Design of a
Rook shaped Microstrip Patch Antenna
for WLAN Applications
Dr. G. Kalpanadevi1, kalapanadevig.ece@krce.ac.in
Faculty, Department of ECE, K. Ramakrishnan College of
Engineering, Tamil Nadu, India
Afshana R2, Dharini N3, Hima Shree S4 and Hinduja KR5
Students, Department of ECE, K. Ramakrishnan College of Engineering, Tamil Nadu, India
afshana2721@gmail.com2,
krhinduja2005@gmail.com5
Abstract— This study presents the design and simulation of a
rook-shaped microstrip patch antenna for 2.4 GHz Wireless Local Area Network
(WLAN) applications. The proposed antenna is made from a FR-4 lossy substrate
with a relative permittivity of 4.4, a loss tangent of 0.02, and a substrate
thickness of 1.6 mm. The radiating patch
is fashioned like a
rook (castle) chess piece by carefully etching rectangular slots around
the edge of a normal
rectangular patch. This increases the current
route length and enhances impedance matching. Both the radiating patch and the ground plane of the antenna are made of copper
(annealed), and it employs edge feeding with a 50 microstrip feed line.
The simulation results from the CST Studio
Suite reveal a resonant frequency. Simulation results from CST Studio Suite
reveal excellent impedance matching, with a resonance frequency of 2.409
GHz, a voltage standing wave ratio
(VSWR) of 1.2583, and a return loss (S₁,₁) of −18.831 dB.
The radiation pattern exhibits
a broadside radiation
characteristic with a peak
gain of −0.286 dBi. Its modest size and
distinctive geometric shape make it an excellent fit for integration into
modern WLAN-capable devices.
Index Terms - WLAN, 2.4 GHz, FR-4 substrate,
rook-shaped antenna, radiation pattern, edge feed, return loss, VSWR, and
microstrip patch antenna are among the index terms.
I. Introduction
The way people, gadgets, and infrastructure interact has changed dramatically in the last several decades due to the advancement of wireless communication. The antenna, a passive radiating component that launches and captures electromagnetic waves that transmit data over free space, is the central component of every wireless system. No matter how advanced the underlying electronics or signal processing algorithms are, no wireless link can be created without well-designed antennas. As a result, antennas are essential in almost every area of contemporary technology, including consumer electronics, cellular networks, broadband internet access, global navigation satellite systems, remote sensing platforms, and biomedical telemetry [1]. The ability of the antenna to effectively radiate power in desired directions, maintain stable impedance characteristics throughout the working band, and do so within the physical limitations set forth by the host device is directly related to the performance of a wireless system.
An ever-growing number of linked devices, each requiring dependable radio frequency links within strictly regulated frequency bands, characterizes modern wireless ecosystems. WLAN under IEEE 802.11b/g/n, Bluetooth, Zigbee, and several proprietary RF protocols used in smart home and industrial automation systems are among the short-range wireless connectivity technologies that rely on the 2.4 GHz ISM band, which is universally designated for unlicensed operation [2]. The sheer number of devices using this spectrum highlights how crucial it is to design antennas that not only precisely resonate at 2.4 GHz but also have well-controlled radiation characteristics, reducing interference with other systems while providing sufficient link margins for dependable data exchange. Antenna geometry, substrate selection, and feeding methodology must be carefully considered during the design phase in order to meet the demands of modern wireless ecosystems, which are characterized by an ever-increasing density of connected devices, each of which requires dependable radio frequency links.
The planar nature of microstrip patch antennas allows them to be deposited directly onto printed circuit boards using the same photolithographic processes used to manufacture the surrounding electronics, drastically reducing assembly complexity and unit cost [3]. Additionally, because they can be printed directly on the device's main board or on a dedicated RF layer, they add negligible thickness to the host device, which is a crucial advantage in the thin-profile consumer electronics market. As a result, this class of antenna is the standard for Wi-Fi modules, router cards, access point hardware, and embedded WLAN chipsets. However, there are well-known performance trade-offs associated with the rectangular and circular geometries that predominate in conventional microstrip antenna practice. These trade-offs include a narrow fractional bandwidth that limits tolerance to manufacturing variations and frequency drift, as well as gain figures that are limited by the electrical size of the patch relative to the operating wavelength [4].
