Since its development under the leadership of the US Department of Defense (DoD) in the late 1970s and extended to the 1980s, the role and application of the Global Positioning System (GPS) have grown exponentially. The system was initially only used for navigation and missile guidance, but has now been integrated into asset tracking and monitoring, autonomous driving in cars, agriculture, wearable devices, and many other end uses that its founders never imagined.
After the successful deployment of GPS in the United States, other countries and regions have also developed and launched corresponding GPS systems, collectively known as Global Navigation Satellite Systems (GNSS). GNSS includes Russia's GLONASS, the European Union's Galileo, and China's Beidou, as well as two regional GNSS systems: Japan's QZSS and India's IRNSS/NavIC.
Although the initial GPS receiver system was bulky and almost impossible to fit into a car trunk, modern technology has simplified the GNSS core engine into a single integrated circuit (IC). Regardless of the type of GNSS, all of these systems require an optimized antenna to receive ultra weak RF signals from GNSS satellite arrays. As the size of GNSS receivers shrinks and power requirements decrease, the size of antennas must also be correspondingly reduced.
However, this is a challenge for receivers that must handle multiple GNSS systems or frequency bands. The receiver requires an antenna that can handle the lower and higher RF bands of different systems used (Figure 1).
Figure 1: Currently, GNSS frequency allocation and frequency bands planned by various in use systems have both overlapping coexistence and cross separation. (Image source: Taoglas Limited)
The allocation of GNSS frequency bands and frequencies is as follows:
1559 to 1610 megahertz (MHz), known as the L1, E1, B1 frequency band
1215 to 1300 MHz, referred to as L2, E6, B3, L6 frequency bands
1164 to 1215 MHz, known as L5, E5, B2, L3 frequency bands
Please note that the L-band refers to the frequency range of 1525 to 1559 MHz, within which various satellites transmit calibration signals.
The demand for broadband or multi band antennas can be traced back to early wireless communication in the early 20th century, and there were two common methods at that time. One method is to use physical "notch filters" or loaded coils to cause a single narrowband antenna to resonate at two different center frequencies. Another approach is to use a single antenna designed for broadband performance.
Both of these solutions are not ideal for GNSS antennas in today's compact system designs. The notch filter method requires relatively large discrete inductors and capacitors, while broadband antennas can compromise performance critical properties such as gain and efficiency.
Better antenna methods
Now a better solution can be achieved through Taoglas Limited's Inception series antennas. For example, HP5354. A (Figure 2) is a multi band, 1160 to 1610 MHz passive GNSS patch antenna designed to improve positioning accuracy. This innovative ceramic based composite patch antenna has optimized gains for the Beidou (B1/B2a), GPS/QZSS (L1/L5), GLONASS (G1), and Galileo (E1/E5a) frequency bands.
Figure 2: HP5354. A is a compact flat antenna optimized for dual band (L1 and L5) GNSS performance. (Image source: Taoglas Limited)
The size of HP5354. A is 35 × 35 millimeters (mm) and the height is 4 mm, which is very suitable for compact and flat designs. The 11 pin package uses three pins as the receiving signal interface (two for L1 frequency band and one for L5 frequency band), and the remaining pins are used for grounding.
After tuning and verification, the HP5354. A multi feed antenna equipped with a 70 × 70 mm grounding plane has excellent radiation characteristics. This antenna can cover the frequency bands required by the new generation L1/L5 GNSS system and fully characterize key frequency related parameters in these two frequency bands, including return loss, voltage standing wave ratio (VSWR), radiation efficiency, average gain, peak gain, axis ratio, phase center offset, phase center drift, and group delay.
Using Taoglas HP5354. A antenna
Although the HP5354. A antenna can be paired with user provided front-end modules, Taoglas' use of the TFM.100A GNSS RF module simplifies the development process of the underlying signal chain. This high-performance module covers L1/L5 dual frequency bands and is designed specifically for multi feed patch antenna systems.
TFM.100A has a two-stage low noise amplifier (LNA) that can provide gain of over 25 decibels (dB) in all frequency bands, while the noise figure is below 3 dB. The module uses surface acoustic wave (SAW)/LNA/SAW/LNA topology in both low and high frequency signal paths to prevent unnecessary out of band (OOB) interference from over driving GNSS LNAs or receivers.
The SAW filter in TFM.100A has been carefully selected and placed to perform excellent OOB suppression while maintaining a low 3 dB noise figure. This easy to integrate surface mount device measures 20 × 18 mm and is powered by a single power supply ranging from 1.8 to 5.5 VDC.
Taoglas also provides a matching AHPD5354A evaluation board (Figure 3), further simplifying the integration of HP5354. A with the complete system. The evaluation board adopts TFM.100A RF preamplifier and Taoglas HC125A, which is a flat high-performance 3 dB hybrid coupler designed for multi feed multi frequency GNSS applications. HP5354. A, TFM.100A, and HC125A work together as an integrated signal chain.