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Difference between Dipole Antenna and Monopole Antenna

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Difference between Dipole Antenna and Monopole Antenna

The main differences between the Dipole Antenna and the Monopole Antenna are the structure and the principle of operation.The main differences are as follows:

1. Structure

A dipole antenna consists of two symmetrical conductor elements, while a monopole antenna consists of a conductor element and a ground plane.Simply put, a dipole antenna has two symmetrical poles, while a monopole antenna has only one pole, and the other half is replaced by a ground plane.As shown in figure:

Project	Dipole Antenna	Monopole Antenna
Number of conductors	Two symmetrical conductors (positive & negative)	Single section conductor
Total length	Typically λ/2 (λ/4 per segment)	Typically λ/4
Grounding requirements	A ground plane is not required	Must rely on ground plane (e.g. metal plate, car body)
Feed mode	Balanced feed (balun may be required)	Unbalanced feed (direct connection to coaxial cable)
Examples	TV antenna, shortwave communication antenna	Vehicle antenna, mobile phone antenna, interphone antenna

Dipole Antenna vs Monopole Antenna

2. Radiation characteristics

The Dipole radiation pattern is a symmetrical "figure-of-eight" (omnidirectional in the equatorial plane, with zero axial radiation).The gain is slightly higher than that of the monopole (about 2.15 dBi).The Monopole radiation pattern is similar to the upper half of a dipole (depending on the ground plane), which is omnidirectional in the horizontal plane.The vertical radiation is concentrated in the upper hemisphere. Gain is about half that of a dipole (about 0-3 dBi, depending on ground plane quality)

Project	Dipole Antenna	Monopole Antenna
Radiation pattern	Symmetrical "figure-of-eight" (equatorial plane omnidirectional, axial non-radiating)	Only the upper hemisphere radiates (like one half of a dipole)
Gain	About 2.15 dBi	~ 0-3 dBi (depending on ground plane quality)
Polarization mode	Linear polarization (usually vertical)	Linear polarization (more affected by ground plane)

Dipole electromagnetic field mode

Lectromagnetic field pattern of monopole antenna

3. Impedance and bandwidth

Dipole has a theoretical input impedance of 73 Ω (in free space), but is actually closer to 50 Ω or 75 Ω (for easy matching with common RF cables).Narrow bandwidth (especially for half-wave dipoles).The Monopole input impedance is half that of a dipole (about 36 Ω) and is typically trimmed to 50 Ω by a matching network.The bandwidth may be wider (especially if the ground plane is large).

Project	Dipole Antenna	Monopole Antenna
Input impedance	Approx. 73 Ω (free space)	Approx. 36 Ω (to be matched to 50 Ω)
Bandwidth	Narrow (especially for half-wave dipoles)	Possibly wider (the larger the ground plane, the better the bandwidth)

4. Application Scenario

Dipole requires symmetrical radiation or high-gain scenarios (such as short-wave communication, directional transmission).Keep away from metal objects (avoid ground plane interference).Monopole is used in portable devices (such as mobile phones, walkie-talkies) and vehicle antennas (using the vehicle body as the ground plane).Suitable for space-constrained scenarios (single conductor only).

Project	Dipole Antenna	Monopole Antenna
Applicable scenarios	High-gain and symmetrical radiation (such as short-wave communication and TV antenna)	Portable equipment (mobile phone, walkie-talkie), vehicle antenna
Installation requirements	Keep away from metal objects (avoid interference)	Dependence on ground plane (e.g. car body, PCB floor)

Dipole antenna

Monopole antenna

Other key differences

Ground Dependence: Monopole must have a ground plane or performance drops dramatically; Dipole does not need a ground.

Size: The Monopole has a shorter physical length (λ/4 vs. λ/2), but the ground plane size is taken into account.

Polarization: Both are linearly polarized (usually vertically), but Monopole is more affected by ground plane irregularities.

Project	Dipole Antenna	Monopole Antenna
Size	Longer (λ/2)	Short (λ/4), but need to consider the size of the ground plane
Performance dependency	Its own structure determines its performance	Performance is highly dependent on ground plane quality
Applicable frequency	Suitable for fixed frequency band	Bandwidth can be optimized by adjusting the ground plan