A great deal of research has been focused on finding creative ways to change the patch geometry in order to get around these intrinsic restrictions. The distribution of surface currents across the radiating element is changed by adding cuts, slots, and notches to the patch. This changes the antenna's radiation behaviour, input impedance characteristics, and resonant frequencies [5]. In particular, it has been demonstrated that periodic boundary alterations can extend a patch's effective electrical length beyond its physical perimeter, allowing resonance at frequencies lower than those anticipated by traditional transmission line models for a patch with the same outside dimensions [6]. This electrical lengthening effect is highly advantageous when strict restrictions on the physical antenna footprint must be followed. Apart from slotted geometries, fractal patch boundaries created by repeated mathematical constructions have been studied as a means of achieving both multiband functioning and size reduction simultaneously [7]. Stacked patch topologies, which divide many resonant layers with thin dielectric spacers, have been utilised to increase the impedance bandwidth at the expense of a greater antenna height [8]. Choosing one of these methods, which all involve deliberate trade-offs between bandwidth, gain, size, fabrication complexity, and cost, requires careful evaluation of the specific requirements of the desired application.
As an alternative design philosophy that combines structural innovation with functional electromagnetic performance, geometrically unique patch shapes have garnered increasing attention. Recent literature has documented patches modelled after alphabetic characters, natural organisms, symbolic icons, and cultural artefacts, showing that non-traditional boundary shapes can generate beneficial radiation characteristics while also setting the design apart from commercial antenna solutions [9]. One of the six-piece chess pieces, the rook, offers an attractive geometric model for antenna construction. Its distinctive battlement pattern, which is typical of mediaeval castle towers, is formed by a solid central body from which a number of uniform rectangular projections stretch upward along the top edge.
The boundary that results from extending this profile to all four sides of a square radiating patch introduces a regular series of rectangular indentations that together lengthen the total perimeter current path, redistribute the surface current density throughout the patch, and alter the fringing field configuration at the radiating edges [10]. Together, these electromagnetic effects of the rook boundary cause the patch's fundamental resonance to shift toward a lower frequency than that of a simple rectangular patch with the same outer dimensions. This effectively provides a degree of electrical miniaturisation without the need for lumped loading elements or high-permittivity substrates.
The microstrip transmission line makes direct physical contact with the radiating patch's lateral edge as part of the edge feed feeding mechanism used for the suggested antenna. With no additional ground plane apertures, via-hole connections, or multilayer transitions needed, this method is one of the most straightforward feeds designs available to the antenna designer [11]. By placing the feed line at a suitable location along the patch edge where the input impedance of the resonant patch equals the characteristic impedance of the line, impedance matching to the standard 50 reference impedance is accomplished. Edge feeding is especially appealing for low-cost fabrication environments where process complexity needs to be kept to a minimum due to its simplicity. In order to accurately represent the metallic layers deposited or laminated during standard PCB manufacturing, the conducting elements of the antenna—the radiating patch and the ground plane—are given the material properties of annealed copper, which has an electrical conductivity of 5.8 × 10² S/m [12].
The glass-reinforced epoxy laminate FR-4 lossy, which has a loss tangent of 0.02 at microwave frequencies and a relative permittivity of 4.4, serves as the substrate for the antenna. Because of its established supply chain availability, dimensional stability, and mechanical resilience, FR-4 is one of the most popular PCB materials in the electronics industry [13]. Higher-performance microwave substrates, like Rogers RT/duroid, provide more precisely regulated permittivity values and reduced dielectric losses, but their substantially higher material costs may be unaffordable for consumer-grade wireless products. Instead of presenting optimistic results obtained under idealised material assumptions, the current work makes sure that the predicted antenna performance reflects the losses and permittivity variations that would be encountered in an actual low-cost fabrication run by purposefully choosing FR-4 as the simulation substrate [14]. CST Studio Suite, a full-wave electromagnetic solver that uses the Finite Integration Technique to precisely resolve the spatial and temporal development of electromagnetic fields within and around the antenna structure, is used to model and characterise the entire antenna structure [15].
The suggested rook-shaped antenna's computed performance shows resonance at 2.409 GHz with a return loss of −18.831 dB, a VSWR of 1.2583, and a broadside radiation pattern with a peak gain of −0.286 dBi. Together, these findings verify that the antenna satisfies the basic electrical specifications needed for WLAN operation in the 2.4 GHz band [16]. The suggested design is easily adaptable to physical prototype production using normal PCB procedures because of the rook shape's geometric simplicity, the use of commonly available materials, and a simple feeding system. A generalisable methodology for adapting patch geometries inspired by chess pieces to additional frequency bands and wireless standards is also provided by the design approach presented in this study [17].
