This video demonstrates the creation and use of a very low-cost antenna test system to measure the actual antenna pattern and element factor of an 8-element "Phaser" phased array. The presenter contrasts this DIY approach with expensive anechoic chambers, aiming to build confidence in using quick, accessible measurements for understanding beamforming principles. The setup utilizes a $3 10 GHz transmitter, the Phaser board, a $20 turntable, and MATLAB scripts, with a large room or open field to minimize reflections. The video details mechanical rotation measurements for both the total array pattern and the individual element factor, highlighting the challenges of fixturing. A precise, manual point-by-point scan is then performed to compare the mechanical pattern with the rapid electrical scans from a previous video. The comparison reveals that while electrical scans are generally accurate for central angles, the element factor causes significant pattern droop at wider steering angles, ultimately limiting a phased array's practical steering range. The video concludes that the quick electrical scan method is highly effective for rapid prototyping and understanding design impacts, though traditional chamber measurements remain necessary for highly precise characterization.
My Very Low Cost Antenna Test System
0:00 Phased Array Antenna Basics & Goal: The video introduces a series on phased array beamforming using the "Phaser" hardware, aiming to measure the actual antenna pattern of the array. The objective is to compare this mechanical measurement with fast electrical scans, acknowledging the high cost of professional antenna chambers.
1:35 Array Factor vs. Element Factor: The presenter recaps two fundamental concepts: the array factor (the combined impact of all antenna elements) and the element factor (the radiating pattern of a single element). The video focuses on measuring both.
2:08 Phaser Hardware & Software: The core hardware is the Analog Devices CN566 "Phaser" kit, an 8-element phased array. A key detail is that each of the 8 "elements" on the Phaser PCB is actually a summation of four individual patch antennas. MATLAB scripts are used for control and measurement.
2:59 Low-Cost Test System Components: An ideal antenna test chamber is juxtaposed with the presenter's budget setup: a $3 HB100 10 GHz transmitter, the 10 GHz Phaser array, a $20 turntable for mechanical rotation, and a large, empty room to reduce RF reflections.
5:38 Mechanical Measurement Procedure: The process involves electronically steering the array to a direction, then mechanically rotating it while recording the received signal strength. This data is plotted as power versus angle, using a constant turntable speed to approximate angle readings.
6:52 Initial Test & Reflection Mitigation: An initial test in a small room produced the expected pattern but also showed an anomalous "wonky side lobe," attributed to reflections. Moving the setup to a larger room significantly improved the measurement's symmetry.
8:41 Element Factor Measurement: To determine the element factor, all but one of the Phaser's elements are deactivated. Rotating the array shows a relatively flat gain that noticeably rolls off towards the horizons. Manually re-fixturing the array for the elevation axis reveals a pattern characteristic of a four-element array, consistent with the hardware design.
10:20 Precise Electrical vs. Mechanical Scan Comparison: A "brute force" method is used for a precise comparison: manually moving the signal source in 1-degree increments around the array using a $12 electronic protractor and recording the signal level. This "mechanical scan" (green) is then directly compared to the rapid "electrical scan" (blue).
11:20 Element Factor Limits Steering Range: The comparison shows that the electrical and mechanical scans are very close up to about 50 degrees. Beyond this, the mechanical scan "droops" away, demonstrating the significant impact of the element factor. The element factor's roll-off near the horizons fundamentally limits a phased array's effective steering range, typically to 60-75 degrees from boresight.
14:10 Conclusion on Method Utility: The video concludes that the fast electrical scan method is highly valuable for quickly assessing the impact of design changes (like tapering or grating lobes) without lengthy setup. It provides a good representation of key beamforming principles, even if it's not the absolute precise antenna pattern.