DYQSA will require a specific balun (balanced to unbalanced converter) design that fits into the geometry without disturbing the electrodynamic response of the antenna. The first straightforward choice for including the balun in DYQSA was inserting it in a metallic cone inside each element (as the green cones). However, this option will generate more performance degradation because of the mutual coupling between elements and the excitation of the common mode, that totally destroy the radiation patterns. To avoid this degradation, a new design including the four baluns at the center of the whole structure is proposed, as it is shown for blue cone.
Although this design provides better performance, it is also a new design challenge due to the small cone dimensions which has a radius 0.9 mm at the upper part of the antenna. Furthermore, the baluns need to provide a constant impedance with frequency with value around 60π Ω to match the self-complementary antennas. The input impedance of the baluns must be matched with 50Ω coaxial lines. The substrate is Duroid5880 with height of 0.254 mm and εr = 2.2. The thickness of the metal is 17 μm.
On the right is shown the DYQSA proposed solution with two options of placing the baluns.
We have 2 ports per balun: one (labeled with odd number) will be connected to the unbalanced part (LNA), the other (labeled with even number) will be connected to the balanced part (antenna).
On the right is the configuration of the proposed 4 baluns.