Microstrip Patch Antenna Design at 10 GHz for X Band Applications

Microstrip patch antennas are used in satellite imaging systems, wireless communication equipment, military radios, GPS (Global Positioning System) and GSM (Global System for Mobile Communications) applications. Its advantages are its small size and light weight, thin structure, low power consumption, use in dual frequency applications, and patching in various geometric shapes. Developing technology has facilitated and accelerated the production of microstrip antennas. In this study, microstrip antenna design operating at 10 GHz frequency for X band applications has been made. X band is used for air traffic control, weather traffic control, vessel traffic control, defense tracking and vehicle speed detection, terrestrial communications and networking, space communications and amateur radio. HFSS program was used in antenna design. AWR program was used to find transmission line parameters. In addition, MATLAB program was used to calculate some parameters. First of all, information is given about the working principle of the antenna, the selected dielectric layer and the working frequency. Schematic drawings of the designed antenna were made from above and from the side. S11 characteristic graphs are drawn below and above the operating frequency. The radiation pattern is drawn for the E-plane and H-plane at the operating frequency. 3-D (dimensional) plot of antenna gain at operating frequency is drawn. The simulations performed have shown that the designed antenna works successfully.


Introduction
Microstrip patch antennas are low profile antennas.They are used in low profile applications at frequencies above 100 MHz (Singh & Tripathi, 2011).A metal patch mounted at a ground level with a dielectric material in between creates a microstrip (Deepa et al., 2022).The patch on the upper surface is made of conductive materials such as copper or gold (Bisht et al., 2014).The geometric shape of the conductor to be used may vary according to the design features.Square, rectangle, ellipse, ring etc. can be used in shapes (Shome et al., 2019).Microstrip antennas could be used in different applications such as aircrafts, spacecrafts, satellites, missiles, mobile radios, and wireless communications (Mishra, 2016).Microstrip patch antennas can also be used in unmanned aerial vehicles due to its miniaturized dimensions (Karahan & Kasnakoglu, 2021).
In this research, a microstrip patch antenna design operating at 10 GHz frequency was carried out.A computer program called HFSS was used for antenna design.AWR program was used to obtain transmission line parameters.The MATLAB program was used to make the necessary mathematical calculations.At certain intervals of the antenna's operating frequency, s11 characteristic graphs were drawn.S11 is a measure of how much power is reflected back at the antenna port due to mismatch from the transmission line (Iqbal et al., 2021).Antenna's radiation pattern is drawn for the E-plane and H-plane at the operating 10 GHz frequency.3-D plot of antenna gain at operating 10 GHz frequency is shown.The obtained simulation results proved that the designed microstrip patch antenna works successfully.

Figure 1: A typical microstrip patch antenna
A typical microstrip patch antenna is shown in Figure 1.The dielectric ground with the patches is not magnetic.The small dielectric constant of the dielectric ground causes the fringe areas to increase, which affects the radiation.In general, when designing the antenna, it is preferred that the dielectric constant is between 2.2 and 12 (Hashim et al., 2022).The length L, width W and thickness H are effective in characterizing this type of antenna.

Patch antenna excitation
Transmission line feeding, coaxial cable feeding or inset (embedded) feeding can be used for patch excitation.In this research, inset feeding was used due to space constraints.In this method, () is pulled to the desired location by starting from the input impedance ((0)) when there is no inset (Figure 2).Its formula is given in equation 1.

Working principle
Excitation of the conductive patch, on the other hand, causes an electromagnetic wave movement from the edges of the patch to the ground.Waves reflected from the ground propagate into space.The areas formed on the edges of the conductive patch are called fringing areas and this phenomenon is called fringing effect (Figure 3).The radiation of the antenna occurs as a result of this event.Waves perpendicular to the patch dampen each other and do not radiate, waves fringing from the corners make the radiation.

Specifying Selected Frequency and Dielectric Layer
It was stated in the design specifications that the communication system uses certain frequencies in the 10-12 GHz range, so 10 GHz within this range was chosen as the center frequency.In the dielectric layer, RO4003 material was chosen because of its high frequency performance, low loss and widespread use in microstrip antenna designs (Khan & Nema, 2012).The dielectric constant of this material is 3.4 and its tangent loss is 0.002.

Design Procedure
In this research, HFFS program was used for simulation and modeling purposes.AWR program is used to organize some graphs and find transmission line parameters.In addition, MATLAB program was used for some calculations.
First of all, the dimensions of the antenna were determined.The operating frequency of the antenna is determined by L (length).The center frequency is calculated approximately as in equation 2, where c is the speed of light.In inset (embedded) feeding, the following equation was obtained by using the equation ( 1) and starting from the input impedance ((0))= 204.75.
Then, using the MATLAB program, R= 2.6689 mm was calculated.The width value at the embedded feed was calculated as w = 0.3313 mm.For the design of the microstrip line, parameters such as line length, line width, line height were found by using the Microstrip section of the AWR program.These parameters are shown in Figure 4.

