Frequency independent shielded loop antenna

DETAILED DESCRIPTION The basis for antenna theory is the Hertzian electric dipole which can be represented, as in FIG.
1A, by two charges +q and -q located at opposite ends of a dipole represented by the vector s.
Time variation of the charges causes a current i to flow from one end of the dipole to the other.
In a practical implementation of that arrangement, shown in FIG.
1B, a generator G forces a current i to flow in the dipole which causes charges +q and -q to appear at opposite ends of the dipole.
Heinrich Hertz solved Maxwell's equations for the electric dipole with a current having a sinusoidal time variation.
See "Electric Waves" by Heinrich Hertz, pp.
137-159, MacMillan, London, 1893.
The solution for general time variation i=i(t) was subsequently elaborated by others in published works such as, Theorie der Elecktrizitat by M.
Abraham, Vol.
2, .
sctn.
13, Teubner, Leipzig 1905; The Classical Theory of Electricity and Magnetism by M.
Abraham and R.
Becker, Part III, Chapter X, section 11, Hafner, New York, 1932; and Theorie der Elecktrizitat by R.
Becker and F.
Sauter, Vol.
1, 18ed.
, D III .
sctn.
67, Teubner, Stuttgart, 1964.
With E=E(r, t-r/c) and H=H(r, t-r/c), one obtains for the electric and magnetic field strengths produced by the dipole at a point at the distance r: ##EQU2## Here, Z.
sub.
o =377 ohms, the wave impedance of free space, c is the velocity of light, s is the previously defined dipole vector of length s, and r is the location vector from the dipole to the point where E and H are produced.
The terms in equations (1) and (2) of primary interest are the ones which decrease with 1/r because those terms dominate in the far field.
The time variation of those terms equals that of the first derivative di/dt of the dipole current; a fact that is usually not recognized for sinusoidal currents i=I.
sub.
o sin .
omega.
t because the derivative di/dt=I.
sub.
o .
omega.
cos .
omega.
t differs only by the factor .
omega.
and a phase shift of the current i.
In order to produce large electric and magnetic field strengths and thus a large power density div P=div (E