Antenna Showdown – Sector vs. Horns
In this technical article, we dig into the major distinguishing features of horn and sector antennas to help you determine the best solution for your wireless deployments. We will focus on how their radiation and physical characteristics differ in both specification and definition and in which application one type is suited over the other
Sector antennas are typically long, narrow, and rectangular in shape and are either partially or fully enclosed inside of a UV-resistant radome. Their interior is composed of multiple antenna elements that are connected and arranged in a vertical array. Despite having 3dB azimuth beamwidths of 33°, 45°, 60°, 90°, or 120°, sector antennas are afforded high gain from their narrow elevation beamwidths which can be as low as 4°. Therefore, a sector’s vertical height dictates its gain and, in a world where gain is king, it is no wonder why they have proliferated as the workhorse in point to multipoint applications. Despite having larger azimuth beamwidths, KP’s sector antennas are optimized to have front to back (F/B) greater than 30dB and reduced side lobes, which mitigates self-interfaces and allows reuse of spectrum on the same tower. Sector antennas are well suited for both rural and suburban environments in which coverage must reach out 200 yards to 10s of miles.
Horn antennas are smaller in size and circular, rectangular, or elliptical in shape. They are constructed from a flared metallic circular or rectangular waveguide with flanges or chokes along its length which provide low side lobe levels and moderate F/B ratios. Because of their nearly symmetric height and width, they have nearly equal elevation and azimuth beamwidth and low-to-moderate gain. Their azimuth and elevation beamwidths are defined using their 6dB beamwidth, which is an apt departure from the standard 3dB beamwidth definition used for sector antennas. When compared to a sector antenna, the horn's overall lower gain will not provide near-to the same level of coverage over a wide range of angles. However, the horn’s small size, highly focused main beam, and reduced side lobes allows for two or more horns to replace a single wide-angle sector antenna, densifying the network and increasing the capacity without overloading the tower. Albeit, additional spectrum is required in this case and the drop-in gain over a sector antenna reduces the radial coverage from the access point.
Asymmetric horns have larger flair angles in the vertical/elevation direction as opposed to the horizontal direction. As a result, their elevation pattern can be more focused then the azimuth pattern, which increases overall higher gain over symmetric, circular horn antennas but at a cost of higher side lobes and worse F/B.
An extremely important consideration when comparing sector and horn antennas is in the definition of beamwidth. As mentioned, a horn antenna’s beamwidth (listed on its datasheet) is defined at 6dB (or ¼ power), whereas a sector antennas beamwidth (listed on its datasheet) is defined at 3dB (or ½ power). As a result, a 13dBi horn antenna with a 60° beamwidth will have the gain drop to 7dBi at the edge of the Horn’s coverage area. A sector antenna with a 17dBi beamwidth and a 60° beamwidth will have the gain drop to only 14dBi at the edge of the sector’s coverage area. The sector’s higher gain across the entire coverage area will increase signal strength in the link and improved coverage.
While all seems lost for the horn antenna, remember that the link budget is highly dependent on both transmit power, antenna gain, and the background noise in the area – whether it is self-interference or external. A horn’s narrow azimuth beamwidth and low side lobes helps improve signal to noise ratio (SNR) by reducing the noise level in the link. As a result, the horn antenna is well suited for environments in which a noise source is not coming from the intended area of coverage.
The above figure depicts the azimuth patterns of a 2-port, 60° (16.5dBi) and 90° (15.5dBi) asymmetric horns with elevation beamwidths approximately 16° as compare to 4-port, 65° sector antenna (17.5dBi) and elevation beamwidth of 8°. Due to the difference in definition of beamwidth between a sector (3dB) and horn (6dB) antenna, the 65° sector antenna is more honestly compared to the 90° horn antenna, since their 3dB beamwidths are nearly equal. This can be seen in the polar plot on the left, in which the normalized patterns for each antenna are shown. It is clear when comparing the sector antenna (red curve) and 90° horn (green curve) that the patterns and side lobes are essentially identical. However, the 65° sector antenna has 1-2dBi higher gain over the intended coverage area of , 5-8dB higher F/B, a lower physical profile, and more ports to support 4x4 MIMO with a single antenna. It goes to show that an asymmetric horn is just another method to realize the patterns from a sector antenna, but with generally worse RF performance.
The above image depicts the RF coverage of 90° and 60° asymmetric horns and the 65° sector. The sector antenna provides higher signal strength and larger coverage area over both asymmetric horns due to the sector’s narrower elevation beamwidth and higher gain. Take note that this study does not account for the impact of noise on SNR. The lower side lobes of the 60° asymmetric horn may result in higher SNR over the sector antenna in environments with external noise.
As a general guideline, the sector antenna’s high gain is ideal for covering large distances and wide areas with a consistently high link strength. A horn antenna’s focused beam is ideal for covering short-to-moderate distances or in areas in which background noise is highly prevalent and can be mitigated. In both cases, the goal is to maintain a high SNR to ensure your network is achieving peak-possible modulation rates.
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