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pSemi: Tabletop 5G NR Antenna Range
Background
The need is growing for faster Internet communication in line with the increase in bandwidth required by Internet contents such as ultra-high definition video, augmented reality (AR), and virtual reality (VR). The next generation of mobile network, 5G, is capable of fulfilling the needs and promises to deliver more. 5G will not only make our smartphones better, but will also redefine a broad range of industries with connected services from retail to education, transportation to entertainment, and everything in between.
Comparing to the 4G LTE mobile network, the 5G mobile network equips with a wide range of technological inventions, such as millimeter waves, beamforming, full duplex, etc.. However, those cutting-edge technologies in the 5G mobile network also create challenges in designing, manufacturing, and characterizing. The sponsor of this project, pSemi Corporation, is working on designing various products, such as the mmWave antenna modulus, for the 5G application. This project aimed to help them solve the challenge in characterizing the 5G devices by designing a cost-effective tabletop antenna range.
Objective
The primary objective of this project is to design, fabricate, and deliver a tabletop antenna range that can measure the radiation pattern of the antenna under test (AUT).
Requirements
Basic Requirements
Rectangular Anechoic Chamber
AUT and receiving antenna must be separated by at least 200mm
Maximum reflectivity of antenna range must be under -20 dB at the operating frequency of AUT
Gantry System
Gantry system must be able to move receiving antenna continuously
Receiving antenna must achieve scan angles of +-30 degrees
Gantry system must achieve a minimum resolution of 10 mm
Gantry system could be controlled with external UI
Cooling System
The cooling system must monitor and keep the temperature of AUT below 40 Celsius at any time during the test
The cooling system can be autonomously switched on and off based on the temperature of AUT
Misc
Total weight of antenna range must be under 18 kg (40 lb)
Final Design
Fig.1 CAD model of the final antenna range design
Fig.2 Photo of the final antenna range design
Rectangular Anechoic Chamber
Fig.3 Final design of the rectangular anechoic chamber
Inner dimensions of 608mm X 608mm X 425mm
Sandwich panels
Laird ECCOSORB HR-25 microwave absorbers + Heavy-duty aluminum foils + Polycarbonate sheets
Used as chamber walls and door
Reinforced by PVC T-slots
Sliding door
Prevent interference during measurements
Easy to replace antenna modules
2-axis Gantry System
Fig.4 Final design of the gantry system
Two NEMA-17 stepper motors
Timing belt drives with CoreXY arrangement
Maximum displacements of 380mm X 380mm
Fiber glass rails
Dry-running sleeve bearings with 3D Printed housing
Arduino Mega 2560 with RAMPS 1.6 shield and Marlin Firmware
Full-featured 150+ G-code commands
External UI
Cooling System
Fig.5 3D Printed PCB board holder and liquid cooler holder
Fig.6 Circuit diagram of the cooling system
Based on liquid cooling for CPU
Thermistor + Relay
Monitor temperature
Autonomously turn on and off based on temperature measurements
Hysteresis control
Microcontroller/Software
Fig.7 Schematic illustration of the RAMPS board
Arduino MEGA 2650 board with RAMPS 1.6 shield
Be capable of accommodating up to five stepper motor drivers, four endstops, and more electronics
Complete G-code movement suite, including lines, arcs, and Bézier curves
Smart motion system with lookahead, interrupt-based movement, linear acceleration
Support for CoreXY kinematics
Support various host software
Performance
Gantry System
Positioning error of 0.18mm/100mm movement
Ideal speed of ~0.05m/s
Capable of moving along a line or circumference of a circle
Fig.8 Position Calibration Curve
Cooling System
Capable of autonomously turn on and off based on temperature measurements
Fig.9 Cooling System Logic Test
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