Design of Microstrip Array Antenna for Vehicle Millimeter Wave Radar

The design and construction of a microstrip array antenna especially intended for vehicle millimeter-wave radar applications in the 77–81 GHz frequency range is presented in this study. This study relies on earlier research on single-patch antennas to provide a full array design that satisfies the demanding performance requirements necessary for sophisticated car radar systems. The study carefully models and analyzes the antenna array using the High-Frequency Structure Simulator (HFSS) to get an azimuth angle of 90° within a 6 dB beamwidth and a pitch angle of 10° ± 1° within a 3 dB beamwidth. Achieving a gain of more than 13 dBi, keeping sidelobe levels below − 15 dB, and guaranteeing isolation of more than 35 dB are all priorities in the design process. Precision and interference avoidance are crucial in high-resolution, short-range radar systems, and these factors are essential to the antenna’s operation. The array’s small form factor, along with factors like easy integration and economical production, make it an excellent choice for contemporary automobile radar applications. The research addresses the wider ramifications of this technology in vehicle safety and navigation in addition to diving into the technical issues of antenna design, such as the optimization of element spacing, array layout, and material selection. By exploring the limits of high-frequency antenna performance, this work advances the fields of autonomous cars and wireless communication technologies. The designed antenna array architecture is very adaptable, as shown by its possible applications ranging from point-to-point transmission and satellite communication to vehicle radar systems. The goal of this effort is to improve the capabilities of vehicle radar systems, which will lead to safer and more effective autonomous navigation solutions.


Introduction
Vehicle millimeter wave radar's use of microstrip array antennas represents a significant development in the field of car safety.As the number of vehicles on the road has increased, so too has the frequency of traffic accidents.
Demanding the development of auxiliary safety systems for vehicles.According to an international statistic survey around 1/8 of all human beings die worldwide and the economic loss of USTD 65 billion [1], [2].Automotive radars have become essential in this context, detecting obstacles and alerting drivers to potential dangers.Millimeter wave radars, known for their high resolution and penetration power are particularly effective, maintaining performance even in adverse weather conditions like fog and heavy rain [3].The typical frequencies used for vehiclemounted anti-collision radars include 24 GHz, 77 GHz, and 79 GHz.The higher frequencies (77 GHz and 79 GHz) offer the benefit of smaller radar sizes due to shorter wavelengths, broadening their application.However, their fabrication requires high precision, often posing challenges given current technological limits.On the other hand, lower frequency radars, such as 24 GHz, tend to perform these Constraints, because they are lightweight, low profile low cost and simple to fabricate, microstrip antennas are used for these kinds of applications [4]- [7].
These antennas must create fixed oblique beams and have great directivity, high gain, and low sidelobes.Microstrip array antennas are used because single microstrip antennas often can't satisfy all these criteria.Comparing these array antennas to single microstrip antennas, the gain and directivity are increased dramatically.To demonstrate its appropriateness for vehicle collision avoidance radars, this research offers a 24 GHz millimeter wave microstrip antenna array.It has a 6 × 8 element structure and an optimized feeding network for reduced sidelobe levels (SLL) [8].The fast increase in the number of automobiles on the road and the resulting need to improve automotive safety and dependability have spurred the development of microstrip array antennas for vehicle millimeter wave radar, which is a crucial milestone in automotive safety technology.The use of millimeter wave radar and other automotive collision avoidance radar systems has grown in importance in averting collisions.Due to its continuous operation, ability to collect multidimensional information, and high-resolution radio and measurement precision, millimeter wave radar is very valuable and has a high market value [9].Major automakers have shown a great deal of interest in using microstrip patch antennas for car accident prevention in recent years.These antennas are favored because they are lightweight, compact, simple to integrate, and easy to fabricate.However, a single microstrip antenna typically has lower gain, wider beamwidth, and larger sidelobe levels.By configuring these antennas into an array, it is possible to achieve higher gain, narrower beamwidth, and lower sidelobe levels, essential features for effective automotive collision avoidance radar systems [10].This study introduces a 12 × 8 microstrip patch antenna array designed for high gain, low sidelobe levels, and narrow half-power beamwidth using a series feed approach.The chosen substrate for this antenna design is Rogers 4350, selected for its cost-effectiveness and optimal properties, with dimensions of 140 mm × 59 mm × 0.254 mm, relative permittivity of 3.66, and a dielectric loss tangent of 0.004.The uniform length of the patches, approximately half the waveguide wavelength corresponding to the center frequency, and the tapered widths of the patches, designed to achieve nonuniform excitation for lower sidelobe levels, are crucial aspects of the design.The spacing between adjacent patch antenna elements is about one waveguide wavelength, ensuring uniform radiation direction for all patches.The microstrip feeders connecting the subarrays are bent to ensure the same direction of signals, which enhances impedance matching and increases gain.Additionally, the impedance of the feeder is increased to reduce its influence on the radiation pattern, and a quarter impedance converter is used to adjust the impedance and return loss of the antenna [11].The market for autonomous vehicles is rapidly expanding, with projections indicating a more than tenfold increase from 2019 to 2026 [12].These vehicles are designed to assist drivers with various tasks such as lane following, maintaining a safe distance from other vehicles, monitoring pedestrians and cyclists, controlling cruises, and executing emergency braking.There is significant ongoing research in automotive radar sensors due to their effective performance in diverse weather and lighting conditions, and their cost-efficient nature.These systems typically necessitate antennas with narrow beam widths and high gain, as well as low side lobe levels (SLLs).For such requirements, planar structures like microstrip patch antennas are ideal due to their straightforward fabrication process, compact profile, and ease of integration with active components [13].Several microstrip patch antenna arrays operating at 24 GHz have been explored for automotive radar applications [14]- [17].However, these designs often involve complex feeding networks, multilayer structures, or the use of expensive printed circuit board (PCB) materials, factors that elevate the cost of the sensing technology.Consequently, this restricts the deployment of such sensors primarily to high-end vehicles [18].The combination of active chips is difficult when the low-temperature shared ceramic process is more flexible than the multilayer printed circuit board (PCB) process, making it easy to realize multi-layer and complex metal via processing, and it is also reported that the MMW radar antenna design used [19], [20].

