A Super Wideband Directional Compact Vivaldi Antenna for Lower 5G and Satellite Applications

In this paper, a super wide band (SWB) Vivaldi antenna has been proposed for lower 5G bands in Sub-6GHz and satellite applications (S, C, X, Ku, and K band) using various performance improvement techniques. In the presented Vivaldi antenna, different slots are applied not only to increase the gain and directivity but also to get operating frequency at the intended specific frequency range. All dimensions of those slots were chosen by using the sweep parameter method. Ten corrugated side slots, two circular slots, and one via have been used to enhance the performance especially bandwidth and gain of the antenna. At the edge of wireless communication, we want to enhance two key aspects within the communication systems: the quality of service and the cost. )e proposed antenna incorporates a simple structure and small size with dimensions of 45× 35× 0.79mm. )us, after design, optimization, and simulation, the antenna produces a good reflection coefficient over the very large operating bandwidth of 23.19GHz, 1<VSWR< 2, maximum gain of 10.2 dBi, and average radiation efficiency of above 90%, which can be recommended as a suitable antenna for lower 5G as well as satellite applications.)e antenna is designed, simulated, and analyzed by using computer simulation technology microwave studio (CST-MWS). Finally, the performance of the Vivaldi antenna has been validated by FEKO and HFSS software, and we achieved a very good matching among the results.


Introduction
Since the first Vivaldi antenna was proposed in 1979 by Gibson [1], it is widely used in ultrawideband applications such as wireless communication, biomedical detection, Radar, Satellite communication system, and so on [2]. A Vivaldi antenna is a planar broadband antenna that is made of a dielectric substrate metalized on both sides. e fedline encircles the microstrip line, terminated with a sectorshaped area that encircles the circular space. e radiating energy at the resonant points reaches over exponential patterns through the symmetrical slot lines [3]. e Vivaldi antennas are categorized into three types: tapered slot Vivaldi antenna (TSVA), antipodal Vivaldi antenna (AVA), and balanced antipodal Vivaldi antenna (BAVA). e authors in [4][5][6] discussed the different parameter variation of the Vivaldi antenna both analytically and experimentally. In today's life, it is inevitable to have very high speed data exchanging channels for wideband applications. A Vivaldi antenna can produce ultrawideband frequencies with high directivity and stable radiation pattern.
ere are several advantages of using a Vivaldi antenna such as broadband characteristics, simple structure, small size, and easy manufacturing. In [7], an ultrawideband patch antenna with a U-shaped slot on the radiating patch is introduced for triband satellite applications. e operating frequency ranges of the proposed structure are 4.9 GHz-7 GHz, 7.92 GHz-11.08 GHz, and 11.85 GHz-15.94 GHz, and gain is varied from 2.3 to 4.5 dBi. In [8], a novel patch antenna is proposed consisting of parasitic elements and rectangular slots on the ground plane.
e proposed structure has a dimension of 16 × 8 mm 2 . e antenna shows the bandwidth of 11.34-17.46 GHz and gain of 4.92-6.30 dBi. A pair of square-shaped slotted Vivaldi antenna with dimension of 110 × 80 mm 2 has been proposed in [9]. Its operating frequency range is 2 GHz-11 GHz and has maximum gain of 10 dBi. To enhance the performance of the traditional Vivaldi antenna, the side-slotted Vivaldi antenna (SSVA) for imaging application is proposed in [10]. It has a size of 45 × 37 mm 2 and covers an ultrawideband frequency range. It possesses a maximum gain of 6.8 dBi and radiation efficiency is about 88%. To detect brain tumor within the human head, a coplanar feed ultrawide band Vivaldi antenna is proposed in [11,12], which has a dimension of 30 × 30 mm 2 and operated at a bandwidth of 3.1 GHz-10.6 GHz. e gain and directivity are improved by applying corrugated slots in both sides and gratings in front of the proposed antenna. A monopole Vivaldi antenna for cellular communication including LTE, GSM, UMTS, WiMAX, and WiFi bands has been simulated and presented in [13]. e novel compact broadband monopole Vivaldi antenna has been fabricated in [14]. e size of the final prototype is 73 × 69 mm 2 . In [15], an ultrawideband novel Vivaldi antenna for mobile communication application with pattern diversity has been proposed and fabricated. It covers 0.7-2.7 GHz. e huge bandwidth and high gain have been achieved by the designed antenna [16]. e operating frequency is 2.5-57 GHz and gain is 16 dBi. To get a huge bandwidth, a comparatively larger size of antenna is opted. It results higher VSWR (<3). A fern leaf inspired fractal structure has been introduced for UWB applications in [17]. In [18], the folding technique is applied on the tapered slot antenna, which shows the peak gain of 15 dBi with a balance radiation pattern to the whole operating range. In another technique, a number of metamaterial structures have been presented to improve the directional property of conventional antenna by reducing side lobe [19]. A miniaturized AVA with slits and dielectric lens has been fabricated in [20], which operated at a bandwidth of 1-30 GHz. In [21], a flexible UWB Vivaldi antenna with 3D-phase adjusting unit has been proposed which has better gain and pattern diversity. It has a dimension of 68 × 52 mm 2 and covers 6-18 GHz. Many other different techniques have been applied to increase antenna performance such as slotting technique, directors, patches, and lens loading technique. e antenna is fabricated by dielectric material of Rogers 5880 with a thickness of 20 mil. After analyzing the newly revealed Vivaldi antennas from [22][23][24][25][26][27][28], the basic motive is to decrease the size of the antenna as well as step up the higher operating bandwidth, gain, and efficiency.
During the design process of an ultra wideband Vivaldi antenna, one faces many challenges. One of them is the miniaturization of the antenna with wide impedance bandwidth and good radiation performance. In some cases, a low gain is exhibited through the entire ultrawide operating band. In the minimization process, reducing the size of the antenna also decreases the performance of the antenna. erefore, developing a compact design of the directional Vivaldi antenna with good gain and directivity, better efficiency, and VSWR for satellite communication and other ultra wideband applications is a very challenging task. In this paper, a super wideband Vivaldi antenna having a huge bandwidth of 23.19 GHz (3.06 GHz-26.25 GHz) and compact size of 45 × 35 × 0.79 mm 3 has been presented and discussed briefly. e main achievement of this research work is to develop a compact and super wide band Vivaldi antenna without compromising stability of gain and high radiation efficiency.

