Monopole Antenna Length Calculator (with Examples)

A Monopole antenna, sometimes called a Vertical is a very popular antenna type. It has a single radiating element erected vertically over the
ground.

The length of the antenna is λ/4, where λ is the wavelength. It uses a conductive surface to create a ground plane.

This calculator gives the physical length of a monopole antenna. Enter either the operating frequency or the wavelength.

Background

This tool computes the dimensions of a quarter-wave monopole.

Monopole antennas can have different physical lengths. For instance, there’s a longer 5λ/8 length monopole which is very popular in the broadcast industry. This antenna radiates most of the power provided to it in the horizontal direction.

Example Calculation

At a frequency of 144 MHz, the wavelength is 2.08 meters and the length of the monopole antenna is 0.52 meters.

As the frequency of operation increases, the length of the monopole decreases and vice versa.

Practical Examples of Monopole Antennas

This video discusses the design of a monopole.

The video touches on a number of important topics such as standing wave ratio (less than 2 for both antennas discussed). Here’s a tool to calculate the effect of VSWR on mismatches and forward and reflected power.

FM Antenna

A whip antenna like the one found on an FM radio shown below is an example of a monopole antenna.

The FM band extends from 88 MHz to 108 MHz. Using the center of the band or 98 MHz for this calculation, the length of an FM monopole antenna is 76 cm or 30 inches.

Wi-Fi Antenna

What’s the length of a Wi-Fi monopole operating at 2400 MHz? Consider the hinged rotatable antenna made by Taoglas shown in the picture below.

Using the calculator, the length of this should be 31.2 mm. Referring to the mechanical drawings in the data sheet we can see that the length is approximately 30 mm. This is consistent with the calculation.