Background of Study
An important development in vehicle safety and autonomous driving systems is the use of millimeter-wave (mmWave) technology in car radar sensor communication and remote sensing [21]- [23].The electromagnetic spectrum is where millimeter-wave radar functions, usually operating in the 30 GHz to 300 GHz frequency range.This high-frequency band has several benefits that are essential for automotive applications, such as strong resistance to environmental elements like fog, dust, or light rain, excellent resolution, and small antenna size.The early uses of radar technology for adaptive cruise control and collision avoidance may be linked to the development of automobile radar systems.These devices were initially only able to function at lower frequencies (such the 24 GHz and 77 GHz bands).Still, the demand for increased resolution, precision, and downsizing of radar components has pushed the move towards higher frequencies, especially in the mmWave range.

Antenna Design and Array Configurations
For mmWave automobile radars, beamforming and high directional gain are requirements that dictate antenna design.Patch antennas and phased arrays are common layouts that provide electronic beam guiding.Adaptive radar systems depend on this guidance since they must quickly shift their focus to monitor various objects in the vehicle.

Integration and Material Considerations
There are difficulties in integrating mmWave antennas into a vehicle's practical and attractive design.The radome's (the cover that covers the radar antenna) materials must be carefully chosen for their longevity and transparency to mmWave frequencies.For this, sophisticated polymers and composites are often used.mmWave radars using MIMO methods have improved object detection and resolution.MIMO radars may create several simultaneous beams by using multiple transmitting and receiving antennas, which enhances spatial resolution and the capacity to discern between objects that are closely separated.

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Design of Microstrip Array Antenna for Vehicle Millimeter Wave Radar

Frequency Modulated Continuous Wave (FMCW) Radar
FMCW radar provides benefits in terms of velocity measurement and range resolution, and it is commonly employed in mmWave automotive applications.FMCW radars can measure an object's speed and range with extreme accuracy by altering the frequency of the wave that is broadcast.To analyze the data from mmWave radars, sophisticated signal processing methods are required.Furthermore, a crucial component of autonomous cars and advanced driver-assistance systems (ADAS) is the integration of radar data with information from other sensors, such as LIDAR, cameras, and ultrasonic sensors.Although mmWave automobile radar sensors have many benefits, they also have drawbacks, including manufacturing costs that are expensive, sensitivity to clutter, and interference from other radar systems.To further increase the performance and dependability of these systems in automotive applications, ongoing research is focused on tackling these issues, improving sensor fusion methodologies, and investigating novel antenna technologies and materials.

