Circularly Polarized Antennas for GNSS Applications

Global navigation satellite system (GNSS) is developing rapidly. Modern GNSS technology is facing challenges for researchers to explore. One hot topic is the multi-system GNSS device. The motivation for the antenna designers is to miniaturize the size of the antenna and meanwhile keep its standard performance. It is a challenging task for an antenna array design to achieve a wide bandwidth, high gain, small size, good coverage, and simple fabrication technique all at the same time. This thesis develops several different novel compacts, high gain, and wide bandwidth circularly polarized (CP) antenna capable of providing wide coverage for GNSS frequency bands from 1.16 GHz to 1.6 GHz to cover the GPS L1-L5 bands, GLONASS G1, G2 and G3 as well as the Galileo E5a, E5b, E6, and E1bands

Reconfigurable Axial Ratio in Compact GNSS Antennas

A new adaptive technique for steering the direction of minimum axial ratio (AR)

Dual Circularly Polarized Antennas with Low Cross-Polarization for GNSS-R Applications

Global Navigation Satellite System-Reflectometry (GNSS-R), has gained increasing interests as an efficient tool for remote sensing. It is based on the concept of utilizing the received signals reflected from the Earth’s surface. Several GNSS-R system configurations were proposed depending on different retrieval algorithms. In a GNSS-R system, the antenna plays a key role as a receiving component. In this paper, in-situ measurements using a commercial dual circular polarized antenna receiving both the left-hand and right-hand circular polarization reflected from the ground are analyzed. A low cost and compact dual-port circular polarized patch antenna is designed and realized to overcome the limitations of the previous configuration. The prototype shows a low level of cross polarization suitable for GNSS-R application

Low-Cost Dual-Band Circularly Polarized Switched-Beam Array for Global Navigation Satellite System

This paper presents the design and development of a dual-band switched-beam microstrip array for global navigation satellite system (GNSS) applications such as ocean reflectometry and remote sensing. In contrast to the traditional Butler matrix, a simple, low cost, broadband and low insertion loss beam switching feed network is proposed, designed and integrated with a dual band antenna array to achieve continuous beam coverage of ±25° around the boresight at the L1 (1.575 GHz) and L2 (1.227 GHz) bands. To reduce the cost, microstrip lines and PIN diode based switches are employed. The proposed switched-beam network is then integrated with dual-band step-shorted annular ring (S-SAR) antenna elements in order to produce a fully integrated compact-sized switched-beam array. Antenna simulation results show that the switched-beam array achieves a maximum gain of 12 dBic at the L1 band and 10 dBic at the L2 band. In order to validate the concept, a scaled down prototype of the simulated design is fabricated and measured. The prototype operates at twice of the original design frequency, i.e., 3.15 GHz and 2.454 GHz and the measured results confirm that the integrated array achieves beam switching and good performance at both bands

Effect of shadowing and diffraction on the received GNSS signal

Abstract. The characteristics of the GNSS received signal depend on the propagation medium environment. Typically, the transmitted signal interacts with several numbers of obstacles which leads to the multipath propagation to receiver end. In such cases, diffraction over the edges or wedges of the obstacles in the propagation path should be considered. The effects of diffraction and shadowing are the important elements in radio wave propagation because of their strong influence on the received signal quality. Especially, received signal strength and characteristics are very significant for GNSS applications. This master’s thesis investigates the effect of knife-edge diffraction model and shadowing environment on the received GNSS signal. Characterization of the received signal is investigated both theoretically and experimentally. In the measurement, a dual circular polarized antenna has been used to receive the multipath GPS signal in the shadow region in which antenna was placed in the zenith direction. The measurement was performed for two scenarios 1) the receiver was in the static position, and 2) in motion for the second measurement. Measurement results show that, the received signals following the Knife-edge diffraction pattern for both measurements case. In the first measurement case, knife-edge diffraction has been identified in received signal attenuation whereas the interference pattern in the LoS propagation can be observed because of multipath effect. In the deep shadow region, a linearly polarized signal has been received in both antennas because the incident RHCP signal turned into a linearly polarized signal after diffraction. For the second measurement case, knife-edge attenuation pattern is also visible. A clear agreement between the measured and theoretical aspects has been achieved in the case of knife-edge diffraction

Inverted-S Antenna with Wideband Circular Polarization and Wide Axial Ratio Beamwidth

A novel broadband circularly polarized (CP) antenna with wide axial ratio (AR) beamwidth is proposed. It is composed of two curved arms shaped like an inverted “S”. The mechanisms of wideband CP operation and wide AR beamwidth are explained. To validate the concept, a prototype at C-band is manufactured and measured. Experimental results confirm that the antenna achieves an impedance bandwidth of 63% and a CP bandwidth of 42%. Furthermore, maximum AR beamwidth of 140o is achieved and wide AR beamwidth can be maintained in a frequency bandwidth of 35% in nearly all elevation planes. In addition, the antenna has the advantage of being easily extended to arrays. A 4-element array using the proposed antenna is investigated through both simulations and experiments, and achieves 60% CP bandwidth and wide AR beamwidth. The proposed inverted-S antenna can realize wide CP bandwidth and wide AR beamwidth, and is easy to form wideband CP arrays

An active wearable dual-band antenna for GPS and Iridium satellite phone deployed in a rescue worker garment

An active wearable dual-band circularly polarized microstrip patch antenna for Global Positioning System and Iridium satellite phone applications is presented. It is constructed using flexible foam and fabric substrates, combined with copper-on-polyimide film conductors. A low-noise amplifier chip is integrated directly underneath the antenna patch. The antenna's performance is examined under bending and on-body conditions. The active antenna gain is higher than 25 dBi and the 3dB axial ratio bandwidth exceeds 183 MHz in free-space conditions. The antenna performance is robust to bending and on-body placement