An example is Amphenol’s ST0543- 00-N04-U passive GNSS patch antenna for operation in the 1.575 and 1.602 GHz frequency bands. The antenna measures 18 x 18 x 4 mm and has an impedance of 50 Ω. Its RL is less than -10 dB for both frequency ranges, and its peak gain is -0.5 dBi in the 1.575 GHz band and 1.0 dBi in the 1.602 GHz band. Its efficiency is 80 and 82%, respectively. External whip antennas, such as the antenna on a Wi-Fi AP, are mounted outside of IoT devices to optimize radio operation. An external whip antenna extends signal range, improves signal quality, and overcomes obstacles or interference. They are useful in environments with weak or obstructed signals, such as those attenuated by walls, ceilings, and furniture in the home. Straight and swivel whip designs, each with standard RF interface connections such as SMA, RP-SMA, and N-Type, are available. An example is Amphenol’s ST0226- 30-002-A 2.4 and 5 GHz SMA RF stick antenna. The antenna is a good solution for Wi-Fi APs and set-top boxes (STBs). It offers an omnidirectional radiation pattern in the 2.4 to 2.5 GHz and 5.15 to 5.85 GHz frequency bands. The antenna measures 88 x 7.9 mm in diameter and has an impedance of 50 Ω. Its RL is less than -10 dB for both frequency ranges, and its peak gain is 3.0 dBi in the 2.4 GHz band and 3.4 dBi in the 5
GHz band. Its efficiency is 86 and 75%, respectively. The antenna is available with either an SMA or RP- SMA plug connector (Figure 7). Helical wire antennas are an inexpensive and simple option for sub-GHz applications such as LoRa IoT devices operating in the 868 MHz frequency band. The antennas are typically soldered directly to the PC board and offer good performance. Some downsides are bulkiness, particularly when operating at low frequencies, and relatively low efficiency compared with some antenna alternatives. An example is Amphenol’s ST0686- 10-N01-U 862 MHz RF antenna (Figure 8). This helical wire antenna operates in the 862 to 874 MHz frequency band and has an impedance of 50 Ω. The antenna features through-hole solder mounting with a maximum height of 38.8 mm. It has an RL less than -9.5 dB, a peak gain of 2.5 dBi, and an average efficiency of 58%. Conclusion Wireless IoT device radio performance depends on antenna selection, so designers must choose carefully from a wide range of antenna designs from suppliers such as Amphenol to best match the application. Datasheets are critical during selection, but following established design guidelines ensures the best wireless performance.
Figure 7: The ST0226-30-002-A external whip antenna for Wi-Fi APs is available with either an SMA or RP-SMA plug connector. Image source: Amphenol
Like PC board antennas, patch antennas are compact and can be directly attached to the PC board. A typical application is an antenna for an asset tracker or other devices with Global Navigation Satellite System (GNSS) capability. GNSS patch antennas comprise a patch element on a dielectric substrate. High efficiency ensures the antenna picks up weak GNSS signals from multiple satellites.
Figure 8: The ST0686-10-N01-U helical wire antenna is a good option for LoRa IoT applications. Image source: Amphenol
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