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 of specific phenomena like null steering.
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 and complexity 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 the element factor and the total antenna pattern.
2:08 Phaser Hardware & Software: The core hardware is the Analog Devices CN566 "Phaser" kit, which includes 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 to control and measure the Phaser.
2:59 Low-Cost Test System Components: An ideal antenna test chamber (featuring an antenna on a rotating gimbal, a precise signal source/receiver, and an anechoic 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 or open field to reduce RF reflections.
5:38 Mechanical Measurement Procedure: The measurement process involves electronically steering the array to a desired direction, then mechanically rotating the array (or the signal source) and recording the received signal strength. This data is then plotted as power versus angle. A constant turntable speed is used to approximate angle readings, prioritizing accurate peak/null levels over exact angular precision.
6:52 Initial Test & Reflection Mitigation: An initial test in a small room produced the expected antenna pattern but also showed an anomalous "wonky side lobe," which was attributed to reflections within the confined space. Moving the setup to a larger, emptier room significantly improved the measurement symmetry and distinctness of the main and side lobes.
8:41 Element Factor Measurement: To determine the element factor, all but one of the Phaser's elements are deactivated. Rotating the array for the azimuth axis shows a relatively flat gain that noticeably rolls off towards the horizons. For the elevation axis, manually re-fixturing the array (highlighting antenna engineering challenges) reveals a pattern characteristic of a four-element array, consistent with how each Phaser element sums four patch antennas.
10:20 Precise Electrical vs. Mechanical Scan Comparison: To obtain more precise angular data for comparison, a "brute force" method is used: 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) from the previous video.
11:20 Element Factor Limits Steering Range: The comparison shows that the electrical and mechanical scans are "pretty close" up to about 50 degrees. Beyond this, the mechanical scan "droops" away from the electrical scan, demonstrating the significant impact of the element factor. The true antenna pattern is the product (or sum in dB) of the array factor and element factor. The element factor's roll-off near 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, while not a traditional anechoic chamber measurement, is highly valuable for quickly assessing the impact of design changes (like tapering or grating lobes) without lengthy setup and calibration. It provides a good representation of key beamforming principles, even if not the absolute precise antenna pattern. However, certain highly sensitive measurements, such as null steering or quantization side lobes, still necessitate the accuracy of a full anechoic chamber.