Search

Passive multifrequency microwave sensors frequently struggle with difficulties of nonuniform spatial resolution among multiple channels. The raw measurements in the land-sea transition zone are seriously contaminated. Conventional analytical deconvolution techniques suffer from the tradeoff between spatial resolution enhancement and noise amplification, leading to low data integrity in the practical spatial resolution matching application. To provide multichannel microwave radiometer (MWR) data with matching levels of spatial resolution, a method based on iterative deconvolution with close loop priors (ICLP) is proposed. Specifically, a destriping module is first utilized as a preprocessing step to maintain high data integrity. Then, the close loop mechanism using sparse adaptive priors is proposed to balance the spatial resolution and data integrity enhancement. Also, progressively iterative deconvolution is introduced to realize controllable levels of spatial resolution enhancement (spatial resolution matching) for multichannel data to reach a consistent level. Experiments performed using both simulated and actual microwave radiation imager (MWRI) data demonstrate the validity and effectiveness of the method., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., EEMS - General

The terahertz frequency modulation continuous-wave (THz FMCW) imaging technology has been widely used in non-destructive testing applications. However, THz FMCW real-aperture radar usually has a small depth of field and poor lateral resolution, thus restricting the high-precision imaging application. This paper proposes a 150-220 GHz FMCW Bessel beam imaging system, effectively doubling the depth of field and unifying the lateral resolution compared to the Gaussian beam quasi-optical system. Moreover, a THz image restoration algorithm based on local gradients and convolution kernel priors is proposed to eliminate further the convolution effect introduced by the Bessel beam, thereby enhancing the lateral resolution to 2 mm. It effectively improves the image under-restoration or over-restoration caused by the mismatch between the ideal and actual point spread function. The imaging results of the resolution test target and semiconductor device verify the advantages of the proposed system and algorithm., EEMS - General

A novel approach is proposed for building a planar array derived from linear arrays using a toolbox of different types of subarrays located parallel and perpendicular to the linear array axes. The array design assumes constant element patterns and focuses on rectangular array applications with one dimensional, wide-angular beam scanning. Optimization criteria concern a trade-off between side lobe level performance, directive gain scan-loss, reducing the number of element controls and maximizing the use of phase-only elements for beam steering. All subarray configurations and functionalities, for improving the full array performance in sidelobe level and scan-loss compensation, are analyzed and validated in detail. The step-by-step integration of different subarrays starts from the center part of the array. This center part is a linear subarray along the major axis of the rectangular array with uniform maximum amplitude and spatially stretched. This subarray is combined with cross-line subarrays perpendicular to this center axis. At both edges of the center array, two in-line, uniform-amplitude and stretched subarrays are added and combined with cross-line subarrays. The amplitude distribution of the 3 in-line subarrays and the cross-line subarrays allows for lowering the sidelobe level in the plane of scanning. Finally, at both ends of the three in-line subarrays, subarrays with two and five elements are applied for reducing the scan-loss. By assuming cos(\vartheta) element pattern results are given for a planar rectangular array with 41 elements length and 3 elements width. To lower cost and higher power efficiency, the array uses only 33 multi-bit phase shifters, 12 1-bit phase switches, and 4 attenuators for amplitude control. Optimized broadside and 60° scanning patterns are compared and show improved performance in directive gain D=24.4 dBi (broadside), D=19.9 dBi (60°) and in \text {SLL}=-21.6 dB (broadside), \text {SLL}=-19.5 dB (60°)., EEMS - General

The scanning performance of wide-angular scanning linear arrays is primarily degraded by the limited angular profile of the employed elements' patterns. This paper introduces an innovative strategy for compensating this degradation by using subarrays. Our design uses a uniform linear array with half-wavelength spaced elements, supplemented by subarrays that are symmetrically placed at its edges. The employed subarrays have controlled patterns, favoring some directions for effective scan-loss compensation (SLC) and suppressing other directions for lowering the sidelobes level (SLL). Two types of feeding configurations, making use of fixed power dividers in combination with 1-bit phase switch, are used for producing the desired patterns. The complete array design and physical validation, starting from the elements, continuing with the subarrays and ending with the system integration are also discussed in detail. The integration of the subarrays yields notable performance improvements at large scanning angles when compared with uniform linear arrays. The peak and first SLL of -14.1 dB, and the SLC of 2 dB are obtained when the array with CUP antennas as elements is scanned to the maximum scan angle direction., International Research Centre for Telecommunication and Radar, Electrical Engineering Education

