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ABSTRACT: This letter presents an analysis of microstrip lines that are printed on substrates composed of numerous dielectric layers using a fast technique that comprises the full-wave equivalent circuit and the discrete mode matching method. The validation of the proposed formulation has been done with a commercial package based on the finite-element method and very good agreement has been obtained. As a special application of our technique, we consider the analysis of microstrip lines printed on substrates with dielectric constants that vary according to given graded-index profiles. The profiles are modelled by replacing the substrate by numerous homogeneous dielectric layers. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1626–1628, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25276
Microwave and Optical Technology Letters 04/2010; 52(7):1626 - 1628. · 0.62 Impact Factor
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ABSTRACT: This paper presents the analysis of waveguides with noncircular cross sections under the application of the discrete mode matching (DMM). The structure is represented by an equivalent circuit, which is used to set up the system equations to compute the propagation constant for the case under analysis. To demonstrate the application of the method, elliptical dielectric waveguides and conformal striplines are analyzed.
Microwave Conference (GeMIC), 2008 German; 04/2008
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ABSTRACT: To transfer broadband services to mobile users by satellite communications a large bandwidth is required. Because the frequency spectrum at lower frequencies is very crowded with different services, free broad frequency bands can be found only at Ka-band or at higher frequencies.
The user terminal antenna for satellite communication should have preferably low profile so that it can be conveniently integrated into e.g. aircraft, ship or vehicle. Antennas based on the reflector technology have necessarily high profile. Antennas with lower profile are based on array technology. They can be fully electronically steered or offer a combination of electrical and mechanical scanning in elevation and azimuth respectively. The lowest profile offer fully electronically steered antennas.
AP-S 2009;
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ABSTRACT: Theoretical overview of phase centre and its definition is presented. Taking into account classical geometry, where shape of the phase-front is observed, different problems and peculiarities of phase centre have been identified and discussed. The intention of this paper is to demonstrate a straightforward method for determination of phase centre in 3D by using Nelder-Mead optimising algorithm. The method has been tested on simulated examples of dipole and patch antennas.
European Microwave Week 2009;
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ABSTRACT: This paper presents an efficient approach for the
analysis of graded-index profile waveguides. The variation of the
index of refraction is modelled considering a sufficient number
of concentric dielectric layers, each with a different index of
refraction. The propagation constant in the layered structure is
calculated by setting up a full-wave equivalent circuit, which
allows the derivation of the system equation for the whole
structure. Two examples are given, including validation with the
commercial software Ansoft HFSS.
Journal of Lightwave Technology · 2.78 Impact Factor
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ABSTRACT: This paper presents the results of the development of a microstrip antenna that presents dual-band operation. Each band is coupled to separated ports, so that no additional diplexer is needed. Simulated results showed that a high isolation between this two ports has been obtained.
IEEE AP-S 2009;
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ABSTRACT: In this contribution, the discrete mode matching method (DMM) is applied to the analysis of waveguides with noncircular cross sections. Initially, elliptical dielectric waveguides are analyzed by applying the DMM to set up a system of equations in the space domain. This allows finding the propagation constants of waves in this structure. One second application presented here is the analysis of conformal striplines with noncircular cross sections.
GeMiC 2008;
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ABSTRACT: The concept for an active circularly polarized phased–array terminal antenna for satellite communication at Ka–band is presented. The proposed antenna is based on a modular architecture with sub-arrays of 4x4 elements. Sequential
rotation of the antenna elements is implemented to improve the polarization purity. Thermal dissipation problems are addressed.
10th European Microwave Week;
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ABSTRACT: In this contribution, the full-wave equivalent circuit and the discrete mode matching (DMM) method are applied to analyze dielectric waveguides and conformal striplines with circular and noncircular cross sections. To demonstrate the techniques, several applications will be shown. Optical fibers with different graded-index profiles are analyzed first. In this case, the variation of the index of refraction is modelled using several homogeneous layers. The second application is the computation of the propagation constants for the two fundamental modes in elliptical dielectric waveguides. Finally, conformal striplines with noncircular top grounds are also analyzed. The comparison of our results with commercial software and with data from other authors shows good agreement.
