The problem
Most retrospective formats tell you what happened this sprint. The happiness radar tells you how the team is doing across time — are they more or less satisfied with their work, their tools, their collaboration, their growth?
The radar format is a spider chart on a whiteboard: axes for Team, Process, Tooling, Product, Learning, and whatever else matters. Each person rates each dimension on a simple scale. The team average creates the radar shape.
The chart looks great on a whiteboard. But a whiteboard chart is useless for trend analysis — you need to compare this sprint's shape to last sprint's. That means documentation, and nobody does it consistently unless the process is nearly effortless.