# Design and Analysis of Dual-Band High-Gain THz Antenna Array for THz Space Applications
## 3 Proposed Array Antenna Design  
This section focuses on the design aspects of antenna array, where an array is a set of identical radiating element separated by distance \(d\); all are used in matrix order for increasing the gain and directivity of the overall antenna. Therefore, in this section, the proposed novel shape dual-band antenna array design is undertaken, as shown in Figure 3.  
As shown in Figure 3, a set of identical elements are placed at a distance of \(d\) away from each other. To work with the THz array, it is required to generate and control the amplitude or at least the time delay or phase shift at each radiating antenna that is controlled by separation distance \(d\)[24]. From this perspective of dual-band THz antenna, the separation distance \(d\) among radiating elements is 533 \(\upmu\)m, which provides good radiation performance in terms of good return loss, gain, and radiation efficiency, as will be discussed in the next section. All the information about the dimension of the primary boundaries of the four kinds of the THz antenna and arrays is recorded in Table 2.  
The maximum output gain of the antenna array is controlled by using the array factor (\(AF\)). The array factor of an antenna array depends upon the order of an array and the distance (\(d\)) between the radiating elements; besides that, the phase \(\beta\) between array elements also takes part in the calculation of the array factor. The array factor (\(AF\)) is calculated by using the following equation [24; 27; 40]:  
\[AF=\sum_{n=1}^{N}e^{i((n-1)\psi)} \tag{7}\]  
\[\psi=kd\cos\theta+\beta \tag{8}\]  
where, the total directivity \(D_{t}\) of the array is controlled by the array factor (\(AF\)) and single-element directivity (\(D_{o}\)). \[D_{t}=AFD_{o} \tag{9}\]  
The total efficiency of the array antenna can be calculated by using the following equation:  
\[ef=\frac{100G_{t}}{D_{t}} \tag{10}\]  
where, \(ef\), \(G_{t}\), and \(D_{t}\) representing the total efficiency (%), total gain (dB), and directivity (dBi) of the antenna array, respectively. From now on, the accompanying labeling classification will be utilized to differentiate between the multiple variations of the designed antenna array that are discussed in this paper:  
Type A: Novel shape dual-band THz antenna, as displayed in Figure 4a. Figure 3: Type C dual-band THz antenna array. The Type A antenna in Figure 4a is designed on a homogeneous polyimide substrate, and this is considered a prospective antenna to assess the performance of different antenna arrays. For increasing the gain of antenna, the order of the antenna array is increased. The Type B antenna array is a 2 \(\times\) 1 novel shape dual-band THz antenna array based on a homogenous substrate of overall volume of 1324 \(\upmu\)m \(\times\) 791 \(\upmu\)m \(\times\)10 \(\upmu\)m, and each radiating element is separated by 533 \(\upmu\)m, as displayed in Figure 4b. Similarly, Type C is displayed in Figure 4c, where four radiating elements are separated by 533 \(\upmu\)m. Subsequently, it will become evident that the Type C provides the ideal presentation as compared to remaining mentioned types; the radiating elements of the array were designed by utilizing the notable microstrip antenna hypothesis [38]. For feasibility purposes, a parametric sweep is run for getting better results, as shown in Figure 9.  
Figure 4: Design procedure of novel shape dual-band THz antenna array: (**a**) Type A antenna; (**b**) Type B antenna array; and (**c**) Type C antenna array. The constructional improvements in the proposed array model are carried out in the following steps, as depicted in Figure 4. These models create a group of reflection coefficients, studied in the next section. The numbers of radiating elements are increased for enhancement purposes in the antenna performance in terms of the high gain, directivity, and low reflection coefficient.