IEEE MTT-S International Mini-Symposium on Electromagnetics and Network Theory and their Microwave Technology Applications;
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ABSTRACT: A systematic way to set up the dyadic Green’s function for multilayer structures using a full-wave equivalent circuit (FWEC) in curvilinear coordinate systems has been presented. The general formulation has been given in the first part of this contribution. Then, an application of the method has been shown for the case of a multilayered cylindrical microstrip line. The results, computed with the discrete mode matching method (DMM), have been validated with simulations done with Ansoft HFSS. The agreement between the simulations is very good, especially if the appropriate edge condition is used in the DMM formulation.
2007 IEEE International Symposium on Antennas and Propagation;
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ABSTRACT: Broadband satellite communications and precise navigation in safety-of-life ap-plications require high-gain terminal antenna arrays with an appropriate size. Drag reduction and aesthetical reasons make it necessary to smoothly integrate the array into the surface of vehicles, vessels or airplanes. For this purpose, the use of microstrip antennas offers several advantages. They are flexible and very well suited for the conformal integration since they can be adapted to almost any kind of structure. In aeronautics, new materials like GLARE (glass-fiber rein-forced aluminum) are composed of several thin layers resulting in a multilayer architecture, if stacked patches have to be integrated for broadband applications. To determine and control the radiation characteristics, every element in an array must be fed with accurate amplitude and phase and thus a good prediction of the characteristics of the microstrip or coplanar lines composing the feed network is needed. The incorporation of extra networks for calibration purposes or the distri-bution of local-oscillator signals results in additional thin layers. The analysis of these stratified structures using commercial simulation tools with full 3D-modeling is difficult and time consuming.
An alternative approach is the use of 2D-procedures like integral-equation tech-niques or discrete mode matching (DMM) that involve the dyadic Green’s func-tion of the layered structure in a suitable coordinate system. This paper presents a systematic way to set up the dyadic Green’s function for multilayer structures us-ing a full-wave equivalent circuit (FWEC) in curvilinear coordinate systems. The FWEC forms a basis for the efficient analysis of planar, cylindrical and spherical structures with the integral-equation technique in the spectral domain, and for the application of DMM on arbitrarily shaped structures (quasi-planar, quasi-circular cylindrical) in the space domain.
In order to test the applicability of the equivalent-circuit approach and demon-strate its excellent potential and versatility, dielectric cylindrical waveguides with an index profile have been investigated, where the profile has been approximated by up to 10,000 homogeneous layers with different permittivity.
Several additional examples are shown for the application of the FWEC like the analysis of patch antennas on a deformed (quasi-planar) substrate and of micro-strip lines on a three-layer cylindrical substrate using DMM, and the coupling of patch antennas on a cylinder using a method-of-moments approach.
All results have been validated as far as possible by using commercial software.
International Radar Symposium 2007;
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ABSTRACT: The assessment of the installed performance of antennas on aircraft is a very difficult task. Patterns can be measured by performing in-flight tests, which are very expensive and allow in general the determination of only few cuts. This costly method can be replaced by down scaling the dimensions of aircraft and antenna, whilst scaling up the frequency, so that all the electrical dimensions (in wavelengths) are kept constant. In such tests, a mock-up of the real aircraft is necessary. A scaled antenna model, which should represent accurately the radiation characteristics of the original antenna without the need to have exactly the same geometry, is also required.
Alternatively to these experimental procedures, computer modelling can be used. The main advantage of using simulations for this purpose is the reduction of time and costs. Moreover, some electromagnetic characteristics, such as the current densities on the aircraft surface, can not directly be measured, but they can be estimated using appropriate computer models.
In order to validate numerical predictions of installed performance, simulated results are compared with measurements performed with different mock-ups of aircraft used in the civil aviation. The antennas used in the experiments are 4x4 microstrip planar arrays, which served as radiation models of a smart GALILEO digital-beamforming antenna under development at the Institute of Communications and Navigation. Two arrays have been used: one broadside and the other with the main lobe pointing to 40° from the boresight. During the measurements, these antennas simulated the real smart array operating under different beamforming conditions. The single elements are right-handed circularly polarized patches that are coupled to the feed lines by means of slots. The optimal axial ratio is obtained at 22 GHz. The top part (patches and slots) is the same for both arrays. For producing different beam directions, different feed networks have been designed. In both cases, all the 16 patches are fed with the same amplitude. For the broadside array, the elements are fed with the same phase, whereas a progressive phase shift of 140° has been applied along the horizontal direction.
