature r 35] for the aperture of a half wave linear electric dipole, one finds…”