A half-wave dipole has total length lambda/2 with:

Two arms of lambda/4 each, fed at the centre

Two arms of lambda/2 each, fed at one end

One arm of lambda/4 fed at the end

Two arms of lambda each, fed at the centre

In a half-wave dipole:

Current is maximum at the centre and voltage is maximum at the ends

Voltage is maximum at the centre and current at the ends

Where is the radiation of a half-wave dipole maximum?

Equally in all directions in 3D

The input resistance of a half-wave dipole is about 73 ohm, which:

Is too low to be fed by any cable

Is equal to the free-space impedance

2067 Mangsir · 6 marks

Short note: λ/2 dipole antenna

Short answer

A half-wave (λ/2) dipole consists of a conductor of total length λ/2, center-fed, with each arm λ/4. Its radiation pattern is doughnut-shaped, maximum broadside; input impedance is about 73 Ω; gain is 2.15 dBi. It is the basic reference antenna in many arrays.

Write a short note on λ/2 dipole antenna.

A half-wave (λ/2) dipole antenna is the basic and most widely used antenna. It is a straight conductor of total length equal to half the wavelength (λ/2), split at the centre where the feed line is connected. Each arm is λ/4 long.

     <----- λ/2 ------>
     ===========+=========
      λ/4     feed    λ/4
                |
         transmission line

 Current:   0 -- max -- 0     (current is max at centre,
 Voltage:  max -- 0 -- max     voltage is max at the ends)

Features

Length: L = λ/2 = c/(2f). In practice the length is about 5 % shorter (end effect), L ≈ 143/f (MHz) metres.
Radiation pattern: doughnut-shaped in 3D; figure-of-eight in the plane containing the wire. Maximum radiation is at right angles to the wire, and zero along its axis.
Input (radiation) resistance: about 73 Ω at the centre, which matches 75 Ω coaxial cable.
Gain: 1.64 (2.15 dBi) over an isotropic antenna; beamwidth about 78°.
Polarization: linear, in the direction of the wire (horizontal or vertical).
Resonant antenna, so it has narrow bandwidth.

Uses

TV and FM receiving antennas, amateur radio, and the driven element in Yagi-Uda arrays; used as a reference for other antennas.

✓ Answer checked by Claude Opus 5.5 (high effort)

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Short note: λ/2 dipole antenna

Features

Uses

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