Antenna Gain Pattern Research Articles

Carrier phase multipath mitigation based on GNSS signal quality measurements

Carrier phase multipath caused by signal reflections in the vicinity of GNSS stations is a ma- jor error source of precise differential positioning. Detection and mitigation of carrier phase multipath errors can be based on signal quality values (e. g. signal-to-noise ratio values) as provided by GNSS re- ceivers. These values are influenced by various fac- tors as e. g.the actual strength of the transmitted sig- nal, space loss, atmospheric effects, and antenna gain pattern. After their removal, deviations from nominal signal quality values mainly contain multipath infor- mation which can be used to calculate carrier phase multipath corrections. The described technique is valid only for observations collected in static mode and sin- gle dominant reflectors. Practical experiences show that corrections based on signal quality observations are able to remove a large portion of the carrier phase multipath errors.

スピンを伴う飛翔体に搭載可能なGPS受信機の開発

This paper describes the design and development of a dedicated GPS receiver for spin stabilized launch vehicles. The receiver is built around a commercially available low cost GPS chip set and operates an enhanced firmware specifically adapted for high dynamics applications. In order to keep tracking a sufficient number of GPS signals even during the spinning motion, we use multiple GPS patch antennas and space them equally apart each other around the cylindrical launcher body. A new signal combining scheme was developed to avoid deep fading in antenna gain pattern. This technique requires phase control to keep signals received on multiple antennas in phase with each other. A dualantenna GPS receiver was developed to evaluate the proposed signal combining algorithm. The result showed that the proposed algorithm was capable of providing stable and continuous signal tracking under a high-rate spinning motion while simple RF combining through a power combiner was failed.

沿岸・浅海域センサネットワーク用高精度1周波GPS受信機の研究

For ubiquitous sensor network applications in shallow water coastal zone, a low-cost consumer L1 C/A-code GPS receiver with a small patch antenna is a suitable sensor for positioning and timing of a node. The goal of this research is to realize a single-frequency RTK-GPS sensor providing precise positioning information in order to improve the underwater ultrasonic communication between sea surface and bottom floor in shallow water, where many multipath echos and non-uniform water flows degrade the communication quality. Since antenna gain pattern is one of the important factors for RTK-GPS, we focused on the optimization of GPS antennas implementation, such as ground plane size and antenna height above sea surface. In this paper, several different combinations of the groud plane and antenna height were evaluated by field tests. The antenna gain paterns including sear-surface effects were also evaluated by an electromagnetic field analysys method called UTD. The results showed that certain combination of ground plane and antenna height provides favorable signal reception condition above sea surface and improves the fix-rate of signle-frequency RTK-GPS positioning.

A WIDEBAND MINIATURIZED DIPOLE ANTENNA ON A PRINTED CIRCUIT BOARD

This paper investigates a miniaturized resonant antenna that comprises a meandered monopole and a partial ground plane. A bandwidth enhancement is found using the ground plane on the back side of the circuit board where the entire communication system resides. The meandered monopole together with the ground plane forms a wideband dipole antenna. The design shows over 25% 10dB impedance bandwidth at 2.5GHz ISM band with a monopole area of 300mils by 166mils on a small circuit board and a backside ground plane 1500mils by 600mils. The wire length is about one third and the Q factor is about twice as compared against the case of using a straight quarter-wave microstrip monopole. The antenna Q factor as a function of the ground plane area is characterized. The use of circuit ground as a part of an antenna should flnd useful applications in portable wireless systems. Good agreements are found between simulated and measured antenna gain patterns and return loss.

A Variational Correction Method as an Alternative to Forced Rejection of Sidelobe-Contaminated Bistatic Doppler Measurements

Abstract The problem of sidelobe contamination of bistatic apparent Doppler velocity measurements involved in a bistatic Doppler radar network is examined. So far in the context of 3D wind field analysis, by combining a traditional Doppler radar with one or more bistatic receivers, identification and hence removal of regions of high degrees of contamination were necessarily crucial steps to obtaining reliable wind fields. This study proposes an alternative solution to the forced rejection of bistatic Doppler data suspected to be contaminated by sidelobe echoes, on the basis of restoring the nonmeasured “actual” (i.e., noncontaminated) bistatic Doppler velocity from both monostatic radar and bistatic receiver measurements. The correction method is based on a modeled expression of the observed bistatic apparent Doppler velocity defined as the reflectivity-weighted average of actual Doppler velocity of particles within individual volume samples, including the antenna gain pattern of both transmitting and receiving radars. The searched actual Doppler velocity is a solution of an underdetermined inverse problem that can be handled as a constrained linear inversion problem, through a variational least squares analysis method. The performances of the proposed method are analyzed, using simulated radar observations involving one remote receiver. An example of application to experimental data collected by the Deutsches Zentrum für Luft und Raumfahrt (DLR) bistatic Doppler radar network within a moderate precipitation system observed on 8 May 2000 in Germany is also presented. Pseudo-Doppler observations of a tropical squall-line system are used to quantify the effective improvement of the correction method on the bistatic Doppler velocity and hence the retrieved 3D wind field. Statistics of the differences are presented between observed and idealized (sidelobe free) velocity structures on the one hand, and corrected and idealized velocity structures on the other hand. Clearly shown is the very low level of the corrected minus idealized differences (mean and standard deviation) against the significantly high level of the observed minus idealized differences. As previously observed, maximum correction occurs in regions of potentially high gradients of reflectivity. It is also found that regions of low observed minus idealized differences remain unchanged after correction, which means that the sidelobe-correction method only acts on needed regions and does not introduce any artificial modification.

