AutoEZ Antenna Modelling: Excel-Based NEC2 Guide

AutoEZ is a Microsoft Excel-based front-end for the EZNEC NEC2 antenna modelling engine, written by Dan Maguire AC6LA. It transforms Excel into a parametric antenna design environment where formulas drive geometry, variables control dimensions, and a full suite of sweeps, optimisations, and antenna comparisons run automatically from a spreadsheet interface. For operators who spend serious time with antenna modelling, AutoEZ dramatically reduces the repetitive work of systematic antenna design exploration.

Standard antenna modelling software — EZNEC, MMANA-GAL, 4NEC2 — requires the operator to manually change parameters and re-run simulations one at a time. Want to see how gain changes as element diameter increases from 12 mm to 50 mm in 2 mm steps? That is 20 manual re-runs in a standard NEC2 tool. In AutoEZ, that sweep runs automatically and the results plot directly in Excel with no manual intervention required. Want to compare twelve different antenna configurations side by side? AutoEZ runs all twelve and generates a comparison table in a single click.

AutoEZ works by using Excel's COM automation interface to control EZNEC, passing parameters to the NEC2 engine, retrieving results, and processing them using Excel formulas and charts. The antenna geometry is defined in Excel cells using formulas rather than fixed numbers — so when a variable changes (say, the element length or the antenna height), all dependent geometry updates automatically through the formula chain, and a new NEC2 run produces the corresponding results. This is parametric design: the antenna description is a set of relationships and rules rather than fixed numbers, and exploring the design space becomes as simple as changing a cell value.

An AutoEZ workbook is an Excel file with a specific sheet structure that AutoEZ reads to build the antenna model and configure the NEC2 run. Understanding this structure is the key to creating your own AutoEZ models rather than just using the provided samples.

The Variables sheet

The Variables sheet is where you define named variables that drive the antenna geometry. Each variable has a name, a current value, and optionally a range (minimum and maximum) for sweep and optimisation operations. Variables can represent element lengths, heights above ground, element diameters, spacing values, or any other parameter that you want to control parametrically.

The power of the Variables sheet is that ArmLen is defined as a formula referencing Freq — change Freq and ArmLen automatically recalculates, the geometry sheet updates, and the next NEC2 run uses the correct dimensions for the new frequency. This is the parametric chain that makes AutoEZ so powerful for systematic design exploration.

The Wires sheet

The Wires sheet defines the antenna geometry in NEC2 GW (Geometry Wire) card format, but using Excel formulas that reference the Variables sheet rather than fixed numbers. Each row defines one wire segment: start coordinates (X1, Y1, Z1), end coordinates (X2, Y2, Z2), wire diameter, and segment count.

The Sources and Loads sheets

The Sources sheet defines feed points in NEC2 EX card format. Like the Wires sheet, it uses formula references to variables. The Loads sheet defines resistive or reactive loads (LD cards) at specific segments — used for modelling loading coils, loss resistors, or trap circuits.

The Results sheet

AutoEZ writes all NEC2 output to the Results sheet after each run. This includes gain, take-off angle, front-to-back ratio, feed point impedance, SWR, and radiation pattern data. Charts on the Results sheet update automatically from this data, providing immediate visual feedback on each design iteration.

The parametric sweep is AutoEZ's most frequently used feature. It varies one or more variables through a specified range, runs the NEC2 simulation at each combination, and collects the results into a table. The sweep results update the Charts sheet automatically, producing gain vs. frequency, SWR vs. frequency, or gain vs. height curves without any manual data collection.

Single-variable sweep: Frequency sweep

The most common sweep varies frequency across the operating band. Set Freq in the Variables sheet as the sweep variable with a range spanning the operating band and a step size giving approximately 10–20 points across the band. Click AutoEZ → Sweep → Variable Sweep. AutoEZ runs one NEC2 calculation per frequency point and plots the results. For a 20 m dipole sweeping from 14.000 to 14.350 MHz in 0.025 MHz steps (14 runs), the entire sweep completes in under 30 seconds on a modern PC.

