Module 3 — Arrays and ADALM-PHASER Beamforming#

ECE 444 · Module 03

Arrays and ADALM-PHASER Beamforming

Point the beam without moving the antenna.

Lessons 15–24 · Antennas, Phased Arrays, and Radar Systems · Dr. Neil Rogers

Where This Module Goes

Amplitude shapes the beam: its sidelobes and beamwidth. Phase steers it.

An array is many small antennas behaving as one large one. Feed the elements with the right phases and the beam points where you choose; feed them with the right amplitudes and you decide how wide the beam is and how much energy leaks into the sidelobes.

This is the longest module in the course, and the most hands-on. Almost every lesson has its own lab on the ADALM-PHASER, done right after it, so you never take the array factor on faith.

The through-line is one equation — the array factor — met four times: derived, steered, tapered, and nulled. Each time it is the same sum over elements with different weights. If you leave this module able to write that sum from memory and say what each term does, the rest is arithmetic.

The Module 3 Roadmap

Amplitudeshapes the beam Phasesteers it Boththe full weight L15 Apertures L16 Array Factor L17 Hardware and CalibrationLab L18 Beam SteeringLab L19 Direction FindingLab L20 BeamwidthLab L21 Antenna PatternLab L22 Tapering L23 Squint and QuantizationL22–L23 Lab L24 NullingLab

Every lesson in this module turns one of two knobs on each element. Lessons 15, 16, 20, and 22 work the amplitude: how the illumination across the aperture sets the beamwidth and the sidelobe level, and what a taper trades for lower sidelobes. Lessons 18, 19, and 23 work the phase: the progressive phase that points the beam, the bearing it lets you measure, and what goes wrong when the phase is only right at one frequency or comes in coarse steps. Lessons 17, 21, and 24 need both. Calibration corrects each channel’s gain and phase, the measured pattern carries the element’s own pattern on top of the array factor, and a null is placed with complex weights.

Learning Objectives 3.1-3.3

  1. I can describe aperture distributions and calculate aperture efficiency for a given illumination.
  2. I can derive the array factor for an arbitrary linear array and apply pattern multiplication.
  3. I can identify the hardware architecture of the ADALM-PHASER and control it via SDR software.

Learning Objectives 3.4-3.6

  1. I can calculate the phase weights required to steer a beam to a given angle and predict the resulting array pattern.
  2. I can implement beam steering on the ADALM-PHASER and verify the steered pattern against theory.
  3. I can distinguish between array factor and true antenna pattern and account for element pattern effects.

Learning Objectives 3.7-3.9

  1. I can apply amplitude tapering (uniform, cosine, Chebyshev, Taylor) to control sidelobe level and predict the pattern trade-off.
  2. I can identify grating lobes, beam squint, and quantization effects in a phased array and describe their impact on system performance.
  3. I can calculate null-steering weights and implement pattern nulls on the ADALM-PHASER.

Where This Is Going

Module 4 gives the array something to look for. The same hardware becomes a radar: send a chirp, listen for the echo, and work out how far away the target is and how fast it is moving.

The steering and tapering you learn in this module point and shape the radar’s beam.