Antenna Pattern Characteristics Research Articles

Analysis and Correction of Antenna Pattern Effects in AMAO Spaceborne SAR Images

Azimuthal multi-angle observation (AMAO) is a novel spaceborne synthetic aperture radar (SAR) technique proposed recently, which significantly improves the acquisition performance of target information. It has highly flexible antenna beams with powerful beam-steering capability while affecting the consistency of radiometric measurements, especially in the high-squint case. This paper mainly focuses on the antenna pattern effect analysis and correction method of AMAO spaceborne SAR. The antenna pattern characteristics of the squint steering beam are first analyzed. On this basis, an analytical model is developed to quantify the antenna pattern effects in AMAO SAR images. Different from the conventional approach that corrects the elevation antenna pattern, an improved antenna pattern correction method, which accounts for the spatial variation in the two-dimensional antenna pattern, is then proposed for AMAO spaceborne SAR. Finally, experiments are conducted to verify the proposed correction method. The results show that the newly proposed method considering the spatial-variant antenna pattern has higher performance than the conventional approach using a reference elevation pattern.

위성탑재용 광대역 영상레이다의 빔 분산 및 고도 변화에 의한 거리 방향 모호성 성능 개선 방안

In a wideband radar, a true time delay line (TTDL) is used to compensate for the propagation delay that has a different value according to the operational frequency. This study analyzes the antenna pattern characteristics of wideband synthetic aperture radar (SAR) that does not require any TTDL. In addition, it defines an antenna pattern to compensate for beam dispersive effects and a method to improve the range ambiguity to signal ratio (RAR). Considering the altitude change that occurs in a SAR satellite, this paper proposes a method to optimize the operational parameters and consequently enhance the RAR performance. The proposed method uses altitude-dependent equations to calculate the operational parameters; hence it can be easily applied to the real operation of a SAR satellite. The RAR analysis for operational altitude variation of 35 km shows that an improvement of approximately 2.1-dB, 0.9-dB, and 2.1-dB is achieved at the stripmap, wide-swath, and high-resolution modes respectively. The RAR is improved to comply with the requirement in the stripmap mode, whereas the wide-swath and high-resolution modes have a sufficient margin.

VHF antenna pattern characterization by the observation of meteor head echoes

Abstract. The Middle Atmosphere Alomar Radar System (MAARSY) with its active phased array antenna is designed and used for studies of phenomena in the mesosphere and lower atmosphere. The flexible beam forming and steering combined with a large aperture array allows for observations with a high temporal and angular resolution. For both the analysis of the radar data and the configuration of experiments, the actual radiation pattern needs to be known. For that purpose, various simulations as well as passive and active experiments have been conducted. Here, results of meteor head echo observations are presented, which allow us to derive detailed information of the actual radiation pattern for different beam-pointing positions and the current health status of the entire radar. For MAARSY, the described method offers robust beam pointing and width estimations for a minimum of a few days of observations.

Fabrication, simulations, and measurements of self-assembled millimeter-wave antennas for system-on-chip applications

A micro-electro-mechanical systems fabrication process has been developed to create self-assembled on-chip high efficiency antennas. The self-assembly creates out-of-plane antenna structures, which can have good radiation efficiency on low resistivity substrates. The structural material is SU-8 and the self-assembly curvatures are defined lithographically. The losses are reduced by having the antennas, transmission lines, and an isolating conducting ground plane placed on top of the supporting (and lossy) dielectric layer. The fabrication process includes deposition of a thick metal layer, which envelopes the antenna structure. This paper presents the fabrication process for a self-assembled monopole antenna, and numerical and physical experiments for the antenna pattern characteristics. The physical measurements show a realized gain (includes mismatch loss) of ?1.29 dBi at 59 GHz.

