Inspired by the successful commercial operation of the Global Positioning System (GPS) in the United States in the late 1980s, many other countries in the world have also developed and launched their own versions of GPS, collectively known as the Global Navigation Satellite System (GNSS). GNSS technology has evolved over the last 25 years and has played a critical role in the interconnected world. Today, GNSS includes European Union Galileo, Russia's GLONASS, China's Beidou, India's IRNSS/NavIC and Japan's QZSS. Compared with the traditional GPS receiver only using GPS satellite system, in order to work with multiple satellite constellations, GNSS receiver system uses multi-band frequency to obtain higher accuracy and reliability.
The antenna is a key component of the receiver and plays a critical role in capturing the weak radio signal from the satellite to determine the precise location, navigation and time of the user. Therefore, the GNSS receiver uses 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 the GNSS receiver are summarized as follows:
The frequency range of L1, E1 and B1 bands is 1559 MHz to 1610 MHz
L2, E6, B3, L6 bands have a frequency range of 1217 MHz to 1300 MHz
The frequency range of L5, E5, B2 and L3 bands is 1164 MHz to 1217 MHz
Therefore, the GNSS receiver uses broadband or multi-band antennas and can handle a variety of frequency ranges used by various space satellite networks. Multi-band frequency can improve the positioning accuracy and reliability of GNSS receiver system, reduce signal error and interference, and provide excellent performance of GNSS antenna in wide and severe environment.
Multi-band nested patch antenna
The need for compact, flat solutions has been high for the past few years, as the original GPS receiver system used large, bulky, stacked antennas that occupied valuable space. In order to meet the requirements of modern GNSS RF front-end modules at high efficiency and low cost,Tailas Limited has designed and developed an outstanding antenna technology for highly constrained precision applications. The company's Inception series HP5354. A is a multiband, 1160 MHz to 1610 MHz passive patch antenna designed to improve location accuracy, robustness, and reliability. It uses an innovative ceramic nested patch antenna technology and embeds two antennas in the same overall dimensions as the single-band GPS antenna (Figure 1). Therefore, it can provide optimized polarization gain for Beidou (B1/2a), GPS/QZSS (L1/L5), GLONASS (G1) and Galileo (E1/E5a) bands (including IRNSS/NavIC (L5)). This also ensures compatibility with a variety of applications wherever possible.
Image of the Douglas Channel entry series HP5354. A antenna
Figure 1: The Inception Series HP5354. A is a flat nested patch antenna for the GNSS receiver system. Picture Source:Taglas Limited)
HP5354. A optimized for dual band performance is a compact, flat shaped antenna with a size of 35 mm x 35 mm and a height of 4 mm. It uses an 11-pin surface-mount ceramic package with three pins for capturing orthogonal radio signals in L1 and L5 bands. Two of these three pins are used to receive signals from L1 frequency band and the third pin is used to receive signals from L5 frequency band. The remaining eight pins are grounded.
In order to obtain optimum axial ratio and right-hand circular polarization (RHCP) signals at the output, the two feed signals of L1 band are combined using the recommended hybrid coupler HC125A (Fig. 2). HC125A adopts flat (1.5 mm high) surface mount package, with low insertion loss and balanced output amplitude, suitable for multi-band GNSS application.
Schematic diagram of combining two feed signals of L1 frequency band with recommended hybrid coupler
Figure 2: The two feed signals from the L1 band are combined in the HC125A hybrid coupler to ensure optimum axial ratio while generating RHCP signals. Picture Source:Taglas Limited)
In addition, the double-feed point antenna has been tuned and tested on a 70 mm x 70 mm horizon and shows an excellent radiometric map. In addition, it fully characterizes frequency-related key parameters in two bands. These parameters include return loss, voltage standing wave ratio (VSWR), efficiency, average gain, peak gain, axial ratio, phase center shift, phase center variation, and group delay.
The double-feed point antenna has a flat shape, which can be widely used in situations where the traditional laminated patch design is too heavy and tall. Recommended applications include navigation, industrial tracking, autonomous vehicles and robotics, as well as wearable devices, small asset trackers and precision agriculture.
Build front-end RF signal link
Although the multi-band GNSS antenna can be combined with the user's own GNSS front-end, Talsignificantly simplifies the signal link design by using the TFM.100B GNSS front-end module specially designed for the multi-feed point patch antenna.
This module consists of a two-level low noise amplifier (LNA) with a gain of more than 25 dB in all frequency bands and a noise figure (NF) of less than 3 dB. It uses a surface acoustic wave (SAW) filter to combine with the LNA to form a SAW/LNA/SWAW/LNA topology, and simultaneously processes low and high frequency band signal paths to suppress unnecessary out-of-band (OOB) interference and prevent overloading of the GNSS low noise amplifier or receiver. The carefully selected and placed SAW filters in TFM.100B provide excellent OOB rejection while maintaining a low 3 dB noise figure. This easy-to-integrate, surface-mount device is 20 x 18 mm in size and uses a single power supply of 1.8 to 5.5 VDC. The wide input voltage range allows the front-end module to be easily integrated into most GNSS receivers.
In order to further help the user understand the integration of the complete GNSS receiver front-end module, Taglas engineer prepared an evaluation board AHPD5354A (Figure 3) as the reference design of front-end signal path. This evaluation board integrates TFM.100B preamplifier, flat high performance HC125A 3 dB hybrid coupler and HP5354. A multiband patch antenna on a single PCB.