http://ijece.iaescore.com Design of microstrip patch antenna to deploy unmanned aerial vehicle as UE in 5G wireless

Info 2021 The use of unmanned aerial vehicle (UAV) has been increasing rapidly in the civilian and military applications, because of UAV's high-performance communication with ground clients, especially for its intrinsic properties such as adaptive altitude, mobility, and flexibility. UAV deployment can be monitored and controlled through 5G wireless network as user equipment (UE) along with other devices. A highly directive microstrip patch antenna (MPA) could establish long-distance communication by overcoming air attenuation and reduce co-channel interference in the limited region if UAV uses a specifically dedicated band, which might enhance spatially reuse of the spectrum. Also, MPA is highly recommended for UAV because of its low weight, low cost, compact size, and flat shape. In this paper, we have designed a highly directive single-band 2×2 and 4×4 antenna array for 5.8 GHz and 28 GHz frequency respectively for UAV application in a focus to deploy UAV through 5G wireless network. Here, The Roger RT5880 (lossy) material utilize as a substrate due to its lower dielectric constant which achieves higher directivity and good mechanical stability. Inset feed technique used to feed antenna for lowering input impedance which provides higher antenna efficiency. The results show a wider bandwidth of 702 MHz and 1.596 GHz for 5.8 GHz and 28 GHz antenna array correspondingly with a compact


INTRODUCTION
The unmanned aerial vehicle (UAV), commonly known as drones, has become an intensive topic of research over the past few years because of its flexibility, autonomy, and wide range of application fields [1], [2]. The use of UAVs for general multi-dimensional performance and low cost has been increasing rapidly in civilian domain applications such as public safety, surveillance, and monitoring, rescue operations, internet of things (IoT) communication, and telecommunications [1]- [3].
Natural disasters such as a tornado, hurricanes, and floods occur tragically almost in all the countries. Still, when they occur extensively, the existing terrestrial communication network can be destroyed Generally, UAV uses a fixed operating frequency for communication. Presently 5.8 GHz is one of the popular choices for the designer. In paper [11]- [20], there has been taken a vital step for designing antenna below 6 GHz frequency but due to multi-band or feedline impedance mismatch, the gain of the antenna degrades or reduced antenna operational bandwidth due to inapt design parameter. A single band antenna with proper feed-line impedance matching can achieve higher gain and better operational bandwidth. A UAV, which is operated at 5.8 GHz, may satisfy the 5G wireless communication requirements. But soon, we will have to move towards higher frequency for achieving more lower latency and wider bandwidth so that we can meet 5G requirement completely, 28 GHz is one of the most attractive higher frequency bands. In paper [22]- [28] there has been designed different microstrip patch antenna array for future upcoming 5G application for the 28 GHz frequency spectrum.
In this perspective, we have presented a microwave and mm-wave antenna with their parameters to focus on UAV deployment in 5G wireless communication. A comparative analysis is also stated to prioritize mm-wave communication with research findings. A compact size, high directional microstrip patch antenna array of 5.8 GHz and 28 GHz resonant frequency is proposed in this paper. The design addressed a nice mix up of high directivity as well as wide bandwidth with a compact size which is achieved by inset feed technique [29], [30], substrate material with lower dielectric constant [23] and optimize design parameters. Only high directivity and fixed operating frequency can mitigate the co-channel interference for an Unmanned Aerial Vehicle of complex implementation procedures and handoff scenarios for 5G wireless communications [21]. Notably, wide bandwidth will increase coverage and capacity where small size reduces cost and antenna installation space, which is a vital point for small size UAV.
The rest of the paper is arranged in the following way. Section 2 discusses the antenna design in detail. In section 3, the output of the proposed antenna is presented with analysis and section 4 draws a comparison of the proposed antenna with recent work [11]- [20], [22]- [28]. Section 5 concludes the paper.

