Capacitors are Key Design Components for 5G Telecommunications Infrastructure

Since before its rollout began in 2018, 5^th Generation (5G) cellular radio frequency (RF) communication protocols have promised orders of magnitude improvements in the way individual users, industrial machines, and cloud computing servers send and receive data. The 5G standard, as established by the 3rd Generation Partnership Project (3GPP) to align with the International Mobile Telecommunications-2020 (IMT-2020) requirements, calls for data rates up to 10 Gbps, 10 to 100 times faster than the previous 4G standards. It also calls for a thousand times greater bandwidth per unit area, permitting up to 100 times more devices to connect in that area compared to 4G LTE protocols. At the same time, they insist on 99.999% network availability and lower energy usage for both network base stations and connected devices.

By mid-2025, there were over 2.25 billion 5G connections worldwide, including over 182 million in North America. Network architects are shifting to standalone (SA) equipment that supports only 5G frequencies and protocols, offering faster upload and download speeds, as well as support for advanced Industrial Internet of Things (IIoT) and machine-to-machine (M2M) communication, with network latency as low as 1 ms.

The development of new equipment to build 5G infrastructure has boosted demand for electronic components of all types, including the ubiquitous capacitor. In 5G applications, capacitors filter out undesirable frequencies and remove RF interference, pair with inductors to tune antennas, decouple power rails to stabilize voltage levels, and balance antenna connections, among other functions. Engineers designing 5G-enabled devices and cellular base stations must choose capacitors that meet the performance, size, and cost requirements of each application.

Capacitors for 5G antenna applications

Antennas for 5G infrastructure support three bands in the higher RF region: low band under 2 GHz, mid band from 2 GHz to 6 GHz, and high band from 24 GHz to 100 GHz. Multi-layer ceramic capacitors (MLCCs) pair with inductors to form antenna oscillators that can tune into specific radio frequencies. Capacitors for 5G infrastructure must be able to handle the protocol’s higher frequencies (Figure 1).

Figure 1: MLCCs are used across the spectrum of RF communication. Engineers must choose their capacitors carefully to manage the higher RF currents used by 5G infrastructure. (Image source: KEMET Corporation)

One such capacitor line is the HiQ-CBR series (Figure 2) from KEMET. Components in this series have capacitance values from 0.1 pF to 100 pF, and they are designed for long-term operation at frequencies from 1 MHz to 50 GHz, without overheating or loss of capacitive properties. Because HiQ-CBR capacitors use a Class I dielectric, they can operate at temperatures from -55°C to +125°C with capacitance changes of less than ±30 ppm/°C. Capacitor performance is also stable over the range of DC voltages from 6.3 V to 500 V and does not experience aging over time.

Figure 2: HiQ-CBR capacitors are MLCCs designed to facilitate the higher frequencies used by 5G infrastructure. A Class I ceramic dielectric pairs with base metal conductors and end caps finished in matte tin in the surface mount devices (SMDs). (Image source: KEMET Corporation)

HiQ-CBR capacitors consist of several layers of base metal electrodes (Figure 3)—in this case copper—separated by and embedded in a ceramic—in this case CaZrO₃, a Class I, C0G dielectric. Metal end caps provide an electrical connection to the electrodes and facilitate soldering this surface-mount device (SMD) onto the printed circuit board (PCB).

Figure 3: MLCCs, like those in the HiQ-CBR series, have layers of internal electrodes embedded in a ceramic dielectric with metallic connections at the end caps. (Image source: KEMET Corporation)

The materials and construction of HiQ-CBR capacitors give them low-loss performance, as denoted by the quality factor Q, which is the inverse of the dissipation factor (DF). HiQ-CBR capacitors with capacitance values of 30 pF or more have a Q greater than or equal to 1,000 when tested at 1 MHz ±100 kHz and 1.0 ±0.2 V_RMS. For capacitors in this product line with lower capacitance, Q = 400 + 20C, where C is the capacitance value.

Engineers designing electronics for high-frequency RF applications also look for capacitors with low equivalent series resistance (ESR) and low equivalent series inductance (ESL), which contribute to a high self-resonant frequency (SRF). SRF is the frequency at which resonance in the capacitor will cause it to lose its capacitance and act as an inductor, so SRF needs to be well above the operating frequency. HiQ-CBR capacitors have SRFs ranging from 600 MHz for 100 pF capacitors to 12,000 MHz for 0.1 pF capacitors.

HiQ-CBR capacitors are designed to be soldered onto standard PCBs using the matte tin finish on their end caps. They are available in common case sizes including 0201 (0.2" by 0.1"), 0402 (0.4" by 0.2"), 0603 (0.6" by 0.3"), and 0805 (0.8" by 0.5"). They are certified lead-free and are RoHS compliant.

Capacitors with the performance characteristics and form factors available in the HiQ-CBR series work well in 5G cellular base stations and telecommunications networks along with RF power amplifiers (PA), wireless local area networks (LANs), global positioning system (GPS) networks, and Bluetooth communications. These capacitors are also found in signal-processing operations like DC blocking, filtering, impedance matching, coupling, and bypass.

