This article was originally published on the Ansys Blog: "An Introduction to Common Antenna Designs".
Introduction
If you are reading this on a mobile phone or a laptop, an antenna is enabling that connection. Antennas are integral to many systems, from video games and car navigation to deep-space asteroid tracking. Although antennas are ubiquitous, their designs and applications vary widely.
How antennas work
All antennas, from simple wire dipoles to MIMO phased arrays, perform the same basic function: they transmit and receive electromagnetic signals. Electrical signals are converted into propagating electromagnetic waves. Information is encoded onto those waves at specific wavelengths, transmitted through space at the speed of light, and then received and decoded by another antenna at the destination.
Horn antenna example
Wireless connectivity enabled by antennas is essential across many sectors, including healthcare, aerospace, telecommunications, and mobile devices. As antenna use grows, the number of antenna types required for different applications also increases.
Why different antenna types exist
Several factors determine the optimal antenna type for a given application, such as coverage area and available physical space. For example, antennas that keep an aircraft in contact with a control tower are very different from the tiny antennas embedded in a Bluetooth-enabled coffee mug. Both may need omnidirectional coverage, but the aircraft antenna requires much larger range while the mug requires a solution that fits into a very small volume.
Antenna design criteria
- Bandwidth: the frequency range for a specific signal
- Polarization: the orientation of the radiated electric field
- Directivity: how concentrated the radiation is in a given direction
- Physical space: the available volume for mounting the antenna
- Gain: transmitted power in the direction of maximum radiation
- Efficiency: the ratio of radiated power to input power
Common antenna types
Understanding the general characteristics of common antenna types helps when selecting an antenna for a practical application.
Sample antenna types from left to right: horn, slot, Yagi-Uda, and rectangular patch antenna
Half-wave dipole
The half-wave dipole is based on the simple dipole, which consists of two conductive rods or wires and is one of the simplest practical antennas. "Half-wave" indicates that the antenna's physical length is half the operating wavelength.
Half-wave dipoles are common because they are easy to design and build. They typically have clean linear polarization and an azimuthally symmetric radiation pattern.
A half-wave dipole consists of a straight conductive element of length L = λ/2, usually fed at the center. While they are often narrowband, increasing the conductor radius used to form the antenna body is an effective way to increase bandwidth.
Planar inverted-F antenna (PIFA)
PIFAs are commonly found in mobile phones and many other electronic devices. They are a variant of the dipole, inexpensive to manufacture, and can be fabricated in many forms to achieve different bandwidths, making them suitable for constrained spaces.
Horn antenna
Horn antennas are used where high directivity is required, such as radar speed guns. They have a relatively simple geometry and can handle higher power with low loss.
A horn antenna consists of a waveguide section that flares outward to an open aperture. The horn increases directivity and narrows the beamwidth in the horn plane. A horn may flare in the electric-field direction only (E-plane sectoral horn), the magnetic-field direction only (H-plane sectoral horn), or both directions (pyramidal horn).
Horn antennas generally have very wide bandwidth, operate above the waveguide cutoff frequency, and radiate linearly polarized waves aligned with the field direction inside the waveguide.
Yagi-Uda antenna
The Yagi-Uda antenna, often called a "Yagi," consists of a single driven dipole working with an array of additional passive linear elements. These antennas are effective in applications requiring high directivity and are commonly used for television reception.
The number of reflector and director elements varies, but a typical design includes one reflector element and three director elements. The reflector is slightly longer than the driven dipole, and the directors are slightly shorter.
Unlike an isolated dipole with azimuthal symmetry, a Yagi exhibits strong directivity, with maximum radiation toward the directors and away from the reflector. Like dipoles, Yagis are narrowband and linearly polarized, with the electric field aligned with the dipole.
Slot antenna
Slot antennas are based on the same principle as dipoles but use magnetic currents rather than electric currents. They are found on aircraft fairings and printed circuit boards.
A slot antenna consists of a rectangular half-wavelength "slot" in a planar conductor. By Babinet's principle, a slot operates similarly to a half-wave dipole. The radiation fields are roughly analogous to those of a dipole, but the roles of the electric and magnetic fields are exchanged. The radiation pattern of a slot approximates that of a dipole, with mild asymmetry due to the truncated ground plane. Bandwidth varies with slot width, and polarization is linear with the electric field oriented perpendicular to the slot length.
Rectangular patch antenna
Rectangular patch antennas are a common choice for low-profile applications and can be printed on flat surfaces such as mobile devices. Though the concept is simple, patches can be modified to widen bandwidth, increase isolation, or operate at multiple frequencies.
A rectangular patch consists of a rectangular conductive element of width W and length L on a dielectric substrate of thickness d and relative permittivity εr, with a conductive ground plane. Radiation arises from resonant fields in the cavity beneath the patch. Resonance occurs when the antenna length is slightly less than half the guided wavelength, since fringing at the patch edges makes the patch appear electrically longer than its physical length.
Patches are typically fed by microstrip lines, coaxial probes through the dielectric, or by coupling to resonators or other nearby structures.
Design validation
To determine the best antenna type for a project, engineers use electromagnetic simulation tools such as Ansys HFSS to test and validate designs. Simulation can reveal performance differences between antenna configurations for satellites, PCBs, and other high-frequency electronic devices.
