How to protect 5G macro base station amplifiers and antennas from electrical hazards

This article takes an in-depth look at protecting 5G macro base station tower amplifiers and advanced antenna systems from electrical hazards.

5G, the next generation of cellular communications, will deliver higher speeds, greater consistency, and lower latency.

Fifth-generation mobile networks are expected to have the capacity to communicate between 1 million devices/km2, which is 10 times higher than 4G technology.

Advances in 5G can enhance consumer experiences and facilitate emerging technologies such as:

Self-driving cars

Smart Home/City

Automated Factory

Agricultural technology progress

While these are just a few of the areas where 5G will have an impact, it is all highly dependent on data centers and the base stations that support communications.

The reliability of infrastructure equipment is critical to the successful adoption of 5G networks.

Electronic design engineers need to protect their 5G infrastructure designs by developing circuits to prevent five electrical hazards that can impact the reliability and lifespan of their equipment.

These sources of danger are:

Surge caused by lightning

Transient voltage surges caused by switching of large inductive loads caused by motors

Electrostatic Discharge (ESD)

Current overload

Short Circuit

This article describes macro base stations in detail and provides recommendations for protecting base station circuits, tower amplifiers and advanced antenna systems from sources of electrical hazards.

Macro Base Station

Base stations connect the core network to personal cell phones and other wireless devices such as watches, tablets, and IoT devices through transmission and reception. Baseband information is modulated and transmitted to mobile devices; and mobile device transmissions are received, demodulated, and transmitted to the wired infrastructure.

Macro base stations are tall towers that range in height from 50 ft to 200 ft. They are usually visible structures and are strategically located to maximize coverage in a geographic area.

A base station must connect to all wireless devices attempting to communicate with the base station within the coverage area it serves.

5G base stations contain advanced active antenna systems consisting of multiple antennas configured using Multiple-Input Multiple-Output (MIMO) technology.

Advanced active antennas provide increased transmit/receive capacity, faster data rates, and more efficient RF power transmission.

Figure 1 shows all the elements that make up a base station, along with the recommended protection, control, and sensing components to protect and improve the efficiency of the base station circuits.

Figure 1. Macro base station with advanced antenna array

Figure 2 shows a block diagram of the base station circuit.

Figure 2. Macro base station block diagram

Protection components inside a surge protector

Surge protection devices are connected to the AC power lines and are subject to transients inherent in the AC power lines.

It is recommended to install a surge suppression fuse at the input of the surge protection circuit. This type of fuse can withstand lightning surges up to 200 kA according to transient surges defined in UL 1449 and IEC 61000-4-5. The fuse can also provide current limiting protection under short-circuit conditions.

After the surge suppression fuse, consider using a series combination of a metal oxide varistor (MOV) and a gas discharge tube (GDT) to absorb lightning strikes and other large transients caused by load changes that occur on the power line.

Place the MOV-GDT combination as close to the input as possible to minimize transient propagation into the circuit.

Connect the MOV between line and neutral and connect the gas discharge device from neutral to ground.

Additionally, high-power transient voltage suppressor (TVS) diodes can replace MOVs if the TVS diode's maximum surge handling capability is sufficient for the AC power line feed. TVS diodes have faster response times and clamp transients at lower voltages.

Protecting tower mounted amplifiers

Tower amplifiers are exposed to outdoor environments and require lightning and ESD protection.

The circuit should have an in-line fuse to protect against current overloads and a parallel TVS diode to absorb lightning or ESD transients.

High power TVS diodes can safely absorb current overloads up to 10 kA. When space constraints are critical, these components are available in surface mount packages.

Protecting Advanced Antenna Systems

As shown in Figure 3, the Advanced Antenna System (AAS) receives and transmits information, audio communications, and data communications from mobile wireless devices in a geographic cell.

Figure 3. High-level antenna system block diagram

Digital data packets from the baseband unit are converted to analog data and up-converted for RF transmission. Received RF signals are down-converted and digitized for transmission to the baseband unit.

Power input circuit

The power input circuit provides DC power to other AAS circuits.

At the input stage, it is recommended to use a fuse for overcurrent protection. For this DC circuit, a fast-acting fuse is a suitable choice. Surface mount fast-acting versions are available for space-saving applications.

Consider connecting an MOV and a gas discharge tube in series to protect the front end of the power input circuit from transients passing through the SPD as well as the power and battery backup circuits.

Since the power input powers all other circuits, consider using TVS diodes downstream of the power input circuit to protect these circuits from transients and ESD. TVS diodes have lower clamping voltages than MOVs, so lower voltage-rated (and lower-cost) components can be used in downstream circuits.

Ethernet and RS-232 or RS-485 communication circuits

To protect the integrity of the communication ports, use transient protection with a crowbar protection assembly.

If you are using a Power over Ethernet (PoE) communications link, consider using a protection thyristor, such as the assembly shown in Figure 4, which protects both data lines from ESD strikes.

Figure 4. Two-wire protection thyristor for protecting Power over Ethernet circuits. Figure 4a. Schematic diagram of a two-wire assembly with a protection thyristor on each wire. Figure 4b. IV curve of a protection thyristor

Another protection solution is to use TVS diode arrays and gas discharge tubes.

Figure 5 shows an example two-line TVS diode array.

Figure 5. Two-wire TVS diode array with parallel Zener diodes

Compared to protection thyristors, this device uses a Zener diode to clamp transients, thereby eliminating transients. Look for low-capacitance versions of these components to minimize the impact on data transmission quality. If the protocol is PoE, include a fuse to protect the Ethernet circuit from overloads caused by crossed wires connected to the circuit.

For RS-232 or RS-485 interfaces, consider using a combination of protection thyristors and gas discharge tubes for transient protection. For current overload and across-the-line protection, consider using resettable polymer positive temperature coefficient fuses for increased design flexibility.

In Part 2 of this series, we will discuss the circuit protection design requirements for 5G baseband processor units, network controllers, RF front-end power amplifiers, and supporting power supplies and battery backup systems.