Rohde & Schwarz is advancing its pioneering sub-THz research in the D-Band and has reached important milestones. In collaboration with the Berkeley Wireless Research Center (BWRC), the test and measurement expert has successfully characterized a TX/RX multi-antenna chip (CHARM) operating at up to 140 GHz, using their D-Band over-the-air (OTA) test chamber. Academia and industry leaders agree that the 110 GHz to 170 GHz frequency range, known as D-Band, is critical for beyond 5G and 6G mobile communications and future automotive radar applications.
Devices supporting mmWave frequencies, antenna systems and RF transceiver modules for future mobile communications standards or automotive radar applications will share the same characteristics that make them challenging to test. The wide frequency range, greater number of antenna elements and lack of conventional external RF connectors will require testing over-the-air in a shielded environment.
Doctoral candidates Ethan Chou and Hesham Beshary of Professor Ali Niknejad’s Berkeley Wireless Research Center (BWRC) at the University of California, Berkeley, in collaboration with test experts from Rohde & Schwarz, conducted tests using the new Rohde & Schwarz D-band over-the-air (OTA) characterization chamber. The tests took place at the Rohde & Schwarz lab in Coppell, TX, where the group evaluated the chips and application boards, they designed and fabricated.
The test setup consisted of the R&S ATS1800C OTA antenna test system, the R&S FSW50 signal and spectrum analyzer, the R&S SMW200A vector signal generator, the R&S SMB100A signal generator for PLL reference, the R&S NGP800 and NGL200 power supplies, and the R&S AMS32 antenna measurement software.
The R&S ATS1800C is a compact and mobile shielded chamber solution for OTA and antenna measurements based on a compact antenna test range (CATR) ideal for 5G mmWave applications. To cover the D-Band frequencies, the R&S FE170SR was installed at the rear of the OTA chamber as an external frontend to the R&S FSW50. The R&S FE170SR integrates easily with the signal and spectrum analyzer, sending calibrated signal data back to it. This setup does not require any mechanical modifications or additional RF cabling to the antenna test system.
The setup measures the amplitude and phase coherent response of the device under test (DUT) radiating in the D-Band. Thanks to the R&S AMS32 software option, which calculates the nearfield-to-farfield transformation, and the high-precision positioner, fully automated 3D-pattern measurements including post-processing can be performed in a short time.
The BWRC researchers provided a TX/RX multi-antenna chip (CHARM) mounted on a power board with an FPGA interface. A laptop connected to the FPGA via USB was used to configure the chip in either TX/RX mode, number of antennas, power settings, etc. An appropriate phase shift between the antennas was applied to configure the beam steering direction.
The EIRP performance of the TX configuration was characterized by spherical measurements in both H and V polarizations. Initially, a continuous sweep was conducted, but more stable results were obtained from discrete-step positioner angles every 5 degrees. Full 3D maps were conducted at 130, 135, and 140 GHz for both 1 and 4 antenna configurations. A total of 20,805 discrete data points were acquired in one day of testing. System path loss was accounted for by calibrating the empty chamber with a known antenna. Additional tests included broadside 8 antennas and 4 antennas with 30-degree beam-steering using two phase-offset IQ channels of the R&S SMW200A and continuous sweep data with finer (1 degree) resolution.
Prof. Ali Niknejad, Faculty Director of BWRC, said: “The OTA chamber gives us the ability to accurately characterize the performance of our D-band modules operating over-the-air. Not only the 3D antenna pattern but also the EVM and EIRP performance of the module in various spatial configurations is a unique capability, giving us important insights into the beamformer performance.”
Dr. Philipp Weigell, Vice President of the Industry, Components, Research & University Market Segment at Rohde & Schwarz says: “We are excited to work with BWRC students and faculty to address the challenges of over-the-air testing at sub-THz frequencies. These efforts will help researchers and key industry players test and characterize antenna systems and transceiver modules for 6G wireless communication standards, massive MIMO testbeds, future automotive radar applications and more.”
At IMS 2024, Rohde & Schwarz is showcasing a demonstration of the characterization of the TX/RX multi-antenna chip (CHARM) operating at up to 140 GHz using the D-Band OTA test solution. Trade show visitors can see the demo at the Rohde & Schwarz booth #1521 in Washington, D.C., from June 18 to 20, 2024.
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