Radio Frequency (RF) Antennas: Types and Selection Criteria
Antennas are so much more than simple devices for transmission and reception. At Summit they are carefully crafted transducers designed and manufactured to optimise maximum energy radiated and received for a given form factor.
The design, manufacturing and selection of antennas are critical factors that determine the overarching performance of a communication system. In this blog, we will discuss the different types of RF antennas and the criteria for selecting the right one for your application.
The first decision to make is an internal or external antenna required.
Internal Antennas:
Internal antennas are located inside device enclosures. Often integrated into the circuit board of the device and not visible from the outside; internal antennas are typically small in size and are used in devices that have limited space, such as smartphones, laptops, portable devices and wearables. Protected from physical damage and the environment by the enclosure; these solutions do not take up additional space, however unfortunately they typically achieve lower gains. In addition, the signal quality can be greatly affected by the presence of metal parts or other electronic components inside the device. Internal antennas therefore often need careful tuning. Internal antennas are therefore not typically “plug and play” solutions. Optimal results can be achieved via use of a VNA Vector Network Analyzer. At Summit, we can support you with such analyses and test equipment - please just reach out and ask us (details at the end of this article).
External Antennas:
External antennas are located outside device enclosures. Typically connected through a connector or cable and normally either mounted on the enclosure, mast, tripod or vehicle roof; these antennas are often larger in size than internal antennas and are used for applications that require longer-range communications. Key advantages include that they can be positioned for optimal signal quality. Performance is also not normally affected by the presence of metal parts or other electronic components inside the device and so this is more of a “plug and play” solution. Larger gain versions are also possible. External antennas are however exposed to the environment and therefore may be more subject to physical damage.
Different form factors available.
Antennas come in different form factors. Each unique design has different characteristics and is optimized for different use-cases and frequency bands. The form factor and associated connector of an antenna play an important role in determining its compatibility for a particular application. Summit offers free CAD models for all our antennas to help you with the integration process.
In addition to this there are also many ways to secure antennas to the equipment - from BNC connector mountings to magnetic securing’s and even specialist double-side tapes.
Here are some of the most common antenna types and form-factors:
Omnidirectional Antennas:
Omnidirectional (often dipole) antennas radiate electromagnetic energy approximately equally in all directions, typically creating a spherical or slightly “donut-shaped” radiation pattern. They are used in applications that require broad coverage such as Wi-Fi, Bluetooth as well as other ISM band applications including Zigbee and LoRa WAN. Internal or external variants are available.
Ceramic or Chip Antennas:
These are compact internal, small, flat, and rectangular antennas that are used in applications that require miniature or low-profile designs, such as wearables, mobile devices and wireless local area networks (WLANs). Normally these are omnidirectional.
Directional Antennas:
Directional antennas, such as beam, patch or dish antennas, concentrate electromagnetic energy in a specific direction, creating a narrow beam of coverage. They are used in applications that require a focused signal, such as point-to-point communication systems, microwave links, and radar systems.
Yagi Antennas:
Yagi antennas are directional antennas that consist of a driven element and multiple parasitic elements. They are highly directional and are used in applications that require long-range communication, such as television broadcasting and amateur radio.
Helical Antennas:
External Helical antennas are directional antennas that consist of a helical resonator and a coaxial feed. They are used in applications that require circular polarization, such as satellite communications and GPS systems.
RF Antenna Selection
In order to select the right RF Antenna please consider the following outline criteria:
Frequency Band(s):
The frequency band of operation is a critical factor in determining the type of antenna to use. Antennas are designed for specific frequency band(s), with converged antennas offering multiple “sweet spot” frequencies. Needless to say, that it is essential to choose the right antenna optimized for the desired frequency band.
Gain:
Gain is a measure of the ability of an antenna to direct its radiated energy in a specific direction. It is expressed in decibels (dB) and is the ratio of the power radiated in the desired direction to the power that would be radiated by an ‘perfect’ isotropic radiator; which is a theoretical antenna that radiates energy perfectly equally in all directions. The gain of an antenna provides an indication of how effectively the device concentrates the radiated energy in a specific direction. A higher gain means that the antenna is able to focus more energy in the desired direction, leading to a stronger signal and longer range (when orientation is possible).
