The arrival of 5G is proving to be the latest disruptor in the RF/microwave industry, leading to an exciting new wave of RF connector innovation. Addressing the challenge of 5G’s requirements, Rosenberger has developed the Efficient Board Connector (EBC®), a new generation board-to-board and board-to-module RF interconnection system. EBC is a low-cost, single design approach for multiple high performance applications, fully optimized and future-proofed for 5G.
The original push on, subminiature connector (SMP) comprised a blind-mate adapter, or bullet, housed between two printed circuit boards (PCB) or panel-mounted receptacles. It gave designers better electrical performance, faster installation and higher density for high frequency applications. In recent years, largely driven by the mobile telecom market’s need for miniaturization, board-to-board and board-to-module connections have become increasingly popular. Able to handle higher power while saving space and weight, these lower cost board-to-board interconnects are replacing RF cable assemblies.
5G is accelerating this trend, adding design challenges for RF connectors:
Massive MIMO - For high data density locations, base stations will use massive MIMO active antennas with 32, 64 or 128 elements. Currently, the concepts integrate sandwiches of several boards with large numbers of board-to-board connections to interconnect the RF transmit and receive circuitry with the antenna array - at least one interconnect for each antenna element. With this added volume, cost will be critical.
Higher Frequency Operation - With the increasing data rates being sent and received, radio access networks (RAN) will add more and higher bands at sub-6 GHz frequencies, as well as mmWave bands extending above 40 GHz. RF connectors must maintain superior performance at frequencies increase.
Constrained Space - Increasing the data capacity of the RAN will lead to a greater density of base stations, with smaller size and weight to be deployed throughout a city. To accommodate these size constraints, the RF interconnects must have small diameter connectors capable of high mating cycles.
VSWR and EMC - Inherently, board-to-board stacking applications have the potential for connector misalignment, which can create an inductive path degrading VSWR if the characteristic geometry of the contact surfaces is altered. The connector design includes the requirement of EMC optimization to avoid poor performance or harmful emissions.
Universal Board-to-Board Connection - In addition to providing a long-term solution to miniaturize high frequency connections, the interconnects must also address the low frequency, high density interface requirements. The interconnect must accommodate sufficient axial float without significantly affecting VSWR. A bullet interface design withstands dimensional changes or misalignment without significantly affecting the character of the transition contact surface, minimizing the effect on signals passing through the connector.
Design to Cost - All of these factors present design engineering challenges to achieve the required RF performance. At the same time, the production cost of the interconnect is under enormous pressure, as it represents a significant financial element of the system. Despite the larger number of antenna elements used in 5G, highly competitive market forces dictate that component costs need to remain the same, preferably lower. To achieve these cost targets, design to cost production methods must be implemented from the beginning of all product design and development.
FUTURE PROOF 5G CONNECTIVITY
As a leading RF connector manufacturer, Rosenberger has developed innovative RF connection solutions. Rosenberger’s new low-cost, high performance EBC enables operators, network equipment manufacturers and component suppliers to meet the interconnect challenges driven by 5G, including:
- The same connector components on both sides of the PCB
- Spring-loaded parts on the PCB
- Simpler and lower cost adaptors
- High volume production
EBC is a new generation universal RF board-to-board, board-to-module adaptor which provides a single design solution for many applications (see Figure 1). Its one-size-fits-all design addresses the mobile industry’s requirement for RF connectors to be easily and readily deployable in various configurations. The EBC integrates both limited detent and smooth bore interfaces in a single bullet, accommodating all the benefits of the most common board-to-board and board-to-module high frequency connections, including SMP, LW-SMP and P-SMP.
Essential characteristics include equalization of radial and axial misalignments; different holding forces; minimum PCB board spacing; and fast, cost-effective assembly. A key mechanical design feature is the locating side, which is integrated in the bullet. One side has a smooth bore, while the other has a limited detent design. The EBC supports a minimum board-to-board distance of 12 mm and a minimum on-board pitch of 6.8 mm. The axial and radial tolerances are ±0.8 mm and 4 degrees, respectively.
With a DC to 8 GHz frequency range, the EBC addresses 5G’s sub-6 GHz bands, supporting both small cell and massive MIMO base stations. Return loss is specified to be 20 dB or better and is typically 30 dB to 6 GHz (see Figure 2). Screening attenuation, a measure of shielding, is specified to be greater than 50 dB to 4 GHz and typically measures greater than 60 dB (see Figure 3). Power handling is 100 W.
RF board-to-board and board-to-module connector systems will play a key role in the 5G RAN. With the newly launched, low-cost EBC connector system, Rosenberger offers board-to-board and board-to-module RF interconnection a new level of performance for the sub-6 GHz 5G bands, with impedance control and ease of installation. It features a universal bullet design suited to multiple applications, which will simplify the design and reduce the cost of complex 5G RANs being rolled out by mobile operators.