Antennas - Navipedia. From a user perspective, antennas are the main interface between the GNSS Space Segment (the satellite constellations) and the User Segment (GNSS receivers), as they are responsible for capturing the L- band signals transmitted from space. Antennas requirements can range from gain vs. Conception of Patch Antennas in the GSM and UMTS Band. The conception of these patch antennas are realized by software HFSS \Ansoft-High Frequency Structure Simulator' and. 2 Design and Analysis of Microstrip Patch Antenna Arrays Ahmed Fatthi Alsager, [email protected] Master thesis Subject Category: Electrical Engineering– Communication and Signal processing University.In fact, as show in Figure 1, antennas can range from large roof- mounted antennas (e. Microstrip patches or aperture- coupled patches can be single frequency or dual frequency, but also broadband. Patches are not circularly polarized by nature, so they achieve circular polarization by quadrature excitation of two linearly polarized ports. The quality of the circular polarization depends largely on the feeding network and may be sensitive to fabrication issues, and the crosspolarization near the horizon tends to be high. They provide an excellent form factor (size and weight), and are used in most aviation GNSS antennas satisfying ARINC 7. A horizontal turnstile antenna in free space is vertically polarized in its plane, and has opposite circular polarizations above and below. Therefore the antenna requires a ground plane for geodetic applications. When combined with a choke ring ground plane, it is a very common element in geodetic applications. In GNSS receivers, the helix antennas can be used as directional antennas, with a radiation pattern along the axis of the antenna. Modeling of the quarter wave patch antenna by the transmission line model (TLM). This method is relatively easy because the patch resonance and the inductance of the coaxial probe will be separately treated. Circular Polarized Microstrip Patch Antenna Works on Triple. Circular Polarized Microstrip Patch Antenna Works on Triple. The conception of these patch antennas are realized by the software HFSS “Ansoft-High Frequency. The antenna is circularly polarized by nature, although the quality of the polarization may depend on the feeding arrangement. Since the basic element radiates equally in both hemispheres, a ground plane of some kind is required. Radomes are usually added to protect the antenna when the site where it is installed demands it (e. Typically, hemispherical radomes are used, because they have little effect on the phase centre stability and symmetry, and non- hemispherical radomes are usually avoided, except when the shape is required by site characteristics (e. Antenna phase centre calibration should be performed with the radome. Conception and Simulation of the Quarter wave Rectangular Patch antenna in the band 'S' A. LATIF** * Ecole Royale de l’Air, BEFRA, Microwaves and Telecommunications Laboratory, Marrakech, Morocco. ANTENNA MAGUS: Complete list of Antennas in the database Q-band Feeding Microstrip Antenna. EL fadl, “Conception of Patch Antenna at Wide Band: Dual and Broadband Patch Antenna na”, ISN: 978-3- 8484-8921-3, Edition LAP - Lambert Academic publishing Germany, 2012. Patch Antenna Calculator. Anurag Ghosh (view profile) 1 file; 39 downloads 3.4. 86 useful links about Antenna design calculators collected in Antennas/Antenna Calculators at The DXZone. Its design is notable for the ability to reject multipath and low elevation signals (including reflections on the ground). Choke Ring antennas reflects signals that come from below, and draw surface wave signals into the choke channels, where they are cancelled or reflected away from the receiving element. Signals that strike the plane lose all energy before they reach the element and cause interference. Resistive Plane antennas provide similar performances as Choke Ring antennas, but with less weight and cost. Each signal from an antenna in the array can be processed by introducing dynamic phase shifts, and when the outputs of the array are summed, the effective radiation pattern can be maximized in some directions and nulled in other (e. Furthermore, beam steering techniques can be used to increase dynamically the antenna gain in a given direction, e. This technique can be used in ground reference antennas in order to maximize the antenna gain. The parabolic antenna is highly directive, so RF signals coming from the satellites can be received from one particular direction only. Its directive build structure and high gain make this type of antenna suitable for Ground Segment stations, such as monitoring or uplink stations, as shown in Figure 2. Due to the need for mobility, the antenna is usually mounted on a handheld pole, stand or tripod. In general, due to size