To reduce interference and signal noise, designers may add a product like KEMET’s FLEX SUPPRESSOR® for Wi-Fi Band and 5G. This polymer-metal composite in sheet or roll form (Figure 4) contains micron-sized magnetic powder dispersed throughout the flexible polymer base to suppress electromagnetic waves or resonance, improve magnetic flux convergence, or reduce the noise generated by electronic devices at frequencies in the 5G bands, from 3 GHz to 40 GHz.

Figure 4: FLEX SUPPRESSOR® for Wi-Fi Band and 5G is a flexible polymer blended with magnetic powders on the micron scale. Users can cut the sheets to size to reduce electromagnetic resonance or encourage magnetic flux convergence. (Image source: KEMET Corporation)

Capacitors for 5G infrastructure beyond oscillators

Capacitors are also found in many other 5G infrastructure applications like DC/DC converters, power-loss protection, solid-state drives, routers, and switches. Polymer electrolytic capacitors, known for their high capacitance values, and metallized film capacitors, which can handle ripple currents, perform better or with higher volumetric efficiency than MLCCs in certain applications.

One type of polymer electrolytic capacitor is KEMET’s T523 series (Figure 5). In these capacitors, a tantalum core, the anode, is surrounded by a tantalum pentoxide (Ta₂O₅) dielectric layer, then by a layer of conductive polymer electrolyte also containing tantalum. This layer, combined with a carbon third layer and a fourth layer of silver, forms the cathode.

Figure 5: The T523 polymer electrolytic capacitors have a tantalum anode and a tantalum-polymer electrolyte forming part of the cathode. The molded epoxy case attaches to PCBs via surface mount technology (SMT). (Image source: KEMET Corporation)

The T523 series capacitors have capacitance values ranging from 47 µF to 1,000 µF, which are stable over their rated voltage of 6.3 V to 35 V. Their ESRs are considered low at 30 mΩ to 100 mΩ, contributing to this stability, up to their rated frequency of 1 MHz.

Polymer electrolyte technology is also found in KEMET’s A798 series polymer aluminum organic capacitors (Figure 6). These capacitors use a solid conductive polymer cathode paired with an aluminum anode to achieve a capacitance of 470 µF that’s stable over operating voltages from 2 V to 2.5 V. ESRs for these capacitors range from 3 mΩ to 9 mΩ, with the lowest ESR values occurring when capacitance peaks at frequencies around 100 kHz.

Figure 6: The A798 series polymer electrolytic capacitors have an aluminum anode and an aluminum polymer cathode. The resulting capacitors have excellent temperature stability and high capacitance. (Image source: KEMET Corporation)

Like MLCCs, both of these capacitor types are rated to operate from -55°C to +125°C. However, unlike MLCCs, polymer-based capacitors have a finite operating life based on operating temperature and humidity. T523 capacitors are rated for 2,000 hours at their rated voltage and +85°C, while A798 capacitors have lasted over 5,500 hours at +125°C at their rated voltage when formulated for extended life. Both types of capacitors would be expected to last 10 years or longer at the rated voltage for temperatures below +85°C.

Both polymer electrolyte lines work with SMT and come in similar sizes with lengths from 0.138" to 0.287", widths from 0.110" to 0.236", and heights from 0.043" to 0.110" Capable of capacitances several orders of magnitude higher than those achievable with MLCCs, these polymer electrolytic capacitors have high volumetric efficiency. In applications that can use them, polymer electrolytic capacitors can supply the same or higher capacitance in a smaller footprint compared with MLCCs.

Another type of capacitor that is frequently used in DC/DC converters is the metallized film pulse capacitor (Figure 7), which operates electrostatically rather than electrolytically. These capacitors consist of layers of non-conductive polypropylene film dielectric, either coated with metal on one side, interspersed with metal-coated polyester, or layered with metallic foil.

Figure 7: Metallized film capacitors typically attach to PCBs with through-hole technology (THT). Their low dissipation factors allow them to manage high dv/dt applications and ripple currents in power conversion. (Image source: KEMET Corporation)

The metallized film pulse capacitors available from KEMET come in a wide range of sizes and properties to fit into many 5G infrastructure applications. Engineers can choose a product by capacitance between 40 pF and 100 µF and by DC voltage between 100 V and 2,500 V (Figure 8). ESRs for this type of capacitor range from 0.5 mΩ to 6.366 Ω.

Their footprint can be as small as 0.283" by 0.098" or as large as 1.634" by 1.181" Most metallized film pulse capacitors attach to PCBs through holes, so they have a slightly higher profile of 0.236" to 1.776".

Figure 8: Metallized film capacitors have a polypropylene film dielectric interlayered with metal. These capacitors typically attach to PCBs with THT. (Image source: KEMET Corporation)

Conclusion

The design of 5G telecommunications infrastructure presents challenges to equal its promised benefits. Capacitors of all types, from MLCCs that have low capacitance for high frequencies to polymer electrolytic capacitors with orders of magnitude greater capacitance, to metallized film capacitors that withstand changes in voltage and ripple currents, have roles to play in the 5G infrastructure of today and tomorrow.