DigiKey-emag-Wireless Modules-Vol-8

Use rugged multiband antennas to solve the mobile connectivity challenge

information. To simplify this task and avoid the need for another external discrete antenna, TE offers the 1-2309646-1. This adds a third, receive-only antenna for GNSS signals between 1562 – 1612 MHz to the two antennas of the dual- antenna unit. However, the need to receive GNSS signals adds another challenge for the system designer that goes back to the basics of the transmit versus receive functions. When used for transmitting, the antenna and its feedline are in a deterministic situation. They take the known, controlled, well-defined signal from the transmitter power amplifier (PA) and radiate it. There is little concern about internal noise on that signal, in-band interference, or out-of-band signals between the PA and the antenna. Due to the reciprocity principle which applies to all antennas, the same physical antenna used for transmitting can be used for receiving. However, the operating conditions for receiving are

quite different than they are for transmitting. Since the antenna is trying to capture a signal with unknowns in the presence of in-band and even out-of-band interference and noise, the desired received signal is not deterministic as it has many random characteristics. In addition, the received signal strength is low (on the order of microvolts to a few millivolts) and the SNR is also low. For GNSS signals, the received signal power is typically between -127 and -25 dB relative to one milliwatt (dBm), while the SNR is typically between 10 and 20 dB. This fragile signal will be attenuated due to losses in the cable between the antenna and receiver front-end, and it will also have its SNR degraded by unavoidable thermal and other noise in the transmission cable. For these reasons, the 1-2309646- 1 incorporates an LNA as another feature for its third, receive-only GNSS antenna. The LNA provides

42 dB gain for the GNSS signals, thereby significantly boosting the received signal strength. To simplify the use of the LNA, it receives its power (3 to 5 volts DC, at no more than 20 milliamps (mA)) via the amplified RF signal’s coaxial cable using a well-established superimposition technique. DC power is sent on the cable between the receiver unit to the LNB (Figure 6). The DC power for the LNA (V1) is blocked from reaching the radio head unit (front- end) by small series capacitors (C1 and C2). These capacitors do allow the amplified RF signal from the antenna (ANT1) to pass to the radio head unit (OUT). At the same time, the amplified RF signal is blocked

mechanical objectives. Two- antenna and three-antenna modules from TE Connectivity provide low band, high band, and optional GNSS band antennas, along with an internal LNA for the latter. These units are equipped with individual coaxial cables and connectors for each antenna, plus a simple surface or panel mount arrangement to facilitate installation and provide critical environmental ruggedness. Figure 7: Each antenna within the 1-2309605-1 and 1-2309646-1 has its own RG-174 coaxial cable with SMA plug termination to simplify installation, attachment, test, and disassembly if needed. Image source: TE Connectivity

the mounting surface.

loosen, or be incorrectly torqued.

from going back to the power supply V1 by series inductors

To meet these goals, each band of the two-band 1-2309605-1 and the three-band 1-2309646-1 is equipped with a 3-meter RG-174 coaxial cable, which is terminated with a standard SMA plug (Figure 7). As a result, connecting or disconnecting one or more of the antennas is straightforward and can easily be done in the factory during system assembly, or in the field as an add-on. Further, attachment of the multi- antenna module to the system’s surface is eased by use of a single internal 18 mm mounting rod, plus an acrylic adhesive pad around the bottom edge of the antenna housing. Attachment of the antenna is a quick operation that leaves no exposed hardware to rust,

The housing of these antennas is optimised for mobile, high- speed motion applications. The streamlined unit is just 45 mm wide and 150 mm long with rounded edges (similar to the ‘shark fin’ on the roof of automobiles) to minimize its drag coefficient and wind resistance. Further, the UV- stabilized material of the enclosure ensures that exposure to sunlight will not weaken the housing over time.

(chokes) L1 and L2. In this way, DC power to the LNA and amplified RF from the LNA to the radio head unit can share the same interconnection coaxial cable.

Making the physical connection

Any antenna or assembly of antenna elements needs to have a reliable, convenient, and electrically and mechanically secure way to be connected and disconnected from the radio front-end they serve. Further, the complete antenna assembly needs to be protected from the environment and be easy to mount with minimal impact on