Building a High-Gain Cubical Quad Antenna for the 2-Meter Band: Tips, Formulas, Pros, and Cons

Introduction

Cubical quad antennas have been a popular choice among amateur radio operators for many years, due to their relatively simple construction and high gain. This type of antenna is especially popular for use on the 2-meter band, as it can provide excellent performance with only a moderate-sized structure. In this blog post, we will discuss the construction of a 2-meter cubical quad antenna, including construction tips, formulas, and the potential pros and cons of using this type of antenna.

What is a Cubical Quad Antenna?

A cubical quad antenna is a type of directional antenna that consists of a square or rectangular loop of wire, supported by a framework of poles or wires. The loop is fed by a single coaxial cable at one corner, and the other three corners are connected to a set of elements called "directors" or "reflectors," depending on their location and function.

The directors and reflectors are typically shorter or longer than the main loop, and their lengths are determined by mathematical formulas that take into account the frequency of operation, the size of the loop, and the desired radiation pattern. By carefully selecting the lengths of these elements, the antenna can be optimized for maximum gain, maximum front-to-back ratio, or other desired characteristics.

Construction Tips

Building a cubical quad antenna for the 2-meter band is a relatively simple process that requires only a few basic tools and materials. Here are some tips to help you get started:

Choose the right wire: The wire used for the loop and the elements should be strong, flexible, and weather-resistant. Copper-clad steel wire is a popular choice, as it combines the strength of steel with the conductivity of copper. However, any type of wire that can handle the necessary power levels and environmental conditions will work.

Calculate the dimensions: The dimensions of the loop and the elements can be calculated using a simple formula that takes into account the wavelength of the frequency of operation. For example, for a frequency of 146 MHz (a common 2-meter frequency), the wavelength is approximately 2 meters (200 cm). A full-wave loop for this frequency would be approximately 200/2 = 100 cm on each side.

Choose the right support structure: The support structure for the antenna should be strong, stable, and lightweight. Many hams use PVC pipe or fiberglass rods to support the wire elements, as these materials are strong and non-conductive.

Use a balun: A balun (short for balanced-to-unbalanced) is a device that helps to balance the electrical signal between the coaxial cable and the antenna elements. A 1:1 balun is recommended for use with a cubical quad antenna, as it will provide the best match between the two.

Test the antenna: Once the antenna is constructed, it should be tested using an SWR meter or antenna analyzer to ensure that it is resonant at the desired frequency. Adjustments can be made to the dimensions of the loop and elements as needed to achieve the best performance.

Formulas

The formulas used to calculate the dimensions of a cubical quad antenna are relatively simple and can be derived using basic trigonometry. Here are some examples:

Loop dimensions: The length of each side of the loop (L) can be calculated using the formula L = λ/4, where λ is the wavelength of the frequency of operation.

Reflector length: The length of the reflector (R) can be calculated using the formula R = 0.45λ, where λ is the wavelength of the frequency of operation.

Director length: The length of the director (D) can be calculated using the formula D = 0.42λ, where λ is the wavelength of the frequency of operation.

Spacing between elements: The spacing between the loop and the reflector (S1) can be calculated using the formula S1 = 0.15λ, while the spacing between the loop and the director (S2) can be calculated using the formula S2 = 0.21λ.

These formulas are based on the design of a 2-element cubical quad antenna, which consists of a loop and either a reflector or a director. For antennas with more elements, the formulas become more complex, as each element affects the dimensions of the others.

Pros and Cons

Like any type of antenna, a cubical quad has its advantages and disadvantages. Here are some of the potential pros and cons of using a cubical quad antenna for the 2-meter band:

Pros:

High gain: A cubical quad antenna can provide high gain, which means it can transmit and receive signals over a longer distance than other types of antennas.

Directional: The directional nature of a cubical quad antenna means it can be aimed at a specific target, such as a distant repeater or station.

Simple construction: Building a cubical quad antenna for the 2-meter band is relatively simple and requires only a few basic tools and materials.

Lightweight: The materials used for a cubical quad antenna are generally lightweight, which makes it easy to install and transport.

Cons:

Large size: While a cubical quad antenna for the 2-meter band relatively small compared to other types of antennas, it still requires a large structure to support it, which may not be practical for all installations.

Directional: While the directional nature of a cubical quad antenna can be an advantage, it can also be a disadvantage if the target station is moving or if there are multiple targets in different directions.

Cost: While a cubical quad antenna is relatively inexpensive to build, it may still be more expensive than other types of antennas, especially if you need to purchase specialized materials or tools.

Conclusion

A cubical quad antenna can be a great choice for amateur radio operators who want to achieve high gain and directional performance on the 2-meter band. With a relatively simple construction process and a few basic formulas, you can build a high-performance antenna that can provide excellent results. However, like any type of antenna, a cubical quad has its advantages and disadvantages, and it may not be the best choice for all situations. If you are considering building a cubical quad antenna for the 2-meter band, be sure to carefully evaluate your needs and the available options before making a final decision.