Transition to Higher Frequency Bands
It became clear that object recognition and range needed to improve in resolution and accuracy as car safety regulations and autonomous driving goals increased.The transition from lower microwave frequencies to the millimeter-wave (mmWave) bands were driven by this necessity.Due to their capacity to provide better resolution, smaller antenna sizes, and less interference all of which are essential in complicated driving environments the 77 GHz and 79 GHz bands in particular gained popularity.The development of ADAS and the goal of autonomous cars are closely related to the progress of automotive radar.Radar systems are now essential for tasks including blind-spot identification, emergency braking, lane change assistance, and pedestrian recognition.To build dependable and durable autonomous driving systems, radar plays a crucial role in sensor fusion, where it supplements information from cameras, LIDAR, and ultrasonic sensors.

Patch Antenna Design
The ground plane, essential for stabilizing the antenna's performance, is made of highly conductive copper, measuring 8 mm in width and 0.025 mm in length, and is positioned strategically in the X, Y, and Z axes.The substrate used is Rogers RO3003™, selected for its impact on the impedance and radiation characteristics, it supports the antenna elements and has precise dimensions and positioning.The design features eight patch elements arranged in a single row, along with three power dividers, each with specific dimensions and locations to create a coherent radiation pattern.For instance, Patch 1, measuring 0.55 mm by 1.12 mm, is strategically placed at designated coordinates.The feedline system is intricately designed, with a main feedline and additional sub-feedlines, each with unique dimensions and positions.These feedlines are crucial for signal transmission to the patches, ensuring coherent phase and amplitude distribution across the array, which is vital for effective beam formation and steering.Additionally, the design includes power dividers that evenly distribute the input signal across each array, maintaining consistent amplitude and phase distribution.The dimensions and positions of these power dividers are calculated.Lumped ports, another key component, are applied to the feedlines to introduce the signal into the antenna structure.Finally, the antenna is encased in a radiation box, essential for recording and examining the radiated fields in HFSS simulations.This box, along with assigned boundaries and perfected edges for the patches and the ground plane, ensures accurate recording and analysis of the antenna's performance.The structured approach ensures a comprehensive understanding of the design and implementation process for a Patch Antenna design as shown in Fig. 1.
Fig. 2 depicts a workflow diagram for the process of designing a microstrip patch antenna.The initial stage is a literature review, which is essential for understanding current technologies and methodologies in antenna design.Next, the workflow progresses to the selection of software, specifically HFSS (High Frequency Structure Simulator), which is a tool used for simulating electromagnetic fields and is vital for antenna design analysis.Following this, a decision is made regarding the design approach.Once the design is selected, the workflow diverges into two paths.The first path leads to the design of a 1 port array microstrip patch antenna, which is a simpler configuration and serves as a fundamental building block for more complex designs.The second path involves designing a more complex 3-port array microstrip patch antenna, which can handle multiple signals and is likely to be used for more advanced applications.Both paths then converge at the fabrication and prototyping stage, where the physical models of the antennas are constructed to assess their realworld performance.Finally, the workflow culminates in  the simulation and results stage, where the antennas are tested using the HFSS software to validate the design, analyze performance, and refine the antenna structure as necessary.This workflow is a systematic approach to antenna design, ensuring a thorough evaluation of performance from theoretical inception to practical application.

Microstrip Patch Array Antenna
Antenna arrays play a pivotal role in enhancing the adaptability and performance of wireless communications, adjusting emission patterns to the demands of specific applications and the signal environment.This is particularly vital for radar technologies in the 77-81 GHz frequency range, which necessitate precise design for optimal detection and resolution.The objective of this design is to develop an efficient phased array system for this spectrum, focusing on optimizing radiation patterns and signal integrity.Utilizing HFSS software enables a comprehensive performance evaluation to ensure compliance with operational parameters.The design influences crucial radar system metrics like range and sensitivity, incorporating multiple patches within each array for improved directional signal control, essential for beam steering and shaping in radar applications.The higher frequency range allows for smaller antennas with better resolution, key in space-conscious, accuracy-dependent applications such as automotive radars.The ensuing research will delve into the antenna design process, outlining component configuration techniques and simulation results to shed light on its applications and operational efficiency.