This is how the paper is organised. The entire antenna design process is covered in detail in Section II, including the analytical formulation used for initial patch sizing, the parameterisation of the rook shape, substrate and conductor parameters, and feed line dimensioning. The complete set of simulated findings is shown in Section III, together with a thorough explanation of the radiation pattern characteristics, VSWR behaviour, and S-parameter response. The study's findings are collected in Section IV, which also suggests future directions for the research.
II. Antenna Design Methodology
A. Substrate Selection and Specifications
The choice of dielectric substrate is the cornerstone of any microstrip patch antenna design since it directly controls the radiating patch's effective permittivity, the feed line's characteristic impedance, the antenna's physical dimensions, and the total dielectric loss added to the system. FR-4 lossy is chosen as the substrate material in the suggested design. The PCB industry makes extensive use of FR-4, a glass-reinforced epoxy laminate, because of its superior mechanical qualities, dimensional stability under a range of thermal conditions, and substantially reduced procurement cost as compared to specialist microwave substrates. At microwave frequencies, FR-4's dielectric characteristics are defined by a loss tangent (tan δ) of 0.02 and a relative permittivity (εᵣ) of 4.4. The most widely used standard laminate thickness in commercial PCB fabrication is represented by the substrate thickness (h), which is set at
1.6 mm. In accordance with the one-ounce copper cladding standard used in PCB manufacturing, the conducting layers—which include the ground plane on the bottom surface and the radiating patch on the top surface—are modeled as annealed copper with a thickness of 0.035 mm and an electrical conductivity of 5.8 × 10² S/m. Table I provides a summary of all substrate and conductor specifications.
The rook-shaped radiating patch installed on the
FR-4 substrate with the ground plane positioned on the bottom surface is
clearly shown in Fig. 1, the three-dimensional picture of the suggested antenna configuration as modelled
in CST Studio Suite. The picture clearly shows
the patch's battlement-like notched border, which depicts the general geometric
profile of the
Fig. 1 3D view of the proposed antenna
Fig. 1. The rook-shaped copper radiating
patch on the top surface of the FR-4 lossy substrate and the entire copper
ground plane on the bottom surface are depicted in this three-dimensional model
of the suggested rook-shaped microstrip patch antenna created in CST Studio
Suite.
TABLE I: Substrate and Conductor Specifications
|
Parameter |
Value |
|
Substrate Material |
FR-4 Lossy |
|
Relative Permittivity (εᵣ) |
4.4 |
|
Loss Tangent (tan δ) |
0.02 |
|
Substrate Thickness (h) |
1.6 mm |
|
Conductor Material |
Copper (Annealed) |
|
Conductor Conductivity (σ) |
5.8 × 10⁷ S/m |
|
Conductor Thickness (t) |
0.035 mm |
|
Operating Frequency (f) |
2.4 GHz |
B. Initial Patch Dimension Calculation
The analytical computation of a traditional rectangular patch that resonates at the intended frequency of 2.4 GHz serves as the foundation for the rook-shaped patch design. The width and length of a rectangular microstrip patch antenna can be found using a well-known set of closed-form formulas provided by the standard transmission line model. The rook geometry is then built and parameterized using these formulas as the baseline dimensions.
The following formula, which strikes a
compromise between radiation efficiency and avoiding higher-order
mode excitation, is used to calculate the width of the
radiating patch (W):
where fᵣ is the resonant frequency (2.4 GHz), εᵣ is the substrate's relative permittivity, and c is the speed of light in empty space (3 × 10¹ m/s). The fringing fields that extend past the patch's physical boundary into the surrounding air medium are taken into account by the effective permittivity (εᵣₑff), which is determined by:
Additionally, the patch's electrical length seems longer than its physical length due to the fringing effect. The expression for this length (ΔL) extension on each side of the patch is:
The resonant frequency and the patch's effective length (Lₑff) are connected by:
The length extensions from both radiating edges are then subtracted to determine the patch's actual physical length (L):
The initial rectangular patch dimensions, which act as the geometric reference for building the rook-shaped boundary, are obtained by substituting the known parameters, fᵣ = 2.4 GHz, εᵣ = 4.4, and h = 1.6 mm, into the preceding formulae. Table II lists the calculated antenna dimensions.
