This video demonstrates a low-cost, DIY approach to measuring the antenna pattern of a phased array, specifically the 8-element "Phaser" kit from Analog Devices, as an alternative to expensive anechoic chambers. The primary objective is to build confidence in a rapid "electrical scan" method, where the antenna beam is electronically steered, by comparing its results against a more traditional "mechanical scan" involving physical rotation.
The presenter details the setup, using a $3 10GHz transmitter, a $20 turntable, and a large room to minimize reflections. Key concepts like the element factor (radiation pattern of a single element) and array factor (impact of combined elements) are explored. Through both continuous rotation and precise manual degree-by-degree measurements, the video reveals that the fast electrical scan provides a good approximation of the antenna pattern near the mechanical boresight. However, a significant "droop" in gain is observed in the mechanical scan at wider angles, attributed to the element factor. This highlights the practical limitations of phased array steering towards the horizons. Ultimately, the low-cost method is deemed sufficiently effective for quickly understanding beamforming concepts and the impact of design changes.
Measuring a Phased Array Antenna Pattern on a Budget
0:00 Introduction & Goal: The video aims to measure the actual antenna pattern of an 8-element phased array, specifically the Analog Devices Phaser kit, and compare it to a quick "electrical scan" method. The goal isn't perfect precision, but to build confidence in the low-cost measurements.
0:32 The Cost of Antenna Chambers: Professional antenna chambers cost tens of thousands of dollars and are time-consuming. The video proposes a $12 rough pattern measurement method.
1:37 Key Antenna Concepts: The total antenna pattern is a combination of the "element factor" (radiating pattern of a single array element) and the "array factor" (impact of all elements summed together).
2:08 Hardware for Measurement: The system uses the Phaser kit (Analog Devices CN566) as the receive array, MATLAB scripts for control, and a key component: a cheap turntable.
3:16 Professional vs. DIY Setup: A professional chamber uses a measured antenna on a rotating gimbal, a signal source/receiver, and an anechoic chamber to prevent reflections. The DIY version substitutes these with an HB100 10 GHz transmitter ($3), the Phaser array, a $20 turntable, and a large, empty room or open field to reduce reflections.
5:45 Measurement Procedure: The array is electronically steered, then mechanically rotated, and received power is plotted against the angle. A constant rotation speed roughly aligns the pattern with angles, ensuring correct peak power levels for main and side lobes.
7:42 Reflection Issues: Initial measurements in a small room showed "wonky side lobes" due to reflections, emphasizing the need for a larger, emptier space.
8:16 Improved Environment: Moving to a bigger room resulted in a much cleaner, symmetric pattern with distinct main and side lobes, indicating a more accurate total antenna pattern.
8:41 Measuring the Element Factor: By activating only one element and rotating the array, the element factor is measured. It shows a relatively flat gain that rolls off near the horizons. Each element has slightly different characteristics, especially at the ends of the array.
9:17 Elevation Element Factor: Manipulating the array fixture to rotate it on the elevation axis reveals a pattern typical of a four-element array, consistent with Phaser's design where each "element" is a summation of four patch antennas.
10:45 Precise Mechanical Scan: For a precise comparison, a brute-force method is used: the signal source is manually moved in one-degree increments around the array using a $12 electronic protractor, and signal levels are recorded.
The fast "electrical scan" (blue line) closely matches the precise "mechanical scan" (green line) near the boresight (center of the beam).
At angles beyond ~50 degrees, the mechanical scan shows a significant "droop" in gain that is not present in the electrical scan.
Key Takeaway: This droop is due to the element factor, as individual antenna elements have reduced gain at extreme angles. This limits how far a phased array can effectively steer towards the horizons (typically 60-75 degrees).
14:10 Conclusion: The electrical scan method, while not fully accurate for side lobe gain at wide angles, is a highly effective and rapid tool for understanding beamforming principles, tapering, and grating lobes in experiments without needing an expensive, time-consuming antenna chamber. More precise measurements may still be needed for specific phenomena like null steering or quantization side lobes.