In-Orbit Analysis of Antenna Pattern Anomalies of GNSS Satellites

The payload of a typical navigation satellite encounters heavy strains during launch. This indicates the need to characterize and assess the antenna and consequently the total signal performance of a satellite in orbit. Using ground measurements with a high gain antenna seems to be a powerful basis for this analysis. This paper introduces the used measurement facility and strategies for obtaining a sufficient amount of measurement data based on the used simplified satellite attitude and yaw steering model. The analysis algorithms will be described in detail and as a side product it will be shown that transmitter power variations of the navigation satellite over time can be characterized and separated from the pure influence of the satellite antenna. The last section presents the exemplary antenna pattern characterization for the second Galileo test satellite GIOVE-B (Galileo In-Orbit Validation Element) based on calibrated flux density measurements taken with DLR's 30 m high gain antenna for the E1 frequency band. Copyright © 2012 Institute of Navigation.

Theory and Practice of the FFT/Matrix Inversion Technique for Probe-Corrected Spherical Near-Field Antenna Measurements With High-Order Probes

A complete antenna pattern characterization procedure for spherical near-field antenna measurements employing a high-order probe and a full probe correction is described. The procedure allows an (almost) arbitrary antenna to be used as a probe. Different measurement steps of the procedure and the associated data processing are described in detail, and comparison to the existing procedure employing a first-order probe is made. The procedure is validated through measurements.

Experimental Demonstration of the Corbella Equation for Aperture Synthesis Microwave Radiometry

The fundamental equation of aperture synthesis microwave radiometry has been recently revised into a new so-called Corbella equation to include antenna coupling effects and the interferometry formulation into a single equation. This equation has been experimentally demonstrated for the first time with a full prototype of the Microwave Imaging Radiometer with Aperture Synthesis. Several tests have been carried out to demonstrate the new visibility equation with different targets. The test results show better agreement with simulations based on the Corbella equation than the old fundamental equation. An initial analysis of the influence of the antenna pattern characterization errors shows the importance of these errors in the final results according to the new formulation

The visibility function in interferometric aperture synthesis radiometry

The fundamental equation of interferometric aperture synthesis radiometry is revised to include full antenna pattern characterization and receivers' interaction. It is shown that the cross correlation between the output signals of a pair of receivers is a Fourier-like integral of the difference between the scene brightness temperature and the physical temperature of the receivers. The derivation is performed using a thermodynamic approach to account for the effects of mutual coupling between antenna elements. The analysis assumes that the receivers include ferrite isolators so that the noise wave passing from the receiver toward the antenna can be modeled as uncorrelated ambient noise. The effect of wide beamwidth antennas on the polarization basis of the retrieved brightness temperature is also discussed.

Characteristics of Dual Reflector Antennas With Gaps Between the Panels Forming the Subreflector: MOM and PO Analysis

Beam shaping is primarily performed by shaping the main reflector. An alternative way to shaping the main reflector is to shape the subreflector in a dual reflector system where mechanically movable panels can be deployed. Panels placed on the subreflector can potentially place their own signature on the antenna pattern, a topic which is investigated in this paper. To visualize and categorize generalized panel alignments as a result of panel movements, MoM and PO/PO methods are devised and applied to 2-D geometries based on TM and TE analysis. It should be noted that the panel movements on the subreflector create gaps between the panels which would also increase antenna cross polarization levels which is not addressed here due to 2-D nature of the analysis. Consequently, this study will focus on the antenna pattern characteristics and the required number of panels in conjunction with minimizing grating/sidelobe signature left by the panels displacements with gaps in axial and lateral directions. In addition, antenna gain loss is quantified based on gap sizes between the panels. Current distribution on the reflector antenna is also studied for both TM and TE polarization and several of their key features are examined based on PO/PO and MoM analysis.

Mutual coupling effects on antenna radiation pattern: An experimental study applied to interferometric radiometers

Antenna pattern mismatches are one of the most important error sources in planned Earth‐observation interferometric radiometers. From a low Earth orbit, the wide field of view, about ±30°, leads to the use of antennas with a large beam. In addition, antennas must be closely spaced to avoid, or at least minimize, aliasing effects in the formation of the synthetic brightness temperature images. The accuracy demanded of these systems requires the precise knowledge of all the antenna radiation voltage patterns (amplitude and phase), which may differ from their theoretical values due to mechanical and electrical tolerances in the manufacturing process and which can change due to the proximity of other structures, i.e., other antennas of the array or the mechanical support. Two approaches are found in the literature to interpret the impact of antenna mutual coupling on the performance of an interferometric radiometer: (1) a modification of the antenna voltage pattern and (2) a mixing of the cross correlations measured between the signals collected by the antennas. The main contribution of the present work is a detailed theoretical analysis of the impact of mutual coupling effects showing the equivalence between both approaches. Theoretical results are corroborated with a set of experimental measurements with two kinds of antennas. Theoretical and experimental results can be used in the design of the antennas of interferometric radiometers in order to predict the impact of mutual coupling on the system's performance and point out the importance of an accurate antenna pattern characterization.

