Qiang Zhang

RF engineer with 9 years of experience in RF system design and optimization. Skilled in identifying and resolving RF frontend issues, with a strong track record of improving wireless performance and system reliability. Recognized the value of Python in debugging and RF validation through hands-on work, and successfully developed in-house automation testing software to significantly enhance testing efficiency.

Situation:

• A central hub for a comprehensive home security system, integrating networking, video transmission, and alarm functionalities. It supports a wide RF frequency range from 600 MHz to 6 GHz and incorporates multiple wireless technologies including Wi-Fi, Zigbee, LTE, and Sub-1GHz.
• When LTE antennas (B71/12/13/14/5) and Sub-1GHz antennas (920MHz) are connected simultaneously , LTE's TIS deteriorates to -65dBm .
• When only LTE antennas are connected , TIS returns to normal.

Task:

My task was to identify the root cause of interference between LTE and Sub-1GHz modules and provide an effective solution.

Action:

• Identify the source of interference: The source of interference is Sub-1GHz chip.
• Interference mechanism analysis: Built a conducted test environment by connecting the spectrum analyzer, communication tester, LTE, and Sub-1GHz modules using power splitters to collect experimental data. Based on abnormal results, designed targeted experiments and identified the interference path as: LTE (Tx) → Sub-1GHz chip (reflection) → LTE (Rx).

Result:

During the troubleshooting process, it was discovered that LTE introduced approximately 80 dB of interference to the Sub-1GHz module, making the LTCC filter solution unsuitable. A SAW filter was ultimately selected, which provides around 60 dB attenuation in the 600–900 MHz band. Combined with an additional 20 dB of antenna isolation, the solution effectively mitigated the mutual interference between LTE and Sub-1GHz systems.

Link:

https://z035pxrxiy.feishu.cn/docx/YKuAdl9XtoaMTsxMHEpcwG8Pnfe?from=from_copylink

Situation:
The company’s gateway product required Wi-Fi chip selection. Multiple suppliers were under consideration, and we needed to identify the most suitable chipset for our specific project requirements.

Task:
Design and execute a systematic evaluation plan, focusing on key performance indicators to fairly compare each chipset's strengths and weaknesses.

Action:
Built a comprehensive test environment to evaluate each chipset's performance metrics, including TX power, EVM, SEM, RSSI, PER, throughput, power consumption, and adjacent channel interference. Developed Python-based automation scripts to ensure efficient and repeatable test execution with consistent results across all candidates.

Result:
The final test results clearly illustrated the strengths and weaknesses of each chipset. The selected chip achieved the optimal balance between performance and power consumption. It performed reliably during certification and mass production phases, significantly reducing compatibility risks and validating the soundness of the selection decision.

Situation:
In a smartphone project, it was observed that enabling the camera caused a 20 dB drop in Wi-Fi 5GHz receiver sensitivity. Initial debugging indicated conducted interference from PCB inner-layer routing.

Task:
Identify the specific interference path on the PCB and provide a feasible layout modification plan to eliminate the issue.

Action:
Performed physical PCB investigation by scraping the GND networks on the Top and Layer2, then cut the suspected signal path on Layer3. Measured the conducted isolation of the routing before and after the cut to verify the interference source.

Result:
It was determined that two vias between Layer3 and Layer8 were placed too closely together, leading to signal coupling from the camera module into the Wi-Fi Rx path. Recommended increasing the spacing between the vias to 1 mm and adding more ground vias to enhance isolation, which effectively resolved the conducted interference issue.

Link：

https://z035pxrxiy.feishu.cn/docx/SqAKdbKLmo3WLFx9qULcYFcVnA9?from=from_copylink