Microstrip Patch Array Antenna Methodology
The antenna design methodology encompasses a meticulous configuration of various components to formulate an array antenna system.In the design methodology for a phased array antenna system, the substrate is chosen as Rogers RO3003™ for its low dielectric loss, crucial in high-frequency applications to minimize signal attenuation.This substrate is carefully dimensioned at 8 mm wide, 26.38 mm long, and 0.127 mm thick, precisely positioned to optimize the antenna's performance as shown in Fig. 3.The ground plane, assumed to be a standard conductive material, supports the substrate with dimensions of 8 mm by 0.025 mm and is positioned to maintain a consistent impedance across the antenna structure.The patches, which are the primary radiating elements, vary in size with the smallest being 0.31 mm by 1.07 mm and the largest 1.27 mm by 1.07 mm.Each patch is strategically placed and has a Perfect E boundary condition applied for effective radiation pattern generation and gain optimization.The feedlines, essential for signal transmission to the patches, are designed with perfect E boundary conditions to ensure coherent phase and amplitude distribution across the array, facilitating precise beam formation and steering.Power dividers are utilized to equally split the input signal to each array, ensuring consistent amplitude and phase

Nabi et al.
Design of Microstrip Array Antenna for Vehicle Millimeter Wave Radar across all arrays.These components are integral to the array's ability to produce a controlled and directed signal, essential for the precise operation of high-frequency radar systems.

Results and Simulation Results for Patch Antenna 3.4.1. S Parameters
Due to their ability to characterize the linear properties of electrical networks, S-parameters, are also known as scattering.Parameters are an effective tool in radio frequency (RF) and microwave engineering.S-parameters (S_ij) define the relationship between incident and dispersed wave quantities in multi-port networks, as the three-port network under consideration here.
Fig. 4 presents the scattering parameters (S-parameters) for an antenna array across a range of frequencies from 76 GHz to 81 GHz.S-parameters describe the response of an electrical system to signal transmission and reflection, which in this context, is crucial for understanding the behavior of the antenna array when subjected to millimeter-wave frequencies.S11, S22, and S33 (shown in red, purple, and dark cyan): These curves represent the return loss or reflection coefficients for three ports of the antenna array, indicating how much power is reflected from the antenna.Ideally, these values should be as low as possible for efficient transmission.The dips in these curves represent resonant frequencies where the antenna is effectively radiating or receiving energy.S21, S31, and S32 (shown in orange, light blue, and yellow in Fig. 4).These are the transmission coefficients between different ports, indicating how much power is transferred from one port to another.These values are important.for understanding the coupling between elements of the array.The highlighted points at −24.11 dB, −29.84 dB, and −50.70 dB signify the return loss at certain resonant frequencies, which are particularly low, suggesting that the antenna is well-tuned at these frequencies.The −52.07 dB point indicates a very low level of signal return at around 81 GHz, which is desirable for minimizing signal loss.The graph provides essential information for evaluating the performance of the antenna array, specifically in terms of efficiency and effectiveness in transmitting and receiving signals at millimeter-wave frequencies for applications such as vehicle radar systems.

Voltage Standing Wave Ratio (VSWR)
In RF engineering, the Voltage Standing Wave Ratio (VSWR) is a metric used to express how much a transmission line and its load (such as an antenna) are mismatched.Perfect impedance matching, or a VSWR value of 1:1, means that all the power is transferred, and none is reflected.More mismatches are indicated by higher VSWR values, which results in more power being reflected and less efficient gearbox.Minimizing VSWR is preferred in practical situations to ensure maximum power transfer and reduce signal loss.In wireless communication systems, VSWR is particularly important for ensuring signal integrity and optimal performance.Fig. 5 illustrates the Voltage Standing Wave Ratio (VSWR) for the system shows significant variation across the frequency range of 70 GHz to 78.78 GHz, as evidenced by the graph.This variation is highlighted by the range between 1.66 dB and 24.28 dB, indicating fluctuating impedance matching throughout this spectrum.Specifically, the maximum VSWR is observed at 70 GHz, reaching 24.28 dB, which represents the point of worst impedance matching and the highest level of signal reflection.This peak suggests that operating at 70 GHz could lead to suboptimal system performance due to increased signal loss.Conversely, the minimum VSWR occurs at 78.78 GHz, marked at 1.66 dB, indicating the most favorable impedance matching within the analyzed frequency range.This minimum point corresponds to the least amount of signal reflection, suggesting optimal operational conditions when the system functions at this frequency. 3.4.3.Gain An antenna's gain is a measurement that indicates how well it can focus the power it radiates in a certain direction.It is defined in relation to a reference antenna, frequently an isotropic antenna or a dipole antenna, and is frequently represented in decibels (dB).Gain sheds light on the antenna's directional qualities by showing how well it converts input power into radio waves in a certain direction.
An antenna with a higher gain may send or receive more power in the main lobe direction.It is essential in figuring out how well wireless communication systems cover the area and maintain links.The following are the observations: • The gain shows a sizable variation when the elevation angle varies, indicating the antenna's directional qualities.
• The two Phi angles' unique patterns show that the radiation pattern is three-dimensional.

