Design of Multi-band Microstrip Antenna with Rectangular Patch for 2.3 GHz, 2.4 GHz, and 3.5 GHz Frequencies

Cellular developments encourage the integration of both 4G, Wi-Fi, and 5G network technologies into one device; an antenna is a tool that can be used to support the integration of these networks. A microstrip antenna is an antenna that is small, light, thin, easy to fabricate, and can be used in long ranges. In this paper, a microstrip antenna is designed on a printed circuit board (PCB) with a permittivity of 4.3 and a thickness of 1.6 mm. This research aims to design a microstrip antenna that is capable of working on 4G (2.3 GHz), Wi-Fi (2.4 GHz), and 5G 3.5 GHZ) frequencies in one antenna. The microstrip antenna is designed on a Printed Circuit Board (PCB) with a permittivity of 4.3 and a thickness of 1.6 mm, rectangular shaped patches, and each patch is connected using a bridging method. Next, the antenna is simulated using CST Suite 2021 software. Simulation results at frequencies of 2.3 GHz, 2.4 GHz, and 3.5 GHz produce return losses of -23.70, -22.87, and -20.60, VSWR values of 1, respectively. .13, 1.15, and 1.20, the bandwidth values are 6.27%, 3.84%, and 5.84%, respectively, and the gain values are 4.69 dBi, 8.53 dBi, and 3.49 dBi.


Introduction
The development of the times demands a change in how people communicate.These developments form an easy way of long-distance communication called telecommunication.Telecommunications is sending and receiving any information in the form of signs, text, images, signals, and sound through media such as cables, wires, optics, and radio [1].At this time, telecommunications has become very important [2].The story of telecommunications, especially wireless communication systems, continues to experience developments in terms of applications [3].
An example of a wireless technology that is being widely used is Wi-Fi [4].Wi-Fi (Wireless Fidelity) is a well-known technology that uses electronic devices to exchange data wirelessly (using radio waves) through a computer network, including a high-speed internet connection capable of sending a network connection to all users in the surrounding location [5].Wi-Fi, according to the IEEE 802.11b and 802.11g standards, works at a frequency of 2.4 GHz [6].
An example of an application for a wireless communication system other than Wi-Fi is the generation of cellular telephone networks, which in their development are divided into several generations, from 0G to 5G. 4G network is a technology currently being developed, known as LTE (Long Term Evolution) or 4G.For most countries in the world, LTE-E 2300 (2300-2400 MHz) and LTE-D 2600 (2570-2640 MHz) are the most widely adopted frequency bands, especially in several Asian countries [7].
The fifth generation (5G) is the latest generation of mobile communications, replacing the fourth generation (4G).5G technology can use the 3.5 GHz frequency, a technological development that uses the mid-band's 3.4 GHz -3.8 GHz frequency range [8].According to the World Radio Communication Conference (WRC), the candidate frequency band is less than 6 GHz.One is the frequency range of 3300 -3800 MHz; the frequency commonly used and widely considered is 3.5 GHz [9].
Mobile developments are integrating 4G, Wi-Fi, and 5G network technologies into a single device [10].This, supported by an antenna in a MIMO (multi-input multi-output) system, must be planar, compact, and easy to manufacture.MIMO is a system consisting of several transmitting and receiving antennas on a wireless communication system transceiver device [11].An antenna is a tool that can be used to support the integration of these networks.Microstrip antenna has many advantages, so it is widely used in various wireless communications, including small size, lightweight, thin, easy to fabricate, low price, can work in several frequency ranges, and can be used in long fields [12].Microstrip antennas have various forms of patches, including rectangular patches.Rectangular patches are one of the patches that can be designed, analyzed, and fabricated easily.The feeding technique in the form of an insert feed has a simple structure compared to other feeding techniques, such as coaxial feed, where it is necessary to make a hole in the PCB for its application [13].Multi-band is an antenna implementation capable of operating at several frequencies [14].One way to support the implementation of multi-band is to use several patches [15].In Fauzan's research, the multi-band microstrip antenna was designed in a rectangular shape and optimized using the bridging method.The results of measuring three working frequencies: the first frequency is 2.4 GHz, the return loss value is -29.09dB, the VSWR value is 1.072, the bandwidth is 10.12%, and the gain is 3.817 dBi.The second frequency is 2.6 GHz, return loss value is -17.08 dB, VSWR 1.325, bandwidth 6.85% GHz, gain 4.145 dBi.The third frequency is 3.5 GHz, the return loss value is -24.57dB, VSWR 1.125, bandwidth 8.67% GHZ, and gain 0.9912 dBi [16].However, the gain value at the 3.5 GHz frequency is not too large.
Therefore, this research aims to design a microstrip antenna that can work in more than two different frequency ranges (multi-bands) in a structured manner.The stacked antenna design has many advantages for application so that it can be used for wireless communication applications in 4G networks at frequencies 2.3 GHz, Wi-Fi at 2.4 GHz frequency, and for the 5G network at 3.5 GHz frequency in one antenna using the bridging method to connect the three patches, with a gain value excellent than in the previous paper.Antenna parameters (return loss, VSWR, bandwidth, and gain) were obtained from simulation results using the CST studio suite 2021 application.
According to the standard definition from the IEEE, an antenna is a device used to transmit or receive radio or electromagnetic waves.A microstrip antenna is an antenna that consists of three elements, namely, the radiation plane (patch), the substrate plane, and the ground plane (ground plane).
The irradiation field (patch) is the upper part of the microstrip antenna substrate layer.The patch is made of a conducting material that radiates electromagnetic waves; in that layer, it can be shaped according to the desired antenna based on the shape of the patch, such as a circular, triangular, rectangular, or circular ring.The substrate field is a layer in the middle of the substrate, which channels electromagnetic waves from the supply to the area under the patch.The ground plane is the lowest part of the substrate; the ground plane is usually made of a conducting material that functions as a reflector to reflect unwanted signals [17].

