What is a Vivaldi Antenna?

A Vivaldi antenna, also known as a tapered-slot antenna (TSA), is a broadband planar antenna that uses a gradually widening slot to radiate electromagnetic energy. It is essentially a planar version of a horn antenna, implemented on a metallic sheet or printed-circuit substrate. Its defining characteristic is the exponential or tapered opening cut into the metal surface, which transforms guided waves into radiated waves over a very wide frequency range. Because the geometry scales with wavelength, Vivaldi antennas can be designed for many microwave and millimeter-wave bands simply by adjusting the taper length and aperture width.

The antenna operates by launching a travelling wave from a feed - typically a microstrip-to-slot transition or coaxial feed - into a narrow slot near the base of the antenna. As this wave moves along the exponentially widening slot, the structure provides a smooth impedance transition from the feed to free space. This gradual expansion is what gives the Vivaldi antenna its ultra-wideband behaviour: reflections are minimised, impedance remains well matched, and radiation increases as the slot opens into a large aperture. The width of this aperture largely determines the lower cutoff frequency and the achievable gain; a wider aperture supports lower-frequency radiation and improves directivity.

Structurally, a Vivaldi antenna consists of a metalised substrate with a tapered slot profile, a feed transition, and an open aperture for radiation. Variants such as antipodal and balanced-antipodal Vivaldi antennas place the tapered shapes on opposite sides of a dielectric to improve bandwidth, control polarisation, or support dual-polarised operation. The planar construction allows easy fabrication on common PCB materials, and the shape can be tuned - by modifying the slot rate, taper length, or substrate - to achieve different bandwidth, pattern, and gain objectives.

Vivaldi antennas are widely used because they combine broad bandwidth, moderate gain, low profile, and good impulse response. Their ability to operate over multi-octave bandwidths makes them attractive for systems that use very short pulses, frequency-hopping waveforms, or wideband sensing. They are also easy to integrate into compact systems where a traditional 3-D horn antenna would be too bulky or expensive. Designers often choose Vivaldi antennas when they need a planar, wideband radiator with stable patterns across the band, or when the antenna must be produced in volume using standard PCB processes.

Typical Specifications

• Frequency Range: Multi-octave, from hundreds of MHz to mmWave bands
• Gain: Typically 5–12 dBi; higher with arrays or reflectors
• Polarization: Linear or dual-polarized (in antipodal designs)
• VSWR: <2:1 across wideband
• Aperture Size: Defines lower cutoff frequency and gain
• Substrate: Common PCB materials (FR-4, Rogers, etc.) or metal plates