and weight constraints, choke ring antennas are not a good solution for rover applications, so higher phase center variations are often seen in rover antennas. Usually single- frequency antennas, they are available in a range of implementations such as helical or patch antennas, both passive and active (see section below for details). Table 1 shows a few relations between antenna applications and characteristics. Typical scenarios for passive antennas are mobile devices, where power consumption is a critical issue. However, passive antennas must connect to the receiver's front end with very low losses, since there is no amplification mechanism involved at signal reception. Their purpose is to amplify the received signal to compensate for potential losses in long coaxial cables, at the cost of higher power consumption (power is usually delivered from the front end through the coaxial cable itself). In this approach, a Low- Noise Amplifier (LNA) is usually added to the antenna setup, in order to ensure a low noise figure in the signals to process. An example of active antenna use is for indoor reradiating purposes, where an active antenna inside a building reradiates the signals coming from another antenna, placed outside the building. In radiation terms, RHCP is referred to as the co- polar component, and LHCP is referred as the cross- polar component. The typical radiation pattern coverage is around 1. This pattern aims at maximizing the gain at zenith, decreasing to near unity at an elevation angle of around 1. At zenith, the ratio of the vertical electric field to the horizontal electric field response is near unity (0 d. B); this ratio is referred to as the axial ratio. The AR tends to degrade towards lower elevations, and it can reach less than 3 to 6 d. B at 1. 0. This phenomenon is called multipath, and since it degrades position accuracy, it should be avoided or reduced. Multipath signals can basically come from three directions: the ground, hitting the back of the antenna, the ground or an object, hitting the antenna at a low elevation, or an object, hitting the antenna at a high elevation. The multipath susceptibility of an antenna can then be quantified, with respect to the antenna. The multipath ratio is computed as the ratio between the RHCP gain at the satellite signal incident angle with respect to the sum of the RHCP and LHCP gains at the multipath signal incident angle. In fact, when a receiver determines a position solution, it is actually estimating the position of the electrical phase centre of the antenna, where the signals are captured, regardless of the distance from the antenna the receiver device really is. This electrical phase centre should not be mistaken with the physical phase centre: although the latter can be observed and is a physical constant, the first may vary, depending on the direction of the signal arrival. See the articles on antenna phase centre and receiver antenna phase centre for more details. RF filters can reduce the out- of- band signals by tens of d. Bs, which is enough in most cases. Of course, filters add insertion loss, amplitude and phase ripple, all of which degrade receiver performance. In- band interferers can be the third- order mixing products, or simply an RF source that transmits inside the GNSS bands. If these are relatively weak, the receiver will handle them; from a certain power level on, however, commercial receivers can do nothing about them. For instance, in GPS, the minimum received power is . Furthermore, the cable and the receiver elements generate noise that can affect the signal. To avoid reducing this effect, the first element following the antenna is usually a Low Noise Amplifier (LNA), so that the power of the GNSS signal is greater than the noise generated by the cable and the receiver elements. This operation, however, will degrade the Noise Figure, so there is a trade- off in the design of the antenna LNA between the Noise Figure and the Out of Band Rejection. Typically, the compromise is reached by distributing the filtering across the LNA in two stages. These values are able to fit most GNSS signals and therefore the limitations on the signal bandwidth is usually concentrated in the front- end block, keeping in mind that both antenna and front- end blocks contribute to this bandwidth. In the case of the antenna being far from the receiver, for physical constraints or application necessity, special attention should be drawn to the choice of the connecting cable. Requirements like cable length, impedance, antenna gain and power supply (for the case of active antennas) need to be taken into account to minimize signal losses. For illustrative purposes, an example of the loss ranges at stake. In this example, from a signal loss point of view, the .
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |