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Antennas have become an integral part of modern technology, serving as crucial communication components for various mainstream devices such as smartphones, IoT devices, and security systems. This prevalence underscores the significance of radio frequency (RF) engineering and design, making it a captivating and influential field. In this context, my objective is to provide readers with a foundational understanding of antennas – their fundamental principles, operation, and the process of constructing a 2.4 GHz antenna design.
Before delving into the details, it's important to note that while I am not an RF expert, I bring forth years of practical experience that can guide individuals in initiating and advancing their projects effectively.
What is Antenna Overview
While the main focus of this article centers around PCB antennas operating at 2.4 GHz, a foundational understanding of antennas can greatly benefit beginners. However, if you're a professional seeking a more advanced insight into PCB antennas, feel free to skip this section.
To grasp antennas more comprehensively, a brief exploration of impedance matching and resonant circuits is essential. To achieve optimal power transfer, the source impedance should ideally match the load impedance.
An antenna essentially constitutes a metallic structure, often composed of wires, serving as a means to convert high-frequency electrical currents into electromagnetic waves and vice versa. In essence, it functions as a specialized transducer that transforms high-frequency electrical current into electromagnetic waves.
For an antenna to efficiently transmit signals, it must effectively match the transmission line and the load impedance. The length of the wire, its dielectric properties, and the frequency play crucial roles in its function. This wire acts as an impedance-matching transmission line, a topic we'll delve into further in this article.
The antenna also operates as a resonant circuit. This means it possesses the capacity to transform energy from electrostatic to electromagnetic, and with proper impedance matching, the energy is transferred and radiated into the surrounding space, akin to how a transformer shifts energy from primary to secondary.
While the above overview simplifies the complexities of RF transmission, it serves as the foundation for further discussions.
In antennas, wavelength, frequency, and antenna length are intertwined. Let's elucidate these parameters with a basic example.
The antenna's length and configuration are interconnected with the wavelength of the transmitting frequency. Specifically, the mechanical length is inversely proportional to the frequency's value.
As we're aware, the formula is:
T = 1 / f
where T represents time and
f signifies frequency.
Consequently, for an antenna operating at 50 MHz,
t = 1 / f = 0.2 μs,
Wavelength (λ) = C / f = 3 * 10^8 / 50 * 10^6 = 6 m,
with C denoting the speed of light.
For a quarter-wavelength antenna, it becomes a constant λ/4.
The simple example provided illustrates how to compute wavelength for a specific frequency.
Applying the same calculations for 2.45 GHz yields an antenna length of 23 mm.
With these foundational concepts in place, we can now delve into the main focus of this blog: PCB design.
Before proceeding, it's important to clarify that I won't be delving into the intricate details of every facet of PCB antenna design step by step. My expertise, tools, and measurements don't extend to such exhaustive explanations.
Instead, I'll explore core concepts, share best practices, and offer key considerations. With that said, let's delve into the design process!
Antenna Schematic
In this phase, our focus is on designing a 2.4 GHz antenna tailored for the ESP8255 Mini board. Below, you'll find the circuit diagram for this endeavor. In the upcoming article, we'll take the schematic and craft an entire PCB based on it.
To ensure the accuracy of our schematic, we'll leverage the ESP8285 design guide thoughtfully provided by Espressif. Upon searching, I located the hardware design guide for the ESP8285, which offers an in-depth resource for crafting a comprehensive hardware design.
Within these hardware design guidelines, I'd like to emphasize a few critical design prerequisites, specifically concerning the analog and digital power supplies for the ESP. While these two power supply aspects will receive comprehensive exploration when we embark on designing the complete PCB for the ESP8285 board, our current focus remains dedicated to the intricacies of antenna design.
2.4 GHz PCB Antenna Design
The antenna segment offers a toggle feature between a PCB antenna and a whip antenna. In case of contingencies, inductors L3 and L4 are included.
Dividing our attention to the PCB, we can distinguish two primary sections: the antenna segment and the crystal oscillator segment. For now, our exclusive focus lies on the antenna component.
The most challenging phase of this project involved strategizing the antenna's placement.
Initial steps encompassed positioning essential junctions and connectors.
Following that, we meticulously positioned the antenna, U.FL connector, programming header, GPIO0 switch, and microcontroller, mirroring the arrangement depicted in the image above.
The subsequent task entails configuring the antenna traces. I'll harness Eagle PCB's polygon tool to fulfill this requirement.
An imperative aspect to bear in mind prior to routing pertains to maintaining a trace impedance of 50 ohms. This impedance is vital as the trace serves as a high-frequency transmission line. However, the exact 50-ohm value hinges considerably on factors such as dielectric material and board thickness. Hence, a meticulous calculation is in order to ensure accurate trace drawing.
For this purpose, we will utilize an online resource called Mantaro.
To compute the optimal trace width, input the necessary parameters, all of which are readily available from the manufacturer's documentation.
Firstly, I manually input a trace width of 70 mils.
Subsequently, the trace thickness is set at 1 ounce, equivalent to 1.4 mils.
The third parameter is the dielectric thickness, i.e., the board's thickness, which stands at 39.3701 or 1.6 mm.
Lastly, the relative dielectric constant, unique to each manufacturer, is sourced from the manufacturer's specifications.
Upon pressing the "calculate" button, the result yielded an impedance of 50 ohms.
A noteworthy observation: The dominant factors shaping impedance are trace width (w) and dielectric thickness (h).
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