Tackling Radio Frequency Communication Hurdles via Gallium Nitride-on-Silicon Carbide Power Amplifiers
Exploring the Role of GaN-on-SiC Power Amplifiers in Overcoming RF Application Challenges in 5G and Beyond
This article delves into the intricate challenges presented by RF applications including 5G, satellite communications, and the aerospace and defense sectors, while discussing the advantages brought by using GaN-on-SiC power amplifiers.
The piece is a collaboration with Bodo's Power Systems and is featured as exclusive digital content on EEPower.
In the realm of RF systems, power amplifiers are critical for ensuring linear, high-efficiency, and considerable output power. RF systems are increasingly adopting complex modulation formats such as 64/128/256 QAM, necessitating PAs that can maintain high linearity and efficiency amidst compact spaces and under robust peak-to-average power ratios (PAPR). Addressing this, the emerging range of Gallium Nitride on Silicon Carbide Monolithic Microwave Integrated Circuit (MMIC) power amplifiers stand out for their superior power density, enabling them to produce high linear output power alongside impressive efficiency levels.
Figure 1. Applications of millimeter-wave 5G.
Prospects and Impediments for RF Power Amplifiers in Modern Communication
Satellite communications and burgeoning 5G networks represent significant opportunities and hurdles for the evolution of RF power amplifiers. Privatization efforts, endorsed by NASA, have seen a surge in the number of low-Earth-orbit (LEO) satellites, which are instrumental in providing an array of services such as broadband Internet, navigational aids, maritime monitoring, remote sensing, and more. These RF-driven services are in constant pursuit of gains in size, weight, power, and cost (SWaP-C). Modern communication trends are moving away from bulky dish antennas toward compact phased array antennas for satellite links, necessitating power amplifiers that are not only smaller and lighter but also deliver robust, efficient RF power. Such characteristics, including high linearity with strong P1dB and IP3 performance, are critical in minimizing distortion and power consumption, which are pivotal for these applications.
The Advent of Millimeter-Wave 5G Communications
The latest wave of millimeter-wave 5G technologies is revolutionizing communication with unparalleled speed, expansive bandwidth, and significantly reduced latency, enhancing the capacity for immediate data sharing and bolstering military operations. While early iterations of 5G within sub-6 GHz bands were prone to high-power signal jamming, the adoption of millimeter-wave frequencies (24 GHz and above) presents a strategic advantage, shielding these networks from such vulnerabilities. This advance in technology is poised to transform both combat and support roles with applications ranging from sensor-laden battlefield networks to augmented reality interfaces, improving command decisions and tactical awareness for service members. Beyond military uses, 5G's promise extends to controlling remote vehicles for various missions and supporting efficient logistics, healthcare, and transport in non-combat settings.
Diverse 5G mmWave Spectrum Allocation
Around the globe, 5G mmWave frequencies vary. In the U.S., the 28 GHz band led the deployment, succeeded by the 39 GHz. Meanwhile, China has commenced 5G mmWave implementation within the 24.25 – 27.5 GHz range, though its adoption of 5G mmWave technologies as a whole has been relatively slower.
Figure 2. 5G mmWave frequency bands globally.
The Structure of 5G Wireless Networks
5G networks blend the use of expansive macro base stations with compact small cell technology. These macro base stations maintain connectivity to the core network by employing mmWave backhaul channels or fiber optic cables. They have the capability to communicate with both user equipment such as cell phones directly or through small cells which play a crucial role in delivering last-mile connectivity. Picocells and femtocells are essential for enhancing network coverage and capacity within indoor environments like office complexes, especially in areas with weak signals or high user concentrations.
Femtocells have been designed for domestic or small-scale commercial use, aimed at bolstering signal strength in limited areas like home offices or specific zones within larger structures that suffer from poor connectivity. These devices are end-user installable, support a small number of users usually up to four or five, and typically handle a limited quantity of concurrent calls with a transmission power capped at roughly 0.2 watts.