The installed performance simulations have been done using the FEKO electromagnetic simulator. Physical optics (PO) and the multi-level fast multipole method (MLFMM) were the numerical techniques used in the analyses. Further information about the choice of the position to install the arrays on the mock-ups and details describing the simulations will be given at the conference.
The measurements with the mock-up have been performed in DLR’s antenna test range. The details concerning the measurement setup will be discussed at the conference. A comparison of computed and measured radiation patterns will be presented. The numerical predictions are in good agreement with the experimental data, especially in terms of co-polarization.
EuCAP 2007;
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Alexander Geise,
Arne F. Jacob,
Karsten Kuhlmann,
Holger Pawlak,
Roman Gieron,
Patrice Siatchoua,
Dirk Lohmann,
Sybille Holzwarth,
Oliver Litschke,
Marcos V. T. Heckler,
Lukasz Greda, Achim Dreher,
Christian Hunscher
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ABSTRACT: Smart antennas employing digital beamforming (DBF) at Ka-band frequencies will be key elements for the next generation of broadband satellite communication systems. This frequency band offers high bandwidth and therefore high data rate capability, whereas digital beamforming provides a high degree of system flexibility.
Within the SANTANA (Smart Antenna Terminal) project, key elements of advanced DBF satellite communication terminals at Ka-band frequencies have been developed. SANTANA is a joint project of IMST GmbH and TU Hamburg-Harburg with DLR Oberpfaffenhofen, EADS Astrium GmbH. Industrial support is provided by Lewicki Microelectronics GmbH, RHe Microsystems, and EPAK GmbH. The project is funded and supported by the German Space Agency (DLR) on behalf of the German Ministry of Economics and Technology (BMWi).
Within the SANTANA project framework of phase 1 (2001 - 2003) and phase 2 (2003 - 2007), a complete medium size DBF system has been realised. It consists of separate transmit (30 GHz) and receive (20 GHz) units with 64 antenna elements each. This DBF system has been successfully demonstrated by establishing bidirectional communication links to moving platforms (car and aircraft) equipped with a conventional transmit/receive unit. The aim of the current project phase 3 is the adaptation of the present technology towards large arrays, the verification of the terminal within a moving environment, and the further industrialisation of several building blocks.
The paper describes the whole system and reports the essential experimental results obtained during the field tests.
1st CEAS European Air and Space Conference;
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ABSTRACT: Mutual coupling is an important parameter in the assessment of the interoperability between two systems located electrically close to each other and operating simultaneously. One example of such a case could be GPS (navigation) and INMARSAT BGAN (communications) installed on a mobile platform (e.g. aircraft). Mutual coupling plays also an important role in the design of arrays of antennas, since it modifies the input impedance of every array element.
Among other antennas, conformal microstrip arrays are very suitable for many applications in aeronautics. The cylindrical cross-section, for instance, is quite often found in aircraft and space vehicles, and is, therefore, of great importance.
In order to compute accurately mutual coupling between microstrip antennas conformed on cylindrical surfaces, DLR has developed a code called MCAT, which is based on the method of moments (MoM) and uses sub-domain basis functions for the calculation of the current densities on the metallizations. In this approach, the dyadic Green’s functions in cylindrical coordinates and in the spectral domain are needed. These are calculated using a full-wave equivalent circuit (FWEC) under the consideration that the structure is infinite in the axial direction.
In this contribution, mutual coupling has been computed between two z-polarized antennas as a function of their separation. Three different configurations have been investigated. For the E-plane coupling, the antennas are moved along the cylinder axis (no azimuthal separation). In the H-plane configuration, the antennas are disposed along the circumference of the cylinder (no axial separation). In the third case, a constant axial displacement is kept, whereas the azimuthal distance is varied.
In order to validate the results calculated with MCAT, computations of mutual coupling as a function of the separation between the two patches have been performed with commercial software for the three configurations. Additionally, experiments have been carried out for the third case. The results obtained with MCAT agreed well with the measurements and with the data provided by the other software. Therefore, this code can be used to obtain good engineering predictions of mutual coupling between cylindrical microstrip antennas. Further details concerning the code, the simulations and the measurements will be discussed at the workshop.