ANTENNA DESIGN
The rectangular patch antenna is chosen as the antenna shape because it provides better results [31]. The antenna parameters have calculated by using equation (1)-(11) [29], [32]. Width of the antenna, where, = Resonant frequency c = Velocity of light = Substrate dielectric constant Antenna length calculated by, The effective length and its deviation calculated by using the equation.
Hight of the Substrate calculated by (5).
Where wavelength, ≈ In the case of antenna design, feeding technique is very important because proper impedance matching in the feed line can ensure no reflection back from antenna which increases antenna efficiency [29]. Inset feed technique provides lowest return loss and highest gain [30].
Inset feed depth and notch gap calculated by (7), (8), Width of 50 feed line calculated by (9), Single antenna ground plane dimension calculated by (10) and (11), width of the ground is length of the ground is .
The Roger RT5880 (lossy) is chosen as substrate material because of its low dielectric constant, which provides higher directivity and low cost with availability [23]. Dielectric constant and loss tangent of the substrate is 2.2 and 0.0009, respectively. Table 1 shows the parameters list of single antennas for both 5.8 GHz and 28 GHz resonant frequency, and Figure 1 shows the front view of a single antenna for both frequencies. CST microwave studio used for designing and simulating all the antennas.  To achieve high directivity and gain, we have designed an antenna array too. Figure 2 shows front view of 2×2 antenna for both 5.83 GHz and 28 GHz frequency. In Table 2 parameters list of 2×2 antenna array is given. The attenuation due to rain, cloud, and fog increases exponentially with the increase of  [33]. The problem, as mentioned earlier, can be solved by increasing antenna gain [34]. That's why we have designed another 4×4 microstrip patch antenna for 28 GHz frequency. Figure 3 shows the front view of the antenna. Where x=2.32 mm, y=4.39 mm, Wf4=0.6 mm, Wf5=1.01 mm, and the dimension of the antenna is 30.14×32.04 mm 2 .

RESULTS AND DISCUSSION
In this section, we discuss the antenna return loss, voltage standing wave ratio, directivity, gain, and radiation pattern. Comparison of different element antenna for 5.8 GHz and 28 GHz shown in Tables 3 and 4, where an assessment of the existing antenna sets with the recommended 5.83 GHz 2×2 antenna array and the 28 GHz 4×4 antenna array is shown in Tables 5 and 6.

Return-loss
Antenna return loss or S11 parameter is a plot that denotes the ratio of the reflected power to the incident power with a dB unit. At the same time, it describes how much antenna matches with transmission line or device, the lower it is, the better the match will be [32]. Figure 4 shows the return loss plot of 5.8 GHz single and 2×2 array antenna where the array antenna resonant frequency moves slightly towards upper at 5.83 GHz due to array antenna feed-line mismatch but it still in acceptable level. With S11 <-10dB criteria the bandwidth of the 2×2 array antenna is 702 MHz. Figure 5 shows the return loss plot of 28 GHz antenna for different elements where the bandwidth of the 4×4 antenna array is 1.596 GHz using S11<-10 dB criteria. Figures 4 and 5 shows that the return loss at the resonant frequency of 2×2 antenna array at 5.83 GHz is -45 dB, on the other hand, the 4×4 antenna array at 28 GHz has a -30 dB return loss. It clarifies that radiation at 5.8 GHz and 28 GHz resonant frequency is quite acceptable and high.

Voltage standing wave ratio
The voltage standing wave ratio (VSWR) parameter of the antenna indicates how much of an antenna is impedance matched with its radio or transmission line [32]. For 5G wireless communication, the value of VSWR should be between 1-2, and the lower the value, the better the antenna will match with the transmission line. The value of the ideal field is 1, which indicates that no power is reflected from the antenna. Figures 6 and 7 show the VSWR plots of all designed 5.83 GHz and 28 GHz antenna respectively, were in all fields VSWR is close to 1 which is an ideal value.

