1 Introduction

Millimeter-wave (mm-wave) front end circuits have created enormous attention in high speed, short range 5G wireless applications over the last few years. Researchers are giving substantial efforts for the development as well as for the standardization of active and passive devices at the unlicensed spectrum (60 GHz) ranging from 38 GHz to 66 GHz where an efficient antenna with enhanced bandwidth is a major component of such systems. With the rapid rise of IoT based devices in recent years, the demand for 5G applications has increased. The traditional communication system's spectrum constraints led to research on 5G communication at frequencies of 28, 38, 60, 71–76, and 81–86 GHz. However, mm-wave is not only advantageous for its tremendous amount of bandwidth, it is also great for high speed data transmission, high definition picture quality and video streaming [1, 2]. Conversely, mm-wave has some issues to deal with regarding sensitivity to blockage, directivity and high propagation loss. Therefore, it sets new challenges for architecture and infrastructure for Mm-wave communication [3].

In terms of novel ideas, researchers have offered many strategies to expand the use of the 5G spectrum. For example, T-slotted microstrip patch antenna for 5G WiFi network of 60 GHz frequency is used to improve the WiFi system data transmission rate [4]. The wearable Mm-wave Triband Antenna embedded on a smart watch for wearable IoT applications. Biomedical telemetry antennas are designed to allow doctors to receive data from patients. Moreover, they can be used for tablets endoscopic, pacers, cardioverter-defibrillators, devices for retinal implants and blood glucose [5]. A compact size low-profile ultra-wideband antenna operating at 28 GHz with a bandwidth of 4.47 GHz was reported in [6]. A fully integrated mm-wave multi beam phased array antenna was analyzed in [7]. In [8] the antenna deals with the polarization and beam scanning ability for mm-wave application. The antenna consists of switchable rejection band capabilities designed to reduce interference from other wireless devices working at 3.37 and ends at 27.71 GHz. The alternating state in the resonator was achieved by using two inserted parallel PIN diodes [9]. A complex microstrip phased array antenna operating at 28 GHz was constructed with a capacitive via fences to reduce the size of the element, to improve the beamwidth of the antenna. A U-shaped decoupling structure was introduced between the antenna elements to reduce mutual coupling and to minimize the overall size of the antenna [10]. The array antennas in [11] are co-designed with an aperture transmission line so that the overall antenna element receives RF signals. However, the antenna operates at a licensed 5G mm-wave spectrum of 24.25–27 GHz. A compact coplanar waveguide (CPW) technique is used to enhance the bandwidth of a Multi-Input-Multi-Output (MIMO) antenna. The antenna design is perfect for ultra wideband wireless communication and portable devices [12]. To resolve aerodynamic issues and the connection loss between the IC chip and antenna band in the mm-wave 5G band, was designed in [13]. The fabricated antenna covers 0.84–1.89 GHz, 2.39–5.12 GHz for LTE/Sub-6 GHz 5G bands, 28.2–32.1 GHz and 33.7–34.9 GHz for the mm-wave communication. The gain of 28 GHz is about 10.95dBi. Therefore, the antenna design stands out to be a good candidate for future V2X (vehicle-to-everything) applications. In reference [14] a dual-band, single-feed mmwave antenna with circular polarization is proposed for 5G communication.

In this paper, a compact co-planar waveguide (CPW) fed mm-wave tri-band antenna for future 5G communication is presented. With a bandwidth of 4 GHz, this tri-band antenna is suitable for multiband operation in 5G communication. The proposed antenna has a compact in design, large bandwidth, and has multiband feature. The suggested antenna is composed of low-cost Rogers RT 5880 material and overall size of 9 mm × 9 mm × 0.127 mm.

Fig. 1.
figure 1

Front view (a) and rear view (b) of the proposed mm-wave tri-band antenna.

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2 Antenna Configuration

A compact CPW fed tri-band monopole antenna has been designed for 5G communication, sized at 9 mm × 9 mm × 0.127 mm which is presented in Fig. 1. The basic antenna consists of a 50Ω CPW feedline, circular ground plane, and a rectangular resonating patch. The width and length of the actual rectangular patch are calculated using Eq. (1) and (2).

$$ W_{p} = \frac{{c_{o} }}{{2f_{o} }}\sqrt {\frac{2}{{1 + \varepsilon_{r} }}} W_{p} = \frac{{c_{o} }}{{2f_{o} }}\sqrt {\frac{2}{{1 + \varepsilon_{r} }}} $$
(1)
$$ L_{p} = c_{o} \frac{1}{{2f_{o} \sqrt {\varepsilon_{reff} } }}L_{p} = c_{o} \frac{1}{{2f_{o} \sqrt {\varepsilon_{reff} } }} - 2\Delta L_{p} \Delta L_{p} $$
(2)

