A Review of mm-wave Antenna Design at 60 GHz for 5G Applications System

The rapid advancement of mobile technology is closely tied to developments in electronic circuit designs and computer science. As a result, it is important to monitor the progress of antenna systems, which form the foundation of wireless technology. Microstrip patch antennas have emerged as a leading design in modern communication methods due to their small size, low cost, and ease of manufacturing. Over the past 40 years, numerous studies have been conducted on antenna systems, and this review article provides a comprehensive overview of the earlier and more recent achievements in microstrip patch antennas in the 60 GHz band, which is a crucial frequency range for fifth-generation (5G) technologies. This article discusses mm-wave antennas operating at 60 GHz and provides brief descriptions of their properties, construction techniques, and some related difficulties


INTRODUCTION
Among the most researched fields in today's communication systems is the wireless standard.The development of millimeter wave frequency for 5G applications has been driven by the need to address the challenges, including path losses, the use of superstrates over the mm-wave antennas, the need for conformality to the phone's shapes, the shared volumes with non-mm-wave antennas, and the high screen-to-body ratios [1].The essential goal about 5G technology is providing higher coverage with minimal power usage and cheap cost by using a band of highfrequency along with large bandwidth for enhancing data transfer data rate [2].In 2015, the World Radio Communications Conference listed several available for 5G wireless cellular network of (24 -86) GHz band and considerable bandwidth of 10 GHz using millimeter waves [3].Microstrip patch antennas (MPA), which are lightweight, small, and incorporated in circuits, are crucial for supporting wireless communication systems' mobile terminals.The creation of an antenna with broad properties, high gain, and the ability to work in high frequencies is being driven by recent trends.As a result, for potential implementation of microstrip antennas, size reduction and capacity improvement have emerged as key layout concerns [4][5].This paper's goal is to present 60 GHz performance characteristics and design versatility for microstrip patch antennas.In order to provide the viewers a feel of the variety given via an MPA and the possible advantages when set side by side with conventional small-gain designs.The survey examines the most recent advancements about MPAs technology providing advancements in various methodologies.This article addresses the variety of MPA models that are now feasible, very small, compact, wide-band; multi bands MPAs with increased gain to meet the major requirements on mm wave antennas to overcome the challenges that comes with the utilization of 60 GHz band.

MICROSTRIP PATCH ANTENNA AT 60 GHZ
As the next-generation wireless technology seeks to cover more customers and even service through a significant increase of mobile implementations, 5G is going to introduce flexibility to mm-wave communications.The advent of 5G grid necessitates antennas with hitherto unknown characteristics on a mobile station, including beamforming capabilities of the radiating pattern to accomplish spatial scans [6][7].Such necessity introduces a number of design difficulties to get an acceptable balance between theoretical design problems and practical requirements profile or low-cost production processes.Broadband antennas are necessary for many current and future communication systems, in addition to numerous radar implementations, work over many frequencies.Depending upon the wanted gain and bandwidth improvement techniques already reviewed, several academics started on working on overcoming the innate drawback of the impedance's limited bandwidth, and they achieved some remarkable findings.

2.1.Compact and Low-Profile Models
This section discusses MPA's made for 60 GHz that are either small in size or low profile and emphasizes the bandwidth performance that may be obtained.These designs are compatible with printed circuit board (PCB) technology and are deemed suitable for use in mobile devices like smart-phones and tablets.

2.1.1.Low-Profile Model
MPAs with lower dielectric constants can be developed for purposes that necessitate low antenna layouts.Figure 1 shows the endfire antenna design which consists of metal cap and substrate [8].The substrate includes microstrip line (MSL), a post-wall waveguide (PWW) and a MSL-PWW adaptation for the antenna feeder.Within the PWW, a matching post is used to cancel reflection.As can be seen, the antenna is made up of a junction in the shape of letter T and two slots to increase the gain and have equal beamwidth in E and H planes.This construction is resistant to manufacturing tolerance and has small dimensions of 8.0×4.5×2.5 mm3 and high gain compared to several reported lower profile MPA designs at high frequencies shown in Table 1.