Top and Side Schematic Drawings of the Designed Antenna
The designed antenna is shown schematically in Figure 5, showing the design parameters and dimensions.It is seen that the total volume rule (1.6cm x 1.6 cm x 1 mm) given in the design specifications is followed here.Of the values calculated in Chapter 3, all but L remained the same.The reason for the change of L is the change of  due to the fringing areas, as emphasized earlier.L was found by modifying it with the HFSS program to provide the center frequency as its graph is given in the next sections.The patch and ground plane parts shown in the figure are taken as PEC (perfect electrical conductor), and the thickness of the conductive surfaces is neglected.

Simulations
In this section, s11 characteristic graphs, antenna input impedance graphs, radiation patterns for E plane and H plane and antenna gain graphs are drawn.

Plotting the 𝑆11 characteristic and showing the bandwidth by frequency in the range of 500 MHz below and above the operating frequency
When 11 is plotted between 500 MHz below and above the determined operating frequency of 10 GHz, as seen in Figure 6, the operating frequency of the antenna has changed due to the fringing areas.Fringing areas cause the effective length to change as mentioned before.Therefore, in HFSS, L length was manually changed and an L providing 10 GHz was obtained (Figure 7).After obtaining Figure 7, the bandwidth at -10 dB is found as in equation 10.
2 − 1 = (10.1307− 9.8475) () = 0.2832  (10) The bandwidth was calculated as in equation 11.This complies with the requirement of design specifications that the -10dB bandwidth (BW) of the desired antenna should be at least 1.6%.

Plotting antenna input impedance in the range 250 MHz below and above operating frequency
In Figure 8, the real graph, the imaginal graph and the magnitude graph of the antenna input impedance are plotted between 9.75 GHz and 10.25 GHz.As can be seen, at 10 GHz, the real impedance is 64 and the imaginal impedance is very close to zero.In general, it can be seen that the antenna input impedance is around 50 between 9.75-10.15GHz. Figure 9 shows the impedance graph of the antenna's input port.For 9.75 GHz and 10.25 GHz, the real impedance is 50 and the imaginal impedance is 0 at all frequency values.

5.3
Plotting the radiation pattern for the E-Plane and the H-Plane at 10 GHz operating frequency Considering the direction of the electric field and the radiation direction, the E plane is the YZ plane, i.e. ∅ = /2 plane, and the H plane is the ∅ = 0 plane.Considering these, radiation patterns at 10 GHz are drawn for E and H planes, respectively, in Figure 10 and Figure 11.

3D plotting of antenna gain at operating frequency
Antenna gain at 10 GHz is plotted in 3D in Figure 12.As can be seen, the antenna gain is higher than 5 dB.

Plotting antenna gain at 250 MHz above and below operating frequency
Antenna gain in the 9.75 and 10.25 GHz range is plotted in Figure 13 depending on .As can be seen, the antenna gain is equal to 6.8 dB when  = 0.

Parameters of the designed antenna
The parameters of the designed antenna are given in Table 1.

Conclusion
In this study, the design of a microstrip patch antenna at 10 GHz frequency for X band applications is explained.First of all, the usage areas, structure and working principles of the microstrip patch antenna are explained.HFSS, AWS and MATLAB programs were used in the antenna design.The equations used in this design are explained one by one.Using MATLAB program, these equations were solved and the values of the parameters were found.The schematic drawings of the antenna are given from the top and from the side.In the simulation section, S11 characteristic graphics, input impedance graphics, E and H plane radiation patterns and antenna gain graphics were drawn.The parameters used in the antenna design are presented in a table.Simulation results show that the antenna works as desired and meets the X Band design criteria.

Figure 4 :
Figure 4: Calculation of microstrip line parameters in AWR.

Figure 5 :
Figure 5: Schematic views of the designed antenna.a) XY (above) view b) YZ (side) view c) XZ (side) view.

Figure 6 :
Figure 6: 11 characteristic according to the frequency in the range of 500 MHz below and above the operating frequency for the antenna according to section 3 and showing the bandwidth.

Figure 7 :
Figure 7: Plotting the 11 characteristic according to the frequency in the range 500 MHz below and above the operating frequency for the manually found L and showing the bandwidth.

Figure 8 :
Figure 8: Antenna input impedance graph in the 9.75 GHz and 10.25 GHz range.

Figure 9 :
Figure 9: Impedance graph of antenna input port in the range of 9.75 GHz and 10.25 GHz.

Figure 10 :
Figure 10: Radiation pattern for the E plane at operating frequency.

Figure 11 :
Figure 11: Radiation pattern for the H plane at operating frequency.

Figure 13 :
Figure 13: The graph of antenna gain connected to θ.

Table 1 :
Design parameters of the 10 GHz X Band microstrip patch antenna