Can Radiators Be Really Isotropic?

Abstract

In search for isotropic radiators with reasonable quality Factor (Q), bandwidth, and efficiency, one looks for practical radiators with a typical resonant length of . We present here a Green's function analysis in Fourier of a microstrip element and a far-field integral method in configuration (real) space of single and dual U-shaped elements. Both solutions analytically prove that the power radiation patterns are isotropic in nature (while the thickness and the width tend to zero), although the polarizations are not symmetrical in all cuts. It is also shown that the power isotropic U-shaped radiator, for which the surface current density is infinite, can be replaced by another finite-size radiator, having finite-surface current density, such that its far-field is exactly the same as the far-field of the U-shaped isotropic radiator.

Low-Profile Implementation of U-Shaped Power Quasi-Isotropic Antennas for Intra-Vehicle Wireless Communications

“…A parameter study shows that when L is around λ/4 and D vanishes, GV approaches 0 dB (e.g. when L = 0.244λ and D = 0.012λ, GV is only 0.3 dB), a result in accordance with previous findings [18]- [20]. Unfortunately, despite the appealing radiation property, the low radiation resistance has severely hindered the practical application of this radiator.…”

“…The physical length of #1 (also #3) and #2 are L and D, respectively, and the total length of the radiator is L . This problem has historically been studied both in the spatial and spectrum domain [18]- [20]. We here present a solution with the assumption that the center fed surface current follows a sinusoidal distribution along the entire radiator, which is more general for a flexible length of #1 to #3 (note that in [18]- [20] only the case for L = λ/4 and a vanishing D is assumed).…”

“…The gain can be calculated via the orientation sensitivity measurement program in the instrument [37]. Since polarization of this tag antenna is orientation dependent [20], partial gains for the two orthogonal polarizations in each direction have been recorded and then added to obtain the actual gain [32]. A complete 3D measurement for the pattern of a tag antenna (terminated with a chip) is quite difficult, and therefore, as a common practice in the community, the tag antenna response was measured for three orthogonal planes.…”

“…Compared to the latter three categories which can mainly rely on intuition and cut and try process, only the U-shaped λ/4 resonators have been theoretically studied and exact analytical solutions have been given. In particular, it has been shown that a U-shaped λ/4 resonator with closely spaced two parallel arms has the potential of a perfect power isotropy (GV = 0 dB) [18], [20]. However, due to the opposite electric current on the two parallel arms, the U-shaped radiator has intrinsically low radiation resistance, leading to the impedance matching difficulty.…”