Why is this not labeled as “exact gain (dBi)” for a commercial Yagi?

Realized gain includes feed losses, mismatch, and ohmic loss; directivity integrates the full 3D pattern. Here we compute a **2D-azimuth teaching slice** and quote **10 log₁₀(max |E|² / mean |E|²)**, which grows when the pattern becomes narrower. Use it for **trends**—more directors and good spacing increase the metric—not for link-budget numbers.

What does the “parasitic phase lag / bay” slider represent?

In a full simulation, element lengths and spacings set induced current phases. This slider condenses that into a **single delay per director stage** so you can see how phase progression steers the superposition. Tuning it mimics why real Yagis are sensitive to small length changes.

How does this differ from the phased-array simulator?

The phased array page shows a **uniform progressive phase** you control directly on identical elements. A Yagi instead gets its phasing mostly from **geometry and detuning**; only the driven element is fed. Our model mirrors that spirit with unequal magnitudes and imposed parasitic lags rather than equal drives.

Why can the polar pattern develop secondary lobes when spacing is large?

Larger inter-element distances increase electrical separation, so additional directions can satisfy constructive interference—similar in spirit to grating lobes in discrete arrays. Physical Yagis trade spacing, element count, and tuning to balance gain, sidelobes, and bandwidth.

Yagi–Uda Antenna

A Yagi–Uda antenna is a classic end-fire array: a reflector element slightly behind a driven element and one or more director elements ahead reshape currents by mutual coupling so that radiation adds constructively along the boom toward the directors. This page uses a pedagogical complex-field model: each element carries a magnitude and phase standing in for induced currents on slightly detuned dipoles; the azimuthal slice |E(φ)| is plotted in polar form, forward corresponds to φ = 0. A companion chart tracks 10 log₁₀(D) versus the number of directors, where D is the ratio of peak to mean power in that slice — a simple scalar “sharpness” metric, not a full 3D directivity or realized gain from a Method-of-Moments solution. Sliders change director count, spacing in wavelengths, reflector setback, and a parasitic phase lag per bay to mimic coupling delays. Real Yagi design depends on exact lengths, wire diameter, boom mounting, and interaction with a feed network; nevertheless the simulator illustrates why longer apertures (more directors, sensible spacing) sharpen the main lobe and raise in-cut directivity in this toy model.

Who it's for: Undergraduates studying antennas and electromagnetics, radio amateurs learning directional arrays, and instructors contrasting phased arrays (active phase control) with parasitic beamforming.

Key terms

Yagi–Uda antenna
Reflector
Director
End-fire array
Mutual coupling
Directivity
Beam pattern
Parasitic element

How it works

Classic end-fire array: a reflector behind and directors ahead of the driven element shape a beam. Explore a teaching pattern model and a live gain vs number of directors curve.

Frequently asked questions

Why is this not labeled as “exact gain (dBi)” for a commercial Yagi?: Realized gain includes feed losses, mismatch, and ohmic loss; directivity integrates the full 3D pattern. Here we compute a 2D-azimuth teaching slice and quote 10 log₁₀(max |E|² / mean |E|²), which grows when the pattern becomes narrower. Use it for trends—more directors and good spacing increase the metric—not for link-budget numbers.
What does the “parasitic phase lag / bay” slider represent?: In a full simulation, element lengths and spacings set induced current phases. This slider condenses that into a single delay per director stage so you can see how phase progression steers the superposition. Tuning it mimics why real Yagis are sensitive to small length changes.
How does this differ from the phased-array simulator?: The phased array page shows a uniform progressive phase you control directly on identical elements. A Yagi instead gets its phasing mostly from geometry and detuning; only the driven element is fed. Our model mirrors that spirit with unequal magnitudes and imposed parasitic lags rather than equal drives.
Why can the polar pattern develop secondary lobes when spacing is large?: Larger inter-element distances increase electrical separation, so additional directions can satisfy constructive interference—similar in spirit to grating lobes in discrete arrays. Physical Yagis trade spacing, element count, and tuning to balance gain, sidelobes, and bandwidth.