The Experts below are selected from a list of 18060 Experts worldwide ranked by ideXlab platform
R Vahldieck - One of the best experts on this subject based on the ideXlab platform.
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comprehensive analysis and simulation of a 1 18 ghz broadband parabolic reflector horn antenna system
IEEE Transactions on Antennas and Propagation, 2003Co-Authors: C Bruns, P Leuchtmann, R VahldieckAbstract:A 1-18 GHz parabolic reflector horn antenna system featuring a broadband double ridged primary horn with a coaxial feed line is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not Maintain a single Main Lobe in the direction of the horn axis over the whole frequency range. Instead, at frequencies above 12 GHz the Main Lobe in the radiation pattern starts to split into four Lobes pointing in off-axis directions with a dip of up to 6 dB between them along the center axis. To investigate this phenomenon in detail, a combined method of moments and physical optics approach has been adopted to simulate the complete antenna system.
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analysis and simulation of a 1 18 ghz broadband double ridged horn antenna
IEEE Transactions on Electromagnetic Compatibility, 2003Co-Authors: C Bruns, P Leuchtmann, R VahldieckAbstract:A 1-18-GHz broadband double-ridged horn antenna with coaxial input feed section is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not Maintain a single Main Lobe in the direction of the horn axis over the full frequency range. Instead, at frequencies above 12 GHz, the Main Lobe in the radiation pattern starts to split into four large side Lobes pointing in off-axis directions with a dip of up to 6 dB between them along the Main axis. Although this type of horn is the preferred test antenna, which is in common use for over four decades, no explanation for this unwanted behavior was found in the open literature. To investigate this phenomenon in detail, a method of moments approach has been adopted to simulate the complete antenna system. The simulations are in good agreement with the measurements over the 1-18-GHz operational bandwidth and indicate that the use of this type of horn antenna in EMC applications reMains questionable.
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full wave analysis and experimental verification of a broadband ridged horn antenna system with parabolic reflector
IEEE Antennas and Propagation Society International Symposium, 2001Co-Authors: C Bruns, P Leuchtmann, R VahldieckAbstract:In this paper we investigate the radiation pattern of a complete 1-18 GHz antenna system featuring a 1.8 in parabolic reflector and a double ridged broadband feed horn with coaxial input using a combination of the method of moments (MoM) and a physical optics (PO) approach. It was found that in the lower frequency range the horn antenna system exhibits a single Main Lobe in the direction of the center horn axis as expected. However, contrary to common belief, at frequencies greater than 12 GHz, the Main Lobe starts to split into four Main Lobes pointing into off-center-axis directions with a broadside gain reduction. This effect was observed both theoretically and experimentally. Although this type of antenna has existed for over four decades, up to now there is no explanation for this unwanted behavior in the open literature. In the past, several electromagnetic simulations of ridged horn antennas were made, but not over such a broad operational frequency range and neither including the coaxial feed nor the complete parabolic reflector system. The purpose of this investigation is to close this gap and to contribute to a better understanding of broadband ridged horn antennas.
Rajiv Saxena - One of the best experts on this subject based on the ideXlab platform.
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analysis of dirichlet and generalized hamming window functions in the fractional fourier transform doMains
Signal Processing, 2011Co-Authors: Sanjay Kumar, Kulbir Singh, Rajiv SaxenaAbstract:A new mathematical model for obtaining the fractional Fourier transforms of Dirichlet and Generalized ''Hamming'' window functions is presented. The different parameters for the window functions are also obtained with the help of simulations. The fractional Fourier transformation contains an adjustable parameter with which the Main Lobe width and correspondingly, the minimum stop band attenuation of the resulting window function can be controlled.
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tuning of fir filter transition bandwidth using fractional fourier transform
Signal Processing, 2007Co-Authors: S N Sharma, Rajiv Saxena, S C SaxenaAbstract:The transition bandwidth of window-based FIR filters is proportional to the window Main-Lobe width, which in turn is proportional to the length of the window function. As such, transition bandwidth of FIR filters can be directly tuned by varying window length for on-line tuning applications. However, analysis of window functions in fractional Fourier doMain, a generalization of Fourier doMain, also establishes the dependence of window Main-Lobe width on the order of fractional Fourier transform (FRFT). Thus, an alternative methodology to tune the transition bandwidth, based on FRFT, is developed in this work. The proposed methodology is useful for frequency doMain filtering and introduces a comparative ease in tuning by eliminating the need to re-compute the impulse response coefficients. Also, significant computational saving has been achieved using FRFT. However, it is observed that the direct approach can introduce a lot more adjustability in the transition bandwidth than the FRFT approach. Apart from Kaiser window, considered to be optimum for FIR filter design, another window with a high side-Lobe fall-off-rate (SLFOR), viz, Parzen-cos6(πt) (PC6), has also been used in the proposed on-line filter tuning. Better performance of windows with high SLFOR in on-line sharpening is illustrated with the aid of simulation results.
Attila Popping - One of the best experts on this subject based on the ideXlab platform.