Microstrip antenna parameters
Antenna parameters are essential in designing and analyzing an antenna because antenna parameters measure the antenna's performance.There are several parameters of the microstrip antenna as follows.

Return loss
Return loss is the ratio of the amplitude of the reflected wave to the amplitude of the emitted wave, as written in Equation (1).
A good return loss value is less than -9.54 dB, so the value of the reflected wave is not too large compared to the emitted wave or, in other words (matching).

Voltage standing wave ratio
VSWR is the ratio between the maximum (Vmax) and minimum (Vmin) standing wave amplitudes.
The transmission line has two voltage wave components: the transmitted Voltage (ܸ ା ) and the reflected Voltage (ܸ ି ).This comparison is the stress reflection coefficient in Equation ( 2).
where, Г = -1 maximum negative reflection when the line is short-connected Г = 0 no reflection when the channels are perfectly matched Г = 1 maximum positive reflection when the line in the circuit is open The above equation Z is the impedance of the load (load), and Z is the impedance of the lossless line.
The formula for finding the VSWR value can be written in equation (3).
The best condition is when the VSWR is 1 (S=1), which means there is no reflection when the channel is in a perfect matching state.A good VSWR value for an antenna is 2.

Bandwidth
Bandwidth is the working frequency range of an antenna following a predetermined standard.Antenna bandwidth can be known through the VSWR value.The bandwidth value depends on the VSWR value, which is still within the limits of 1 ≤ VSWR < 2. The bandwidth value is determined by equations ( 4) and (5).

Gain
Gain is the character of the antenna capable of directing signal radiation or receiving signals from a certain direction.The method of measuring gain is by comparing the tested antenna against a standard antenna with calibrated gain, usually called the gain transfer technique.The formula for finding the gain value can be written in Equation (6).
where, ‫ܩ‬ = antenna gain to be calculated ‫ܩ‬ ௦ = standard antenna amplifier ܲ ௧ = antenna transmitting power ܲ ௦ = antenna receiving power

Design stage
The top part of the antenna structure is a patch, the middle part is a substrate, and the bottom is a ground plane.In this study, the substrate used was FR-4 with a dielectric constant of 4.3 and substrate thickness (h) of 1.6.The steps for simulating a multi-band antenna using the bridging method can be seen in Figure 2.

Determining the antenna design
The design of a multi-band microstrip antenna with a rectangular patch that works in the 2.3 GHz, 2.4 GHz, and 3.5 GHz frequencies can be seen in Figure 3.

