The Pros and Cons of Vivaldi Antennas
An Introduction to Vivaldi Antennas
There are three main types of Vivaldi antennas: the coplanar Vivaldi, the antipodal Vivaldi and Balanced Antipodal Vivaldi antenna. What are the pros and cons of Vivaldi antennas? What are the advantages and disadvantages of these Vivaldi antenna designs?
The Advantages of Vivaldi Antennas
Vivaldi antennas are planar antennas that work over a wide frequency range. Vivaldi antennas, like ridge horn antennas, have high gain due to their tapered slot design.
Vivaldis fit into smaller spaces than a ridge horn antenna because they can be made out of flat laminate.
Vivaldi antennas are usually ultra-wide band antennas and always count as broadband antennas. They can be used with both multi-band and impulse technologies.
When used for pulse technologies like radar, Vivaldi antennas have a high peak value for the pulse envelope. They offer stable group delay and allow for a narrow pulse width.
Their upper frequency is limited by the width of the gap, while the lower frequency by the size of the opening.
The design is simple compared to log periodic antennas and fractal designs. And all antenna designs can be scaled for use at any frequency.
Impedance matching is easy with Vivaldi antennas.
The coplanar Vivaldi is the original design. It features two radiator planes on the same side of the dielectric sheet, the other side of which is a neutral material. This design and the more complex ones can all be made via printed circuit board technology.
You can make the Vivaldi antenna notch using egg crate construction. In the egg crate design, the boards cross at the edge of each element. Notching the boards helps hold them in place with positional accuracy. The PCB manufacturing method allows them to be made in strips that are readily put in these “egg crate” configurations.
Vivaldi antennas can be fed a signal directly from a strip line or microstrip line, which also allows them to work in phased array applications. You don't have this flexibility with many antenna designs.
The Disadvantages of Vivaldi Antennas
If you only plan to use the Vivaldi antenna on one frequency or a small range of frequencies there are smaller and higher gain antenna designs. Gain refers to the ability of the antenna to radiate power in a specified direction.
They cannot really be extended beyond 10 dBi of gain, unless used as a dish feed.
The Balanced Antipodal Vivaldi antenna or BAVA usually suffer from tilted beams and low axial gains.
A Vivaldi antenna can be fed by an aperture coupling or broadband balun, but this can add complexity to the design. Making an antipodal Vivaldi antenna with the antenna elements printed on opposite sides of the PCB substrate, is more expensive than the basic design. The antipodal Vivaldi antenna’s impedance matching can be done through a transition from strip line to a micro-strip line. However, this design increases cross polarized radiation.
The balanced antipodal Vivaldi antenna tries to prevent this cross polarized radiation by adding yet another dielectric sheet on top of the antipodal structure, while a metal plate is put on the bottom of the antenna. The downside of this design is that the cost of a printed circuit board is significantly related to the number of layers and complexity of the design.
Antenna depth is a common problem for Vivaldi antennas. This is only partially resolved by putting dielectric covers at the aperture of the Vivaldi antenna.