Tapered Slot Vivaldi Antenna Geometry
e geometrical structure of a microstrip line fed tapered slot super wideband compact Vivaldi antenna is described in this section. It is an exponential double-sided corrugated tapered slot Vivaldi antenna. e total design processes have been presented in five steps. Figure 1(a) represents a simple tapered Vivaldi aerial which is the first step of our proposed antenna. Two exponential tapered slots are placed symmetrically on the top of the substrate. Rogers RT 5880 dielectric material has been used as substrate of the antenna, having a relative permittivity of 2.2, tangent loss of 0.0009, and thickness of 0.79 mm. e microstrip line feeding is used as a feeding technique, which connects the two exponential tapered slots. e overall dimension (L×W) of the Vivaldi antenna is 45 mm × 35 mm. e thickness of the copper plate which is used as a radiating patch is 0.035 mm. e exponential profile of the designed Vivaldi antenna can be described by the following equation [11]: where Here, the points (x 1 , z 1 ) and (x 2 , z 2 ) are the endpoints of the flare. In this case, the taper rate is 0.135 which results in a wide mouth opening of 25.34 mm at the upper edge between the flares. At the second step, four corrugated slots are created in the top two sides of the metallic plates, which are shown in Figure 1(b). Each flare has two corrugated slots. e width of the slots is 2 mm. e lengths of the slots are 4 mm and 4.5 mm. In the third step, similarly additional six corrugated slots are made with the previous four slots and optimized the dimensions of the corrugated slots to ensure better performance than previous steps. e dimensions of the slots are 5 mm and 5.5 mm. e described structure of the antenna is presented in Figure 1(c). Two identical circular slots having a radius of 5 mm are added at the fourth step. e tapered slot Vivaldi antenna with all corrugated and circular slots is shown in Figure 1(d).
All the slots including corrugated slots make the antenna ultrawideband and enhance gain as well as increase the efficiency than previous steps. And finally, a shorting pin named via has been used which makes direct connection between the feed line and metal flare. is via promotes the antennas bandwidth from ultrawideband to super wideband. e via also enhances the surface current distribution throughout the antenna.
e metal via has a height of 0.86 mm and radius of 0.6 mm as shown in Figure 1(e). Figure 1(f ) shows the structure of the microstrip line feed of the proposed Vivaldi antenna. After applying all different techniques (like corrugated both sided slots, circular slots, and via) to enhance the antenna performance and using sweep parameters process, finally a super wideband compact tapered slot Vivaldi antenna has been proposed whose 3D view with port is depicted in Figure 1(g). e geometrical parameters of the proposed SWB Vivaldi antenna are listed in Table 1.

