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Errors and Accuracy Issues
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
When dealing with typical accuracy values of around a few meters, the question of knowing the exact position of the calculated point does not arise. In such cases it is assumed to be ‘the receiver’s antenna’ that is usually a few centimetres tall or wide. However, this question should be considered when dealing with high-accuracy positioning. The physical point where signals are ‘collected’ is the centre of phase (also called phase centre) of the antenna. This point is very difficult to define precisely and depends on the incident angle of incoming signal; thus, this point is not necessarily geometrically fixed. Remember that the phase centre is not the physical centre of the antenna; therefore, perfect calibration of the antenna is required. When centimetre accuracy is needed, this is fundamental.
Ultra-Wideband Antenna Technology
Published in James D. Taylor, Introduction to Ultra-Wideband Radar Systems, 2020
P. R. Foster, J. Doss Halsey, Malek G. M. Hussain
The phase center of an antenna is a frequency concept and is defined as the apparent point from which the antenna radiates at a specified frequency. This radiating center is often a function of frequency and is an important aspect of antennas for UWB radars, as it may add a frequency-dependent time lag to the arrival times for off-axis angles. This will affect the transfer function of the antenna, particularly if it is an array of elementary antennas (see Part 2, Section III below). Typical examples of antennas which have phase centers variable with frequency are log-periodic dipole arrays (LPDAs) and many horns. On the other hand, some antennas such as dipoles have a phase center which remains stationary with frequency.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Because of the high frequency of the GPS signals, multipath effects may hamper final accuracy; the signal arriving at the receiver through a reflected path may be stronger then the direct signal. By careful antenna design and positioning, multipath effects are reduced. The phase center of the antenna must be calibrated carefully with respect to a geometric reference point on the antenna assembly. However, because of the varying inclination angle of the incoming electromagnetic signals, effects of a moving phase center may be present at all times.
UWB full polarization single-plane monopulse reflector antenna
Published in Electromagnetics, 2023
An important design parameter for reflector antennas is the ratio of the focal length F to the antenna diameter D, or F/D ratio. The appropriate choice of the F/D is based on mechanical and electrical considerations. Most of the ordinary reflectors with a single feed have F/D ratio between 0.3–0.5 (Skolnik 1980). For monopulse applications, the F/D ratio affects the beam deviation and should be chosen more carefully. Figure 5 shows angle of maximum beam for different values of F/D when the lateral feed distance are 0.5, 1 and 2 The simulation was performed for 15 reflector diameter and infinite small dipole is used as illuminator. Using infinite small antennas ensures that the phase center is located at the antenna position.
A novel algorithm to compute 3D phase center
Published in Electromagnetics, 2020
Haobo Yuan, Hongwei Liu, Jiansheng Jia, Tao Su, Cao Zeng
The phase center is critical for the description and design of many antennas, such as the horn antenna (Muehldorf 1970), the phased array (Aumann, Willwerth, and Tuttle 2004), and the GPS antenna (Kolesnikoff 1991). The array antenna will cause errors due to the accuracy of manufacturing, which will lead to the actual effect of the designed array is not in accordance with the expectation. For example, for the processed uniform linear array (ULA), the actual phase center of each array element can be calculated to verify whether the processed array has the characteristics of uniform linear array (ULA). Moreover, in satellite navigation and attitude control, it is necessary to know exactly the position of GPS antenna which generates submillimeter-wave signal, and the phase center is one of the important parameters to determine its position information. By definition, the phase center is the point from which the electromagnetic radiation spreads spherically outward, with the phase of the signal being equal at any point on the sphere.
The comparison of two structures of wide band horn antenna
Published in International Journal of Electronics Letters, 2019
Saeed Manshari, Farokh Hojjat-Kashani, gholamreza Moradi, Mohamad Sarijlo
Also, it is obvious that the total gains for two antennas are very close and almost the same. In Table 2, the aperture efficiencies of the antennas versus frequency are presented. The aperture efficiency depends on the TE10 mode distribution on the aperture and quadratic phase error (Balanis, 2005b). By increasing frequency due to changing phase distribution on the aperture, quadratic phase error is increased and the efficiency is decreased. Table 3 presents the location of the phase centre of these antennas at 45° rotated state for vertical and horizontal polarisations versus frequency. The phase centre measurements have been done in anechoic chamber of K.N. Toosi University of Technology. By moving the antenna axis of rotation on horn axis and measuring phase patterns, location of the phase centre has been obtained (Teichman, 1997; Teichman, 1973). Variation of phase centre location of the dual section horn for vertical and horizontal polarizations are 33 and 33.5 mm, respectively. However, for common horn these amounts are 71.5 and 38 mm. Distance of phase centre (on horn axis) from the aperture by increasing of frequency is increased (Teichman, 1973). But variation of the location of phase centre of one-step horn versus of frequency is non-linear. Figure 6 shows the simulated and measured VSWR of the two antennas. The simulation and measured results show that the antennas have good impedance characteristics in the operation band. Reason of little difference between these two results is manufacture tolerances (Jacobs, Odendaal, & Joubert, 2010). Also, lossless conditions have been assumed in simulations. The fabricated antennas in anechoic chamber are shown in Figure 7.