Gain 2-D Plot
The gain in decibels is plotted against the elevation angle (Theta) and azimuth angle (Phi) in a 2D contour plot shown in Fig. 7.The gain magnitude is represented by a color gradient, with lighter hues denoting more gain and darker hues denoting lesser gain.

Gain-3D Plot
The gain is shown in the spatial coordinates (X, Y, and Z) in the 3D polar plot shown in Fig. 8, which shows the gain in dB.The directional properties of the antenna in three dimensions are revealed by this visualization.
In Fig. 8a, the plot shows gain variation in all directions, defined by phi and theta angles, to visualize the antenna's radiation pattern.In Fig. 8b, the gain ranges from −27.33 dB to 7.75 dB in the 3D plot.Corresponding to the highest gain, troughs or nulls represent the lowest gain.

Observations and Considerations
The plot shows the three-dimensional radiation pattern of the antenna and shows how the gain varies with both azimuth (Phi) and elevation (Theta) angles.The 3D structure's peaks and nulls show where the radiation is coming from most and least, respectively.For the antenna to be positioned to maximize signal transmission and reception in real-world applications, it is essential to comprehend these 3D radiation characteristics.Maximum and Minimum Gain: The gain ranges from −27.33 dB to 7.75 dB, as seen in the 2D graphic.Peaks in the 3D plot correspond to the highest gain, whilst troughs or nulls represent the lowest gain.The 3D map clarifies the antenna's directionality, which is crucial for engineers and system designers to properly align the antenna in communication systems.Radiation Pattern: A thorough picture of the radiation pattern is provided by the 3D plot, allowing for a thorough review of the antenna's performance in all spatial directions.

Results for Microstrip Patch Antenna 3.5.1. S Parameters
It describes the input-output relationship for RF (radio frequency) and microwave frequency ranges between ports (or terminals) in electrical systems.They basically specify how an RF device reacts to an input signal and how it impacts the signal as it passes through the device.The value of S 11, which is frequently stated in decibels (dB), explicitly specifies how much signal is reflected from the input (or port 1).S 11 should ideally be as low as feasible, signifying little reflection and lots of transmission.
Fig. 9 presented is a detailed visualization of the reflection coefficient (S_11) across frequencies for an antenna or RF component, where the X-axis represents frequency in gigahertz and the Y-axis shows the S_11 parameter in decibels (dB).The red line traces the S_11 value across varying frequencies, indicating the amount of reflected power, with lower values (more negative) signifying better impedance matching.A dashed blue line marks the −10 dB threshold, commonly used as a reference for determining the bandwidth, highlighting the operational frequency range of the antenna.The bandwidth is defined by the frequencies between which S_11 remains below −10 dB, specifically from a minimum frequency of 76.32 GHz to a maximum frequency of 77.63 GHz.The graph's most critical point is the minimum S_11 value at 76.64 GHz, plunging to −43.29 dB, denoting the point of optimal impedance matching, which is a significant marker of the antenna's performance.

VSMR
The maximum to minimum amplitude (or voltage) in a standing wave pattern along a transmission line is known as the VSWR.Radiofrequency (RF) engineering uses the Voltage Standing Wave Ratio (VSWR) metric to measure the degree of mismatch between a transmission line and its load, which is frequently an antenna.A VSWR of 1:1 implies perfect matching, in which case all the power is transmitted to the load; a greater VSWR, on highlights the operational frequency range of the antenna.The bandwidth is defined by the frequencies between which S_11 remains below −10 dB, specifically from a minimum frequency of 76.32 GHz to a maximum frequency of 77.63 GHz.The graph's most critical point is the minimum S_11 value at 76.64 GHz, plunging to −43.29 dB, denoting the point of optimal impedance matching, which is a significant marker of the antenna's performance.
Other hand, denotes a higher degree of mismatch and power reflection.Signal distortion and decreased gearbox efficiency can be caused by a high VSWR.To achieve optimal performance and minimal signal loss, engineers frequently work to lower VSWR in RF systems.Understanding and improving the impedance matching in communication systems and antennas depends on VSWR.
According to Fig. 10 the minimum VSR at 76.64 GHZ (Green Point), is 0.12 db and Maximum VSWR measured at 81.00 GHz (Red Point) was 14.59 dB.

