Solve Wi-Fi Interference Problems with BAW Filters

What you’ll learn:

The necessity of filters in Wi-Fi CPE access points.
How interference impacts performance.
Advantages of BAW filters over other filter technologies.

The demand for seamless and reliable Wi-Fi connectivity has surged in today's interconnected world, driven by the proliferation of smart devices and high-bandwidth applications. Wi-Fi customer premises equipment (CPE) access points (APs) ensure robust wireless communication within homes and offices (Fig. 1).

1. Wi-Fi customer premises equipment (CPE) access points (APs) help to ensure robust wireless communication within homes and offices.

However, the crowded radio-frequency (RF) spectrum and the intricacies of multi-band operations present significant challenges. On that front, bulk-acoustic-wave (BAW) filter technology has emerged as a way to boost Wi-Fi performance by mitigating interference and optimizing signal integrity.

The Necessity of Filters in Wi-Fi CPE Access Points

Modern Wi-Fi access points operate across multiple frequency bands—2.4-GHz, 5-GHz, and the newer 6-GHz spectrum—to accommodate increasing demands for high-speed internet and the growing number of connected devices. Tri-band Wi-Fi enhances network flexibility and performance by enabling multiple devices to communicate simultaneously without congestion. But, this multi-band capability also introduces a significant technical challenge: self-generated interference.

Self-generated interference occurs when strong RF signals from one band leak into adjacent bands, disrupting the operation of Wi-Fi receivers. This interference leads to receiver desensitization, meaning a stronger nearby signal compromises that receiver's ability to detect and process weak signals.

Interference between 5 GHz and the new 6-GHz band (Wi-Fi 6E) is another growing challenge. The proximity of the upper 5-GHz channels (such as channel 149 at 5.745 GHz) to lower 6-GHz channels can reduce the effective range and data rates for 6-GHz devices (Fig. 2).

Proximity of upper 5-GHz channels to lower 6-GHz channels can reduce the effective range and data rates for 6-GHz devices — 2. The proximity of the upper 5-GHz channels (such as channel 149 at 5.745 GHz) to lower 6-GHz channels can reduce the effective range and data rates for 6-GHz devices.

Multi-device environments further exacerbate this issue. Imagine a household with a smart TV streaming 4K content over 5 GHz, a laptop video conferencing on 6 GHz, and a smart-home hub connected via 2.4 GHz. Without proper filtering, the high transmit power from one band can degrade performance across the others, leading to network instability, buffering, and inconsistent speeds.

How Interference Impacts Performance

Beyond self-generated interference, Wi-Fi APs must contend with external sources of RF noise that can disrupt performance. Common sources include microwave ovens emitting interference in the 2.4-GHz range and cordless phones and baby monitors operating in the same band. Dense urban environments with multiple overlapping Wi-Fi networks further contribute to congestion. 5G cellular networks and radar systems can also introduce interference, particularly in the 5-GHz spectrum.

Since Wi-Fi receivers must detect and amplify weak signals, any external or internal interference could degrade performance, cause packet loss, and increase retransmissions. This results in slowdowns, higher latency, and poor connectivity in high-interference environments.

As Wi-Fi networks evolve to support higher data rates, increased device connectivity, and expanded frequency bands, the challenge of managing interference has become more pronounced. Interference, whether self-generated (from overlapping bands within the same device) or external (from nearby wireless sources and environmental noise), can degrade Wi-Fi performance, reducing range, throughput, and reliability.

To address these challenges, modern Wi-Fi access points integrate RF filtering solutions to block unwanted signals while preserving the integrity of desired transmissions (Fig. 3).

The Role of Filters in Mitigating Interference

Among these solutions, BAW filters have emerged as a critical technology in Wi-Fi system design. Unlike traditional filtering methods, BAW filters provide high selectivity, effectively suppressing out-of-band interference while maintaining minimal signal loss in the operational band. This precision enables Wi-Fi APs to detect and amplify weaker signals—a crucial factor in high-density environments where interference is prevalent.

One of the most significant advantages of BAW filters is their ability to support simultaneous multi-band operation. Modern Wi-Fi APs often transmit and receive signals across the 2.4-, 5-, and 6-GHz bands, all within the same hardware unit. Strong signals from one band can desensitize the receiver in another without proper filtering, leading to dropped connections, increased latency, and reduced network efficiency.

