## 3 Antenna Structure
Therefore, uncertainties remain regarding the performance of existing designs in the entire upper hemisphere. The overall structure has been explained above using Figure 1. Detailed structural configurations of the proposed antenna are illustrated in Figures 2 and 3. Figure 2 shows the two dipoles and associated monopoles along with the feed lines. The dipole is fed by a microstrip line to slotline transition and an integrated balun. The microstrip line mode is converted to the slotline mode by coupling between the slot with a strip. The width of the microstrip line in the coupling region is halved so the feed point of Dipole \(A\) and Dipole \(B\) is as close to each other as possible. This ensures nearly identical performance of the two dipoles. Figure 3: Detailed view of connecting antenna elements: (**a**) 3D view; (**b**) short-circuiting Dipole \(B\)’s slotline; (**c**) connecting the QHC to the dipole feed line; (**d**) connecting the QHC to a coaxial cable. Figure 2: Dipole feed line with an integrated balun for (**a**) Dipole A and (**b**) Dipole B. The microstrip feed line is terminated in an open circuit at a quarter-wave point, while the slotline is short-circuited at a quarter-wave distance from the microstrip-slotline coupling point. This structure is geometrically as symmetric as possible, resulting in the balanced excitation of the current on the two arms of the dipole. The combination of a quarter-wave open-circuited microstrip line and a quarter-wave short-circuited slotline yields a broadband transition between a microstrip line and a slotline. This idea of feeding a printed dipole was first proposed by [PERSON] and [PERSON] in 1987 [32] and has widely been employed in feeding the broadband printed dipole antenna [33; 34; 35; 36; 37]. To assemble two dipole PCBs in a cross configuration, a cutaway slot is formed on the Dipole \(A\) PCB and on the Dipole \(B\) PCB. The width of the cutaway slot is slightly larger than the thickness of the PCB. The cutaway slot ranges from just above the microstrip line to the top edge in the Dipole \(A\) PCB, while it ranges from the bottom edge to just below the microstrip line. The slotline of Dipole \(A\) is short-circuited at a quarter-wavelength distance from the slot-strip coupling point, while the short-circuiting of the slotline of Dipole \(B\) is realized using a via on the PCB of Dipole \(A\). Wideband impedance matching is possible by a proper choice of the position of the slot-strip coupling point and by the combined frequency characteristics of the slotline short circuit and the microstrip line open circuit. The resulting balun structure provides the balanced feeding of the dipole over a broad bandwidth. Structures for the interconnection of the antenna components are highlighted in Figure 3 through magnified drawings. The box 1 in Figure 3a denotes the short-circuiting of the slotline of Dipole \(B\) using a via on the PCB of Dipole \(A\). It is presented in a magnified drawing of Figure 3b, where via pads in the Dipole \(A\) PCB are soldered to the slotline conductor in the Dipole \(B\) PCB. Via and via pads on each side of the dipole \(A\) PCB can be identified. The short-circuiting of the slotline balun for Dipole \(B\) can be completed by soldering the via pad on the Dipole \(A\) PCB to the conductor trace on both sides of the slotline of Dipole \(B\). In simulation, the soldering is emulated by joining the two metal surfaces. The slot width of the slotline above the via In the Dipole \(B\) PCB is about three times wider than the one below the via. This is performed to prevent the slotline in the Dipole \(B\) PCB from touching the slotline in the Dipole \(A\) PCB. The slot width of the slotline below the via is about the same as the thickness of the Dipole \(A\) PCB, as shown in Figure 2b. The box 2 in Figure 3a is the structure for connecting the output of the QHC to the input of the dipole feed line. Two vias are utilized to connect the output of the quadrature hybrid coupler to the microstrip line feeding the dipole.