Deciphering the Engineering Challenges in Using Wi-Fi Antennas

The placement of a Wi-Fi antenna is essential for optimal performance. Antennas are sensitive to their surroundings and antenna performance can be affected by materials, RF devices, objects, and electronic devices in their proximity.

The location of an antenna can determine how well it can transmit and receive signals, its sensitivity to interference, and its overall efficiency in a wireless communication system. Proper placement can greatly enhance the wireless performance of the antenna, while poor placement can lead to weak signal strength, increased interference, and poorer functionality. It is critical to follow manufacturer guidelines and take into consideration factors such as the required ground plane, nearby components, and the overall plan of the PCB during the design phase.

If you are in any doubt, consult an expert before committing to the design-in of an antenna. Antennas are often under-appreciated in their overall effect on a device and its performance. Fixing the placement after a device design or system layout is finalized can be a costly undertaking.

There are several factors which affect Wi-Fi antenna performance:

• Frequency: Wi-Fi antennas operate in a specific frequency band, usually the 2.4, 5, or 6 GHz bands. The antenna must be designed to effectively transmit and receive signals within those frequency ranges.
• Gain: Gain measures how much an antenna amplifies a signal. The higher gain that an antenna has, the stronger signal and longer range it will provide. How much gain is required is dependent on the application and distance between the antenna and the router or access point.
• Beamwidth: Beamwidth is the angle over which the antenna transmits or receives signals. With a wider beamwidth, coverage is provided in a broader area. With a narrower beamwidth, the signal is focused in a specific direction, which increases range and reduces interference.
• Polarization: Polarization is the positioning of the electric field of a radio wave. Typically, Wi-Fi antennas use vertical polarization, but some devices may use horizontal, circular, slant, or a combination of these polarizations. The antenna must be compatible with the polarization of the receiving device.
• Impedance: Impedance refers to antenna resistance to electrical current flow. The impedance of the antenna must meet the impedance of the transceiver circuitry to enable effective signal transfer.
• Environmental Factors: An antenna needs to be able to withstand the environmental conditions it will be exposed to, such as temperature, humidity, and weather elements. 
• Cost: The cost of an antenna should be in line with the performance needs of the application.
• Size and Weight: The size and weight of an antenna can be important to consider for some applications, such as portable devices.
• Aesthetics: The appearance of the antenna can be significant for some applications, including home or office environments, or where the antenna is mounted externally on a device.
• Regulations Compliance: Antennas must comply with all applicable regulations, including regulations that govern radio frequency emissions.

As mentioned, placement is crucial so when putting a wi-fi antenna on a PCB, keep these points in mind.  

• General Placement: Wi-Fi antennas’ radiation patterns and layout of the PCB should determine the placement on the PCB.
• Avoid Interference: No components should be placed near the field around the antenna since they can interfere with antenna performance. This includes maintaining a clear “keep out” area and considering the ground plane. It’s also important to avoid placing an antenna near items that could interfere with the antenna’s radiation, including batteries, LCDs, and metal components.
• Mitigate Antenna Interaction: Distance or orientation adjustments will be needed to avoid detuning if there are other antennas nearby that are operating on similar frequencies.
• Transmission Line Design: For board mounted antennas, the RF trace carrying energy to and from the antenna needs to be designed carefully to prevent signal reflection and degradation.

Proper installation, placement and operation are critical for enabling high performance and signal strength of Wi-Fi antennas. Below is a step-by-step guide to install and operate a Wi-Fi antenna.

Installation

• Pick the Right Antenna: Choose the correct antenna type based on specific needs and requirements. Omnidirectional antennas are ideal for coverage in every direction around the antenna, while directional antennas are best suited for point-to-point communication.
• For Existing Devices, Identify the Antenna Connector Required: Find the antenna connector on your device or router.
• Attach the Antenna: Carefully fix the antenna onto the connector, creating a secure and snug fit. Overtightening should be avoided, as it could damage the connector or antenna. 
• Position the Antenna: Put the antenna in a location that has minimal obstructions, avoiding for example walls, furniture, or electronic devices. A central location is ideal for omnidirectional antennas, while directional antennas should be pointed towards the receiving device.
• Connect to the Network: Once the antenna is installed, turn on the device or router to connect to the Wi-Fi network.

Operation

• Minimize Interference: The antenna should be kept away from electromagnetic interference sources such as microwaves, cordless phones, and other electronic devices.
• Maintain Correct Orientation: Ensure directional antennas remain pointed towards the router or access point. For omnidirectional antennas, provide the correct placement so the signal radiates around the antenna, as opposed to being directed into walls, floors, or other obstructions.
• Update Firmware: Check if your router or device has firmware updates regularly. Updates could include improvements to Wi-Fi performance and antenna compatibility.
• Consider Antenna Upgrades: Consider upgrading to a different antenna that has higher gain or better directional capabilities if your wireless network needs change over time.

Below are additional considerations when working with Wi-Fi antennas.

• Antenna Diversity in Multipath Environments: Using multiple antennas or accurate antenna placement can address issues in environments where signals reflect off a variety of surfaces. Reflection causes signal nulls and multipath distortion. Diversity is critical to maximizing throughput by minimizing dropped packets.
• Signal Quality vs Signal Strength: In multipath environments, strong RF signals may still have subpar quality. Antenna diversity can sample signals from multiple inputs to determine the ideal combination of signal quality and strength.
• MIMO Configurations: The use of multiple-input multiple-output (MIMO) configurations can improve both the speed and reliability of transmissions. For instance, a 2x2 MIMO configuration can double the potential successful throughput of a router. However, this calls for the receiving devices to also support multiple data streams using multiple antennas or specific MIMO-enabled antennas.
• Minimizing Interference: Wi-Fi antennas must be able to minimize interference from other sources, including other electronic devices, natural sources of radiation, or even metal or solid objects. Especially in dense populations, this can be challenging to achieve.
• Designing Antennas to be Affordable and Easy to Manufacture: Wi-Fi antennas must be reasonably priced and easy to manufacture to be appealing for use in a variety of devices. This can be difficult to accomplish in high-performance antennas.