Overview of VSWR
VSWR is a measurement of the signal's reflection along a transmission line that shows how well the antenna's impedance is matched to the line.Lower VSWR values are preferable since they signify less reflection and better matching.

Optimal Matching Position
The transmission line and load (antenna) should be impedance matched at a position where the minimum VSWR value is 0.12 dB at 76.64 GHz.Given that the reflected power is reduced, this frequency can be regarded as the optimal operational frequency.

Mismatch and Reflection
The maximum VSWR of 14.59 14.59 dB at 81.00 81.00 GHz indicates a reasonably strong reflection at this frequency, indicating a large impedance mismatch between the transmission line and the load (antenna).This might lead to greater transmission losses and possibly altered signal quality at this frequency.

Operational Bandwidth
By observing the VSWR across the frequency range, we can determine the operational bandwidth, which is typically 2:1:2 or 3:1:3 when the VSWR is below a predetermined acceptable level.This bandwidth identifies the frequency range in which the antenna can function properly with reasonable amounts of reflection. 3.5.3.Gain An antenna's gain, which is commonly represented in decibels (dB), is a measurement that describes its capacity to convert input power into radiation in a specific direction.It is a crucial metric since it measures how well the antenna can concentrate energy in each direction, boosting the signal in that orientation.Antenna gain redistributes the energy it receives to offer more signal power in preferred directions and less in others, rather than amplifying the signal.By focusing the available power into focused beams, high-gain antennas can significantly improve the range and quality of wireless communication.To ensure the best signal quality and coverage for a given communication or radar application, the gain is crucial in evaluating and choosing antennas.Fig. 11 shows for antenna gain illustrates the variation in gain values across different angles, with the minimum gain recorded at −26.61 dB and the maximum at 17.90 dB.The blue line represents the gain at Phi = 0 degrees, showcasing a main lobe with a radius at Theta = 180 degrees, alongside several side lobes.Conversely, the gain at Phi = 90 degrees is depicted by the green line, indicating a distinct radiation pattern that significantly differs from the former, suggesting an anisotropic behavior of the antenna.These patterns are measured in degrees (Theta [deg]) and presented in decibels (dB (Gain Total)), providing insights into the gain values at a frequency of 77 GHz for two principal Phi angles of 0 and 90 degrees.The graphical representation demonstrates the intricate relationship between gain and theta at these specific phi angles, offering a two-dimensional perspective of the antenna's emission pattern at 77 GHz.
Fig. 12 presents a comprehensive 2D visualization of the antenna's radiation pattern, where the X-axis represents the azimuth angle (Phi) in degrees and the Y-axis the elevation angle (theta), also in degrees.A color gradient indicates the gain in decibels, with lighter colors signifying higher gain and darker hues indicating lower gain.This graphical representation effectively demonstrates the variation of gain with respect to both azimuth and elevation angles, providing a detailed insight into the directional characteristics of the antenna's performance.The gain values range from a minimum of −26.61 dB to a maximum of 17.90 dB, illustrating the dynamic range of the antenna's radiative capabilities.
The radiation pattern of the antenna is depicted in a three-dimensional plot, where each point's position is defined by the angles Theta and Phi, and the associated color represents the gain magnitude in decibels (dB).The spatial coordinates X, Y, and Z are extrapolated from these gain values and their corresponding angles, providing a visual representation of the antenna's directional gain in 3D space.Lighter colors on the plot signify higher gain, while darker colors represent lower gain, with the color gradient across the plot indicating the range of gain values.This visualization method effectively illustrates the antenna's radiation pattern, offering insight into its performance and how it interacts with the environment.According to Fig. 13a    −26.61 dB to a maximum of 17.90 dB, and in Fig. 13b the gain extends from a minimum of −25 dB to a maximum of 15 dB and capturing the dynamic radiative behavior of the antenna system.A graphical depiction of an antenna's radiation qualities as a function of space coordinates is provided by the radiation pattern of an antenna, which shows how the antenna directs the energy it radiates or absorbs into space.In essence, it defines how the antenna radiates power into the surrounding area.This information is often displayed in both the azimuthal and elevation planes.In determining the antenna's directional properties, it is essential to identify the areas where radiation (or reception) is maximized.The main lobe, side lobes, back lobe, and nulls in the radiation pattern reveal important details regarding the antenna's effectiveness, directivity, and potential for interference from/to other systems.Understanding the radiation pattern is essential for maximizing antenna placement and orientation, assuring clear transmission, and reducing interference in wireless communication system.

