How to evaluate 5G mmWave Phased Array Antenna Modules
5G New Radio (5G NR) is the industry-standard, global specification for air interface or radio access network (RAN) technology. It covers operation at frequencies of 6 GHz and below, called FR1, and bands from 24 GHz to 50 GHz or higher, called FR2 or mmWave. The technology can be deployed for fixed or mobile access, for backhaul, and for increasingly popular private networks, for which Open RAN has helped diversify the supplier ecosystem and reduce costs.
It’s at mmWave frequencies that 5G networks deliver on their biggest promises – huge bandwidth and incredibly low latency. But one big challenge for mmWave radios is that their range is limited because signals are susceptible to absorption and attenuation by everything from buildings to foliage. Antenna arrays must use beamforming to combat these propagation losses, which involves phasing techniques in multi-antenna arrays to focus radio signals in the direction of network users, who will often be mobile. Accurate direction tracking needs to be achieved at high speed, as does dynamic channel allocation for when interference is encountered, or users move between access points.
Radios and antenna arrays need to be small. Because of the restricted range of 5G NR radios, typically around 250 meters, depending on the environment, many more are needed to service a given geographical area than with lower band systems. As a result, their aesthetic impact is an important consideration. Small dimensions are also needed for technical reasons. At mmWave frequencies, signal paths must be kept as short as possible to avoid unwanted radiation, electromagnetic interference, crosstalk, and signal attenuation. However, making radios small poses thermal management challenges. mmWave RF amplifiers may sometimes be only 10% efficient, so 90% of the DC power fed into them needs to be dissipated as heat. The reliability and operating life of electronic systems can be severely compromised at elevated temperatures.
Improvements in power semiconductor efficiency (in both components and modules), increased functional integration throughout the signal chain, more effective test and simulation tools, and high-performance interconnect all contribute to the goal of designing effective, efficient, compact radios for mmWave 5G NR applications.
With ever-present time-to-market pressures on system designers, development platforms play a vital role in accelerating the design process and ensuring predictable operation when mmWave radios are deployed and commissioned.
The functions of a 5G mmWave test and simulation platform
Evaluating a 5G signal chain involves measurements of the frequency range, bandwidth, transmit power and effective isotropic radiated power (EIRP), receiver sensitivity and noise figure, and analog and digital beamforming capabilities. Engineers need to examine antenna characteristics, including gain, polarisation, and radiation patterns. Furthermore, modulation accuracy tests may be needed, for example, to establish error vector magnitude (EVM), which reveals any differences between expected and actual signal constellation points. Other measurements can include receiver signal-to-noise ratio (SNR), link latency, and assessments of interference and coexistence performance. It’s also vital to check compliance with standards and regulations, such as those of FCC, ITU, or ETSI.
Avnet has combined offerings from AMD, Fujikura, Mathworks, Rohde & Schwarz, and Samtec to create an end-to-end 5G development and test platform for measuring such parameters. The constituent parts of this setup are an AMD Xilinx XCU208 RFSoC board, Avnet’s RFSoC Explorer application software, the Fujikura phased antenna array module (PAAM), a Rohde & Schwarz RTP oscilloscope, and high-frequency interconnect cables assemblies and connectors from Samtec. The device under test is the Fujikura PAAM.
Avnet-Fujikura 5G mmWave PAAM Development Platform Connections
The RFSoC board
The AMD XILINX Zynq UltraScale+ RFSoC ZCU208 is used to drive the signal chain. This board features a Zynq UltraScale+ RFSoC ZU48DR. It’s crammed with digital functionality: eight 14-bit 5GSPS ADCs, eight 14-bit 10GSPS DACs, and eight soft decision forward error correction (SD-FEC) cores. The board combines Arm® Cortex®-A53 and Cortex-R5 subsystems, UltraScale+ programmable logic, and provides 0 – 6 GHz IF bandwidth.
5G PAAM high-performance features
The Fujikura PAAM covers frequency bands n257 (28 GHz), n258 (26 GHz), and n261 (27 GHz) and is designed for indoor or outdoor applications. It is a highly integrated module with an 8x8 antenna element, RF ICs, and filtering.
The PAAM supports concurrent dual-polarized beams for both transmission and reception. Its SiGe BiCMOS RF ICs enable greater than 20% power-added efficiency, which simplifies thermal management, and the module’s low noise figure (NF), maximizes the link margin and coverage. The PAAM enables on-chip support for thousands of beam configurations, guaranteeing application flexibility. Its 8 x 8, 64-element array is scalable to 2048 elements or more.
Independent phase and amplitude control over a wide frequency range delivers precise control of the tuneable true-time-delay phase shifters, enabling simple and accurate, high-resolution beam steering that supports over 30,000 directions. Beam switching is exceptionally fast at less than 220 ns, ensuring a seamless end-user experience and the PAAM’s phase shifter maintains undistorted transmitted or received signals by ensuring invariant group delay and unchanged beam direction over a wide frequency range. Calibration-free operation simplifies installation.
Bringing it all together: Avnet’s RFSoC Explorer Toolbox
The free Avnet RFSoC Explorer Toolbox Version 3.0 provides support for over-the-air antenna-to-bits prototyping with the RFSoC board and Fujikura PAAM. Using MATLAB and Simulink, the toolbox’s graphical user interface (GUI) and intuitive API provide programmatic control of RF-ADC and RF-DAC parameters, signal generation, and acquisition. Standards-compliant and custom waveforms can be streamed to and from hardware. The GUI or programmatic API with auto-complete scripting is used to perform the system tests.
Rohde & Schwarz test equipment complements the platform
Rohde & Schwarz makes several products suited to 5G RF tests, including vector signal generators and analyzers. A suitable oscilloscope to complement the test setup described here is one from the company’s RTP product family. These offer bandwidth up to 16 GHz, a maximum sample rate of 40 Gsamples/s, and up to 16-bit resolution. The instruments have a flat frequency response of ± 0.25 dB, which ensures accurate measurements.
The importance of precision interconnect at mmWave frequencies
Systems working at frequencies of 24GHz and above demand that particular attention is paid to cables and connectors to achieve accurate impedance matching, minimize losses, prevent unwanted radiation, protect against EMI, and ensure signal integrity.
Samtec makes various precision RF connectors and cable assemblies that are suitable for frequencies between 18 GHz and 110 GHz. For compact 5G modules, the 50 Ohm SMP and SMPM families are often preferred due to their small size, availability in single-port and multi-port versions, and low SWR (<1.4:1). The company has also recently introduced new coax cables with distinctive orange jackets. They use Nitrowave™ technology to ensure phase and amplitude stability when the cables are flexed and feature low-density PTFE dielectric to minimize losses, consistent contact resistance between layers, and layered shielding to minimize interference.
Note: This demonstration platform will be shown in the Samtec booth (#1531) at IMS Microwave Week, 16-21 June 2024 in Washington, DC.
