Analyzing the Influence of a Superstrate and Slot on a Circular Patch Antenna Operating at 2.4 GHz Resonance Frequency

: The study of antenna design involved the application of a transmission line and cavity model at a 2.4 GHz frequency. The primary focus of this investigation was the impact of dielectric superstrates and a single slot on various performance metrics, encompassing aspects such as bandwidth, beamwidth, gain, resonance frequency, input impedance, return loss, and VSWR. This ongoing research builds upon the findings presented in different Article. The assessment considered factors like return loss and bandwidth to drive improvements and optimizations. Furthermore, a comprehensive examination of each antenna parameter was conducted using a parametric approach. Additionally, the study explored how the introduction of a slot affected the characteristics of circular patch antennas fed via coaxial probes, facilitating a comparative analysis based on their properties.


Introduction
A microstrip antenna comprises a radiating patch situated on one side of a dielectric substrate, with a ground plane located on the opposite side.Its notable advantages include its lightweight construction, ease of manufacture, adaptability to both planar and nonplanar surfaces, and its compact, streamlined form.Due to its unobtrusive design and flat geometry, this antenna finds particular relevance in applications involving high-speed vehicles, aircraft, spacecraft, and missiles [2].Numerous studies (references [1] - [7]) have investigated various configurations of microstrip antennas featuring rectangular and circular patchs.Notably, some researchers have explored antenna designs incorporating superstrates.Typically, a dielectric superstrate shields the patch from external influences and environmental conditions, thereby augmenting antenna performance [5].In our investigation, we extended the antenna's bandwidth by introducing a slot positioned above the radiating element through the use of various superstrate configurations.Our results indicate significant improvements compared to previous studies.The development of a circular microstrip patch antenna energized by a coaxial cable was accomplished using HFSS software.Subsequent sections of this paper will provide detailed references and elaboration on these findings.ibrahimkhouyaoui@gmail.com

Circular patch antenna design
The antenna is engineered to operate at a central frequency of 2.4 GHz and is constructed on an FR4_epoxy dielectric substrate.This substrate possesses specific characteristics, including a dielectric constant (εr) of 4.4, a loss tangent (tan δ) of 0.02, a thickness (h) measuring 5 mm, and dimensions of 61.23 mm x 72.8 mm.As for the Superstrate material, Arlon diclad 880 dielectric has been chosen [1].In the field of antenna design, the selection of substrate materials holds paramount significance.Similar to substrate thickness, the dielectric constant (εr) profoundly impacts performance.Opting for a substrate with a lower dielectric constant can lead to an increase in the patch's fringing field and radiated power.Conversely, a higher loss tangent (tan δ) results in elevated dielectric loss, subsequently affecting antenna efficiency.Utilizing materials with lower dielectric constants enhances radiation efficiency, bandwidth, and overall effectiveness.These insights are comprehensively presented in Table 1 [5].1).The feed point position (F) was iteratively determined to be X = -12 mm through a trial-and-error process.Equations ( 1) and ( 2) from references [7] and [1] are employed in these calculations.5 Studying the impact of an antenna parameter on fr,BW and S11

Effect of substrate height h
While maintaining all other antenna characteristics constant, we systematically alter the substrate's thickness within a range spanning from 1 mm to 11 mm.This deliberate variation aims to evaluate the influence of the dielectric substrate's thickness (h) on not only the antenna's overall performance but also its resonance frequency and bandwidth, specifically.The findings of this experimentation are meticulously structured and visually depicted in Figure 7, with a more comprehensive analysis of the results available in Table 3 illustrates the influence of varying substrate thickness on the characteristics of the circular patch antenna, specifically focusing on parameters such as resonance frequency (fr), S11, and bandwidth (BW).Notably, when h=9mm, the bandwidth reaches its maximum value, albeit with a resonance frequency significantly distant from the target frequency of 2.4 GHz.Meanwhile, Table 3 underscores that the optimal combination of bandwidth (BW) and S11 value is achieved when the substrate thickness is set at h=7mm

Inserting a rectangular slot on the patch
In an effort to enhance the antennas' performance, we endeavored to incorporate rectangular slots of various dimensions above the patch, as depicted in Figure 8.

Effect of slot width wslt for circular patch
We systematically employed a range of values, specifically within the interval of 1 mm < Wslt < 11 mm, to determine the width (Wslt) of the introduced slot.The investigation focused on assessing how this slot width affected the performance of the circular patch antenna.The results of this analysis are graphically represented in Figure 9, with a more comprehensive breakdown available in   The influence of slots on the attributes of circular microstrip patch antennas reveals that the presence of the superstrate affects not only the resonant frequency but also other parameters, notably including the return loss represented by S11.

Effect of superstrate in circular patch
The circular microstrip patch antenna, as proposed in this study, underwent a comprehensive examination employing Superstrates of varying thicknesses (hsp), specifically 1mm, 2mm, and 4mm.The frequency range under investigation ranged from 2.33 GHz to 2.26 GHz.Throughout this scrutiny, the observed gain exhibited a spectrum spanning from 3.3 dB to 4 dB, while the bandwidth extended from 200 to 220 units.The half-power beam-width (HPBW) in the horizontal polarization mode varied between 80 and 90 units, while in vertical polarization, it ranged from 60.33 to 70.21 units.Simultaneously, the input impedance exhibited fluctuations within the range of 36.53 -j15.

Circular antenna optimal
The concluding set of parameters, which yield an exceptionally wide bandwidth and optimize the S11 performance at the 2.4 GHz resonance frequency, are deduced from the previously conducted parametric investigations.These paramount parameters are presented in

conclusion
The study delves into the response of microstrip antennas, encompassing circular patches, when subjected to dielectric superstrate characterized by varying dielectric constants.This investigation underscores that the impact of the superstrate extends beyond merely affecting the resonant frequency.It also exerts influence on additional parameters, such as gain, bandwidth, beamwidth, VSWR, and return loss.Notably, the presence of the superstrate leads to a downward shift in the resonant frequency.Furthermore, it is noteworthy that when maintaining a consistent resonant frequency of 2.4 GHz, the introduction of a slot to a circular patch results in a broader bandwidth and induces a reduction in the S11 reflection coefficient.

*
Figures 1 and 2 illustrate the geometric specifications of circular microstrip patch antennas, which are fed via coaxial probes.The substrate of the patch antenna possesses specific dimensions, with a width denoted as Ws measuring 72.8mm, a length designated as Ls measuring 61.23mm, and a critical parameter, the feed point position (F), positioned at -12.75mm from a reference point.

Table .
The creation of the patch antenna operating at 2.4 GHz is achieved by employing a transmission line and cavity model, with construction taking place on a substrate possessing a dielectric constant of 4.4.The determination of the circular patch antenna's Fig. 2. Circular patch structure with substrate and dielectric Superstrates Fig. 1.Circular patch microstrip antenna (CP) E3S Web of Conferences 469, 00077 (2023) ICEGC'2023 https://doi.org/10.1051/e3sconf/202346900077diameter (Dp), which equals 31.34 mm, can be facilitated through Equation (

Table . 2
. Comparison of simulation results for circular patch antennas without dielectric superstrate

Table . 3
. Impact of substrate height h of (CP)

Table 5
Fig. 8. Circular patch with slot Fig. 9. Variation of S11 ,fr and BW in relation to variation of Wslt in (CP)

Table . 4
. Impact of slot to S11,fr and BW of (CP) Table 8 below, and their graphical representations can be found in Figures 11 to 14.

Table . 6
. Final results for the optimized circular patch antenna