The design concept of passive and active reconfigurable reflectarray antennas has been proposed and tested. The antenna elements in the array are identical hollowed patches. In the first phase of study the slots are loaded with a SMD capacitor to set the required phase shift needed for array implementation. Simulations show promising results. Mounting a SMD capacitor in such a configuration can be considered as the first step in using capacitive loading on a slotted patch for active microstrip reflectarrays. It is shown that by adjusting the capacitance values it is possible to scan the beam. In the second phase, the patch elements are loaded with active varactor-diode device which its reflected phase can be varied. This phase alteration is based on the variation of the diode capacitance which can be achieved by varying the biasing voltage of the active varactor device. In latter approach by activating these varactor devices, the phase of each antenna element in the array configuration can be adopted dynamically and consequently, its beam direction can be reconfigured. The reflectarrays incorporating passive and active elements have been built and tested at 7.0 GHz and 6.0GHz, respectively. The performance of the proposed reconfigurable antennas is excellent, and there is good agreement between the theoretical and measurement results which pioneers design of arbitrarily reconfigurable antennas., Design Engineering, Industrial Design Engineering

Cognitive radio (CR) is an intelligent radio system and is able to share the spectrum with licensed users (LU). By adopting adaptive beam forming techniques, CR can reuse the spectrum with LU via directing main beams towards CR users while displaying nulls towards LU. In this article, we present a new distributed beam forming (DB) technique, and study the performance of its application to decentralized CR networks. The presented DB method only controls the phase of the transmitted signal of each CR node in the CR network, and therefore, it is called phase-only DB (PODB) method. It can be implemented at each node independently with only prior knowledge of its own location, and directions of distant CR (DCR) users and LU. The average beam pattern and the average gains for an arbitrary number of CR nodes of PODB method are discussed, showing that CR nodes can constructively transmit signals to DCR users with less interferences to LU via employing the PODB method to form and direct main beams towards directions of DCR users while nulls towards directions of LU. PODB proves to be a green DB method by prolonging the lifetime of the CR network due to effective battery power consumptions at CR nodes. The cumulative distributed function of the beam pattern for a large number of CR nodes is derived and analysed to demonstrate that the PODB method increases the possibility that the transmitted power of the whole CR network at the directions of LU is lower than a certain threshold, which guarantees that CR network causes less disturbing effect to LU., Telecommunications, Electrical Engineering, Mathematics and Computer Science

Ultra-wideband radio technology (UWB-RT) inherited a potential of extremely high rate of data communications, Claude Shannon discovered this in 1948 and derived the later-called-as Shannon-Hartley‘s channel capacity laws. This famous theoretical law however was not able to substantiate in practice until the development of the sampling oscilloscope by Hewlett-Packard in 1962, which, in accordance with the Nyquist-Shannon sampling theorem, was then capable to reconstruct at-that-time rather large UWB signals (Wilson, 2002)., Applied mathematics, Electrical Engineering, Mathematics and Computer Science

In this paper, we introduce Adaptive Beamforming (AB) and Distributed Beamforming (DB) as two efficient techniques for IntelligentWiMAX (I-WiMAX). I-WiMAX is a new maritime communication system, consisting of Smart Radio (SR) principles and mobile WiMAX based on the IEEE 802.16e standard. Adopting AB, the same spectrum can accommodate more users by directing the main beam towards desired users while antenna pattern nulls towards others. To reduce the channel interferences caused by spectrum reusing, the Null Broadening (NB) method is required for downlink beamforming of I-WiMAX. A new NB method is presented in this paper with iterative weights computing for different OFDM subcarriers. Considering the spatial channel model seen at Subscriber Stations (SS) based on the von Mises distribution, the coverage range of one Base Station (BS) is dramatically enlarged by employing the NB technique. Meanwhile, assuming those SS which are within the coverage range as nodes of a relay network, the DB technique is introduced to forward signals to distant SS by forming the main beams towards them instead of deploying more BS to increase the communication range. It is proven in this paper that DB can successfully do the job. To reuse the spectrum, two DB methods are presented by directing different beams towards different required directions at the same time. With the AB and DB techniques, reliable I-WiMAX links can be established for long distances, with more optimum spectrum use and less infrastructure, International Research Center for Telecommunications and Radar IRCTR, Electrical Engineering, Mathematics and Computer Science