Efficiency:
Efficiency is a measure of how effectively an antenna converts the input power into radiated energy. It is defined as the ratio of the output power to the input power, expressed as a percentage. Efficiency is affected by a number of factors, including the design and construction of the antenna, the materials used, and the environment in which the antenna is located. Antennas with high efficiency are able to convert more of the input power into radiated energy, leading to a stronger signal, better signal to noise ratios and hence longer ranges.
Polarization:
Polarization refers to the orientation of the electromagnetic wave with respect to the ground. Linear polarization, either horizontal or vertical, is the most common polarization for RF antennas. Circular polarization is used in applications that require improved immunity to multipath fading, for example satellite communications.
Size and Shape:
The size and shape of the antenna are crucial factors that determine its ability to fit into the desired application use-case environment. Antennas come in different shapes and sizes, from small chip antennas to large Yagi antennas.
Cost:
The cost of an antenna is an important consideration, especially for large-scale deployment. Antennas vary widely in cost, depending on the size, frequency band(s), gain, polarization, and other criteria.
Which Connectors are commonly used?
SMA Connector:
The SMA connector (male/female) is a widely used connector for antennas due to its compact size and high frequency range. It is commonly used for Wi-Fi, Bluetooth, and Zigbee applications. Watch out (below) because there are also reverse versions where the center pin is inverted!
RP-SMA Connector:
The Reverse Polarity-SMA connector (male/female) is similar to the SMA connector but has a reversed center pin polarity, which makes it less commonly used than the SMA connector. Nevertheless it can be extremely frustrating as it’s easy to order the wrong thing….(not that I have ever done that J…..)
N-Type Connector:
The N-type connector is a larger connector that provides a higher level of performance compared to SMAs. It is commonly used for microwave and millimeter-wave applications.
TNC Connector:
The TNC connector is a medium-sized connector that also provides a higher level of performance compared to SMA. It is commonly used for Wi-Fi and cellular applications.
U.FL Connector: (also called IPEX connectors)
U.FL or IPEX connectors are small, compact, and low-profile connectors that are designed to be used in tight spaces, such as in small electronic devices such as routers and laptops. They are typically used in combination with both internal or external antennas in these devices. These connectors although small are also designed to be mechanically robust and to provide a reliable connection even in harsh environments such as drop conditions.
The importance of impedance matching
Impedance is an extremely important parameter in the design and performance of an antenna. Impedance refers to the resistance that an antenna offers to the flow of electrical current. It is a complex quantity that is defined as the ratio of the voltage to the current at a particular point in the antenna. Impedance is measured in ohms and is represented by the symbol Z.
The impedance of an antenna must as closely as possibly match the impedance of the transmission line that is connected to it. For microwave and millimeter waves, this includes the “stripline” waveguide design of the PCB to/from the transceiver. Any mismatch between the impedance of the antenna and the transmission line results in reflections, power loss and waisted energy. In other words, if the impedance of the antenna is not correctly matched to the impedance of the transmission line, a part of the energy transmitted by the antenna will be reflected back into the transmission line, resulting in a reduction of the overall radiated power and decreasing the performance of the system and antenna.
In portable and wearable systems, it is especially important to minimize waisted energy hence it becomes even more critical to ensure correct antenna matching. Once again, optimal tuning results can be achieved with a VNA Vector Network Analyzer. We can support you with such analyses and test equipment. Please reach out and ask us.
Impedance also plays an important role in the stability and performance of the wireless communication system as a whole. A well-designed antenna system with a well-matched load and source impedance can provide stable and consistent performance over a wide range of operating conditions, while a poorly designed antenna system with a poorly matched impedance can result in poor performance and instability.
In conclusion, the correct selection of an RF antenna is crucial for achieving optimal performance in wireless communication systems. It is essential to consider the frequency band(s) required, gain, polarization, size and shape, and cost when selecting the best fit of antenna for your application. The impedance of an antenna must match the impedance of the transmission line that is connected to it in order to minimize reflections, power loss and waisted energy. Impedance also plays an important role in the stability and performance of the wireless communication system as a whole.
Summit’s antenna design and manufacturing strategy is based around the premise that attention to detail is important. We care about things like uniformity over different manufacturing lots as well as long life construction and consistent performance. Reliable repeatable antenna performance is essential for certification and production. We have a large and ever-evolving product range that covers all major standards (Wi-Fi, Bluetooth, LTE, GSM, Zigbee, IoT, ISM, LoRa WAN GPS, GLONASS Bands.
Want to know more? Reach out now and let us assist you with choosing the right Antenna for your application.
Summit: Innovation, quality engineering and attention to detail.