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Overview
For terminal-mount external omnidirectional antennas, their sizes and frequency range directly influence the antenna gain. The 2dBi, 3dBi, or 5dBi gain of these antennas is determined by their operating frequency and physical dimensions (length). When the antenna’s size is insufficient, achieving the intended omnidirectional gain becomes impossible.
This article aims to offer a comprehensive antenna selection guide by understanding the relationship between the terminal antenna’s size and gain.
What is antenna gain?
Antenna gain refers to the ability of an antenna to focus signals in a specific direction. It’s like an amplifier that helps concentrate the signal in a particular direction, making the signal stronger and farther-reaching.
In electromagnetics, an antenna’s gain is a key performance parameter that combines the antenna’s directivity and radiation efficiency. Gain or ‘absolute gain’ is defined as “The ratio of the radiation intensity in a given direction to the radiation intensity that would be produced if the power accepted by the antenna were isotropically radiated”. Usually, this ratio is expressed in decibels concerning an isotropic radiator (dBi).
What is the relationship between the antenna’s size and gain?
1.1 Low-gain (≤2dBi) External Omnidirectional Antenna with Terminal Mount
1.1.1 Implementation Method
From the perspective of structural design principles, low-gain external omnidirectional antennas widely used in terminal devices are mostly in the form of monopole antennas (ground-dependent antennas) or dipole antennas (ground-independent antennas).
Definition of Ground-Dependent Antennas (Taking the monopole antenna as an example):
An antenna that requires the ground (the metal part of the terminal) to form a complete electromagnetic radiation circuit for normal operation is called a ground-dependent antenna.
The monopole antenna is a typical ground-dependent antenna. It consists of a metal conductor that is perpendicular to the ground, with a length typically about a quarter of the wavelength of the operating frequency.
Definition of Ground Independent Antennas (Taking the dipole antenna as an example):
Ground-independent antennas refer to antennas that can form complete electromagnetic oscillations and radiation systems on their own, without relying on the ground (the metal part of the terminal) for radiation.
The dipole antenna consists of two metal conductors of equal length and the same thickness. They are separated by a certain distance at the center and electrically insulated from each other, forming a symmetrical structure.
1.1.2 Physical Characteristics
Usually, omnidirectional terminal antennas with a gain below 2dBi are physically small and light. However, when the required omnidirectional gain exceeds 3dBi, their size becomes larger than that of a 2dBi antenna.
| Wireless Technology | Frequency (MHz) | Monopole (mm，1/4λ) | Dipole (mm，1/2λ) | Reference Products | ||
| The minimum antenna length | Antenna length (mm) | Theoretical gain (dB) | Antenna size (with enclosure) (mm) | Gain (dBi) | ||
| 433 LoRa | 433 | 173 | 346 | 2.15 | / | / |
| LoRa | 868 | 86.5 | 173 | 2.15 | Φ13 x 195 | 2.15 |
| 4G | 800 | 93.75 | 187.5 | 2.15 | 58 x 221.7 | 1.72 |
| WiFi | 2450 | 30.6 | 61.2 | 2.15 | Φ13 x 195 | 2.0 |
Note: When the antenna gain is not an important factor, we can design the antenna in a helical form to achieve miniaturization.
2.1 High-gain (≥3dBi) External Omnidirectional Antenna with Terminal Mount
2.1.1 Implementation Method
To achieve high-gain external omnidirectional antennas with 3dBi or higher, traditional monopole or dipole antenna structures often fail to meet performance requirements. Instead, array antenna technology is typically utilized.
A common example is the two-element or three-element linear array omnidirectional antenna. The principle behind achieving high gain in such designs relies on the coherent superposition effect of antenna arrays. Multiple identical radiating elements, such as dipole elements, are arranged in a straight line with precise spacing to form a linear array.
For example, some of Aboosty’s fiberglass antennas adopt the dipole colinear array antenna structure above.
Theoretically, when stacking idealized lossless dipole antennas in such a fashion, doubling their number will produce double the gain, with an increase of 3.01 dB. In practice, the gain realized will be below this due to imperfect radiation spread and losses.
2.1.2 Physical Characteristics
High-gain external omnidirectional antennas, owing to their array design, exhibit distinct physical characteristics compared to low-gain single-element antennas.
Taking high-gain omnidirectional antennas used in outdoor LoRa base stations as an example, they typically feature multiple metal radiating elements (such as dipoles) neatly aligned along a vertical supporting mast, resulting in a pole-like shape.
The outer shell of the antenna is typically made from waterproof, UV-resistant, and corrosion-resistant engineering plastics or metal materials. This ensures durability in harsh outdoor environments and enhances its reliability.
Conclusion
For external terminal antennas with omnidirectional radiation patterns, the antenna gain is closely related to the antenna’s size, primarily its length, under a fixed operating frequency determined by the network protocol.
When the antenna length is equal to half the wavelength of the operating frequency, its gain is approximately 2 dBi.
When the antenna length exceeds one wavelength of the operating frequency, its gain can potentially exceed 3 dBi.
Of course, other factors also influence antenna gain, such as material, manufacturing processes, and the surrounding electromagnetic environment. However, antenna length plays a vital role among these factors.
For more detailed guidance and to explore our range of antennas, please visit our product collections. If you have specific requirements or need technical support, feel free to reach out to us. Stay tuned with technical insights and industry updates by subscribing to our blog.
FAQs
Is a higher terminal antenna gain always better?
A higher-gain antenna is not always the best choice. For terminal internal antennas, because the direction of the received signals is unpredictable, it’s crucial to ensure a stable signal reception from all directions rather than pursuing higher gain.
If the antenna provides horizontal omnidirectional coverage for terminal external antennas, a higher gain can help receive further signals. However, if omnidirectional coverage is not required, higher gain only enhances signal reception in specific directions, which may increase the antenna’s size and cost. Thus, a higher gain is not always better.
Why do antennas of the same size have gain differences? Why is your antenna gain 1dBi lower than that of other manufacturers? If the customer requires the antenna gain to reach 5dBi, is it achievable?
1) Variations in testing environments, mounting heights, and design priorities result in gain and performance differences.
2) Our antenna may have a 1dBi lower gain, for we focus more on the stability of omnidirectional signal coverage rather than merely achieving a higher gain.
3) It is possible to achieve 5dBi gain through design optimization, but this may increase costs and production time.
Can I increase the gain by 2dB without changing the antenna housing?
Yes. Without changing the antenna housing, it is possible to increase the gain by up to 1dB through internal structure optimization and material upgrades. However, it would likely require design modifications or new components to achieve an additional 2dB gain.
What are the scenarios for high-gain and low-gain antennas (e.g., urban vs. rural)?
High-gain antennas are suitable for rural or open areas:
High-gain antennas have strong directionality, making them ideal for long-distance communication, though their coverage is narrower.
Common application scenarios include remote base station coverage, rural broadband networks, highway monitoring, and drone communications.
Low-gain antennas are suitable for urban or complex environments:
Low-gain antennas provide more uniform coverage, making them suitable for receiving signals from all directions.
Common application scenarios include urban IoT devices (e.g., smart streetlights), indoor communication in shopping malls or underground parking lots, and areas with significant multipath interference.