The number of topside shipboard antennas doubled every decade; in 1990s they were close to 200 and have no sight of stop growing (Tavik, 2005). The over-crowded present of such many topside antennas in a limited-space of littoral warfare ship has created/caused many critical, unavoidable problem like antenna blockage, electromagnetic interference, increase RCS, worsen the effective stealthy signature of combatant ships, which is stealthy-intended designed, and most of all is the maintenance costs of multiple systems, huge numbers of repair-personnel and operators (Tibbitts & Baron, 1999). This publication is sponsored by the Open Access Fund TU Delft. OA-fund TU Delft, Applied Sciences

This paper presents the development of a reconfigurable receiver to undertake challenging signal processing tasks for a novel polarimetric radar system. The field-programmable gate arrays (FPGAs)-based digital receiver samples incoming signals at intermediate frequency (IF) and processes signals digitally instead of using conventional analog approaches. It offers more robust system stability and avoids unnecessary multichannel calibrations of analog circuits for a full polarimetric radar. Two kinds of dual-orthogonal signals together with corresponding processing algorithms have been investigated; the digital implementation architectures for all algorithms are then presented. Processing algorithms implemented in FPGA chips can be reconfigured adaptively regarding to different transmitted waveforms without modification of hardware. The successful development of such reconfigurable receiver extends our radar capacity and thus yields tremendous experimental flexibility for atmospheric remote sensing and polarimetric studies of ground-based targets., International Research Centre for Telecommunications and Radar, IRCTR, Electrical Engineering, Mathematics and Computer Science

In this paper, we investigate the diversity, capacity and complexity issues of cooperative Zero-Padding (ZP)-Orthogonal FrequencyDivisionMultiplexing (OFDM) communication. We consider cooperative ZP-OFDM communication over a multipath Rayleigh channel and with multiple Carrier Frequency Offsets (CFOs) existing at different relays. We use a cooperative tall Toeplitz scheme to achieve full cooperative and multipath diversity, while simultaneously combat the CFOs. Importantly, this full diversity scheme only requires Linear Equalizers (LEs), such as Zero-Forcing (ZF) and Minimum Mean Square Error (MMSE) equalizers, an issue which reduces the system complexity when compared to a Maximum-Likelihood Equalizer (MLE) or other near-MLEs. Theoretical analysis of the proposed cooperative tall Toeplitz scheme is provided on the basis of the analytical upper bound of the channel orthogonality deficiency derived in this paper. Utilizing only low-complexity linear equalizers, theoretical analysis and simulation results show that the proposed Toeplitz scheme achieves the full cooperative, multipath and outage diversity., Telecommunications, Electrical Engineering, Mathematics and Computer Science

The article describes the IRCTR PARSAX radar system, the S-band high-resolution Doppler polarimetric frequency modulated continuous wave (FM-CW) radar with dual-orthogonal sounding signals, which has the possibility to measure all elements of the radar target polarization scattering matrix simultaneously, in one sweep. The performance of such radar depends of the level of sounding signals orthogonality. In the main operational mode, the radar will be used for atmospheric remote sensing and polarimetric studies of ground-based targets. In such mode it will use a pair of synchronous linearly- frequency modulated (LFM) continuous signals with opposite frequency excursions of 50 MHz and duration of 1 ms. Such a combination of sounding signals has limited orthogonality even for huge BT-products, which produce cross-channel interferences. These interferences in case of radar scene with multiple pointed and distributed targets can completely degrade radar operational performance. In this article, we propose simple and effective technique to suppress interferences and to restore radar performance. The technique has been tested using simulation and has been implemented in multi-channel digital receiver of the PARSAX radar. The real radar measurements presented to illustrate effectiveness of cross-channel interferences suppression. The proposed technique can be useful not only for polarimetric radar design, but also in much wide radar applications, which use waveforms with high orthogonality., International Research Centre for Telecommunications and Radar, IRCTR, Electrical Engineering, Mathematics and Computer Science

