Documentation sections

Yagi-Uda Antenna Design Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug yagi-antenna. Calculate Yagi-Uda antenna element lengths, gain, spacing, and impedance. Design directional Yagi antennas for any frequency. Free, instant results.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of yagi-antenna
Name	Unit	Range	Default	Description
frequencynumber	MHz	1 … 10000	144	Operating frequency in MHz
numElementsnumber	none	2 … 20	5	Total number of elements including reflector, driver, and directors

Retired, still accepted and ignored with a warning: boomLength (Boom Length, 2026-10-12).

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of yagi-antenna
Field	Unit	Description
gainheadline	dBi	Estimated Gain
driverLength	mm	Driver (Dipole) Length
reflectorLength	mm	Reflector Length
directorLength	mm	Director Length
spacing	mm	Element Spacing (0.2λ)
impedance	Ω	Feed Impedance (approx)
assumedBoomLength	m	The boom the model assumes: N − 1 gaps of 0.2λ between N elements

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "yagi-antenna",
    "inputs": {
      "frequency": 144,
      "numElements": 5
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("yagi-antenna", {"frequency": 144, "numElements": 5})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "yagi-antenna",
    "inputs": {
      "frequency": 144,
      "numElements": 5
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "yagi-antenna",
	  "inputs": {
	    "frequency": 144,
	    "numElements": 5
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "yagi-antenna",
  "values": {
    "gain": 8.170599913279624,
    "driverLength": 978.4892726388887,
    "reflectorLength": 1040.946034722222,
    "directorLength": 936.8514312499999,
    "spacing": 416.3784138888889,
    "impedance": 67.16,
    "assumedBoomLength": 1.6655136555555554
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:yagi-antenna",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Antenna Theory: Analysis and Design, 4th ed., Constantine A. Balanis (2016), Chapter 10 — Yagi-Uda array design",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "frequency": {
          "min": 1,
          "max": 10000,
          "unit": "MHz"
        },
        "numElements": {
          "min": 2,
          "max": 20,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "frequency": 144,
      "numElements": 5
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "frequency"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageYagi-Uda Antenna Design Calculator, at these values