# Antennas for Licensed Shared Access in 5G Communications with LTE Mid- and High-Band Coverage
## 3 Dual-Band Antenna for LSA Bands and LTE Mid and High Bands
### Design Procedure and Working Principle  
The design procedure of Ant#2 is divided into two main steps. The first step is to design an antenna for the 1427-2690 MHZ band. The second step is to add a new element to cover the high (3300-3800 MHz) band. These two steps are divided into four basic steps that illustrate the working principle. The evolution of the antenna and the corresponding predicted reflection coefficients are shown in Figures 7 and 8, respectively.  
In Step 1, the middle element MNO (inset of Figure 6) is designed and optimized. The effective length of this element is \(l_{ILE}=l_{1}+l_{2}+(w_{1}+w_{2}+w_{3})/2=14.2\) mm. Step 1 is completed by adding an L-shaped strip QQG with an effective length of \(w_{3}/2+w_{5}+w_{7}/2+l_{3}=26.8\) mm to the edge OQ so that the antenna covers the mid (1427-2690 MHz) band. The antenna then resonates at 1.67 GHz, as shown in Figure 8 (Step 1 curve). The effective length of the antenna (\(l_{ILE}+26.8=41\) mm) is close to a quarter wavelength at 1.67 GHz.  
In Step 2, an L-shaped strip OUH with a length of \(w_{3}/2+w_{6}+w_{8}/2+l_{4}=15.7\) mm is attached to the edge OU of the feed element, extending the length of the antenna by 29.9 mm. As can be seen in Figure 8 (Step 2 curve), the antenna then resonates at two frequencies, 1.98 and 2.68 GHz, because of the two different electrical paths MNOQG  
Figure 8: Reflection coefficient for each step in the dual-band antenna (Ant#2) evolution.  
Figure 7: The four steps of the evolution of the dual-band antenna (Ant#2).  
and MNOUH, respectively. In this step, the \(-6\) dB reflection coefficient bandwidth of the antenna in the lower band is 1.35 GHz (1.51-2.86 GHz).  
However, the lower-frequency limit needed to be shifted to 1.42 GHz to cover all the LTE mid and LSA bands. To achieve this, a vertical plate of height \(h_{1}\) is loaded onto the edge GQ in Step 3. The vertical plate shifts the lower frequency limit to 1.41 GHz, with a negligible variation in the upper-frequency limit (2.85 GHz).  
Our next target is to cover the high band (3300-3800 MHz), together with the mid band, with the same antenna. To achieve this, an L-shaped element VKL with an effective length of \(w_{2}+l_{5}+w_{12}+l_{6}\) is introduced into the top of the middle element MN in Step 4. The effective length (right side of the middle element) of the new element is 24.75 mm; it generated a resonance at 3.51 GHz.  
The final antenna design (Figure 6) consists of three electrical paths MNOQG (=41 mm), MNUHOG (=56.7 mm), and MNVKL (=24.75 mm), which make the antenna resonate at 1.96, 2.65, and 3.51 GHz, respectively. At 1.96 and 3.51 GHz, the antenna resonates in the quarter-wavelength modes, and at 2.65 GHz, the antenna resonates in the half-wavelength mode. The \(-6\) dB reflection coefficient bandwidths of this dual-band antenna are 1.45 GHz (1.39-2.84 GHz) and 700 MHz (3.27-3.97 GHz), respectively, covering the targeted mid (1427-2690 MHz) and high (3300-3800 MHz) bands.  
The current distributions of this antenna at the three frequencies are shown in Figure 9 to illustrate the working modes. For better presentation, the vertical plate is unfolded along the \(+y\)-axis. It can be seen in Figure 9(a) that the current is at a minimum close to G and a maximum close to M, meaning that the antenna resonates in the quarter-wavelength mode at 1.8 GHz. In addition, strong currents can be observed in the arm OUH at 1.8 GHz, meaning that the arm OUH is radiating at this frequency. At 2.6 GHz, the current is at a maximum close to M and there are two minima at H and G, as shown in Figure 9(b), which also indicates that the antenna is resonating in the half-wavelength mode. Figure 9(c) illustrates that the antenna resonates in the quarter-wavelength mode at 3.6 GHz since the current is at a maximum at M and a minimum at edge KL.  
Figure 9: Surface current distributions of the dual-band antenna (Ant#2) at (**a**) 1.8, (**b**) 2.6, and (**c**) 3.6 GHz.