RF Antennas are the primary method for RF communication and sensing systems to convert electrical signals to RF and vice versa. A subset of RF antennas is fixed antennas, which is mainly a description of how they are mounted, installed and generally used. A fixed antenna is any RF antenna that is incapable of motion or steering that is fixed rigidly to a platform. The platform used to support this type of antenna is typically a telecommunications post/pole or tower. There are a variety of different types of antennas that can be classified as fixed antennas, including omnidirectional antennas, dipole antennas, folded dipole antennas, log periodic antennas, exposed dipole antennas, collinear omnidirectional antennas, and more.
Fixed antennas are constructed of an antenna element, interconnect for the antenna element, and some type of mounting structure/fixturing system to allow for the antenna to be securely mounted to the exterior of a structure. As fixed antennas are typically mounted on the exterior of a structure and exposed to the elements, these antennas often are built with environmental protection or some sort of cover/radome. These are most often constructed of fiberglass for environmental ruggedness and physical protection of the otherwise delicate antenna elements.
The most common applications for fixed antennas are GPS, cellular, IoT, and other communications use cases. What a fixed antenna is useful for depends on the frequency range capability of the antenna, gain, and the directionality of the antenna. Omnidirectional antennas, or omni-antennas, have a 360 degrees of horizontal antenna pattern, while directional antennas have a narrow antenna pattern and typically higher overall gain in a given direction due to the enhanced directionality.
Primary Applications for Fixed Antennas
- Global Positioning System (GPS)/Global’naya Navigatsionnaya Sputnikovaya Sistema (GLNSS) Antenna
- CDMA, 2G, 3G, 4G, 5G, LTE, and/or other cellular technologies
- Low-power Wide Area Network (LPWAN)
- Internet-of-Things (IoT), narrow-band IoT (NB-IoT), LTE-machine (LTE-M), and/or long-range (LoRa)
- Machine-to-machine (M2M) communications
- Bluetooth, Zigbee, Wi-Fi, or other wireless communications
The gain of a fixed antenna is always referenced to an ideal isotropic radiator. Higher gain generally means that an antenna is larger, more directional, or otherwise designed and fabricated in such a way to yield a larger gain. As there are practical limits to gain/directionality and other key antenna performance metrics, such as bandwidth, ultra-high gain antennas aren’t generally used for the same applications as fixed antennas, which are generally more affordable than laboratory, mobile, or other antennas designed for specific applications.
Key RF Fixed Antenna Electrical Specifications & Features
- Frequency range [Hz]
- VSWR [ratio]
- Insertion loss [dB]
- Impedance [Ohms]
- Gain [dBi]
- Gain Variation {dBi]
- Out of band rejection [dB]
- Axial Ratio [dB]
- Operating DC Voltage [Volts]
- Power handling (CW, peak) [Watts]
- Interconnect type (coaxial, waveguide, etc)
- Temperature range of operation [deg C]