This paper presents design and practical implementation of the method for cross-channel interference suppression in polarimetric LFM-CW radar with dual-orthogonal sounding signals. Simultaneously transmitted and received signals have limited orthogonality, what results in the interfering signals in the processing channels of the radar receiver. The suppression of the interfering signals is implemented in real time, characterized by simplicity and low increase of computational resources. The efficiency of the cross-channel interference suppression is demonstrated experimentally., International Research Centre for Telecommunication and Radar, Electrical Engineering, Mathematics and Computer Science

An optimized coplanar waveguide fed quasimagnetic printed antenna for ultra wideband applications is described. A parameter study, motivated by a design procedure, allowed a substantial increase in the return-loss operational bandwidth. The numerically predicted performance was validated by means of physical measurements of fabricated samples. The measured radiation patterns of the antenna demonstrated its adequate radiation characteristics. The feed radiation was also investigated by means of physical measurements., Telecommunications, Electrical Engineering, Mathematics and Computer Science

An effective and robust strategy for concurrently designing the transmit and receive antennas of a frequency-modulated, continuos-wave radar is discussed. The aperture architecture is based on the use of non-periodic, interleaved sub-arrays. Deterministic element placement is employed for ensuring design efficiency. The procedure yields controllable sub-array radiation patterns and two-way side-lobe levels below - 30 dB, that are also stable over a wide frequency range., Telecommunications, Electrical Engineering, Mathematics and Computer Science

This article presents the performance comparison of TDCS and OFDM based cognitive radio for MIMO system using VBLAST receiver architecture to reconstruct the transmitted data. The interference avoidance performance in terms of BER and bitrate are improved by adding multiple antennas to the system and the use of V-BLAST technique at the receiver. The results show the most promising interference avoidance technique combined with MIMO V-BLAST architecture to be applied in the CR system., Telecommunications, Electrical Engineering, Mathematics and Computer Science

Ultrawideband (UWB) technology is an attractive alternative for short-range applications, e.g., wireless personal area networks. In these applications, transmit and receive antennas are very close to each other and the far-field condition assumed in most of the link budget models may not be satisfied. Under near-field conditions, variations in the link budget and pulse shape compared to the far-field can be observed. In this work, a novel line-of-sight UWB link budget model for very short distances is proposed and validated with measurements using different types of antennas. The proposed model, which takes into account all main near-field effects (i.e., phase error, antenna mismatch and reradiation between antennas) and includes frequency, antenna size and orientation as parameters, shows a good agreement with the simulations and the measurements. This model has also been applied to dispersive antennas (e.g., notch-antennas), and can be used in the design and analysis of short-range UWB communication systems., Microelectronics & Computer Engineering, Electrical Engineering, Mathematics and Computer Science

Telecommunications, Electrical Engineering, Mathematics and Computer Science

This paper presents a 3-D imaging technique for an ultra-wideband (UWB) ground penetrating radar (GPR) with a single transmit antenna and a linear receive array. The video impulse GPR working in the frequency band of 0.3–3 GHz has been designed in IRCTR for landmine detection, i.e., for a near-field application. Installed on a vehicle it can image in one mechanical scan a strip of 84 cm width due to the length of array aperture. The imaging is done by software means only. The developed imaging technique combines a real aperture focusing in the array plane with a synthetic aperture focusing in the mechanical scan direction. To compensate for parasitic time delays in the array channels, a calibration procedure is also described. Owing to directional properties of transmit antenna, the distribution of signal strength over the array is nonuniform that requires an amplitude correction when focusing the real aperture. The authors analyzed how this affects the footprint of the focused array, its cross-range resolution capability and the image quality of antipersonnel plastic landmines which were buried under different array channels. The analysis bases on experimental data sets acquired in the facilities of IRCTR and TNO-DSS. As a result, the authors propose a weighted array focusing that improves the cross-range resolution and provides proper imaging of typical buried landmines., International Research Centre for Telecommunication and Radar, Electrical Engineering, Mathematics and Computer Science

Electrical Engineering, Mathematics and Computer Science

Microwave Technology and Systems for Radar, Aerospace Engineering

Electrical Engineering, Mathematics and Computer Science

Electrical Engineering, Mathematics and Computer Science