BAW filters ensure that each band operates independently, minimizing crosstalk and self-interference and allowing devices to utilize the benefits of tri-band connectivity.

In addition, BAW filters play a crucial role in regulatory compliance. In regions such as the United States, the Federal Communications Commission (FCC) imposes strict limits on out-of-band emissions to prevent interference with adjacent frequency allocations. By integrating BAW filters, Wi-Fi manufacturers can ensure that their devices operate at maximum RF output power while staying within legal limits, thereby optimizing range and performance without violating regulatory standards.

By leveraging high-performance BAW filtering technology, Wi-Fi access points can maintain signal clarity, improve network stability, and enhance overall connectivity even in challenging RF environments. Thus, BAW filters are essential in delivering the faster, more reliable Wi-Fi experience demanded by consumers and enterprises.

Advantages of BAW Filters Over Other Filter Technologies

Several key performance factors must be considered when selecting a filter to mitigate Wi-Fi band-edge interference. An ideal filter should exhibit:

Low in-band insertion loss: Ensures minimal signal attenuation, preserving transmission power and maintaining strong connectivity.
High out-of-band attenuation: Prevents unwanted signals from interfering with neighboring bands, improving spectral efficiency.
High power-handling capability: Allows the filter to function effectively under high transmission power levels, essential for long-range Wi-Fi coverage.
Low nonlinearity: Reduces distortion and maintains signal integrity, improving data rates and overall network performance.
Low temperature coefficient of frequency (TCF): Ensures stable performance across varying environmental conditions, such as temperature fluctuations.
Compact footprint: Enables integration into modern, space-constrained Wi-Fi access points and routers.
Cost-effectiveness: Balances performance with manufacturing feasibility to keep consumer and enterprise Wi-Fi equipment affordable.

Compared to surface-acoustic-wave (SAW) filters traditionally used in RF applications, BAW filters offer superior performance, particularly at higher frequencies (above 2.5 GHz). Due to increased insertion loss and reduced power-handling capabilities, SAW filters become less effective at higher frequencies. In contrast, BAW filters maintain high rejection efficiency, low loss, and greater thermal stability, making them the preferred choice for Wi-Fi 6 and Wi-Fi 6E applications.

Implementing BAW Filters in Wi-Fi System Design

The effectiveness of BAW filters depends not only on their inherent properties, but also on their strategic placement within the Wi-Fi system. The ideal positioning of a BAW filter is between the power amplifier (PA) and the switch on the transmit side. This configuration ensures maximum out-of-band rejection, prevents unwanted harmonics from interfering with other frequency bands, and minimizes overall system distortion.

In cases where integrated front-end modules (FEMs) are used, BAW filters are best placed at the common antenna port. Though such a setup improves out-of-band rejection for the entire RF path, it may also introduce additional insertion loss. This tradeoff can slightly reduce receiver sensitivity and transmit power. Designers must carefully evaluate these tradeoffs to balance filter performance, system efficiency, and end-user experience.

By adopting advanced BAW filtering solutions, Wi-Fi manufacturers can ensure that their devices operate at peak efficiency, providing seamless, interference-free connectivity in increasingly crowded RF environments. With the continued expansion of high-speed Wi-Fi applications, BAW filters will remain a critical enabler of next-generation wireless performance and reliability.

Companies like Qorvo have been at the forefront of BAW filter technology, offering solutions that address the stringent requirements of modern Wi-Fi systems. For example, the company’s edgeBoost filters are designed to improve Wi-Fi range and capacity by allowing systems to maintain maximum RF output power on all channels in the 2.4-GHz band. These filters enable operation at rated power in channels 1 and 11 without violating FCC limits, significantly enhancing performance.

Defeating Interference with BAW Filters

As Wi-Fi technology continues to evolve to meet the demands of a connected world, addressing interference challenges becomes increasingly critical. BAW filter technology offers a viable solution to mitigate both external and self-generated interference, ensuring robust and reliable Wi-Fi performance.

By integrating BAW filters into Wi-Fi CPE APs, manufacturers can enhance signal integrity, extend coverage, and improve overall network capacity, meeting the ever-growing expectations of consumers and businesses alike.