6G Vector Component Analysis

Introduction

The Keysight 6G Vector Component Analyzer (VCA), based on the new N524XB series PNA-X Microwave Network Analyzers, offers a modulation bandwidth of 4/10/40 GHz which makes it the ideal choice to develop and characterize components for sub-THz communication systems for emerging 6G applications.

6G Vector Component Analysis (VCA)

Accelerating characterization of 6G sub-THz components

As the world becomes increasingly reliant on wireless connectivity, the need for faster and more reliable communication networks has never been greater. While the wireless industry touted 5G as a game[1]changing technology, the research and development of 6G is already well underway. Researchers expect sub-THz (sub-terahertz) frequencies to play a significant role in 6G wireless communication networks thanks to their ability to provide the tens of GHz of bandwidth necessary to the Terabit per second data rates required for some emerging applications.

However, to realize the full potential of the sub-THz bands in 6G, building a component ecosystem like that available today for millimeter wave (mm-Wave) frequencies remains crucial. As such, ensuring successful proof of concept demonstrations depends on accurate early-stage development testing and verification of the various sub-THz transceiver components.

Sub-THz test challenges

Testing devices at sub-THz frequencies presents many challenges:

• Degraded SNR: Set by physics, the thermal noise power of an ideal receiver (kTB) is directly proportional to the acquired signal bandwidth. Transitioning from 400 MHz component carriers in 5G FR-2 to component carriers of over 4 GHz means that our noise power will increase by an order of magnitude. Conversely, the maximum output power of all semiconductor technologies decreases with frequency. This poses a significant challenge for traditional wideband signal analysis approaches.

• Non-idealities of test fixtures: Due to the ultra-wide bandwidths used at sub-THz frequencies, the frequency response and mismatch of test fixtures such as attenuators or amplifiers required to test devices will vary significantly over the band of interest. Furthermore, during the early stage of development, many of the devices will require on-wafer testing. Hence, calibration to the device under test (DUT) reference plane becomes essential to accurately characterize components.

• Phase noise: Despite the significant phase noise performance improvement of modern vector signal sources and analyzers at 5G FR2, sub-THz measurement systems typically rely on large numbers of frequency multiplication in the LO to reach hundreds of GHz, degrading the phase noise of the test system. In addition, frequency locking of multiple instruments is performed at a significantly lower frequency relative to the target measurement frequency. This mimics the real system use case where transmitters and receivers lock to a global satellite system at 10 MHz. However, for component test, where the contribution of the test system should be reduced as much as possible, the relative phase drift between multiple instruments becomes a limiting factor.

Test requirements

Typically, active component designers begin verifying a new device by turning it on and measuring small signal performance, usually through S-parameters. These measurements allow designers to see how well their simulation results align with their fabricated device and optimize their models for future iterations.

However, predicting system level performance requires more than just S-parameters. Other key small signal performance metrics for active components include:

• Noise Figure

• Gain Compression

• Power Added Efficiency (PAE)

• TOI or IIP3

• Conversion gain and group delay

• I/Q imbalance (amplitude and phase)

• LO feedthrough

• Image Rejection

• Spurious testing

• Error Vector Magnitude

• Adjacent Channel Power Ration (ACPR)

While Vector Network Analyzers traditionally perform some of these measurements, extending these capabilities to sub-THz presents many challenges.

6G Sub-THz Vector Component Analyzer

Keysight’s new 6G Vector Component Analyzer (VCA) extends the unique capabilities of Keysight Vector Network Analyzers to measure component behavior under modulated signal stimulus to sub-THz frequencies. This solution offers several significant benefits over traditional signal analyzer and signal generator approaches for component test:

• Improved SNR: The VCA uses the VNA’s narrowband receiver and repetitive acquisitions to reconstruct the wideband signal. Using a narrow band receiver reduces the noise power captured in each acquisition. Furthermore, since component test uses a repetitive stimulus signal, applying (coherent) vector averaging improves the SNR. Finally, using signal compaction to transform the stimulus signal into a compact test signal, the Power Spectral Density (PSD) of the stimulus can be further improved.

• Full Vector Calibration: Leveraging the VNA S-parameter and power calibration techniques, the VCA removes the effects of the test system and any fixtures used for measurement. Moreover, through the application of source calibration, the VCA ensures an ideal test signal at the DUT input reference plane.

• Fully Clock Locked Test System: Unlike other sub-THz test systems where the instruments are locked to a low frequency clock through Phase-Locked Loops (PLL), the VCA uses fully digitally clock locked.