On the other hand, picocells are engineered for larger spaces and can support approximately 100 users, extending coverage up to 300 meters. Picocells are particularly useful in indoor venues where wireless reception needs reinforcement, such as specific floors in office buildings or particular sections of retail environments. They can be set up temporarily to accommodate expected surges in demand, like at sporting events, or embedded permanently within mobile networks where they complement macro cells in a heterogeneous network configuration, ensuring seamless connectivity for end-users. Picocells emit a higher power output, which can be as much as 2 watts.
Macro base stations are designed to provide coverage across vast areas exceeding 1 km and are equipped with a significant power output that can reach beyond 100 watts, thus serving as the backbone of extensive 5G network coverage.
| Type | Output Power | Distance |
| Femto Cell | 10 mW to 200 mW | 10 m to 50 m |
| Pico Cell | 200 mW to 2 W | 50 m to 300 m |
| Macro Base Station | 10 W to >100 W | >1 km |
Figure 3. 5G network architecture comprising small cells and macro base station.
Radar Communications
Radar systems operate in the 1 gigahertz (GHz) to 2 GHz L band for applications including “identify friend or foe,” distance-measuring equipment, and tracking and surveillance. S-band (2 GHz to 4 GHz) is used for selective response Mode S applications and weather radar systems. X Band (8 GHz to 12 GHz) is used for weather and aircraft radar, while C Band (4 GHz to 8 GHz) is used for 5G and other sub-7 GHz communications applications. 5G mmWave provides the highest bandwidths and data rates, operating in 24 GHz and higher frequency bands. Satellite communications for LEO and geosynchronous communication operate in the K band, spanning 12 GHz to 40 GHz.
Figure 4. Marine Radar communication uses frequencies in the S-band, L-band, C-band, and X-band up to Ku/Ka-band. Image used courtesy of Bodo’s Power Systems [PDF]
RF Beamforming
Different types of phased array beamforming architectures used in these RF applications are:
- Analog
- Digital
- Hybrid
Analog Beamforming
For any phased array, the ideal separation between elements is wavelength lambda by 2.
Figure 5 shows analog beamforming. There are four phased array elements separated by wavelength lambda by 2. For a 30 GHz signal, there will be a 5 mm separation between phased array elements. In analog beam forming, the phase shifter does the beam forming by changing phase to do constructive interference for receiving and transmitting the signal by focusing the energy from the beam in a particular direction. This is all done at RF frequency; hence, it is most sensitive to interconnect losses. Then, the signal from the phase shifter goes to the power combiner/splitter, followed by the down converter and ADC/DAC to the baseband. In this case, only one digital front end exists for N-phased array elements. As seen in Figure 5, there is only one digital front end comprising ADC/DAC for four phased array elements. The benefit of this architecture is the smallest number of components and lowest power dissipation. However, as the phase shifting is done in RF bands, this beamforming architecture is most sensitive to interconnect losses and complexity in phase shifting.
Figure 5. Block diagram of analog beamforming with four-phased array elements.
Digital Beamforming
Digital beamforming has traditional up-down conversion to the baseband band frequency, and digital phase shifting is done. This architecture provides more precision as digital beamforming is done in the baseband. However, there is ADC/DAC for each phased array element, resulting in many components and high-power dissipation. In this case, for N phased array elements, there are N digital front ends. Figure 6 shows four digital front ends comprise ADC/DACs for four phased array elements.
Figure 6. Block diagram of digital beamforming with four phased array elements.
Hybrid Beamforming
Hybrid beamforming combining digital and analog beamforming is optimal for larger phased arrays to get the efficiency of analog beamforming with fewer elements, power dissipation, and precision of digital beamforming. Figure 7 shows two digital front ends comprise ADC/DAC for four phased array elements. Compared with analog beamforming, there was only a single digital front-end ADC/DAC; with digital beamforming, there were four digital front-end ADC/DACs.
Figure 7. Block diagram of hybrid beamforming with four phased array elements.