Gain, detuning, and radiation patterns of nanoparticle optical antennas

For their capability to localize and redirect electromagnetic field, metal nanoparticles have been recently viewed as efficient nanoantenna operating in the optical regime. In this article, we experimentally investigated the optical responses of coupled gold antenna pairs and measured the critical parameters defining antenna characteristics: resonant frequencies and bandwidths, detuning and gains, and radiation patterns.

Modeling the meteor head echo using Arecibo radar observations

This paper reports results obtained using a combined set of models to determine meteoroid properties by comparing expected and observed meteor head-echo signal-to-noise ratio (SNR) and line-of-sight Doppler velocity as measured in high-power and large-aperture (HPLA) radar observations. For this task we model: (1) meteor ablation and ionization processes, (2) meteor head-echo radar cross-section (RCS), (3) the radar equation, and (4) the radar antenna gain pattern, together with an automated least-squares fitting procedure to estimate meteoroid and observation parameters (i.e. aspect angle, location within the radar beam, etc.). We compared our simulated results with 236 head-echo events observed using the Arecibo 430 MHz radar in Puerto Rico. We found good agreement between modeled and observed SNR versus meteor altitude profiles for a broad range of head-echo observations. We also find reasonable agreement between meteoroid mass distributions resulting from these models and estimated using dynamical arguments, with the dynamical mass generally resulting in lower values by about 1–2 orders of magnitude. A characteristic of our methodology is that we can trace back the original mass and velocity of the meteoroid “above” the atmosphere (∼150 km altitude) required to produce the observed meteors. We find that, the original mass is required to be, on average, 1–2 orders of magnitude larger than that at the time of observation, and 3 orders of magnitude larger than estimated using dynamical equations. These results suggest that many meteor head echoes are observed towards the end of the particle's life, which has significant implications for the use of these observations for the determination of meteoroid properties. The automated fitting procedure is very sensitive to the antenna pattern, and therefore allows for precise estimates of the location of the meteoroid's trajectory within the Arecibo radar beam. The results indicate a noticeable, but weak, dependence between the distance of the particle's trajectory from the center of the beam (i.e. maximum gain) and the mass and velocity of the meteoroid. This suggests that the Arecibo radar is not particularly biased toward a specific velocity population of meteoroids (i.e. high velocity) as has been suggested in previous work.

On-Body Antennas and Propagation: Recent Development

The paper reviews recent advances in on-body antennas and propagation under a joint UK EPSRC research project between Queen Mary College, University of London and University of Birmingham. The study of on-body radio propagation has been extended by using various small antennas. The effect of antenna size, gain and radiation patterns on on-body channel characteristics has been studied. A practical wearable sensor antenna design is presented and it is demonstrated that a global simulation including sensor environment and human body is needed for accurate antenna characterisation. A 3D animation design software, POSER 6 has been used together with XFDTD to predict the on-body path loss variation due to changes in human postures and human motion. Finally, a preliminary study on the feasibility of a diversity scheme in an on-body environment has been carried out.

Brightness Temperature Reconstruction Using BGI

This paper departs from the popular usage of the Backus-Gilbert inversion (BGI) method as a tool for inversion of antenna temperature measurements in microwave radiometry. The BGI method is applied in this paper to enhance the information content of an existing set of oversampled brightness-temperature (TB) data. The purpose is to isolate the inversion process from its resolution enhancement counterpart. The advantage gained is that the resolution enhancement can be performed in a simplified way and in a different level of processing that starts with the scan-mode TB data product and simply requires with it the knowledge of the antenna gain pattern and the sensor's scan geometry. The technique is demonstrated with the 19.35-GHz Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) channel, which provides oversampled TB data. The radiometric resemblance of this channel with that of the 37 GHz and geocollocation of their TB footprints facilitate validation of the enhancement of features. The significance of oversampling the low-frequency (LF) radiometer channels is underscored in the process, which gives the authors the confidence to propose oversampling of the LF data for the forthcoming sensor Microwave Analysis and Detection of Rain and Atmospheric Structures (MADRAS) onboard the Megha_Tropiques mission, which is a joint ISRO-CNES collaboration (due for launch in 2009).