Vector analysis and satellite footprints

Projections of antenna pattern characteristics from a satellite in circular orbit onto the Earth's surface, referred to as footprints, are derived using vector analyses. These vector analyses are described along with a winding number approach used to determine whether a given point on the Earth's surface lies within the footprint contour. The utility of this program is illustrated using a Sun-synchronous satellite and a radiometric antenna that is mechanically scanned at a constant offset angle about the satellite nadir axis. The time sequence of the antenna pattern as the antenna scans and translates past a specified point on the Earth's surface can be generated. This program has the generality to illustrate the effects of satellite attitude variations on the footprint contour. In addition, footprints for a nonspherical Earth are contrasted with those for a spherical Earth. >

Effects of polarization coupling loss mechanism on design of meteor scatter antennas for short‐ and long‐range communication

This paper considers the effect of the polarization coupling loss phenomenon on the design of antennas for meteor scatter communication at short and long ranges. It will be demonstrated that this mechanism strongly influences the spatial arrival pattern of usable meteor trails, and antenna patterns need to be designed around this effect. Characteristics of antenna patterns which exploit the spatial arrival pattern of meteor trails at short and long ranges will be given.

Multiple beam feed networks using an even number of beam ports

An aperture illumination compatible with the use of an even number of adjacent beam ports in a multiple beam feed network is discussed. The antenna pattern characteristics of near-in sidelobe levels, half-power beamwidth, aperture efficiency, and feed network loss are evaluated. Maximization of the available antenna gain at adjacent beam crossover points is shown to be possible for either sequential or simultaneons operation of a receiving system. The results presented indicate that lossy feed networks are quite suitable for certain array antenna applications.

Lossy-feed networks in multiple-beam arrays

Using a lossy-feed network in a multiple-beam array antenna, particularly a receiving system without active amplifying components embedded in the network, has generally been avoided. Attention is called to certain antenna pattern characteristics that should be evaluated with respect to the system application involved. Lossless-feed networks often possess one or more of these pattern characteristics which can possibly be enchanced when the capabilities of a lossy network are properly traded off. Maximizing available antenna gain at the beam crossover points, for example, is shown to be one possible advantage for employing a lossy network instead of a lossless design. Near-in sidelobe levels can readily be controlled with a lossy network.

Theory of Scalloping Amplitude Errors in Standard VOR Bearing Indications

A rigorous theory is developed for the course scalloping amplitudes observed in the bearing indications of an airborne standard VOR receiver in the presence of multipath signals. The VOR transmitting antenna pattern characteristics, the scattering properties of the multipath source, and the effects of ground reflection are all built into the theory so that their combined effects on the scalloping may be quantitatively investigated. The analysis assumes that the VOR receiver characteristics are ideal.

Transient and steady-state antenna pattern characteristics for arbitrary time signals

Abstract : This report presents a simplified method for the analytical determination of the transient and steady state pattern characteristics of an antenna for arbitrary time signals and arbitrary aperture distributions. For uniform aperture illumination, the pattern response of an antenna for any time signal, no matter how complicated, can be found through simple shifts of the signal, and both the transient and the steady-state behavior can be determined without performing any integration. Examples are given for responses to suddenly applied excitations, to rectangular pulses, to excitations for electronic scanning, and to time signals in a pulse compression system. For pulse signals, a steady state is not reached in any given direction, theta, if the duration of the pulse T is less than (a/c) sin theta, where a is maximum aperture dimension and c is velocity of light. Graphical representations for easy interpretation of the different states of pattern characteristics are included.