**1. Introduction**

Global navigation satellite systems (GNSSs) are indispensible in positioning, navigation, and timing (PNT) and have become an integral part of many outdoor positioning applications such as surveying, vehicle localization, parcel and container tracking, precision timing, synchronization of communication networks and radars, atmospheric observation, and meteorology. Although GNSS has started with US Global Satellite System (GPS) only, with the addition of new GNSS services introduced by Russia, China, and European Union, GNSS has evolved to multi-constellation and multi-band system. Regional satellite navigation system by India and GNSS assistance services such as QRZZ also complement global satellite navigation system. All global service providers of GNSS offer worldwide positioning for mobile and stationary platforms and assets.

patch antennas and antenna performance on the platform [1–7], wideband antennas [8, 9], wide beam width antenna [10], miniature and multi-functional antennas [11–18], dual/triple GNSS band antennas [19–25], conformal and missile application antennas [26–29], array antennas for anti-jam and anti-spoofing applications [30–35], cellular phone isolation [36, 37],

Antennas and Front-End in GNSS

167

http://dx.doi.org/10.5772/intechopen.74971

Depending on the antenna location inside the platform and available antenna space, antenna designers routinely face challenges to meet acceptable performance. Most utilized forms of GNSS antennas are microstrip antennas, helical antennas, slot-based antennas and miniature (chip-scale) antennas. GNSS antenna arrays are often essential for critical applications where precise positioning is required along with counter measures for jamming and spoofing.

GNSS passive antenna performance is usually quantified in terms of operational frequency band, gain pattern, half-power beam width (HPBW), polarization, axial ratio, cross-polariza-

The passive antenna must be functional within the desired GNSS service band. The operation frequencies of current GNSS services are tabulated in **Table 1**. A passive antenna that is capable of receiving entire GNSS services must be operational from 1164 to 1610 MHz (32.1% fractional bandwidth), covering either entire band or multi-band within lower L-band (1164–

L-band satellite navigation systems utilize right-hand circular polarization (RHCP) signals. Two orthogonal components of circular polarization signal at high elevations undergo same level of Faraday rotation when passing through ionosphere which does not degrade the

L1: 1567–1587 MHz

G1: 1593–1610 MHz

B1I: 1553–1569 MHz

E1: 1559–1591

tion discrimination or multipath discrimination, and phase centre stability.

**Service Lower L-band Upper L-band**

L2: 1215–1239.6 MHz

E6:1260–1300 MHz

G2: 1237–1254 MHz

B3: 1256–1280

metamaterial and plasma-supported antennas [38–41] are reported in the literature.

**2.1. GNSS passive antenna requirements**

1300 MHz) and upper L-band (1559–1610 MHz).

GPS L5: 1164–1189 MHz

GLONASS G3: 1189–1214 MHz

BeiDou/compass B2I: 1179–1203 MHz

**Table 1.** GNSS frequency bands.

Galileo E5: 1164–1215

*2.1.1. Operational frequency band*

*2.1.2. Polarization*

While multiple GNSS services at different frequency bands offer tremendous advantages for the user which were not possible with single service provider, multi-band and multi-constellation receivers and antennas possess new challenges in the system design. For precise positioning, multiple satellites, at least four for each service provider, must be tracked simultaneously. One of the key components of the system is the GNSS passive antenna, which is vital to establish a good carrier-to-noise ratio for seamless positioning with minimum acquisition time. The antenna beam width must be broad to cover as much as possible the sky view while its axial ratio must be low throughout its coverage. The antenna must maintain these features throughout the target frequency bands. The receiver, on the other hand, must be able to handle multi-constellation GNSS signals. Instead of classical receiver architectures, software-defined, user-configurable GNSS architectures are much more in demand due to the flexibility in software they offer.

One of the key challenges in any GNSS is the susceptance of receiver to interference. The signals transmitted through satellites are at low power such that the received signals are very weak on earth and usually under the thermal noise floor of the receiver. Intentional and unintentional jamming of GNSS signals is common and still presents the biggest problem in GNSS applications. Especially, in urban environment where tall buildings block clear view of the antenna and multipath propagation is dominant, the receiver performance deteriorates significantly. Unintentional blockage of GNSS due to other communication systems is also common. Strong out-of-band signals or signal bleeding from nearby frequency bands can cause interruptions of GNSS service. Due to very weak signal levels on earth, intentional jamming with inexpensive hardware has also proven to be harmful for GNSS service. Jamming mitigation at the hardware and software are essential components of the mission-critical GNSS receivers.
