"This knowledge is not too cold" Understanding antenna multiplexers

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"This knowledge is not too cold" Understanding antenna multiplexers [Copy link]

Manufacturers today face an important architectural decision. They can try to add more antennas into ever-shrinking device areas, but this can potentially degrade antenna performance, impacting the overall performance of the device. Alternatively, they can choose to use a new alternative: antenna multiplexers, which reduce the need to add antennas and meet coexistence filtering and insertion loss requirements.

In this chapter, you will learn how antenna duplexers can achieve more functionality with fewer antennas and understand the advantages of using them in many wireless applications.

Why Today’s Devices Require Antenna Duplexers

Let’s go back to Figure 7 from Understanding RF Front Ends and Filters, which shows the difference between an antenna splitter and a multiplexer. Note that the antenna splitter is used close to the antenna to reduce complexity, while the multiplexer is closer to the RF front end (RFFE), near the power amplifier (PA).

Antenna duplexers address a key challenge facing wireless manufacturers of 5G systems: how to cope with the dramatic increase in radio frequency (RF) complexity as industrial design evolves and available antenna area continues to shrink. By leveraging antenna duplexers, manufacturers can use fewer antennas to meet new 5G frequency bands, 4x4 multiple-input/multiple-output (MIMO), diversity capabilities and other new requirements without compromising existing form factors or functionality.

Antenna duplexer filters play a key role in reducing design complexity and facilitating coexistence in mobile device Wi-Fi applications. They also help provide high isolation, helping to reduce isolation parameters in antenna design and allowing the use of lower cost antennas. In this way, RFFE isolation parameters no longer need to be completely dependent on the antenna. This can reduce the cost of antennas and shielding by up to 20%.

The addition of new cellular and non-cellular frequency bands increases the total number of radio frequency (RF) paths in all wireless electronic devices, including smartphones, cars, Wi-Fi gateways, etc. For example, a typical 5G smartphone (supporting millimeter wave (mmWave) and ultra-wideband (UWB) bands) has twice the number of RF paths as a traditional 4G phone. Many mobile phones today require six or more antennas to use the main cell and various receive functions. Each RF path needs to be connected to an antenna, but doubling the number of antennas is simply not possible due to the limited space available.

Furthermore, increasing the number of antennas means they must be placed closer together, which reduces the isolation between the antennas. This can lead to coupling-related issues, increasing the likelihood of nonlinear elements in the RF front end (RFFE), which can desensitize the receiver.

Figure 1 shows several frequency bands; note how closely these bands fit into each other. For example, Wi-Fi 2.4 GHz and GPS L5 both fall between the low-band and mid- and high-band cellular bands.

Figure 1: Multiple frequency bands used in smartphone devices

Antenna multiplexers help these individual frequency bands coexist with each other. It allows a large bandwidth to be transmitted through a single antenna, reducing the complexity of using antennas for engineers. The antenna multiplexer then divides this large bandwidth into multiple bands. Without antenna multiplexers, more antennas and switches would be required.

Antenna duplexers play a key role in separating individual low, mid, and high cellular band, Wi-Fi, and GPS (L5, L1) signals while helping to eliminate interference and reduce system losses. In Figure 2, the top smartphone image shows that there are many individual filters on the antenna. In addition, there are three antennas in the upper left image. The bottom smartphone image shows how using an antenna duplexer in this design can help reduce complexity, component count, and size. As shown in the lower left figure, by using an antenna duplexer, you can reduce the number of antennas from 3 to 1, and the number of components from 4 to 1. In addition, as shown in the lower right figure, adding an antenna duplexer can reduce the number of components from 4 to 2. This proves that antenna duplexers can make it easier for system engineers to build designs.

Figure 2: Smartphone with and without antenna duplexer solution

Antenna duplexers offer many advantages to system and module designers. Not only does it reduce the number of antennas required, it also maximizes performance while reducing system-level desensitization. It also helps increase design flexibility to support changes in architecture and industrial design. By using antenna duplexers, devices such as smartphones can use existing antenna area more efficiently while adding support for new frequency bands without any impact on existing form factors or functionality.

Learn more about antenna duplexer technology

Now that you understand why you would use an antenna duplexer, let’s look at how it is used. You will learn about the types of antenna duplexers and isolation.

Understanding the Types of Antenna Duplexers

Figure 3 shows several antenna duplexer versions, all using a single shared antenna. For example, the triplexer shown in the upper right corner of the figure splits Wi-Fi, mid-band, and UHF transmissions to one antenna while providing the out-of-band (OOB) suppression required for optimal coexistence. The remaining two antenna duplexers in Figure 3 perform similar functions but are implemented by addressing cellular, Wi-Fi, and global navigation satellite systems (GNSS) in the system. However, a variety of antenna duplexer filter combinations can be implemented.

Figure 3: Some examples of antenna multiplexers

Understanding Antenna Multiplexer Isolation

Like multiplexers, antenna duplexers also need to provide high isolation between filters and frequency bands, as shown in Figure 4. The figure shows the global positioning L5 and GNSS filters measuring isolation in this antenna duplexer.

Figure 4: Antenna multiplexer isolation measurement

The figure on the right shows the signal isolation level between two filters integrated in the same package design. Generally, antenna duplexers based on acoustic wave filters have the best performance because they integrate low insertion loss, address OOB suppression for multi-band coexistence, and high isolation between RF frequencies of shared antennas. They also support ultra-high frequencies for 5G, Wi-Fi, and UWB.