Basics of Waveguide Antennas

A waveguide antenna is a type of antenna that channels RF energy from an air medium into a waveguide, or vice versa. Once the RF energy has been captured, it is either conducted through waveguide interconnect, or picked up by a coaxial interface to later be transmitted through a coaxial assembly. The reverse is also true, as waveguide antenna are symmetric systems. The range of frequencies and antenna polarization depend on the size and type of waveguide antenna, of which there are many standard forms. Much like with any antenna, the following parameters are key when selecting a waveguide antenna.

Key Takeaways: 

• Waveguide antennas use hollow metallic structures to guide and radiate electromagnetic waves efficiently, minimizing loss at high frequencies.
   

• The internal dimensions of the waveguide are proportional to the operating wavelength, directly affecting bandwidth and cutoff frequency.
   

• Common types include horn, conical, probe, and omnidirectional waveguide antennas, each designed for specific beamwidth and gain needs.
   

• Horn antennas, one of the most popular waveguide designs, transition energy smoothly from the waveguide to free space for high directivity.
   

• Waveguide antennas provide low insertion loss, high power handling, and excellent isolation, ideal for radar, satellite, and test equipment.
   

• Proper polarization alignment and waveguide interface compatibility are critical for minimizing reflection and maximizing performance.
   
• Their robust construction makes them reliable in harsh environments, supporting long-term stability in defense and aerospace applications. 

Important Waveguide Antenna Parameters

•  Frequency Range (waveguide band or coaxial bandwidth for broadband waveguide antenna)
• Gain
• Beam Width (Horizontal Beam Width)
• Beam Height (Vertical Beam Width)
• Impedance
• Input VSWR
• Antenna Pattern
• Polarization
• Interface (Coaxial or waveguide)
• Size
• Weight
• Input Power Handling

Waveguide antennas are also limited in frequency by the size of waveguide internal to the antenna, as well as the antennas physical dimensions. In some cases, such as with broadband antenna with a coaxial interface, the frequency range is limited by the design of the antenna and the coaxial interface. In general, the strengths of waveguide interconnect, such as high power handling, enhanced shielding, and low loss, are also shared with waveguide antenna with the exception of waveguide antenna with coaxial interface. Moreover, waveguide antenna frequency operation is also dependent on physical dimensions, and lower frequency waveguide antenna tend to be impractically sized for many applications.

There are several varieties of waveguide antenna, each with their specific advantage for a given set of applications. The commonly available varieties are included in a list below:

Waveguide Antenna Types

• Standard Gain Horn
• Conical Horn
• Conical Gain Horn
• Probe
• Lens Horn
• Sector
• Omni-directional
• Broadband Horn
• Wide Angle Scalar Feed Horn
• Circular Scalar Feed Horn
• Dual Polarized Horn
• Dual Polarized Feed Horn
• Dual Polarized Scalar Feed Horn

Waveguide Standard Horn Antenna, Conical (Circular) Horn Antenna, Exponential (Scalar) Horn, & Sector (Sectoral or Wide Angle) Horn Antenna

A horn antenna is a waveguide antenna with a flaring metal shape that resembles a musical horn, hence its name. Horn antennas are directional antennas that are either rectangular (standard or pyramidal horn) or circular (conical) in nature. These shapes lead to varying polarizations, either linear or circularly polarized. A horn antenna can also be designed with curved sides, which can have a pyramidal or conical cross section. This design allows for minimized internal reflections and near constant impedance over a wide frequency range. Sectoral horns are also possible with one side of a pyramidal horn being parallel instead of flared, which produces a fan-shaped beam pattern.

Waveguide Gain Antenna

The low loss of a waveguide antenna allows for ints directivity to be almost equal to the antenna’s gain. Hence, these antennas may exhibit a high gain if the directivity of the antenna is very narrow, which is determined by the shape and size of the antenna.

Waveguide Probe Antenna

Waveguide probe antennas are generally designed for sampling radiated electromagnetic fields of an antenna under test while only minimally disturbing the incident field. They are often used to measure the near-field of test antenna structures.

Waveguide Lens Antenna

A lens antenna uses the properties of a lens (convergence and divergence) to focus the RF energy captured by a waveguide antenna to a point source, which is typically a coaxial probe (receptor) with a waveguide antenna as the feed antenna. Lens antennas are generally used in applications that require wide bandwidth and highly directive antenna.

Waveguide Omni-direction Antenna

An omni-directional waveguide antenna is designed in such a way that the antenna pattern radiates in 360 degrees, as opposed to a fan-shape or single lobe with horn antennas.

Waveguide Broadband Antenna

A broadband waveguide antenna is designed in such a way to direct RF energy over a wide bandwidth to an interface receptor (typically coaxial) that can handle the desired bandwidth of the antenna. The design consists of exponential sloping waveguide sides and possibly inserts that enable the wide bandwidth operation.

Waveguide Feed Antenna

A feed antenna is used to direct RF energy to another antenna or receptor. Hence waveguide antennas are sometimes called feed antennas or feed horns depending on the type of waveguide antenna.

Waveguide Dual Polarized Antenna

Dual polarized waveguide antenna are designed to support both linear and elliptical polarized waveforms.

Learn more about Pasternack’s Expansive line of Waveguide Antennas

FAQs (Frequently Asked Questions) 

Q1: What is a waveguide antenna? 

 A: A waveguide antenna channels RF energy between free space and a waveguide or vice versa essentially coupling radiated electromagnetic waves into (or out of) a metallic waveguide structure.  

Q2: What are the core parameters to check when selecting a waveguide antenna?
A: Key parameters include frequency range (waveguide band or coaxial interface), gain, beam width (horizontal and vertical), impedance, input VSWR, antenna pattern, polarization, interface type (coax or waveguide), size, weight, and power-handling.  

Q3: Why is the size of a waveguide antenna linked to frequency?
A: Because the internal dimensions of the waveguide must support the waveguide mode (e.g., TE10 for a rectangular waveguide). Lower frequencies have longer wavelengths → larger waveguide dimensions → often impractical size for many applications.  

Q4: What types of waveguide antennas exist?
A: Some common types: standard (pyramidal/rectangular) horn, conical horn, probe antenna, lens horn, sector horn, omnidirectional waveguide, dual-polarized waveguide, broadband waveguide antennas.  

Q5: What makes waveguide antennas suitable for high-power or high-frequency systems?
A: Waveguide structures inherently provide low loss, high isolation, and high power-handling capacity compared to many coaxial systems — these advantages carry over waveguide-antenna designs too.