How to Determine Whether a Single- or Multi-Feed GNSS Antenna is Right for Your Application
When it comes to global navigation satellite system (GNSS) antennas, there’s strength in numbers — literally. That’s one key aspect to consider when choosing a GNSS antenna system for vehicle telematics, asset tracking and other location-based applications.
GNSS patch antenna solutions can be grouped into two types based on the number of feeds. As its name implies, a single-feed antenna system provides the GNSS receiver with one antenna’s worth of signal. By comparison, a multi-feed antenna system provides two or more antennas’ signals, which a hybrid coupler then combines before sending to the receiver or goes through an active circuit to the receiver.
A multi-feed antenna is ideal for applications that require high performance. One example is ensuring reliable, precise navigation even in urban concrete canyons and places with heavy foliage, both of which can severely attenuate satellite signals.
Single-feed antennas are less complex, so they’re easier and cheaper to integrate, and take up less space. Those attributes can make them a good fit for IoT applications where low device costs and/or a small form factor are more important than ultra-high performance.
GNSS satellites transmit signals using right-hand circular polarization (RHCP). One reason why single-feed antennas have lower performance is due to lower RHCP gain. When a device’s antenna and the satellite don’t have the same polarization — a problem known as mismatch — at least (most) half of the signal (~3 dB) can be lost. (Keep in mind that GNSS signals are already relatively weak, so the choice of antenna can either exacerbate or mitigate that challenge.)
A multi-feed antenna’s hybrid coupler converts the polarization from linear to circular, which provides the necessary RCHP gain to overcome mismatch attenuation. This significantly improves performance, including by rejecting unwanted multipath signals that also undermine accuracy. When comparing circularly polarized antennas, the axial ratio is a key metric to look for. It measures how well the antenna can reject the left-hand circular polarized (LHCP) signals relative to the RHCP signals.
One way to better understand these concepts and benefits is to compare the multi-feed Taoglas HP24510.A antenna to the single-feed Taoglas HP2258.
The HP24510.A is a dual-stack patch antenna where each patch has two feeds. The top patch covers L/L1 constellations (1525-1610 MHz) and the bottom patch covers L2 constellations (1207-1248MHz). The feeds from each patch are fed to a hybrid coupler, resulting in an RHCP signal.
The HP2258 is dual-stack patch antenna where the single feed is connected to both patches. The polarization of this antenna will not be a mixture of RHCP and linear polarization and thus could result in up to a 3 dB loss in signal.
Below is a comparison of the RHCP gain that was measured for each antenna.
The above results show that the RHCP gain for multi-feed antenna is higher than a single-feed antenna, resulting in higher carrier-to-noise values and better positional accuracy.
GNSS applications are complex and often require expert advice to find the right solutions. Antennas play a significant role in performance, and design engineers must consider factors like form, size, weight, and RF signal paths. Taoglas can guide you through the key considerations to enhance your GNSS solution. We’ve developed a helpful workflow to explore our extensive range of antenna design and testing services, accessible via the button below.