A PCB antenna transforms current in high frequency into electromagnetic waves that end up propagating into the air. A high frequency circuit board has two different PCB antennas which are embedded in the circuit board. One of the antenna functions as the transmitted radio frequency signal while the other one functions as the RG signal receiver.
The base materials of the circuit board transfer the signals to the antenna when the high-frequency PCB produces radio frequency waves. High frequency circuit and PCB antennas make up the RF system of the high-frequency circuit board. There are different types of PCB antennas. We have the loop antenna, patch antenna, slot antenna, and more.
However, our main focus here is the loop antenna. We will be giving some detailed explanations about PCB loop antenna.
What is a PCB Loop Antenna?
Antennas are used in developing a high-frequency PCB. These antennas are embedded in the circuit board. To have a clear understanding of how PCB loop antennas, one must read more about them.
The loop antenna is a type of PCB antenna whose simple closed loop is linked with transmitter or receiver terminals. This type of PCB antenna has round shape. The copper materials used in the antenna design and the size of the loop determine the efficiency of PCB loop antenna.
PCB loop antennas are inefficient when you compare them with the wavelength. Therefore, they are not ideal for transmitting signals but can serve as receptors.
The PCB loop antenna comes with a directional pattern which makes it very easy to locate the transmitter also known as radio direction finding (RDF). You need to fix a capacitor in parallel with a PCB antenna. To achieve maximum efficiency, there is a need for an impedance matching network.
This antenna is usually created by bending a uniform wire in a loop form. The RF coil is usually bent to different shapes like eclipse, circle, square, and rectangle. Therefore, a loop antenna is simply a current-carrying coil bent in the form of loops. These loops can have different shapes. Also, PCB loop antennas are inexpensive, versatile, and simple. Therefore, these antennas have different applications.
The antenna can form various types of loops by bending the wires into various shapes forms. This loop can be rectangular, elliptical, circular, triangular, etc. Circular PCB loop antenna is commonly used. This is because circular PCB loop antennas provide a level of simplicity in construction and also analysis.
What are the Types of a PCB Loop Antenna?
A PCB loop antenna forms a conducting path between a two-wire transmission line. This antenna is in three different categories which are small, medium, and large. A loop antenna is said to be small if its circumference is below one forth of a wavelength.
Furthermore, the majority of directional receiving loops are about 10% of a wavelength.
Small loop antenna
A small loop antenna is more sensitive to the magnetic components of an electromagnetic wave. This is one reason why it is called the magnetic loop. However, this loop antenna has less sensitivity to electric noise that is close. It is possible to increase the received voltage of a small loop when it is brought into resonance.
When a signal gets to the axis of the loop, it will induce an equal voltage in each limb in order to account for symmetry. The loop’s output should be zero since it is the difference in voltage between the two limbs.
Medium loop
A loop antenna is categorized as a medium loop antenna for two reasons. The first reason is when you mount a half-wavelength loop on a horizontal plane. This results on an antenna that evenly emits power in the horizontal plane.
The second reason occurs when a full-wavelength loop emits on its axis. These medium loops are often considered as elements of the quad antennas. Also, they are polarized based on the feed point’s position.
Large loop antenna
The third type of loop antenna is the large loop antenna. This type of antenna is a dipole antenna linked at the ends to create a triangle, circle, or a square. Loop antenna formed in the shape of a triangle is a delta loop antenna.
The loops formed into a circle have almost 10% higher gain than any of the other shapes. However, these loops can be very difficult to support due to their shape. Therefore, the square and triangle loops more common than the circular loop. Furthermore, large loops always better signal in the plane of the loop. This is very true as long as the loop maintains a good shape and size.
How to Design a PCB antenna
Generally, antennas are sensitive to their environment and as such, when installed into a circuit board, it is crucial to consider the layout and design as regards the requirements. This is because these factors may affect the functioning of the wireless device. Simple factors such as layer thickness, material, and layer count can even affect the performance of a PCB loop antenna.
Therefore, there are different steps to take when designing a circuit board antenna. These steps will help you to achieve a functioning PCB antenna.
Antenna positioning
There are different operation modes for antennas. Therefore, the antenna’s radiation level will determine their placements. For instance, they can be positioned in a PCB’s corner, along the short side or the long side of a board. The PCB corner is one of the most suitable places to place an antenna. This position enables the PCB antenna to experience clearance in about five spatial directions
There are different types of antenna designs that are ideal for various positions. Therefore, PCB designers need to understand the principles of antenna positioning. Also, they need to choose the appropriate antenna based on their layout and application.
Keep-out area
It is crucial for PCB designers to avoid placing components in the near field close to the antenna. Otherwise, this may cause signal interference, which will have a negative impact on the circuit’s functionality. Furthermore, they should ensure spacing between the area around the antenna and the metallic objects.