EWCA 2007;
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ABSTRACT: Future navigation services provided by upcoming global navigation satellite systems like Galileo will require corresponding improvements on the navigation receiving systems. Therefore, the Institute of Communciations and Navigation of the German Aerospace Center originated the development of a GNSS prototyping platform for development and research on navigation receivers with improved capabilities for interference and multipath mitigation by utilization of array antenna processing techniques. Interference and multipath signals can cause serious performance degradations, which cannot be tolerated for Sol applications. New digital beam-forming and signal-processing algorithms will contribute to overcome this problem by suppressing interference and multipath signals and improving the reception of useful line-of-sight satellite signals and thus enable a more accurate and reliable navigation solution. The aim is to develop a complete Safety-of-Life (SoL) receiver demonstration system which includes the whole chain including array antenna, RF front-end, digital signal processing, navigation solution and integrity assessment.
The paper presents an overview of the whole platform architecture. In its first realization the platform consists of a two times two array antenna and a subsequent four channel RF front-end for GPS/Galileo L1 signal reception. The received signals are down-converted, digitized and recorded for off-line processing. In the first part of the paper the two by two antenna array and the L1 front-end concept are discussed. Basic design issues of the front-end concerning interference robustness and low noise are pointed out. The second part of the paper introduces the architecture of the FPGA implementation, which is used to record 250 MByte of data with a data rate of 1 GByte/s. In the following, the basic digital receiver design and its implementation in an offline SW-receiver are described. Also, a possible future FPGA-implementation for real-time processing will be discussed. The next chapter provides an overview of the digital beam-forming and direction finding techniques that are used. Finally, first results are presented and an outline for the future platform development is given.
ENC GNSS 2008;
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ABSTRACT: Advanced global navigation satellite systems (GNSS) like Galileo and modernized GPS will provide new services and thus require corresponding improvements on the navigation receiving systems, since interference and multipath signals can cause unacceptable performance degradation. For safety-of-life (SoL) applications, new beam-forming and signal-processing algorithms will be employed to overcome this problem. These procedures enable a more accurate and reliable navigation solution by suppressing interference and multipath signals and improving the reception of useful line-of-sight satellite signals. For the development and testing of these algorithms and in order to demonstrate new applications the Institute of Communications and Navigation of the German Aerospace Center (DLR) is building up a GNSS receiver demonstrator with improved capabilities for interference and multipath mitigation by utilization of array processing techniques. The aim is to develop a complete safety-of-life (SoL) receiver system including antenna array, RF front-end, digital signal processing, navigation solution and integrity assessment.
This paper gives an overview of the general terminal concept and the system architecture. Also a first realization comprising a sub-array of four modules (2x2 array) with a subsequent four channel RF front end for GPS/Galileo L1 signal reception is presented.
30th ESA Antenna Workshop on Antennas for Earth Observation, Science, Telecommunication and Navigation Space Missions;
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ABSTRACT: The design of navigation receivers for safety-of-life (SoL) applications requires the system to be robust against interference coming from several different sources, such as hand-sets and base stations for mobile communications, and radars. One way to minimize the effects introduced by such interferers is to place a filter with low insertion loss between the antenna and the low-noise amplifier (LNA). In order to increase robustness, the antenna itself can be designed to be narrow-band, so that only low power levels in the out-of-band region are received.
In order to receive only the L1 band of the Galileo system (1.565 – 1.585 GHz), a narrow-band antenna may be used. This paper describes the design of an active microstrip antenna array that is under development with this frequency-selective characteristic. The geometry of the single antenna is composed of a square patch, which is located at the top of the multilayer structure, the slots, which are in the middle, and the feeding system, which is at the bottom. During the design process of this antenna, several parameters can be used to obtain a good matching inside the band of interest and a strong reflection (low gain) outside of it. A 90°-hybrid has been integrated in order to generate circularly polarized waves. The variation of the gain in the band of interest is about 0.6 dB. At the region of GSM, the rejection is at least 14 dB, which is higher than it would be obtained with an ordinary microstrip antenna.
The antenna described above will be used in a 2x2 array, where each patch will be connected to an LNA. In order to compensate for the differences of the S-parameters of the used amplifiers, a calibration is necessary. For this purpose, a directional coupler has been integrated at the output of the 90°-hybrid. It will be used to couple the calibration signal to the input of the active part. The structure described above is under construction at the moment and a better description will be given in the final version of this paper and in the conference. Also, a study of the radiation properties of the 2x2 array under different beamforming conditions will be presented.