Observing the Moon at Microwave Frequencies Using a Large-Diameter Deep Space Network Antenna

The Moon radiates energy at infrared and microwave wavelengths, in addition to reflecting sunlight at optical wavelengths. As a result, an antenna pointed at or near the Moon will result in an increase in system operating noise temperature, which needs to be accounted for in RF telecommunications, radio science or radiometric link calculations. The NASA Deep Space Network (DSN) may use its large-diameter antennas in future lunar robotic or human missions, and thus it is important to understand the nature of this temperature increase as a function of observing frequency, lunar phase, and angular position of the antenna beam on the lunar disk. This paper reports on a comprehensive lunar noise temperature measurement campaign and associated theoretical treatment for a 34-m diameter Deep Space Network antenna observing an extended source such as the Moon. A set of measurements over a wide range of lunar phase angles was acquired at DSS-13, a 34-m diameter beam waveguide antenna (BWG) located at Goldstone, California at 2.3 GHz (S-band), 8.4 GHz (X-band) and 32 GHz (Ka-band). For validation purposes, independent predictions of noise temperature increase were derived using a physical optics characterization of the 34-m diameter antenna gain patterns and Apollo model-based brightness temperature maps of the Moon as input. The model-based predictions of noise temperature increase were compared with the measurements at all three frequencies. In addition, a methodology is presented that relates noise temperature increase due to the Moon to disk-centered or disk-averaged brightness temperature of the Moon at the microwave frequencies of interest. Comparisons were made between the measurements and models in the domain of lunar disk-centered and disk-averaged brightness temperatures. It is anticipated that the measurements and associated theoretical development will be useful in developing telecommunications strategies for future high-rate Ka-band communications where large diameter DSN antennas will be required.

Radiobrightness at 6.7-, 19-, and 37-GHz Downwelling From Mature Evergreen Trees Observed During the Cold Lands Processes Experiment in Colorado

The University of Michigan Microwave Geophysics Group participated in the Cold Lands Processes Experiment from February to April 2003 by deploying its Truck Mounted Radiometer System-3 (TMRS-3) to perform temporal monitoring of the snow pack at the local scale observation site (LSOS). The LSOS was located at the Fraser Experimental Forest headquarters in the mountains near Fraser, CO. The small clearing in which the TMRS-3 was deployed was adjacent to tall evergreen trees. To quantify the amount of the downwelling brightness from these trees onto the snow pack, the TMRS-3 periodically observed these trees. Microwave brightness data were collected from the trees every 15 from horizontal incidence to 45 from zenith. Both polarizations were observed for 6.7, 19, and 37 GHz. A rapid decrease in brightness is evident as the radiometers were pointed progressively upward. The next May, an upward-looking hemispherical (ldquofish-eyerdquo) photograph was taken from the center of the clearing, and it reveals a significant sky background through the incomplete canopy. By superimposing Gaussian approximations to the microwave antenna gain pattern of the individual TMRS-3 radiometers onto the photograph, we estimated the amount that the main beams were filled with canopy and with sky. Comparison of the measured data to that expected for a partially filled main beam indicates that the needle-leaf canopy is roughly an isotropic emitter having emissivities at frequencies between 6.7 and 37 GHz of between 0.93 and 0.97 with air temperature as a proxy for tree temperature.

Planar monopole antenna with wideband operation

AbstractA simple printed monopole antenna with wideband operation is presented. The proposed antenna has excellent impedance bandwidth coving the range from 1.926 to 4.9 GHz. The obtained impedance bandwidth reaches ∼123.9% (10‐dB return loss) for 2.4 GHz, which meets the required bandwidth specifications of IEEE 802.11 b/g standards. The simulated return loss shows good agreement with the measured data. Good antenna gain and radiation patterns of the proposed antenna have also been observed across the operating band. Details of the proposed antenna design and experimental results are presented and discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 696–699, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22241

Design of Multiband UWB Planarized Monopole Using DMS Technique

A variation of the novel technique called defected microstrip structure (DMS) is employed to enlarge the bandwidth of a planarized ultrawideband (UWB) monopole. It is demonstrated that introducing a defect in the feeding microstrip line, the lower bandwidth limit is lowered without affecting the antenna gain and radiation pattern. The bevel technique in the ground plane near to the feeding point is used to increase the highest bandwidth limit. By using these techniques, a 50 mm times 50-mm planarized omnidirectional antenna was developed, achieving a voltage standing wave ratio (VSWR) < 2 from 2.1 to 12.3 GHz

Single Antenna Attitude Algorithm for Nonuniform Antenna Gain Patterns

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Virtual Anechoic Chamber using GPS Signals

Using GPS for animal tracking applications presents many significant challenges; not least the integration of the antenna in what is usually a miniature device. This paper describes a test setup that has been constructed to allow the user to perform something close to a full antenna gain pattern test using a simple turntable and relying on the GPS satellite motion to collect all angles required for a 3D gain plot. This has proved invaluable when predicting the expected performance of various antenna/packaging options for animal tags.

