RF board-to-board and panel-mount connectors play a key role in wireless equipment ecosystems. These types of connectors provide the internal “plumbing” to connect functions in macro radio units (RUs) and active antenna units (AAUs) in current 4G/5G mobile wireless networks as well as future 6G mobile networks that will see broader deployments by the end of this decade. These new applications become important because demand for mobile networks in the U.S. is continuing to decline since mobile operators have nearly completed their 5G deployments in the C-Band spectrum. Demand in the European region remains sluggish due to macro-economic and political events, while other regions, such as Latin America and India, have also completed initial coverage deployments across the region and country. China is the only region to see stability as the mobile operators continue to upgrade and prepare for their 5G NR Advanced (5.5G) upgrades in 2025/2026, with these deployments charting a different course than the rest of the world. The goal of 5.5G Advanced in China is to achieve 10 Gbps downlink speeds on mobile devices using a combination of FR1 and FR2 frequency bands, along with the migration to higher-order massive MIMO (mMIMO) AAUs that support 128 and 256 radio channels in frequency bands between 4 GHz and 7 GHz.
MMIMO AAU IMPACT ON RF BOARD-TO-BOARD CONNECTORS
Figure 1 5.5G AAU demand for RF board-to-board connectors. Source: EJL Wireless Research LLC, January 2024.
Figure 2 5G AAU demand for RF board-to-board connectors. Source: EJL Wireless Research LLC, January 2024.
Figure 3 4G/5G macro RU demand for RF connectors. Source: EJL Wireless Research LLC, January 2024.
While the wireless market may be in a downturn, the development of next-generation mMIMO AAUs continues. The majority of the global regions are using 32T32R systems for their mobile networks, while the U.S. and China have focused on 64T64R systems. The introduction of mMIMO AAUs in the 6 to 7 GHz frequency bands in China and possibly in some European countries will increase the demand for RF board-to-board connectors per system by 2× to 4×.
The expectation is that the first mMIMO AAUs in the 6 to 7 GHz frequency range will start shipping by the end of 2024 with volumes entering full production in 2025. The volumes will primarily support the rollout of 5.5G networks in China. Elsewhere, the anticipation is that there will be continued softness in demand for 32T/64T AAUs. There is the potential for volume shipments in India, should Vodafone Idea secure funding and BSNL complete its 4G rollout on time.
The latest forecast from EJL Wireless has demand for RF board-to-board connectors, like SMP and SMP-MAX, that will be used to support 5.5G mMIMO AAUs exceeding one billion units by 2026. This connector forecast is based on current AAU forecasts. This forecast is shown in Figure 1.
The situation for 5G AAUs is much different, as shown in Figure 2. The latest forecast shows demand for RF board-to-board connectors declining by 20 percent from 2023 levels before reaching a bottom with a stable outlook through 2027.
The migration to multi-band RUs, globally, is negatively impacting the demand for both RF board-to-board connectors as well as panel-mount connectors and RF jumper cable connectors. For this analysis, Nex10, 4.3-10 and 7/16 DIN connectors are included in the panel-mount and RF jumper cable categories. With the migration to multi-band macro RUs, the RF power levels per channel continue to increase, requiring high-power capabilities for the RF connectors.
As an example, single-band macro RU RF power per channel has steadily increased over the past 20 years to get to the current estimate of 140 W. The current generation of multi-band macro RUs supports up to 80 W per frequency band per channel or in some cases, up to 180 W or more per RF connector port. The combined RF power output per frequency band per channel is increasing the power handling requirements for all of the RF connectors within the macro RU system. Taking these trends into account, Figure 3 represents the latest 4G/5G macro RU forecast for RF connectors, segmented by the connector types.
MMIMO AAU
So where are these millions of SMP/SMP-MAX connectors being used? This section illustrates the different subsystems within an mMIMO AAU design that require the SMP/SMP-MAX connectors. In the traditional AAU architecture that uses separate multi-channel RF cavity filters, the SMP/SMP-MAX surface-mount male connectors are typically used on the main TRx printed circuit board (PCB) and the antenna/combiner PCB. The SMP/SMP-MAX female-to-female barrel connectors are used to connect the input/output of the RF TRx to one port of the cavity filter and to connect the cavity filter to the antenna/combiner PCB. Additionally, there are typically screw-in type SMP male connectors used on the RF cavity filters instead of the surface-mount versions used on the PCBs. Table 1 shows the location, type and quantity of the SMP/SMP-MAX connectors.
A total of six RF SMP/SMP-MAX connectors are needed for each TRx channel. Additionally, each antenna array typically requires two sets of SMP/SMP-MAX connectors for the calibration circuits. One set of connectors is defined as 2× male + 1× female-to-female barrel. It is easy to see how quickly the quantity increases. A 64T64R mMIMO AAU requires 390 of these RF connectors per system. A side view drawing of a traditional mMIMO board assembly with cavity filters, showing the location and functionality of these SMP/SMP-MAX connectors is shown in Figure 4.
Figure 4 Connector location in mMIMO architecture with cavity RF filters. Source: EJL Wireless Research LLC, January 2024.
The newer AAU architectures that use surface-mount ceramic waveguide RF filters eliminate the male screw-in type RF connectors for the RF filter as well as one of the female-to-female barrel connectors. A total of three RF SMP/SMP-MAX connectors are needed for each TRx channel. Additionally, each antenna array still requires two sets of SMP/SMP-MAX connectors for the calibration circuits. The elimination of the RF cavity filters does not impact the requirements for the antenna calibration circuits. Table 2 shows the connector requirements for the new AAU architectures.
A 64T64R mMIMO AAU using this newer architecture would require only 198 of these RF connectors per system instead of the 390 connectors required in the older design. This represents a reduction of nearly 50 percent in the total number of RF connectors required per system. Figure 5 shows a cutaway view and the location of the SMP/SMP-MAX connectors in this new AAU architecture.
Figure 5 New mMIMO architecture with ceramic waveguide RF filters. Source: EJL Wireless Research LLC, January 2024.
While the selling price of each connector is low, the number of connectors per system and the number of systems that are expected to be deployed make this an interesting opportunity. Figure 6 shows an SMP male surface-mount connector on the TRx PCB. Figure 7 shows an SMP male surface-mount connector with a female-to-female SMP barrel connector inserted on a TRx PCB.
Figure 6 SMP male connector. Source: EJL Wireless Research LLC, January 2024
Figure 7 SMP male connector with SMP female-to-female barrel connector. Source: EJL Wireless Research LLC, January 2024.
MACROCELL RU
Current macro RU architectures shipping into the market today rely on SMP/SMP-MAX connectors to interface between the radio TRx PCB and the RF cavity filter. The frequency-division duplex (FDD) types of macro RUs have separate interfaces for the transmit (Tx) and receive (Rx) paths on the PCB. In some architectures, a diversity Rx may be used, which would increase the number of Rx paths by 2×, thus requiring more connectors.
