Loop antennas are widely used in radio communications and reception due to their ability to provide excellent signal capture, low noise characteristics, and directional performance. Traditional loop antenna designs often follow square or circular geometries, but a relatively less common shape—the Octaloop—offers significant advantages. This article explores why an octagonal loop design outperforms square and circular loop configurations.

1. Improved Efficiency and Radiation Pattern

Square vs. Octagonal Loop

A square loop consists of four sides, each acting as a radiating element. However, the sharp corners create impedance discontinuities and result in current concentration, leading to increased losses and suboptimal radiation efficiency.

An octagonal loop, on the other hand, smooths out these discontinuities by increasing the number of segments. This results in a more uniform current distribution, reducing unwanted reactive components and improving radiation efficiency. The more continuous structure of the Octaloop contributes to better electromagnetic wave propagation and reduced signal degradation.

Circular vs. Octagonal Loop

A circular loop provides the most uniform current distribution and minimizes impedance discontinuities. However, constructing a perfect circle with rigid conductors is impractical, and slight deformations from the ideal shape can cause inconsistencies. An octagonal loop closely approximates a circle while being easier to construct and maintain structural integrity, offering the benefits of a circular loop without the practical challenges.

2. Structural and Mechanical Stability

A square loop can suffer from mechanical weakness due to stress concentration at its corners, leading to potential bending or damage under physical strain (e.g., wind loading). A circular loop, while structurally efficient, often requires specialized rigid materials and complex mounting techniques.

The Octaloop design balances structural integrity and ease of construction. By incorporating more sides, stress distribution is improved, making the antenna more resistant to mechanical failure while still being easier to build than a perfect circle. This makes it an excellent choice for portable and permanent installations.

3. Optimized Inductance and Impedance Matching

Loop antennas inherently rely on inductance for their operation. The inductance of a square loop is slightly lower due to its corner discontinuities, while a circular loop maximizes inductance by maintaining a constant radius.

The Octaloop achieves a near-optimal inductance level without the complexity of a circular structure. This allows for better impedance matching, reducing the need for additional matching networks. In practical terms, this means lower losses and better performance in terms of SWR (standing wave ratio) and efficiency across a wider frequency range.

4. Reduced Proximity Effects and Mutual Coupling

When deploying loop antennas in arrays or close to other conductive structures, mutual coupling can degrade performance. Square loops have concentrated fields near corners, making them more susceptible to interference. Circular loops distribute the field more evenly but can still exhibit excessive coupling effects in closely spaced configurations.

An Octaloop mitigates these issues by spreading the electromagnetic field more uniformly than a square while reducing excessive field interactions found in circular loops. This makes it an excellent choice for phased array systems and multiple-loop deployments.

5. Broadband Performance Enhancement

A well-designed loop antenna should perform effectively over a broad frequency range. Due to its improved current distribution and reduced impedance variations, the Octaloop offers better bandwidth characteristics compared to square and circular loops. This is particularly beneficial for multi-band HF, VHF, and UHF applications, where broadband capabilities are essential.

Conclusion

The Octaloop provides a superior alternative to both square and circular loop antennas by balancing efficiency, structural integrity, impedance matching, and field distribution. While a circular loop may offer theoretical advantages in current distribution, its practical limitations make the Octaloop a more feasible and effective choice. Compared to square loops, the Octaloop significantly reduces discontinuities, improving radiation efficiency and mechanical durability.

For radio amateurs, professional communication systems, and scientific applications, the Octaloop represents an ideal compromise between performance and practicality, making it the preferred choice for modern loop antenna designs.

Article written by Joeri Van Dooren, ON6URE – RF engineer, antenna designer, and founder of RF.Guru. With extensive experience in active and passive antenna systems, high-power RF transformers, and custom RF solutions, Joeri shares insights into cutting-edge radio communication technologies.