Radiation Pattern
Fig. 14 illustrates the radiation pattern of an antenna by depicting gain across varying elevation angles (theta) in degrees, as shown on the X-axis, while the Y-axis quantifies the gain in decibels (dB).The blue line illustrates the radiation pattern at a Phi angle of 0 degrees, and the green line represents the radiation pattern at Phi 90 degrees.These lines chart the gain at 77 GHz for their respective Phi angles, conveying how the antenna directs energy.Gain is a measure of the antenna's ability to focus radiation in a specific direction compared to an isotropic source.Theta represents the elevation angle, ranging from 0 to 360 degrees, while Phi indicates the azimuth angle on the horizontal plane.The distinct lines for each Phi value highlight the differences in the radiation pattern as theta varies, providing a clear graphical representation of the antenna's power distribution and directional radiation capability.
There are two polar graphs shown in Fig. 15: • Radiation pattern at (Phi = 0): Left Plot.
• Radiation pattern at (Phi = 90): Right Plot.• The antenna's main lobe (the region with the maximum gain) and side lobes, which are crucial for determining the directionality and potential interference of the device, may be seen.
For system design and analysis in wireless communication, these 2D polar plots provide an intuitive visualization of how the antenna radiates power in various directions.
Fig. 16 shows spatial coordinates X, Y, and Z are determined from the gain and angles ("Theta" and "Phi"): • Surface Colour: The colour, which ranges from blue (lower gain) to red (greater gain), represents the gain in dB.The colour gradient adds another level of information by illuminating the gain magnitude.• Radiation Pattern: A 3D surface is used to show how the radiated power is distributed spatially.• Gain: A surface representation of the radiation pattern's strength and directionality that is both spatially and color-coded.• Theta & Phi: Elevation and azimuth angles, which define the direction of radiation or reception in three-dimensional space, respectively.• 3D Surface: Using triangulation, a smooth depiction of the radiation pattern was created, giving users a thorough understanding of how the antenna transmits power in various spatial directions.
Gain values are as follows: • Minimum Gain: (−26.61 dB) • Maximum Gain: (17.90 dB) This 3D graphic gives a spatial depiction of the radiation pattern, showing the main lobes and nulls, or directions where the antenna emits or receives the least amount of power:

Bandwidth
The range of frequencies that an antenna or other RF component may efficiently function over is referred to as bandwidth in the context of antenna and RF (Radio Frequency) engineering.It is specifically the frequency range where the reflected power parameter (S_11) is predetermined level, often −10 dB.The antenna's bandwidth determines the frequencies at which it can transmit or receive signals effectively.In wireless communications, it's critical to make sure a system's operational frequency is within the useful bandwidth of the antennas being used.As a result, communication system performance is optimized with low signal reflection and maximum signal transmission or reception.The difference between the range's top and lower frequencies is used to describe it.Fig. 17 shows the examination provides a clear depiction of the reflection coefficient (S_11) against frequency for an RF component or antenna.On the X-axis, frequency is measured in gigahertz, while the Y-axis quantifies S_11 in decibels (dB).The blue line charts the variation of S_11 with frequency, illustrating the reflected power at each point.A dashed red line marks the −10 dB threshold, a standard benchmark in antenna and RF studies for acceptable performance.The bandwidth, or the frequency range over which S_11 remains below −10 dB, is determined to be 1.31 GHz, spanning from a minimum frequency of 76.32 GHz to a maximum of 77.63 GHz.The most significant point on the curve is the minimum S_11 value of −43.29 dB at 76.64 GHz, indicating the point of optimal impedance matching.This point is crucial as it represents the condition where the least power is reflected to the

Conclusion
The goal of this study is to clarify the complexities involved in creating a microstrip array antenna specifically for vehicle millimeter-wave radar systems operating in the 77-81 GHz frequency band.Our study has advanced the understanding of the antenna's performance characteristics and potential applications in various domains, particularly in autonomous vehicle navigation and wireless communication technologies, through meticulous modeling, simulation, and optimization using the High-Frequency Structure Simulator (HFSS).