Dimensional calculation and antenna simulation.
The top part of the antenna structure is a patch, the middle part is a substrate, and the bottom is a ground plane.In this study, the substrate used was FR-4 with a dielectric constant of 4.3 and substrate thickness (h) of 1.6.The steps for simulating a multi-band antenna using the bridging method can be seen in Figure 3.
The antenna design consists of 3 parallel patches; the middle patch is a 3.5 GHz frequency patch.To determine a multi-band microstrip antenna using the bridging method, first, determine the wavelength of 3.5 GHz (λ).The 3.5 wavelength equation is as follows.
The distance between patches can be calculated using Equation ( 5) by obtaining the wavelength (6).
The patch used is rectangular; Equations ( 8) to ( 20) are used to calculate the dimensions of the patch.
1. Calculate the width of the patch.
4. Calculating G (inset feed width) 5. Calculating yo (inset feed length) 6. Calculating feedline width (Wf) where, B = line impedance (ohm) Z0 = load impedance (ohm) 7. Calculates the horizontal feedline width (Wf1 dan Wf2) 8. Calculating feedline length (Lf1,2) where, ߣ = wavelength (m) ܿ = speed of light (m/s) Based on the above equations, calculations are then carried out to obtain the size of the initial design microstrip antenna, as shown in Figure 4.  Based on the initial calculated values, the antenna parameter values do not meet the standards.Therefore, it is necessary to optimize several antenna dimensions.After optimizing the simulation results at working frequencies of 2.3 GHz, 2.4 GHz, and 3.5 GHz, the optimal antenna parameter values such as return loss, VSWR, and bandwidth are obtained.

Determining the antenna design
After calculating the antenna dimensions, the next step is to carry out an antenna design simulation using CST Studio Suite 2021.The simulation is carried out to depict an antenna that has been previously designed.The method used is finite element method (FEM), spectral domain technique (SDT), and finite integration technique (FIT).Finite Element Method (FEM), This method uses a three-dimensional configuration that involves the integration of basic functions across multiple divided conductor patches part.Spectral Domain Technique (SDT In the SDT method, the two-dimensional Fourier transform uses a two-way orthogonal patch plane substrate.Finite Integration Technique (FIT): This (FIT) method makes it possible to prove the conservation of properties in discrete fields in inhomogeneous media.However, FIT changes Maxwell's equations in integral form to a system of linear equations [19].

Results and Discussion
The results of the antenna design simulation using the CST suite 2021 software based on the calculated values after optimization, the simulation results at working frequencies of 2.3 GHz, 2.4 GHz, and 3.5 GHz obtained the importance of the antenna parameter return loss, VSWR, and bandwidth (see Figure 6).Where the value of return loss already meets a good standard, namely ≤-9.54 dB (see Figure 7).An antenna can be good when it has a VSWR value ≤ 2 at the desired frequency; the best condition is when the VSWR value = 1, which means there is no reflection when the antenna is in perfect impedance matching.Figure 7 shows the results of antenna design simulations that work at multiple frequencies, namely 2.3 GHz, 2.4 GHz, and 3.5 GHz, with VSWR values of 1.13, 1.15, and 1.20, where the VSWR value is good because it follows the VSWR standard (see Figure 8).

Conclusion
In this study, the following conclusions were obtained: The simulation results of the microstrip antenna can work on a multi-band frequency response with rectangular patches at a frequency of 2.312 GHz, 2.444 GHz, and 3.556 GHz, Return loss of -23.70dB, -22.87 dB, and -20.60dB.VSWR of 1.13, 1.15, and 1.20.Bandwidth of 6.27%, 3.84%, and 5.84%.Gain of 4.69 dBi, 8.53 dBi, and 3.49 dBi.

2 . 3 .
Calculating patch lengthBefore looking for the ‫ܮ‬ value, first, determine the value of the dielectric constant ɛ and look for the value of ΔL.Calculating patch length using the equation ΔL[18]

Figure 4 .
Figure 4. Initial calculation of microstrip antenna design.

Figure 6 .
Figure 6.Data on return loss results.

Figure 6
Figure 6 shows the simulation results of antenna designs that work at multiple frequencies, namely 2.3 GHz, 2.4 GHz, and 3.5 GHz, with return loss values of -23.70, -22.87, and -20.60, respectively.Where the value of return loss already meets a good standard, namely ≤-9.54 dB (see Figure7).

Figures 11 ,
Figures 11,12,and 13 show the antenna gain of 4.69 dBi at a frequency of 2.3 GHz, 8.53 dBi at a frequency of 2.4 GHz, and 3.49 dBi at 3.5 GHz.The radiation pattern obtained from the antenna simulation is directional.Directorial is direction antenna beams in the same direction[20].

Table 2 .
Calculated dimensions of the antenna after optimization.