This video presents the construction and validation of a very low-cost antenna test system designed to measure the actual antenna patterns of an 8-element "Phaser" phased array. The primary objective is to compare these mechanical measurements with rapid "electrical scans" previously demonstrated, without the need for expensive anechoic chambers.
The setup utilizes a $3 10 GHz transmitter, the Phaser board, a $20 turntable, and a large room to minimize reflections. The presenter details mechanical rotation measurements for both the total array pattern and the individual element factor. A precise, manual point-by-point scan is conducted using a $12 electronic protractor for direct comparison. The findings show that while the rapid electrical scans are accurate near the antenna's boresight, the mechanical measurements reveal a significant "droop" at wider steering angles. This effect is attributed to the element factor, which inherently limits a phased array's effective steering range to approximately 60-75 degrees from boresight. The video concludes that the quick electrical scan method is highly effective for rapid prototyping and understanding beamforming principles, 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 Basics & Measurement 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. The goal is to build confidence in using quick, accessible measurements for understanding beamforming principles.
1:35 Array Factor vs. Element Factor: The presenter explains 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 for the Phaser array.
2:08 Phaser Hardware & Software: The core hardware is the Analog Devices CN566 "Phaser" kit, an 8-element phased array. 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 a rotating gimbal, precise signal source/receiver, and an anechoic chamber) is contrasted 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 involves electronically steering the array, then mechanically rotating it (or the signal source) and recording the received signal strength. 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 showed an anomalous "wonky side lobe" due to reflections. Moving the setup to a larger, emptier room significantly improved measurement symmetry and distinctness of the main and side lobes.
8:41 Element Factor Measurement: By deactivating all but one Phaser element, the element factor is measured. For the azimuth axis, a relatively flat gain is observed, rolling off towards the horizons. For the elevation axis, after manual re-fixturing (highlighting antenna engineering challenges), a pattern characteristic of a four-element array is revealed, consistent with how each Phaser element sums four patch antennas.
10:20 Precise Electrical vs. Mechanical Scan Comparison Method: To obtain more precise angular data, 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 a previous video.
11:20 Element Factor Limits Steering Range: The comparison shows that 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 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.