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From: Alan G3NOQ
Date: 20 Nov 2002
Time: 09:07:26
Remote Name: 20.138.254.2
David - I was pleased to see Rosser confirming that fields can be traced back to the current and charge densities, as this is of course a central plank of the standard theory via the inhomogeneous Helmholtz equations for the potentials. It is tempting to say therefore that displacement currents "don't radiate" but Michele said somewhere that radiation from a slot antenna can be traced to the displacement current in the slot. . . I do not think there is a contradiction provided we are not too dogmatic about cause and effect. It is possible to calculate a slot's radiated field from the E-field distribution in the slot, so in that sense the displacement current does radiate. On the other hand, it is also possible to calculate the field from the electric currents in the sheet that the slot is cut into. Both are right, although using the currents is less convenient because the integration has to be done over the whole infinite sheet. So we can uphold the principle that fields are radiated from currents and charges, while accepting formulas in which the E-field distribution in the aperture is a convenient way of calculating patterns, as is done for slots, waveguide apertures and sometimes also reflector antennas . . . . Best regards, Alan