this comprehensive guide from Doodle Labs highlights the crucial function of antennas in optimizing the performance of UAS (Unmanned Aerial Systems) radios, along with general recommendations for antenna selection tailored to various UAS applications.
Key Factors to Consider When Choosing an Antenna
- Center Frequency, Bandwidth, VSWR, and Impedance
- Antenna Gain, Radiation Pattern, and Beam Width
- Polarization (single or Dual)
- Antenna Type and Ground Plane Selection
Center Frequency, Bandwidth, and VSWR
- Select an antenna that operates at the correct frequency and bandwidth, ensuring a favorable VSWR.
- Doodle Labs radios are optimized for a 50 Ohm impedance for optimal performance. Be aware that even antennas rated for 50 Ohms can exhibit meaningful impedance variations, so opt for high-quality options.
- Examine the radiation pattern to ensure it aligns with your request needs.
- Avoid antennas with a 75-ohm impedance, such as those typically used for television.
Antenna Gain, Radiation Pattern, and Beam Width
Just as a megaphone amplifies sound, antennas enhance RF waves. Antenna gain refers to the degree of signal amplification,while the radiation pattern indicates the directionality of RF wave emission. Beam width defines the angle over which the radio waves maintain 3dB of peak gain.
To determine the necessary antenna gain, perform a link-budget analysis based on the required network capacity and distance. Be mindful of factors that can influence RF propagation loss, such as reflections from large structures and the clearance of the fresnel Zone. For more details, refer to the Application Note, “Optimizing the RF Link” in our Technical Library.
Some antennas, like patch and parabolic dish antennas, concentrate RF waves into a cone shape, providing considerable gain but requiring precise alignment with the target.
Conversely,high-gain omnidirectional antennas spread RF waves horizontally,resembling a pancake,and offer reduced gain in the vertical plane.
Understanding Polarization
Antennas can be linearly polarized (either horizontal or vertical) or circularly polarized (CP). Polarization describes the orientation of RF waves; antennas with vertical polarization cannot receive horizontally polarized signals. Since RF wave polarization can change upon reflection from surfaces, it’s advisable to install antennas that accommodate both types of polarization.
CP antennas can be right-hand or left-hand circularly polarized, with RHCP antennas unable to receive LHCP signals. CP antennas incur a 3dB penalty when receiving linearly polarized RF waves.
Choosing Antennas for UAS
The selection of antennas for UAS is vital for ensuring optimal link performance. Given the dynamic nature of UAS,which frequently alters its orientation,omnidirectional antennas are typically preferred. Size and weight are also critical factors, leading to the use of compact 2-3 dBi dipole or monopole antennas. While monopole antennas can be quite small, they must be mounted on a ground plane for effective operation.
Mounting Considerations for UAS
Due to the high mobility of UAS,proper antenna mounting is essential.
- Utilize 2×2 MIMO antennas to enhance diversity from the moving platform.
- ideally, antennas should be spaced at least 1/4 wavelength apart (preferably 1/2 wavelength) to prevent interference with each othre’s radiation patterns.For instance, at 900 MHz, the wavelength is approximately 33 cm (13 inches), necessitating a minimum separation of 9 cm (3.5 inches), with greater distances recommended.
- Position antennas in a V-shape to optimize diversity and capture scattered RF signal polarizations.
- Ensure the antennas’ radiation patterns are directed downwards and outwards for effective interaction with the Ground Control Station (GCS).
- As UAS bodies are often constructed from carbon fiber, which has low conductivity, they can obstruct or reflect RF waves, potentially altering the antenna’s radiation pattern. Careful placement is necessary to avoid interference from the UAS structure.
- We suggest testing antenna placement by flying the UAS at an altitude of 10-20 meters and rotating it while monitoring the Received Signal strength Indicator (RSSI) from the radio.
Selecting Antennas for the GCS
Typically, the GCS is stationary, allowing for the use of larger, higher-gain antennas to extend range. Ensure that the antennas are oriented upwards and outwards,and confirm that the UAS remains within the antenna’s radiation pattern. For short to medium-range operations, 6 dBi omnidirectional antennas are effective. For long-range communications, directional antennas are advisable, and for very long distances, tracking dish antennas might potentially be appropriate.
Recommended Antenna Choices
When selecting antennas, prioritize reputable manufacturers and avoid low-cost options that lack comprehensive specifications. If an antenna is significantly smaller than 1/2 wavelength, its performance might potentially be questionable.
The ideal antenna datasheet should include radiation patterns to verify uniformity. If the radiation pattern is not provided, the manufacturer may only list peak gain, which may not be practical for real-world applications. Aim for a VSWR of less than 2:1. The adage “you get what you pay for” holds notably true in the realm of antennas.
Doodle Labs Antennas
Doodle Labs provides antennas specifically optimized for use with thier radios across various frequency bands. These antennas are included in the radio evaluation kit and are available for bulk purchase.
