For a future work, we will do the same study using this time the 3D spherical antenna that we designed in [17] which produces a quasi-isotropic radiation diagram with 360[degrees] of opening angle in the whole space.

Belkadid, "Design and development of a new electrically small 3D UHF spherical antenna with 360[degrees] of opening angle in the whole space for RFiD, WSN, and RSN applications," International Journal of Antennas and Propagation, vol.

According to the company, its network engineers tested a new 12-beam

spherical antenna to enhance coverage and capacity for the over 150,000 attendees at the race held between 10 April 2015 and 11 April 2015.

A spherical antenna in which a slot couples free space outside of a spherical scatterer and an inner antenna region in a form of hollow spherical cavity was solved in the first paper [16], and an analogues configuration with a spherical cavity containing a conducting sphere of smaller radius concentrically nested in it [17].

The system of equations for the spherical antenna under consideration can be formulated by considering continuity conditions for tangential components of the magnetic fields on the inner and outer slot apertures [19]

Thus, using a rigorous definition, the problem for the slotted spherical antenna will be solved using the Equation (2).

[1.] Knott, P., "Design and experimental results of a

spherical antenna array for a conformal array demonstrator," INICA'07, 2nd International ITG Conference on Antennas, Mar.

When [P.sub.e] = [P.sub.m], the

spherical antenna radiates equal power in the electric and magnetic dipole fields and both [Q.sup.nc,sph.sub.e,lb] and [Q.sup.nc,sph.sub.m,lb] become equal to one half the minimum Q of a single electric or magnetic dipole because the two spherical dipoles form a self-tuned antenna requiring no external tuning capacitor or inductor.

As shown in Figure 1, there are several typical antenna array configurations for massive MIMO systems, that is, linear antenna array,

spherical antenna array, cylindrical antenna array, rectangular antenna array, and distributed antenna array [6].

This gives analytic expressions for the lower bound on Q for small spherical antennas [5, 8].

Breinbjerg, "Stored energy and quality factor of spherical wave functions--In relation to spherical antennas with material cores," IEEE Trans.

In these early stages metallic lens antennas such as metal-lens antennas and wire-grid lens antennas [1], reflector lens antennas [2],

spherical antennas [3], dual lens antennas [4], as well as dielectric lens antennas [5], and substrate lens antennas [6] were successfully investigated.