Directivity and gain
Directivity of the antenna indicates the maximum gain in a direction. If an antenna radiates evenly in all directions, then it has zero directionality, and the directivity is 1 or 0 dB. In contrast, the antenna gain shows how much power the antenna can transmit towards peak radiation compared to the isotropic source [32]. 5G communication requires high directivity and gain for overcoming attenuation and increasing communication range. The proposed 5.83 GHz 2×2 antenna array and 28 GHz 4×4 antenna array, have achieved 12 dBi and 18.4 dBi directivity respectively, and 12 dB and 17.9 dB gain correspondingly. Higher directivity is achieved because the antenna resonates at optimum frequency band towards a single direction and substrate material is used with lower dielectric constant [23]. Tables 3 and 4 show the gain and directivity of the all 5.8 GHz and 28 GHz antennas.

Efficiency
The antenna efficiency is the ratio of the power delivered to the antenna and the radiated power from the antenna. High efficiency means that the maximum input power of the antenna has been radiated [32]. For 5G wireless communication, efficiency needs to be above 70%. The efficiency of the recommended 5.83 GHz 2×2 antenna array is 99%, and the efficiency of 28 GHz 4×4 antenna array is 88.5% which is a good value where inset feed technique with proper impedance matching play a vital rule [29], [30]. Figures 8 and 9 show the efficiency vs frequency plot for 5.8 GHz and 28 GHz frequency respectively.

Radiation pattern
The radiation pattern of the antenna indicates the directional (angular) dependence of the strength of radio waves [32]. The 3-dimensional (3D) radiation pattern of the proposed 5.83 GHz 2×2 antenna array and 28 GHz 4×4 antenna array has been shown in Figure 10(a) and 10(b), respectively. Figure 11

COMPARISON
Firstly, a single element 5.8 GHz rectangular patch antenna designed than a 2×2 array antenna designed using by the single element where gain and directivity increases significantly also bandwidth is wider compare to the single antenna but resonant frequency shifted 5.8 GHz to 5.83 GHz where return loss remain constant shown in Table 3. 28 GHz frequency is considered as high gain and directivity is required for UAV but higher frequency introduces higher attenuation in the air [33], [34]. So a 4×4 array antenna also designed at 28 GHz frequency which provides better gain and directivity than single and 2×2 array antenna shown in Table 4. Although there is a reduction of bandwidth and return loss, but enough for 5G communications of UAV.
The proposed 5.83 GHz 2×2 antenna array has a compact size than all antenna listed in Table 5 with a simple rectangular patch where microstrip line feed [11], [12] quarter-wavelength transmission line [13] and coaxial feed technique [14]- [20] has been used to feed the antenna. Designed inset-feed antenna has achieved a high gain better than the entire antennas listed in Table 5 except [13], [17] and also has realized a wider bandwidth with good return loss which will be more effective for UAV application. The recommended 28 GHz 4×4 antenna has higher gain than antenna enlisted in Table 6 although has lesser bandwidth than [22], [27]. Still, size reduction is significant, which reduce the fabrication cost and also weight, which allow UAV to carry the antenna effortlessly.

CONCLUSION
UAV deployment for wireless communications is not a regular case rather it is used for emergency support to an accident or event. Obviously, in consideration of flight time and battery lifetime, all must encourage getting a handsome bandwidth to cover more people to make the deployment cost-effective. The high directive and wide bandwidth microstrip patch antenna are preferable for UAVs because of it's lightweight, low cost, and ease of fabrication. In this paper, two compact size planes 5.8 GHz 2×2 antenna array and 28 GHz 4×4 antenna array are proposed, where higher directivity has been achieved because antennas resonate in a single direction.The high directivity increases the antenna's coverage as well as reduces co-channel interference with the surrounding UAVs or UEs, which enable smooth UAV deployment through 5G network. Tables 5 and 6 show that the proposed antennas are smaller than the existing antenna, which can be set to any surface of the UAV because of its flat shape. Also, small size will reduce fabrication cost and provide scope to attach more payloads to the UAV. The proposed work has found wider bandwidth at 28 GHz than 5.8 GHz. Use of 28 GHz can aid high speed and low latency at 5G communications than 5.8 GHz. 5G specifications had adopted higher frequencies as a key enbler due to the aforementioned advantages.