2.1.2.Compact MPA'S
Wireless technology has advanced significantly, and several cellular gadgets are getting increasingly compact.Size reduction necessitates the use of small antennas.The form of the radiating patch, feed strategy, substrate material, and configuration of parasitic element are recognized to be the key variables influencing the bandwidth of an MPA.A variety of broadband approaches have been developed for the construction of small and broadband patch antennas.Figure 2 depicts a compact design using approaches such as the design structure of substrateintegrated waveguide (SIW) feeder [9].The feeding structure makes production relatively easy and inexpensive and more suitable for frequency up-conversion due to the demand for accuracy in the manufacturing process employed.In [10] a gridded patch is made up of nine equal rectangular sections spaced by a length substantially less than the wavelength in free-space at a given center frequency.A bonding film has been deployed and a PTFE (polytetrafluoroethylene) substrate to form a structure of compact three-layers observed in figure 3.For the antenna layout, a beam shifting mechanism has been also suggested by joining neighboring outer sections in the gridded patch.

Wideband MPA's Models
Broadband antennas are important since many wireless applications, both new and old, operate on broadbands.This section presents the MPAs' attainable bandwidth for various bandwidth-enhancing approaches.Because the MPAs' bandwidth is proportional inversely to their dielectric constant, MPAs with small εr values provide the optimum wideband efficiency.Various designs on broadband, multiband antennas , different-slot shapes, directional, array design are shown next.

2.2.1.Microstrip patch antenna arrays
A group of two or more antennas is called to by the term antenna array (sometimes known as a phased array.The efficiency of a single antenna is increased by combining or processing the antenna signals.The antenna array might be utilized to: improve overall gain; offer variety reception; and ascertain the orientation of received signal [11] [12].Linear arrays are employed in situations where fan-shaped radiation patterns are required. Figure 4 shows a 2×2 sub-array fed a Groove Gap Waveguide (GGW) E-plane corporate feed network.It has the potential of feeding high-gain of 32 dB single-sheet slot array.The distinguishing characteristic of the design is the ability of switching from linear to circular polarization using nails of same bed and wide bandwidth of 9 GHz.As for figure 5, in addition to the use of 8x1 patches that covers a wide bandwidth of 45GHz, a single frequency selective surface FSS is introduced.The spacing between frequency selective surfaces and antennas was shown to have a major influence on providing the optimum performance in terms of gain while maintaining the wide bandwidth.

2.2.2.Electromagnetic Bandgap (EBG) structures
A group of two or more antennas is called to by the term antenna array (sometimes known as a phased array.The efficiency of a single antenna is increased by combining or processing the antenna signals.The antenna array might be utilized to: improve overall gain; offer variety reception; and ascertain the orientation of received signal [11][12].Linear arrays are employed in situations where fan-shaped radiation patterns are required as can be depict in figure 6..

2.2.3.1.Slot resonators MPA's
The Introduction of slots on the radiating patch not only improves performance and minimize antenna layout but also increases bandwidth.Various mm wave antenna and method designs, reconfigurable, tunable, and array antennas for various purposes are associated with the slot concept.Figures 7 and 8 show antennas with Q and Lsquare slots in the radiator with microstrip feeder.Further details of the effect of the different shapes of slots on the antenna's behavior are shown in table 2.

2.2.3.2.Slots in Ground Structure
The main idea of introducing a slot within the ground plane of the MPA, it behaves like some load.It may be utilized to move the input impedance value closer to the characteristic impedance.This optimizes the input impedance match and the return loss (RL).Figure 9 displays a four-element regular patch antenna with Z-shaped slots on the ground plane.A standard patch antenna with four elements and ground plane Z-slots.As shown in Figure 9(b), the addition of a slot in the shape of a Z has increased the resonance frequency and bandwidth of the MPA from 60.7 GHz with a restricted band when the ground plane is full into 60 GHz and a bandwidth of 5.9 GHz.

2.2.4.Reconfigurable designs with beam-steering ability
The capacity to modify the radiation pattern direction has several applications in various systems which need scanning or interfering signal reduction.Beam patterns are adjusted via moving the MPA physically or electronically controlling certain antenna properties.Fig. 10 depicts an example of beam steering capability.The antenna layout starts with a standard circle-shape antenna with an annular slot.Two electronic switches have been used to produce triple distinct beam configurations.Using either switch separately leads to a 70° change in the central radiation pattern path within similar band properties.In [19] a new millimeter wave band with reconfigurable orientation antennas is presented.A multilayered pyramidal Dielectric Resonator Antenna DRA excitation origin is topped with a superstrate of frequency selective surface to form a hybrid antenna.An easy 45° mechanical rotation of the pyramidal DRA allows that device to change from circular to linear polarization as seen in Figure 11.