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the standing wave phenomenon in radio telescopes frequency modulation of the wsrt primary beam
Astronomy and Astrophysics, 2008Co-Authors: Attila Popping, R BraunAbstract:Context. Inadequacies in the knowledge of the primary beam response of current interferometric arrays often form a limitation to the image fidelity, particularly when “mosaicing” over multiple tele scope pointings. Aims. We hope to overcome these limitations by constructing a frequency-resolved, full-polarization empirical model for th e primary beam of the Westerbork Synthesis Radio Telescope (WSRT). Methods. Holographic observations, sampling angular scales between about 5 arcmin and 11 degrees, were obtained of a bright compact source (3C147). These permitted measurement of voltage response patterns for seven of the fourteen telescopes in the array and allowed calculation of the mean cross-correlated power beam. Good sampling of the Main-Lobe, near-in, and far-side-Lobes out to a radius of more than 5 degrees was obtained. Results. A robust empirical beam model was detemined in all polarization products (XX, XY, YX and YY) and at frequencies between 1322 and 1457 MHz with 1 MHz resolution. Substantial departures from axi-symmetry are apparent in the Main-Lobe as well as systematic differences between the polarization properties. Surprisingly, many beam properties are modulated at the 5 to 10% level with changing frequency. These include: (1) the Main beam area, (2) the side-Lobe to Main-Lobe power ratio, and (3) the effective telescope aperture. These semi-sinusoidsal modulations have a basic period of about 17 MHz, consistent with the natural “standing wave” period of a 8.75 m focal distance. The deduced frequency modulations of the beam pattern were verified in an independent long duration observation using compact continuum sources at very large off-axis distances. Conclusions. Application of our frequency-resolved beam model should enable higher dynamic range and improved image fidelity for int erferometric observations in complex fields, although at the e xpense of an increased computational load. The beam modulation with frequency can not be as easily overcome in total power observations. In that case it may prove effective to combat the underlying multi-path interference by coating all shadowed telescope surfaces with a broad-band isotropic scattering treatment.
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the standing wave phenomenon in radio telescopes frequency modulation of the wsrt primary beam
arXiv: Astrophysics, 2007Co-Authors: Attila Popping, R BraunAbstract:Inadequacies in the knowledge of the primary beam response of current interferometric arrays often form a limitation to the image fidelity. We hope to overcome these limitations by constructing a frequency-resolved, full-polarization empirical model for the primary beam of the Westerbork Synthesis Radio Telescope (WSRT). Holographic observations, sampling angular scales between about 5 arcmin and 11 degrees, were obtained of a bright compact source (3C147). These permitted measurement of voltage response patterns for seven of the fourteen telescopes in the array and allowed calculation of the mean cross-correlated power beam. Good sampling of the Main-Lobe, near-in, and far-side-Lobes out to a radius of more than 5 degrees was obtained. A robust empirical beam model was detemined in all polarization products and at frequencies between 1322 and 1457 MHz with 1 MHz resolution. Substantial departures from axi-symmetry are apparent in the Main-Lobe as well as systematic differences between the polarization properties. Surprisingly, many beam properties are modulated at the 5 to 10% level with changing frequency. These include: (1) the Main beam area, (2) the side-Lobe to Main-Lobe power ratio, and (3) the effective telescope aperture. These semi-sinusoidsal modulations have a basic period of about 17 MHz, consistent with the natural 'standing wave' period of a 8.75 m focal distance. The deduced frequency modulations of the beam pattern were verified in an independent long duration observation using compact continuum sources at very large off-axis distances. Application of our frequency-resolved beam model should enable higher dynamic range and improved image fidelity for interferometric observations in complex fields. (abridged)
C Bruns - One of the best experts on this subject based on the ideXlab platform.
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comprehensive analysis and simulation of a 1 18 ghz broadband parabolic reflector horn antenna system
IEEE Transactions on Antennas and Propagation, 2003Co-Authors: C Bruns, P Leuchtmann, R VahldieckAbstract:A 1-18 GHz parabolic reflector horn antenna system featuring a broadband double ridged primary horn with a coaxial feed line is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not Maintain a single Main Lobe in the direction of the horn axis over the whole frequency range. Instead, at frequencies above 12 GHz the Main Lobe in the radiation pattern starts to split into four Lobes pointing in off-axis directions with a dip of up to 6 dB between them along the center axis. To investigate this phenomenon in detail, a combined method of moments and physical optics approach has been adopted to simulate the complete antenna system.
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analysis and simulation of a 1 18 ghz broadband double ridged horn antenna
IEEE Transactions on Electromagnetic Compatibility, 2003Co-Authors: C Bruns, P Leuchtmann, R VahldieckAbstract:A 1-18-GHz broadband double-ridged horn antenna with coaxial input feed section is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not Maintain a single Main Lobe in the direction of the horn axis over the full frequency range. Instead, at frequencies above 12 GHz, the Main Lobe in the radiation pattern starts to split into four large side Lobes pointing in off-axis directions with a dip of up to 6 dB between them along the Main axis. Although this type of horn is the preferred test antenna, which is in common use for over four decades, no explanation for this unwanted behavior was found in the open literature. To investigate this phenomenon in detail, a method of moments approach has been adopted to simulate the complete antenna system. The simulations are in good agreement with the measurements over the 1-18-GHz operational bandwidth and indicate that the use of this type of horn antenna in EMC applications reMains questionable.