Furthermore, a PCB antenna usually emits signal against a ground plane. This ground plane works with the operational frequency of the antenna. Therefore, proper spacing and size is crucial for the ground plane of the antenna. While many designers ignore the keep-out area, this can cause problems during the design process.
Size of the ground plane
The PCB ground plane size is crucial when designing a PCB antenna. This is because wires integrated for communicating with various batteries and devices may alter. Therefore, designers need to ensure that the size of the ground planes is appropriate as it helps the connection of the batteries and cables to that device would have lesser effects on that antenna.
Some PCB antennas depend on ground planes. This means the circuit board serves as the ground area of the antenna in order to strike a balance between the lower PCB layers and antenna currents. In the long run, this may make the antenna to perform poorly. In cases like this, PCB designers need to avoid placing battery close to the antenna.
Distance from other PCB components
When designing a circuit board, it is important to keep the antenna far from other components that may disrupt the radiation of the antenna. This will help in avoiding any further problem with the components.
The width and height of the PCB components determine the distance between the antenna and other components. Furthermore, components such as LCDs and batteries, different connectors such as Ethernet cables feature switching speeds. This could increase the likelihood of signal interference when the device is in operation.
Designing the transmission line
PCB antennas have a transmission line. The transmission line is the radio frequency trace that transmits the radiofrequency energy which transfers the signal to the reception. Designers need to design the transmission line at 50 Ω. Otherwise; these lines may reflect signals to the reception which may result in a degraded signal-to-noise ratio (SNR).
Therefore, designers must pay attention when designing the transmission line. They must ensure this line is straight since there is a chance for increase in signal loss if there are any bends or corners. To achieve reduction in signal losses, the designer must place vias along the two sides of the trace. This will help to isolate noise that travels along nearby traces and as such improving performance.
How to Achieve Better Performance
There are different ways you can enhance the efficiency of an antenna and have better results. Some useful ways for achieving this include:
- Tuning the antenna with matching networks will help to compensate for any factor that may have an effect on the performance of the antenna.
- Ensuring the selected the ground plane is appropriate. This will result in crosstalk between the signals otherwise. In such a case, the antenna will have to be placed in the edge of the circuit board.
- Avoid doing the antenna’s external casing since the antenna signals don’t pass through metal.
- The antenna shouldn’t be placed near plastic surface as this can affect the performance of the antenna. This is because plastic features a high dielectric constant which dampens the radio frequency signal and as well creates losses. This will increase the antenna’s electrical length of the antenna and minimize the radiating frequency of the antenna.
- A high-quality FR4 is a great option. You can make use of this laminate in order to achieve excellent RF performance.
Other Types of PCB Antennas
Apart from the PCB loop antenna, there are other types of PCB antennas.
Patch antenna
Patch antenna has a rectangular or circular shape. The patch antenna’s span is almost one-half of the wavelength of radio waves. Since it has short wavelengths, the patch antenna is usually integrated in microwave frequencies. Most portable devices integrate patch antennas because of its ease of design. Patch antennas are ideal for portable devices with wireless functionality.
There is another variant of the patch antenna known as the planar inverted type. Phased arrays and WLAN antennas integrate this variant in order to achieve maximum gain.
The planar inverted type has a bandwidth problem. However, the use of a thicker dielectric between ground and patch plane can increase the antenna’s bandwidth.
Meander Line Antenna
The construction process of this type of antenna involves folding the conductors to make the antenna shorter. This construction leads to a smaller compact size. However, the loss of resistance, radiation, and efficiency contribute to the size. Several experiments are usually carried out to choose the perfect combination for a particular application. To achieve impedance matching, external components are crucial.
Inverted-F antenna
The WLAN hardware on cell phones integrates the Inverted-F PCB antenna. This antenna is omnidirectional and as such features a large ground plane for optimal efficiency. Copper isn’t used in some part of F antenna. However, it is a plane surface that increases the antenna’s bandwidth.
Slot Antenna
Due to the construction of this antenna, it is called slot. Its construction comprises a metal plate with several cuts or slots or in it. Just like dipole, slot antenna has opposite magnetic and electric fields. Due to the features of slot antennas, they are commonly used in phased arrays and aircraft radars.
Conclusion
The PCB loop antenna comes with a directional pattern which makes it very easy to locate the transmitter also known as radio direction finding (RDF). You need to fix a capacitor in parallel with a PCB antenna. To achieve maximum efficiency, there is a need for an impedance matching network.
A PCB loop antenna forms a conducting path between a two-wire transmission line. The loop antenna plays a significant role when integrated in a PCB. It offers more benefits than other types of PCB antennas. However, it is crucial that a PCB designer considers the applications and requirements of a PCB antenna before to determine the best PCB antenna.