RF Signal Chain
Figure 8 shows the RF signal chain block diagram. At the receiver, the RF signal comes in through the antenna, goes through a limiter diode, followed by a switch, and the desired RF frequency is selected through the saw filters. The desired signal is then amplified through the low noise amplifier with an extremely low noise figure to minimize degradation in the signal-to-noise ratio of the received signal. Then, it is down-converted using a mixer. The local oscillator (LO) signal is generated using discrete PLL components comprising of a phase frequency detector and pre-scaler to provide the LO frequency to the mixer to down-convert the signal to an intermediate frequency (IF), followed by a conversion from IF to baseband for signal processing.
Figure 8. RF signal chain block diagram.
At the transmitter, the base-band signal is upconverted to IF and then to the desired RF frequency. The RF signal is amplified using a power amplifier to transmit the signal.
RF Figure of Merit
The table demonstrates the RF Figure of Merit and the benefits of components used in the RF block diagram.
RF Figure of Merit |
||
| Product Type | Key Parameter | Key Benefit |
| LNA | Noise Figure (dB) | Improved Range/Signal Sensitivity |
| PA | OIP3 (dBm) & P1dB (dBm) PAE (%) | Linear Efficient Power – Low Distortion |
| Prescale | Phase Noise (dBc) @ kHz offset | Low Noise Floor – More Range |
| Wideband Switches | Low Loss (dB) / High Isolation (dB) | Low Harmonics in System |
Power Amplifiers Requirements
Power amplifiers play a key role as the transmitter in RF applications. One of the biggest PA requirements is that it can operate in its linear region to minimize RF distortion. Satellite communications systems that use higher-order modulation schemes such as 64/128/256 Quadrature Amplitude Modulation (QAM) are extremely sensitive to non-linear behavior. Another challenge is achieving a satisfactory peak-to-average power ratio (PAPR)—the ratio of the highest power the PA will produce to its average power. PAPR determines how much data can be sent and is proportional to the average power. At the same time, the size of the PA needed for a given format depends on the peak power. 5G mmWave effective isotropic radiated power (EIRP) requirements mandated by FCC include 43 dBm EIRP transmit power for the mobile handsets and base station transportable power of 55 dBm EIRP. These and other conflicting challenges can be met with GaN-on-SiC power amplifiers for satellite communication, 5G, aerospace, and defense applications.
GaN-on-SiC Power Amplifiers
GaN-on-SiC has the highest power density to generate high linear output power with high efficiency. GaN-on-SiC power amplifiers can operate at high frequencies in the Ka and Ku bands from 12 GHz to 40 GHz for satellite communication and 5G and have broad bandwidths, high gain, and better thermal properties, meeting the requirements of RF applications. Microchip provides RF solutions using GaN-on-SiC technology, meeting the SWaP-C requirement for components. ICP2840 is a flagship device that operates in 27.5–31 GHz, providing continuous wave (CW) output power of 9 watts and pulsed output power of 10 watts with a gain of 22 dB and power added efficiency of 22%.
Figure 9. ICP2840 linear PAE across frequency and output power levels.
Figure 10. ICP2840 linear gain across frequency and output power levels.
Microchip K Band Power Amplifiers
ICP2840 generates 9W continuous wave output power in the Ka-band from 27.5–31 GHz for uplink frequency for satellite communication and 28 GHz 5G frequency band.
ICP2637 has a wide bandwidth from 23–30 GHz, generates 5 watts of CW output power, and is offered in a QFN package and die form.
ICP1445 generates 35 watts of pulsed output power in the 13–15.5 GHz frequency Band.
ICP1543 operates in the Ku band at 12 to 18 GHz, generating 20 watts of CW output power.
Figure 11. Microchip
Technology’s Ku Ka-band GaN-on-SiC MMIC power amplifiers include
ICP2840, which generates 9 W of continuous wave output power in the
Ka-band from 27.5 – 31 GHz for uplink.
These PAs have high gain and power-added efficiency using GaN-on-SiC technology and meet the Ku/Ka band requirements for 5G, satellite communication, aerospace, and defense applications. GaN-on-SiC, with its highest power density, provides the optimal power amplifier solutions for these applications.
