Monopole vs Dipole Antenna

Key Takeaways

• Monopole antennas depend on a physical ground plane for operation, while dipole antennas use an additional radiator to create a virtual ground plane.
• Monopole antennas have directional radiation patterns influenced by the ground plane's orientation and lack vertical symmetry. In contrast, dipole antennas feature a bi-directional, vertically symmetric pattern, offering more flexibility in placement and orientation.
• Monopole antennas can use unbalanced (coaxial) feedlines without additional components, simplifying their integration into certain systems.

Dipole (left) vs monopole (right) antenna diagrams

Linear antennas are one of the most common types,  encompassing both monopole and dipole variants. These antennas have electrically conductive radiating components that are powered symmetrically at the midpoint or asymmetrically at the base against the ground. The core difference between monopole vs dipole antenna is that a dipole incorporates an extra radiator to create a faux ground plane, while a monopole antenna requires an actual ground plane. Continue reading as we delve into the details of what this entails.

Comparing Monopole vs Dipole Antennas 

The Main Difference Between Monopole vs Dipole Antennas Is the Ground Plane 

Contrary to what its name suggests, a monopole antenna relies on a conductive ground plane to facilitate the flow and return of opposite currents to the feedpoint. A dipole antenna employs an additional radiator to create an artificial ground plane situated between its symmetric radiating elements.

Voltage always needs a reference point, and so in a dipole, the voltage is measured across the two ends of the antenna. In the case of a monopole, the voltage is measured between one end of the antenna and the ground plane. Essentially, the ground plane acts as a substitute for one of the rods in a dipole antenna configuration.

Explaining Ground Planes

When a point charge is positioned above an infinitely large grounded conducting plate, according to Gauss' Law—the scenario becomes electrically equivalent to having an electric dipole in open space, aligned vertically and centered directly above where the plate's surface would be, affecting only the region above the plate.

In both cases, shown in the image below, the resulting electric field in the space above the plate mirrors what would occur if, instead of the plate, there was a negative point charge located symmetrically below the positive charge.

Diagram explanation of how the ground plane mimics the other end of the dipole antenna in a monopole antenna.

Therefore, when placing a monopole antenna above this infinite conducting plate, the electromagnetic fields (both E-electric and H-magnetic fields) generated above the plate are analogous to those produced by a dipole antenna. This means the radiation patterns of quarter-wave monopoles and half-wave dipoles above the plate are effectively identical.

Think of the ground plane as a reflective mirror. Placing a monopole antenna protruding from such a mirror creates the visual and electrical illusion of a dipole antenna to receivers due to the mirror image effect, even though there's actually just one antenna element present.

While it's impossible to have truly infinite plates in reality, using sufficiently large conducting surfaces can serve as an effective approximation of this concept.

Radiation Pattern

Monopole and dipole antennas share similar radiation patterns and levels of performance, but monopoles lack vertical symmetry. Dipoles are more commonly used due to their flexibility. The requirement for a ground plane in monopole antennas introduces size and design limitations, and the monopole's radiation pattern is influenced by how the ground plane is positioned. Conversely, dipole antennas feature a radiation pattern that is symmetric along the vertical axis, making them easier to align for optimal signal reception or transmission.

Unlike dipoles, the radiation from monopole antennas is affected by the ground plane's orientation. Dipoles offer the advantage of being able to radiate effectively regardless of a device's ground plane orientation, providing more flexibility in their placement and orientation.

Monopole vs Dipole Antenna Types

Dipole antennas are more prevalent than monopole antennas, leading to a wider array of types and designs, such as the widely used half-wavelength dipoles. In contrast, examples of commonly found monopole antennas are those used in automotive AM radio systems and low-frequency antennas used in naval applications.

Radiating Element Orientation

In a dipole antenna, the radiating elements are aligned in opposition to each other by 180 degrees, similar to the configuration of the inner and outer conductors in a coaxial cable. Conversely, for a monopole antenna, the transmission line's reference plane, or the coaxial cable's outer conductor, serves as the monopole's ground plane.

Use of Baluns at the Feed Point

Dipole antennas are inherently balanced and require either a balanced feedline or a balun at its feed point for proper operation. Unlike dipoles, monopoles can efficiently utilize unbalanced (coaxial) feedlines without complications.

Simulating Monopole and Dipole Antennas With Cadence AWR tools

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