EuCAP 2009;
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ABSTRACT: For safety critical applications of satellite navigation, an accurate and robust positioning is essential. In many fields of application like aviation, rail and maritime, radio interference and multipath signals can cause serious and not acceptable performance degradations, which require dedicated countermeasures and the revision of the whole receiver signal processing chain.
Therefore, the Institute of Communications and Navigation of the German Aerospace Center (DLR) has started an initiative to develop a Safety-of-Life (SoL) receiver demonstrator for the Galileo satellite navigation system. The aim of this project is to perform the necessary pre-development research as well as to develop, build and demonstrate an integrated SoL receiver system, which is robust against interference and multipath effects. Since array antennas with digital beamforming offer a very high potential for suppression of interference and multipath signals, the integration of an array antenna has been included in the receiver design from the early beginning of the project. Some of the most challenging tasks to achieve this goal include:
- Development of optimized antenna elements and arrays
- Design of a robust frontend suitable for multi constellation multi frequency reception with multiple antenna elements
- Development and analysis of powerful interference detection and mitigation techniques enhanced for Galileo
ION GNSS 2008;
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ABSTRACT: Advanced global navigation satellite systems (GNSS) like Galileo and modernized GPS will provide additional services which among others qualify these systems for safety-of-life (SoL) applications. The stringend requirements which have to be fulfilled for SoL applications require several improvements on the navigation receiving systems – especially since interference and multipath signals can cause unacceptable performance degradation. Also in the case of ground stations for monitoring and reference purposes, it has been shown that a high robustness with respect to interference and multipath is crucial for a correct functionalty.
In order to overcome the aforementioned problem new digital beam-forming and signal-processing algorithms will be employed. These procedures enable a more accurate and reliable navigation solution by suppressing interference and multipath signals and by improving the reception of useful line-of-sight satellite signals. Digital beam-forming utilizing group antennas offers a large potential for the suppression of undesired signal.
Hence, the Institute of Communications and Navigation of the German Aerospace Center (DLR) has started an initiative to develop a Safety-of-Life (SoL) receiver demonstrator for the Galileo satellite navigation system. The aim of this project is to perform the necessary pre-development research as well as to develop, to build and demonstrate an integrated SoL receiver system, which is robust against interference and multipath effects. Some of the most challenging tasks to achieve this goal include:
- Development of optimized antenna elements and arrays
- Design of a robust frontend suitable for multi constellation multi frequency reception with multiple antennas
- Development and analysis of powerful interference detection and mitigation techniques enhanced for Galileo
Navitec 2008;
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ABSTRACT: The research in the field of microstrip antennas and arrays has boomed in the last three decades, due to several improvements made in the fabrication of microwave laminates with low losses. Owing to their favourable aerodynamic profile, low weight and low cost for mass production, the range of applications is now very broad and one can find such antennas installed on mobile platforms, satellites, etc.
By using flexible substrates, microstrip antennas may be conformed (installed) on curved surfaces. Typical applications are antennas for sounding and launching rockets, aircraft, etc. Whereas the research on simple microstrip structures with planar cross sections has nearly achieved maturity, the development of effective numerical techniques for conformal antennas is still far behind. Several methods have been proposed to the analysis of such antennas. Volumetric techniques, such as the finite element method (FEM) and the finite-difference time domain (FDTD) use 3D meshes to discretize the computational domain. This leads to the need of large computational memory and long computing times.
In this paper, the analysis of rectangular patches conformed on cylindrical surfaces under the application of the discrete mode matching method (DMM) will be discussed. This technique employs the Green’s function in the spectral domain, which is obtained using a full-wave equivalent circuit (FWEC) that models the layered structure, so that fast and accurate analyses can be performed. In the DMM, the computational domain must be bounded by suitable lateral boundary conditions. For the analysis of microstrip antennas, absorbing boundaries are used that will be described in the final version of this paper.
To demonstrate the technique, calculations of the resonance frequencies of patch antennas will be shown. In this case, an eigenvalue problem has to be solved. The radiation pattern at the resonance frequency is also computed. Validations of our results have been done with the cavity model and good agreement between the results obtained with both techniques has been achieved.
Joint 5th ESA Workshop on Millimetre Wave Technology and Applications and 31st ESA Antenna Workshop;
