Use rugged multiband antennas to solve the mobile connectivity challenge
line. In an ideal scenario, the VSWR would be 1:1. While this is often difficult to achieve, it’s usually acceptable practice to work with a VSWR in the low single digits. For the 1-2309605-1 M2M MiMo LTE dual antenna, which can handle up to 20 watts of transmit power, the maximum VSWR when measured with 3 meters (m) of RG174 cable is around 3:1 at one end, and closer to 1.5:1 through most of its bands of operation (Figure 4). In general, this is low enough for many of the targeted applications. In Figure 4, green is the lower- frequency element #1, red is the
bandwidth, from the lower end at around 700 MHz, extending through to the upper frequencies, at about 900 MHz (Figure 3). At 700 MHz (the low end of the frequency band), the gain in decibels relative to an isotropic antenna (dBi) – a standard metric indicating antenna directivity – is just 1.5 dBi, which represents a fairly uniform radiation pattern. This uniformity and evenness contributes Figure 2: The TE Connectivity 1-2309605-1 is a single module comprising two independent antennas, one for 698 to 960 MHz operation and the other for 1710 to 3800 MHz operation. Image source: TE Connectivity
Figure 4: The VSWR (vertical axis) for the 1-2309605-1 M2M MiMo LTE dual antenna as measured with 3 m of RG174 cable shows a low value over the entire active frequency range (x-axis). Image source: TE Connectivity
about unexpected or unforeseen interaction. For the 1-2309605- 1 M2M MiMo LTE dual antenna, the isolation is at least 15 dB, increasing towards the centers of both bands which the unit serves (Figure 5). An active receive-antenna function In addition to the two bands covered by the 1-2309605-1 dual antenna, many applications such as asset tracking also need to receive signals from GPS (US), Galileo (Europe), and Beidou (China) GNSS systems for position or timing
random and changing, making it important for them to have a consistent, omnidirectional pattern for the top and side views throughout the specified band. For example, the TE Connectivity 1-2309605-1 M2M MiMo LTE dual antenna is designed for both 698 to 960 megahertz (MHz) and 1710 to 3800 MHz bands and targets 2G, 3G, 4G, cellular, GSM, and LTE applications (Figure 2). A single antenna can be effective for this list of standards because it is agnostic with respect to the specific signal format it is conveying or standard it is supporting; its design is primarily defined by frequency, bandwidth, and power. Note that a ‘dual’ antenna is not the same as a ‘dual-band’ antenna. A dual antenna, such as the 1-2309605-1, has two independent antennas in a single housing and each has its own feed; a dual-band unit is a single antenna with one feed, designed to support two (or more) bands. Looking at the lower-band antenna of the 1-2309605-1, its radiation pattern for both top and side orientations is uniform across the
radiation from another antenna.
higher-frequency element #2, and black is for elements #1 and #2 in free space, while blue is for elements #1 and #2 on a 400 × 400 millimeter (mm) ground plane. Co-sited antennas It is possible to co-locate two or more separate antennas to cover multiple bands. However, this leads to several potential problems. First, there’s the obvious issue of space and mounting hardware required on a panel or other surface, as well
The solution to this quandary is to use a single antenna unit that combines multiple antennas within a single housing or enclosure. Mechanically, this reduces overall size, simplifies installation and antenna-cable routing, and presents a streamlined external appearance. Electrically, it means that the isolation between the antennas can be measured and specified in advance, minimizing concerns
to consistent performance, regardless of antenna orientation. Further, the radiation pattern for the 900 MHz higher-frequency end is also fairly even with gain of just 4.5 dBi. Another important antenna parameter is the VSWR, which is formally defined as the ratio of the maximum to minimum voltage, or the ratio between transmitted and reflected voltage standing waves on a lossless transmission
as the associated installation costs. Second, there are concerns about EM interaction between antennas which will affect their patterns and performance; this constrains how they can be placed with respect to each other. This interaction is measured as antenna isolation, defining to what extent an antenna will pick up
Figure 3: The side (left) and top (right) gain plots of the 1-2309605-1 at 700, 800, and 900 MHz (top row, middle row, bottom row, respectively) show a fairly uniform radiation pattern. Image source: TE Connectivity
Figure 5: The isolation (y-axis, dB) between the two antennas within the 2309605-1 M2M MiMo LTE dual antenna module is 15 dB or better, measured as a function of frequency (x-axis, MHz). Image source: TE Connectivity
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