To achieve compact size with multiband as well as to keep the value of reflection coefficient, S11 less than -10dB with high gain have become the main focus of our research work. In addition, a coplanar waveguide technique with circular ground plane, rectangular slot and parasitic elements are used to achieve multiband operation. The main radiating element is tapered at the top and at the bottom to shift the radiation towards the desired band for 5G communication as well as to achieve desired frequency bands i.e., 28 GHz and 38 GHz and 61.5 GHz keeping the overall size of the antenna compact. Two L shaped parasitic elements are added to the antenna design to improve overall radiation pattern. The proposed design is made up of three layers: a circular ground plane of height 0.035 mm, a low-cost 0.127 mm-thick (Sh) Rogers RT5880 substrate (εr = 2.20 and tanδ = 0.0009), and a radiating patch of 0.035 mm thickness. The radiating patch is trimmed to a unique form to enable multiband operation. The parasitic element is then truncated from the radiating patch to smooth and enhance the radiation pattern while maintaining a small size for the final design. However, the optimized values of the proposed antenna are summarized in Table 1.

Table 1. Optimized Parameters of the Proposed Design
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3 Simulated Results and Analysis

The simulated reflection co-efficient (S11) is presented in Fig. 2. Where it is clear that for 28 GHz, 38 GHz and for 61 GHz S11 remains at – 17 dB, -11.9 dB and -23.7 dB respectively with a wideband operation at 28 and 61.5 GHz with bandwidth of 4 GHz which are ideal frequency for the 5G communication. Moreover, in all desired frequency range VSWR remain less than 2 depicted in Fig. 3. The gain of the of the designed antenna gradually increasing with increasing the frequency starting from the 1.365 dB, 3.147 dB and 4.520 dB for the 28 GHz, 38 GHz and 61 GHz respectively. Additionally, although for the 28 GHz directivity was 4.355 dBi with the increasing the frequency directivity peaks at 8.026 dBi. The maximum gain over frequency plot and the overall efficiency vs frequency of the proposed antenna have been presented in Fig. 4 and Fig. 5 respectively.

Fig. 2.
figure 2

Simulated result of reflection coefficient, S11 of the proposed mm-wave tri-band antenna

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Fig. 3.
figure 3

VSWR reading of the proposed tri-band mm-wave antenna showing the reading below 1.7 for 28 GHz, 38 GHz and 61 GHz.

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Fig. 4.
figure 4

Maximum gain over frequency for the designed tri-band antenna.

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Fig. 5.
figure 5

Efficiency Vs frequency graph for the designed tri-band antenna.

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Fig. 6.
figure 6

Three-dimensional gain plots of the design antenna at (a) 28 GHz, (b) 38 GHz and (c) 61 GHz

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Three-dimensional gain plots are presented in Fig. 6 where we have achieved maximum 4.52 dB gain at 61GHz for the proposed tri-band mm-wave antenna with different patterns which degrades it from a general tri-band antenna. However, the current density of the tri-band antenna is presented in Fig. 7. By using the current density, we can find out the resonating elements inside the patch antenna as well as assist us to realize the direction of the flow of current inside the antenna.

Fig. 7.
figure 7

Surface current distribution of the design antenna at (a) 28 GHz, (b) 38 GHz and (c) 61 GHz.

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In 28 GHz the maximum current distribution is on the microstrip line and bottom of the radiating patch. In 38 GHz current distribution extends upto the top of the radiating patch and lastly in 61.5 GHz the maximum current distribution is towards almost whole area of M-shaped resonator, microstrip line and slightly lower part of the I-shaped resonator.

Table 2 shows the comparative analysis of the antenna dimension, material, frequency and gain of the proposed design with the reference antenna. It is shown that the all the reference design used Rogers RT 5880 material except for one in [14] which achieves to work on 5G single band with a gain of 5.32 dB. However, from [15] to [16] all the reference antenna is working in multiband operation but not on the desired band for mmwave frequency. In [17] a good antenna gain is spotted but still not functioning on the desired 5G mmwave band. However, our proposed design is performing in multiband suitable for 5G communication and the overall gain of the antenna gradually increases with the increase in frequency.

Table 2. Comparative Analaysis With Previous Research
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4 Conclusion

The design and simulated result of a CPW fed tri-band antenna is presented for future 5G communication. The proposed antenna works as a tri-band antenna at 28 GHz, 38 GHz and 61.5 GHz in the 5G millimeter wave frequency band with enhanced gain and efficiency as the frequency increases. The antenna is compact in size and can be easily fabricated inside 5G devices for wireless communication with a wideband operation at 28 GHz and 61.5 GHz with bandwidth of 4 GHz. Thus, the proposed triband antenna is a perfect candidate for 5G communication.