2.2.5.Periodic/fractal designs
Regarding the antennas created at mm-wave bands, there are many issues through the fabrication process such as: micromachining, complexity, cost, and vulnerability.Many design approaches, including the numerous strategies discussed above, are employed simply to enhance the bandwidth of a microstrip antenna.Another approach is by using repetitive shapes.
In [21], the log-periodic structure where the Yagi-Uda antenna concept influenced antenna geometry.A logperiodic dipole is often constructed from a sequence of dipoles arranged in lateral way to the design axis.The components' various sizes resulted in distinct resonance frequencies, allowing for a broadband functioning.Such addition resulted in a succession of shorter dipoles pointing to the "large side" of the proposed antenna as shown in figure 12. Figure 13 shows a modified antenna design with a typical circular-shaped patch with second fractal circular-shaped patch along with triple elliptical patches to increase the operating range of the antenna.A round slit is carved on the radiating patch to optimize the antenna's radiating pattern.

2.2.6.Multi band microstrip patch antenna
When 5G mobile communication is used, wireless channel capacity may be expanded without the need for extra spectrum or power in scattering-rich situations.This can be accomplished by increasing the number of antennas at the wireless link's transmitter and/or receiver.Because many antennas are needed in a compact system such as a mobile device, the single antenna must be compact and operate at multiple operational frequencies as needed [23][24].In [25], a patch antenna in the shape of an umbrella has been seen.The design resonates throughout three frequency bands 28, 38, and 55 GHz.A circular patch antenna resonating at a higher frequency of 44 GHz was created.The circular radiator is then etched with two identical rectangular slots, resulting in the construction of a semi-circular-shaped radiator and another band at 30 GHz.A rectangular shaped stub is inserted and two triangular shaped protrusions are incorporated to get the required bands as shown in Figure 14.
Comparatives analysis of different antenna designs for millimeter waves applications are listed in Table 1.The references are sorted in accordance to the array factor.The majority of the 60 GHz antenna models reviewed in the literature utilizes a substrate with a dielectric constant of 2.2.As the number of antenna elements increases, the gain is improved but at the cost of larger dimensions [26][27][28][29][30][31][32][33][34].According to [35], the gain and area performance of single element designs are better than those presented in [36][37], but this comes at the expense of bandwidth.Table 2 shows that most of the slot resonators have a single operating frequency and a bandwidth above 2 GHz.However, when combined with an array of elements, the bandwidth of the slot resonators can be widened.In one study [44], using two F-shaped slots resulted in a very low profile antenna with an area of less than 1 mm 2 and high gain compared to other designs.

SUMMARY AND CONCLUSION
The antenna field has had a very prosperous time in engineering over the last many years.Technology innovations in some new antennas, such as mm-wave antennas, the wideband, dual-band, multi-band or reconfigurable structures, low profile, compact, impedance bandwidth, high gain or linear/circular polarization implementations, and so on, have contributed to its success.The focus of this article is on antennas that operate in the millimeter wave (mm-wave) frequency band at 60 GHz.The article provides an overview of the properties of these antennas, as well as various construction techniques that are used to make them.Additionally, the article discusses some of the challenges and issues that are associated with mm-wave antennas operating at this frequency.

Figure 1
Figure 1 An example of a PCB-integratable metal cap slot antenna: a. antenna in 3-D b. upper view of the substrate c.waveguide microstrip line transition, fc=60 GHz, gain= 7.8 dB, BW=17.8GHz from [8].

Figure 6
Figure 6 An example of 60 GHz mm-wave MSA with three types of electromagnetic bandgap surface as a ground plane[15]: a. mushroom EBG b. cross EBG c. hexagonal EBG: fc = 60 GHz, Gain=8.3 dB, BW=11 GHz.

Figure 7 Figure 8 A
Figure 7 An example of a Q slot mm-wave antenna for body centric communication from [16]: a. top view b. bottom view.Fc=60.06GHz, Gain=8.62 dB, BW=12.11GHz.

Figure 9 Figure 10
Figure 9 An example of MIMO antenna of four-elements and Z slots on the ground plane: a. 3 D view b. effect of slot the ground plane on the S11.[18]Fc=60 GHz, Gain=14.8,BW=6 GHz.

Table 1
Comparative analysis of different antenna designs for millimetre wave applications

Table 2
Comparative analysis of various slot shapes at 60 GHz