Substrate
Mouth opening

Results and Performance Estimation
is section describes all the results and analysis of the proposed Vivaldi antenna that is presented in previous sections. Initially, the proposed Vivaldi antenna is analyzed and optimized using 3D EM simulator software named CSTmicrowave studio. At the end, the obtained results are also verified by other two professional softwares: FEKO and HFSS. A comparison of the S 11 curves from Step 1 to Step 5 is depicted in Figure 2 to understand the successive bandwidth improvement after applying different aforementioned techniques on the designed SWB Vivaldi antenna. It can be easily noted that no other steps except Step 5 has operating bandwidth after 16 GHz, and only for Step 5, it holds up to 26.25 GHz. So, Step 5 has a larger bandwidth than the previous four steps. In this case, the metal via has a great influence on extending the UWB to SWB and also improves the current distribution of the antenna. e final Step 5 also provides much better return loss than any others. e antenna possesses the maximum return loss of −40.322 dB at 13.86 GHz. Figure 3 illustrates the gain of the five consecutive steps of this presented work. e average gain of the proposed antenna is above 8 dBi through the whole operating super wideband ranging from 3.06 GHz to 26.25 GHz. e comparison of radiation efficiency between Step 1 to Step 5 is shown in Figure 4. e maximum radiation efficiency of the proposed antenna is approximately 99%, and the average is above 95%. erefore, the antenna reveals good efficacy to radiate energy. e voltage standing wave ratios of all the stages of the antenna at the frequency range of 3 GHz to 27 GHz are displayed in Figure 5. It is certified that the VSWR of a radiating antenna varies from 1 to 2. For the best performance, the value tends to unity at every resonant frequency of the finally proposed compact Vivaldi antenna. It can be seen that the VSWR of the proposed antenna is 1.01, 1.  Figure 7. It can also be seen that the current of the antenna is mostly spread on the radiating fins at both lower and higher frequencies, which favors to assemble the electromagnetic energy and expand the stability of radiation of the proposed SWB Vivaldi antenna.  Step-1 (Without slot) Step-2 (Upper corrugated slots) Step-3 (All corrugated slots) Step-4 (All slots) Step-5 (Proposed)  Step-1 (Without slots) Step-2 (Upper corrugated slots) Step-3 (All corrugated slots) Step-4 (All slots) Step-5 (Proposed)

Conclusion
A super wideband Vivaldi antenna for lower 5G and satellite applications at C-, X-, Ku-, and K-bands has been presented. Different strategies are applied to enhance the performance as well as to make it compact. It is achieved by etching ten opposite corrugated slots and two circular slots in the metallic flares. e material of substrate, radiating fins, cavity diameter, stub radius, stub angle etc. parameters are optimized to reduce the size of the antenna and to get better performance especially to get super wideband. Results show that the modified flares change electrical length and enhance the gain greater than 8 dBi, by adjusting the radius and angle of stub. ere is an important effect of substrate material over the performance parameters, especially bandwidth and efficiency. e proposed Vivaldi antenna covers super wideband (3.06 GHz to 26.25 GHz), showing a returning loss of −40.322 dB, maximum gain of 10.2 dBi, VSWR of 1.07, and average radiation efficiency of above 95%. Given that, there are very good matching index during performance validation by the CST, FEKO, and HFSS. erefore, the proposed design can be considered as an excellent model for the lower 5G and satellite applications.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.