In the late 1980s, the Global Positioning System (GPS) was successfully put into commercial operation in the United States. Inspired by this, many other countries in the world also developed and launched their own versions of GPS, collectively known as Global Navigation Satellite Systems (GNSS). In the past 25 years, GNSS technology has continuously developed and played a crucial role in the interconnected world. Nowadays, GNSS includes Galileo from the European Union, GLONASS from Russia, Beidou from China, IRNSS/NavIC from India, and QZSS from Japan. Compared to traditional GPS receivers that only use GPS satellite systems, GNSS receiver systems use multiple frequency bands to work in coordination with multiple satellite constellations, achieving higher accuracy and reliability.
Antenna is a key component of the receiver, playing a crucial role in capturing the weak radio signals emitted by satellites to determine the precise location, navigation, and time of the user. Therefore, GNSS receivers need to use multiple frequency bands, which correspond to the lower and higher radio frequency (RF) bands transmitted by different satellite navigation systems in space. The frequency bands and frequencies covered by GNSS receivers are summarized as follows:
The frequency range of L1, E1, and B1 frequency bands is 1559 MHz to 1610 MHz
The frequency range of L2, E6, B3, and L6 frequency bands is 1217 MHz to 1300 MHz
The frequency range of L5, E5, B2, and L3 frequency bands is 1164 MHz to 1217 MHz
Therefore, GNSS receivers use broadband or multi band antennas that can handle multiple frequency ranges used by various space satellite networks. The use of multi band frequencies can improve the positioning accuracy and reliability of GNSS receiver systems, reduce signal errors and interference, and enable GNSS antennas to provide excellent performance in wide and harsh environments.
Multi band nested patch antenna
Due to the use of large and bulky stacked antennas in the initial GPS receiver systems, which took up valuable space, there has been a high demand for compact and flat solutions in recent years. In order to efficiently and cost effectively meet the requirements of modern GNSS RF front-end modules, Taoglas Limited has designed and developed an excellent antenna technology for highly restricted and precise applications. The company's Inception series HP5354. A is a passive patch antenna with multiple frequency bands ranging from 1160 MHz to 1610 MHz, designed to improve positioning accuracy, robustness, and reliability. It adopts innovative ceramic nested patch antenna technology, embedding two antennas within the same external dimensions as the single frequency GPS antenna (Figure 1). Therefore, it can ensure optimized polarization gain for the Beidou (B1/B2a), GPS/QZSS (L1/L5), GLONASS (G1), and Galileo (E1/E5a) frequency bands (including IRNSS/NavIC (L5)). This also ensures compatibility with various applications at any location.
Image of the HP5354. A antenna in the entry-level series of Tao Glass Co., Ltd
Figure 1: Inception series HP5354. A is a flat nested patch antenna used for GNSS receiver systems. (Image source: Taoglas Limited)
HP5354. A has been optimized for dual band performance and is a compact and flat antenna with dimensions of 35 mm x 35 mm and a height of 4 mm. It features an 11 pin surface mount ceramic package, with three pins used to capture orthogonal radio signals in the L1 and L5 frequency bands. Two of these three pins are used to receive signals in the L1 frequency band, and the third pin is used to receive signals in the L5 frequency band. The remaining eight pins are grounded.
In order to obtain the optimal axial ratio and right-handed circularly polarized (RHCP) signal at the output end, the two input signals in the L1 frequency band are combined using the recommended hybrid coupler HC125A (Figure 2). HC125A adopts a flat (1.5 mm high) surface mount package, with low insertion loss and balanced output amplitude, suitable for multi band GNSS applications.
Schematic diagram of using the recommended hybrid coupler to combine two input signals in the L1 frequency band
Figure 2: Two input signals from the L1 frequency band are combined in the HC125A hybrid coupler to ensure optimal axis ratio while generating RHCP signal. (Image source: Taoglas Limited)
In addition, the doubly fed point antenna has been tuned and tested on a ground plane of 70 mm x 70 mm, and has shown excellent radiation patterns. In addition, it comprehensively characterizes key parameters related to frequency in two frequency bands. These parameters include return loss, voltage standing wave ratio (VSWR), efficiency, average gain, peak gain, axial ratio, phase center offset, phase center variation, and group delay.
The double fed point antenna has a flat shape and can be widely used in situations where traditional stacked patch designs are too bulky and tall. Recommended applications include navigation, industrial tracking, autonomous vehicle and robotics, as well as wearable devices, small asset trackers and precision agriculture.
Building a front-end RF signal chain
Although the multi band GNSS antenna can be combined with the user's own GNSS front-end, Taoglas significantly simplifies the design of the signal chain by using the TFM.100A GNSS front-end module designed specifically for multi feed point patch antennas.
This module includes a two-stage low noise amplifier (LNA) with a gain exceeding 25 decibels (dB) in all frequency bands and a noise figure (NF) of less than 3 dB. It uses a surface acoustic wave (SAW) filter combined with the LNA to form a SAW/LNA/SAW/LNA topology, while processing low-frequency and high-frequency signal paths to suppress unnecessary out of band (OOB) interference and prevent overload of GNSS low-noise amplifiers 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. The wide input voltage range enables the front-end module to be easily integrated into most GNSS receivers.