C. Feed Line Design
The suggested antenna uses an edge feeding arrangement where a microstrip transmission line comes into direct touch with the patch's radiating edge. In order to ensure compatibility with common RF test equipment and system interfaces, the width of the microstrip feed line (Wf) is determined to present a characteristic impedance of 50 Ω. The following formulas, which are developed from the microstrip transmission line model, are used to calculate the feed line width.
For W/h > 2:
To maintain symmetric current distribution over the radiating aperture and excite the dominant TM₁¹ mode, the feed line is placed at the middle of the patch's non-radiating edge. In order to have the best impedance match at the resonant frequency, the feed line's length is tuned during simulation. In this design, the feed line connects directly to the patch edge, depending on the natural input impedance at the patch border for impedance matching, rather than using the inset depth. The feed line width of 3.06 mm, which was determined using the transmission line impedance formula and confirmed through parametric simulation in CST Studio Suite, is equivalent to the typical 50 Ω line width for the specified substrate parameters.
D. Rook-Shaped Patch Geometry
The unique feature of the proposed antenna is the rook-shaped boundary of the radiating patch, which is created by methodically adding uniform rectangular notches along all four sides of the baseline rectangular patch. This geometric modification is inspired by the chess rook piece's silhouette, which is characterized by a series of rectangular battlements projecting from the top of a solid tower body. When this battlement pattern is symmetrically replicated on all four sides of the patch, the resulting shape acquires the appearance of a rook when viewed from above, thereby achieving both aesthetically pleasing profile and a functionally modified electromagnetic boundary.
Surface currents that would normally flow straight across the patch edge are forced to avoid the notch borders because each notch added to the patch boundary eliminates a rectangular portion of conducting material from the patch's edge. The resonant surface currents' overall travel length is effectively increased by this detour, which is electromagnetically comparable to running a physically bigger patch at the same frequency. Consequently, the rook-shaped patch achieves a target resonance frequency with a smaller outer footprint than a traditional rectangular design, or it resonates at a lower frequency than a simple rectangular patch with the same outer dimensions.
In order to properly locate the resonant frequency at 2.4 GHz while preserving a symmetric current distribution that supports a well-formed broadside radiation pattern, the notch dimensions and their spatial arrangement along the patch perimeter are meticulously specified. To maintain the periodic nature of the rook geometry, the notches' breadth and depth remain consistent, and the distance between neighboring notches is likewise kept constant. The patch's bottom border is altered to make room for the feed line. The 50 Ω microstrip line extends downward toward the discrete port from the middle area of the bottom side, which is set up as the feed stub connection point.
Fig. 2 shows an annotated top-view schematic of the
radiating element with all important geometric characteristics clearly labeled,
along with the precise dimensions of the rook-shaped patch as taken from the CST
Studio Suite simulation model. The
figure shows how the rectangular notches are symmetrically arranged along the
patch's top and side edges,
how the bottom
edge is set up to accommodate the feed line connection,
and the exact millimeter-level measurements that control each notch's width,
depth, inter-notch spacing, and lateral wing extension. Together, Figs. 1 and 2
offer a comprehensive geometric description of the suggested antenna,
communicating the two-dimensional dimensional detail required for precise design
replication as well as the three-dimensional physical structure. Table III provides a summary of the rook-shaped patch's
primary geometric properties.
Fig. 2 Top view of the patch with dimensions
Fig. 2. shows the top view of the rook-shaped radiating patch with full dimensional annotations, showing the bottom feed connection area, the lateral wing extensions, and the periodic rectangular notch arrangement along all four sides.
TABLE III: Rook-Shaped Patch Geometric Parameters
|
Parameter |
Description |
Value |
|
Notch Width (top) |
Width of
each rectangular notch |
4.00 mm |
|
Notch Spacing |
Gap between adjacent
notches |
4.00 mm |
|
Notch Depth 1 |
Depth of upper-row notches |
6.00 mm |
|
Notch Depth 2 |
Depth of middle-row notches |
5.00 mm |
|
Notch Separation |
Vertical gap
between notch rows |
1.00 mm |
|
Side Notch Depth |
Depth of
side boundary notches |
6.00 mm |
|
Side Extension |
Horizontal protrusion at lower sides |
5.62 mm |
|
Lower Tab Width |
Feed-side central tab width |
4.00 mm |
|
Lower Tab Length |
Feed-side central tab length |
9.50 mm |
|
Feed Tab Base
Width |
Base width
of feed tab |
6.00 mm |
|
Lateral Extension |
Horizontal extent of lower wings |
11.62 mm |
|
Wing Height |
Vertical height
of lower side wings |
7.00 mm |