Single-variable sweep: Height optimisation

Sweep the Height variable from 6 m to 20 m in 0.5 m steps while monitoring gain and take-off angle. The resulting chart shows the classic relationship between height and take-off angle — and reveals the heights at which the main lobe splits into two lobes. This sweep answers the question "how much does raising the antenna by 2 m actually improve my DX signal?" with real NEC2 data for your specific antenna at your specific site.

Two-variable sweep: Element diameter vs. bandwidth

Sweep both element diameter (from 12 mm to 50 mm in 2 mm steps) and height (from 8 m to 15 m in 1 m steps) simultaneously. This produces a matrix of results showing bandwidth and gain for every combination. AutoEZ organises these results in a pivot-table-style layout and can produce 3D surface charts in Excel showing how gain varies across both dimensions simultaneously.

One of AutoEZ's most powerful features is the ability to run multiple antenna configurations in sequence and compare their results side by side. This is ideal for answering questions like "which performs better on 40 m: my dipole at 10 m or an inverted-V with the apex at 12 m?" without manually re-running and recording each simulation.

AutoEZ integrates with Excel's built-in Solver add-in to perform NEC2-driven optimisation. Solver adjusts one or more variables to minimise or maximise a target cell — typically gain at the design frequency — subject to constraints such as SWR limits and element length bounds. This is the AutoEZ equivalent of the genetic optimiser in YO, but driven by Solver's gradient-descent algorithm and running real NEC2 calculations for each evaluation.

Setting up Solver optimisation in AutoEZ

• Enable the Solver add-in in Excel (File → Options → Add-ins → Manage: Excel Add-ins → check Solver Add-in)
• In the AutoEZ workbook, identify the objective cell (e.g., gain at design frequency) and the variable cells to optimise (element lengths, spacing)
• Set the Solver objective to maximise gain, with constraints: SWR at design frequency ≤ 1.3 (cell reference), SWR at band edges ≤ 2.0, and each variable within its physical bounds
• AutoEZ provides a "Solver Callback" function that Solver calls after each variable change — this callback triggers a new NEC2 run and updates the result cells that Solver uses to evaluate the objective function
• Click Solve — Solver adjusts variables, AutoEZ runs NEC2 after each adjustment, and Solver converges on the optimum within the specified constraints

Workflow 1: Dipole height optimisation for DX

Variables: Height (swept 6–20 m). Fixed: Freq = 14.175 MHz, ArmLen = λ/4 × 0.97. Results swept: Gain (dBi) at 15° elevation, take-off angle (degrees). Output: Chart of gain at DX angles vs. height. Decision: Find the height giving maximum gain at 10–20° elevation for your target DX region.

Workflow 2: Fan dipole bandwidth validation

Variables: Freq (swept 7.0–7.3 MHz, then 14.0–14.35 MHz). Multiple scenarios for three fan arms at different lengths. Results: SWR vs. frequency for each arm combination. Output: Side-by-side SWR curves showing which arm-length combination minimises SWR across both bands simultaneously.

Workflow 3: Vertical antenna ground radial system comparison

Variables: NumRad (4, 8, 16, 32 radials). Fixed: antenna height = λ/4, frequency = 7.15 MHz. Results: Feed point resistance (=R_rad + R_ground), efficiency, gain. Output: Table and chart showing efficiency vs. radial count. Confirms the point of diminishing returns where adding more radials produces negligible improvement.

Workflow 4: Yagi element diameter sensitivity analysis

Starting from a YO-optimised 5-element Yagi design, import the NEC2 file into EZNEC, then open AutoEZ and set up a sweep of element diameter from 12 mm to 50 mm. Results: SWR 2:1 bandwidth vs. diameter, gain vs. diameter. Output: Chart confirming that increasing element diameter from 25 mm to 38 mm adds 200 kHz of bandwidth with negligible gain penalty — validating the use of thicker tubing despite its higher cost and wind loading.