A compact‐size circularly polarized antenna using low‐loss alumina substrates

AbstractA compact‐size circularly polarized antenna is investigated by employing high‐permittivity and low‐loss substrate (i.e., high Q × f value) for 2.5‐GHz application. The antenna was individually fabricated on nano‐Al2O3 (εr = 9.7, Q × f value of 500,000 GHz) and Al2O3 (εr = 9.7, Q × f value of 200,000 GHz) substrates. The high‐permittivity and low‐loss ceramic substrate (nano‐Al2O3 substrate) was used to reduce the microstrip antenna dimension on patch size. In addition, the ceramic substrate was studied for broadening the 3‐dB axial ratio bandwidth [circular polarization (CP) bandwidth]. The obtained CP bandwidth is about 80 MHz (∼3.2%) at 2.5 GHz. The proposed antenna occupies a size of 23.4 × 23.4 × 4 mm3 and obtains the operation bandwidth of about 90.96 MHz. Good antenna gain and CP radiation patterns have also been observed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2317–2320, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21909

Study of a CPW‐fed circular slot antenna for UWB communications

AbstractA numerical and experimental study of a circular‐slot antenna, fed by a coplanar waveguide with a rectangular stub, is proposed in this paper for ultra‐wideband communications. The antenna impedance bandwidth, phase linearity, gain and radiation patterns are presented, together with the time‐domain impulse response. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2272–2277, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21900

Dual‐wideband rectangular dielectric resonator antenna for WLAN communications

AbstractA dual and wideband single‐element rectangular dielectric resonator antenna (DRA) excited by a microstrip aperture is investigated experimentally. It provides two passbands in the ranges of 2.21–2.855 GHz and 4.385–5.455 GHz, which are popular bands for wireless local‐area networks (WLANs). The return loss, antenna gain, and radiation patterns of the proposed configuration are measured. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 378–380, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21355

CryoSat: A mission to determine the fluctuations in Earth’s land and marine ice fields

This paper describes the CryoSat satellite mission, due for launch in 2005, whose aim is to accurately determine the trends in Earth’s continental and marine ice fields. The paper’s purpose is to provide scientific users of the CryoSat data with a description of the design and operation of the SIRAL radar and the CryoSat platform, the data products, and the expected error budget. The ‘low-resolution mode’ (LRM), ‘synthetic aperture mode’ (SARM) and “synthetic aperture interferometric mode’ (SARInM) of the SIRAL radar are described, together with its system parameters, its antenna gain pattern and interferometer phase difference pattern, and its calibration modes. The orbit is described, together with the platform attitude and altitude control law and control systems, and the expected pointing and altitude knowledge. The geographical masks that are used to determine acquisitions in the three SIRAL modes are described. The SIRAL data products, and the processing applied to produce them, are described. Level 1b, level 2 and higher-level products are described in turn, with a particular emphasis on the new procedures applied to the SARInM and SARM processing over ice surfaces. The beam forming and multi-looking is summarised, and a description is given of the behaviour of the SARM and SARInM echoes over idealised surfaces. These inform descriptions of the elevation retrievals of the level 2 processing, including the SARInM retrieval of interferometric phase. The combination of these data, through cross-over analysis over continental ice sheets, and through averaging over sea-ice, to determine areal averages of ice sheet elevation change or sea-ice thickness, is described. The error budget in these higher-level products is described, together with its breakdown into errors arising from the instrument and errors arising from the retrievals. The importance of the co-variance of these errors in determining the final error is stressed. The description of the errors also includes a summary of the experiments required following the launch to validate the CryoSat mission data. An estimate of the mission performance over ice surfaces is made at various spatial scales, and it is concluded that even the relatively short, three-year duration of the CryoSat mission will allow it to make an important scientific contribution, particularly when combined with results from earlier satellite missions.

Effects of a smaller unit cell planar EBG structure on the mutual coupling of a printed dipole array

A new smaller unit-cell planar electromagnetic bandgap (EBG) structure is proposed on low dielectric constant low-cost substrate (TMM: /spl epsiv//sub r/=4.5,thickness=25 mils) that has a stopband frequency at around 4 GHz. The proposed structure when placed in between a two-element printed dipole array results in over 13-dB reduction in mutual coupling and a significant improvement in antenna return loss bandwidth and gain pattern.