In-Depth Analysis and Optimization
The design of the microstrip array antenna has been thoroughly examined in our work, with a focus on the significance of obtaining an azimuth angle of 90°within a 6 dB beamwidth and a pitch angle of 10°± 1°within a 3 dB beamwidth.The ground plane, substrate material (Rogers RO3003TM), patch elements, feedline system, and power dividers are all carefully configured in the antenna, which helps to optimize its overall performance.We have shown our dedication to satisfying strict performance standards by achieving a gain of more than 13 dBi, keeping sidelobe levels below −15 dB, and guaranteeing an isolation of more than 35 dB.The microstrip array antenna architecture that was built demonstrates its versatility by providing a small form factor that is appropriate for modern car radar applications.Its adaptability includes point-to-point transmission, satellite communication, and other wireless communication applications in addition to vehicle radar systems.The antenna's versatility makes it a promising technology with a wide range of applications in many communication settings.Our study explores the wider ramifications of using this technology in vehicle safety and navigation, in addition to the technical elements of antenna design.The antenna's short-range, high-resolution radar capabilities help with interference avoidance and accuracy, two important aspects of improving autonomous vehicle safety features.Thus, the overall objective of improving vehicle radar systems to provide safer and more efficient autonomous navigation options is aligned with our study.Meticulous attention to detail characterizes the research methods used in this study.Robust engineering concepts provide the basis for the selection of materials, component sizes, and locations.A thorough grasp of the antenna's behavior in various conditions is ensured by using the HFSS program for modeling and performance assessment.The study employs three independent methodologies that together provide a comprehensive examination of the design space, highlighting the importance of phased array systems in improving wireless communications performance and flexibility.

Future Implications and Advancements
Beyond the current study, this research provides insights into future developments in high-frequency antenna performance.Our study establishes the groundwork for future investigations into driverless cars, wireless communication, and radar technologies by pushing the frontiers of design and investigating innovative combinations.In summary, the developed microstrip array antenna has made a substantial contribution to the changing field of highfrequency communication technologies with its improved performance, versatility, and improvements to vehicle safety.This study advances our knowledge of antenna design principles and opens new avenues for innovation in the rapidly developing fields of wireless communication systems and driverless cars.

Vol 8 |
Issue 2 | April 2024 77 Design of Microstrip Array Antenna for Vehicle Millimeter Wave Radar Nabi et al.

Fig. 5 .
Fig. 5.The graphical representation of the Voltage Standing Wave Ratio (VSWR) as a function of frequency, demonstrating the system's impedance matching performance across the range of 70 GHz to 90 GHz.

Fig. 6 .Fig. 7 .
Fig. 6.Gain patterns of a patch antenna at 77 GHz, plotted as a function of the theta angle for two different phi angles (0°and 90°), illustrating the antenna's directional gain characteristics in different planes.

Fig. 8 .Fig. 9 .
Fig. 8. 3D polar plot of an antenna's total gain: A) With the color scale indicating gain values in dB; B) With direction scale indicating a gain range from −27.33 dB to 7.75 dB.

Fig. 11 .
Fig. 10.Frequency graph showing the voltage standing wave ratio across a frequency range of 76 to 81 GHz, with a minimum VSWR of 2.8 dB at 76.76 GHz and a maximum of 14.58 dB at 81.0 GHz.
the gain extends from a minimum of Design of Microstrip Array Antenna for Vehicle Millimeter Wave Radar Nabi et al.

Fig. 12 .
Fig. 12. 2D contour map illustrating the antenna's gain distribution over theta and phi angles, with color gradients representing gain levels from −25 dB to 15 dB.

Fig. 13 .
Fig. 13.3D polar plot of gain depicting the spatial distribution of antenna gain: a) With color-coded points representing gain values from −26.61 dB to 17.90 dB across the XYZ coordinates, b) With color-coded points representing gain values from −25 dB to 15 dB across the XYZ coordinate.
Fig. 14. 1D plot of radiation pattern versus theta, showing the gain in dB at Phi angles of 0°and 90°, with distinct radiation characteristics at each angle.

Fig. 16 .
Fig. 16.3D Radiation Pattern, displaying the complex spatial distribution of an antenna's gain, visualized through a multi-colored geometric surface plot.

Fig. 17 .
Fig. 17.Graph showing S11 vs. Frequency, highlighting a bandwidth of 1.31 GHz with the minimum point at 76.64 GHz (−43.29 dB) and the maximum frequency within the bandwidth at 77.63 GHz.