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full wave analysis and experimental verification of a broadband ridged horn antenna system with parabolic reflector
IEEE Antennas and Propagation Society International Symposium, 2001Co-Authors: C Bruns, P Leuchtmann, R VahldieckAbstract:In this paper we investigate the radiation pattern of a complete 1-18 GHz antenna system featuring a 1.8 in parabolic reflector and a double ridged broadband feed horn with coaxial input using a combination of the method of moments (MoM) and a physical optics (PO) approach. It was found that in the lower frequency range the horn antenna system exhibits a single Main Lobe in the direction of the center horn axis as expected. However, contrary to common belief, at frequencies greater than 12 GHz, the Main Lobe starts to split into four Main Lobes pointing into off-center-axis directions with a broadside gain reduction. This effect was observed both theoretically and experimentally. Although this type of antenna has existed for over four decades, up to now there is no explanation for this unwanted behavior in the open literature. In the past, several electromagnetic simulations of ridged horn antennas were made, but not over such a broad operational frequency range and neither including the coaxial feed nor the complete parabolic reflector system. The purpose of this investigation is to close this gap and to contribute to a better understanding of broadband ridged horn antennas.
R Braun - One of the best experts on this subject based on the ideXlab platform.
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the standing wave phenomenon in radio telescopes frequency modulation of the wsrt primary beam
Astronomy and Astrophysics, 2008Co-Authors: Attila Popping, R BraunAbstract:Context. Inadequacies in the knowledge of the primary beam response of current interferometric arrays often form a limitation to the image fidelity, particularly when “mosaicing” over multiple tele scope pointings. Aims. We hope to overcome these limitations by constructing a frequency-resolved, full-polarization empirical model for th e primary beam of the Westerbork Synthesis Radio Telescope (WSRT). Methods. Holographic observations, sampling angular scales between about 5 arcmin and 11 degrees, were obtained of a bright compact source (3C147). These permitted measurement of voltage response patterns for seven of the fourteen telescopes in the array and allowed calculation of the mean cross-correlated power beam. Good sampling of the Main-Lobe, near-in, and far-side-Lobes out to a radius of more than 5 degrees was obtained. Results. A robust empirical beam model was detemined in all polarization products (XX, XY, YX and YY) and at frequencies between 1322 and 1457 MHz with 1 MHz resolution. Substantial departures from axi-symmetry are apparent in the Main-Lobe as well as systematic differences between the polarization properties. Surprisingly, many beam properties are modulated at the 5 to 10% level with changing frequency. These include: (1) the Main beam area, (2) the side-Lobe to Main-Lobe power ratio, and (3) the effective telescope aperture. These semi-sinusoidsal modulations have a basic period of about 17 MHz, consistent with the natural “standing wave” period of a 8.75 m focal distance. The deduced frequency modulations of the beam pattern were verified in an independent long duration observation using compact continuum sources at very large off-axis distances. Conclusions. Application of our frequency-resolved beam model should enable higher dynamic range and improved image fidelity for int erferometric observations in complex fields, although at the e xpense of an increased computational load. The beam modulation with frequency can not be as easily overcome in total power observations. In that case it may prove effective to combat the underlying multi-path interference by coating all shadowed telescope surfaces with a broad-band isotropic scattering treatment.
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the standing wave phenomenon in radio telescopes frequency modulation of the wsrt primary beam
arXiv: Astrophysics, 2007Co-Authors: Attila Popping, R BraunAbstract:Inadequacies in the knowledge of the primary beam response of current interferometric arrays often form a limitation to the image fidelity. We hope to overcome these limitations by constructing a frequency-resolved, full-polarization empirical model for the primary beam of the Westerbork Synthesis Radio Telescope (WSRT). Holographic observations, sampling angular scales between about 5 arcmin and 11 degrees, were obtained of a bright compact source (3C147). These permitted measurement of voltage response patterns for seven of the fourteen telescopes in the array and allowed calculation of the mean cross-correlated power beam. Good sampling of the Main-Lobe, near-in, and far-side-Lobes out to a radius of more than 5 degrees was obtained. A robust empirical beam model was detemined in all polarization products and at frequencies between 1322 and 1457 MHz with 1 MHz resolution. Substantial departures from axi-symmetry are apparent in the Main-Lobe as well as systematic differences between the polarization properties. Surprisingly, many beam properties are modulated at the 5 to 10% level with changing frequency. These include: (1) the Main beam area, (2) the side-Lobe to Main-Lobe power ratio, and (3) the effective telescope aperture. These semi-sinusoidsal modulations have a basic period of about 17 MHz, consistent with the natural 'standing wave' period of a 8.75 m focal distance. The deduced frequency modulations of the beam pattern were verified in an independent long duration observation using compact continuum sources at very large off-axis distances. Application of our frequency-resolved beam model should enable higher dynamic range and improved image fidelity for interferometric observations in complex fields. (abridged)
