Cluster-sparse multipath channels, i.e., non-zero taps occurring in clusters, exist frequently in many communication systems, e.g., underwater acoustic (UWA), ultra-wide band (UWB), and multiple-antenna communication systems. Conventional sparse channel estimation methods often ignore the additional structure in the problem formulation. In this paper, we propose an improved compressive channel estimation (CCE) method using block orthogonal matching pursuit algorithm (BOMP) based on the cluster-sparse channel model. Making explicit use of the concept of cluster-sparsity can yield better estimation performance than the conventional sparse channel estimation methods. Compressive sensing utilizes cluster-sparse information to improve the estimation performance by further mitigating the coherence in training signal matrix. Finally, we present the simulation results to confirm the performance of the proposed method based on cluster-sparse.
A tri-band four-element MIMO (multiple-input-multiple-output) antenna with high isolation is presented. The MIMO antenna consists of four symmetrical antenna elements. To relieve the degradation of the operation bandwidth caused by the strong mutual coupling among the four antenna elements, four symmetrical rectangles are removed from the four corners of the ground plane, respectively. The effect of the cutting of the four rectangles on the isolation is slight. Two kinds of isolation structure are applied to reduce the mutual coupling among the elements. The first kind of isolation consists of two slits and a protruded ground branch, and the second kind of isolation structure consists of four symmetrical slits etched into the ground plane. The mutual coupling caused by surface currents is reduced by slits, the mutual coupling resulted from near-field is suppressed by the ground branches, and thus high isolation for the MIMO antenna is achieved. Moreover, the effects of the slits and the ground branches on the operation bandwidth are slight, thus the operation bandwidth and the mutual coupling can be controlled independently, to some degree. A tri-band operation bandwidth (2.34-2.95 GHz, 3.38-3.75 GHz, and 4.4-6.7 GHz) with VSWR ≤ 2 and isolation ≥ 20 dB, is achieved. The results, including S-parameters, radiation patterns, mean effective gain (MEG), radiation efficiency and signal correlations, indicate that the proposed MIMO antenna can provide spatial or pattern diversity to increase data capacity of wireless communication systems.
A novel planar ultra wideband (UWB) antenna using a second iteration Sierpinski carpet fractal shape with circular boundary is presented in this paper. The antenna covers the frequency band from 3 GHz to 12 GHz (VSWR ≤ 2). The proposed antenna has a meander shaped slot that renders the capability to reject 5.15-5.825 GHz band assigned for IEEE802.11a and HIPERLAN/2. The gain is suppressed very well in the desired WLAN bands. The measured antenna peak gain varies from 1.85 dBi to 6 dBi within the band. The time domain characteristics show that the antenna is not dispersive. A fabricated prototype is developed with close agreement between simulated and measured resonance as well as radiation characteristics.
This paper presents a novel conformal end-fire antenna whose design employs the Competitive Algorithm of Simulating Natural Tree Growth. This algorithm is based on the idea of simulating the processes of growth and wilting of natural trees and can search from simple to complicated structures with rapid convergence. Four optimized radiation elements were designed on a cross structure to verify the performance of the algorithm. A prototype of the designed antenna was also fabricated and tested. The antenna resonates at the center frequency of 2.45 GHz, exhibiting an ideal end-fire property. In addition, the measured and simulated results are in good agreement. Finally, we propose a novel end-fire antenna array based on the cross structure, with a radiation gain reaching 17.6 dBi.
This paper presents the design of a broadband circular polarization truncated horn antenna with single feed. It does not require any complex feeding structure and uses only a coaxial feed extended with a simple electric field coupling probe. The corners of the horn are truncated to generate circular polarization modes, and a broad axial ratio bandwidth which is insensitive to the probe feed dimension is achieved. Simulated and measured results of an S band truncated horn antenna are presented. The antenna has a broad 3 dB axial ratio bandwidth of 26% with aperture efficiency of 60%.
This paper presents a new quadrature voltage-controlled oscillator (QVCO), which consists of two p-core Colpitts cross-coupled voltage-controlled oscillators (VCOs) with an LC ring resonator to provide the quadrature outputs. The proposed CMOS QVCO has been implemented with the TSMC 0.18 μm CMOS technology and the die area is 0.478 x 0.82 mm2. At the supply voltage of 1.5 V, the total power consumption is 20.4 mW. The free-running frequency of the QVCO is tunable from 9.69 GHz to 10.52 GHz as the tuning voltage is varied from 0.0 V to 2 V. The measured phase noise at 1 MHz frequency offset is -122.41 dBc/Hz at the oscillation frequency of 10.52 GHz and the figure of merit (FOM) of the proposed QVCO is -189.7 dBc/Hz.
This paper deals with an investigation on the polarization of an antenna array with a circular geometry. The theory shows that the polarization of a circular array exhibits a circular polarization independent of the antenna elements. Circular polarization is then achieved whatever the polarization of the elements of the array. Moreover, due to the circular geometry of the array, the entire far field pattern of the array can be obtained with the measurement or the simulation of only one antenna inside the array. The influence of the array radius on the polarization performances has been investigated. An antenna array has been built, and measurements have been performed in order to corroborate the theoretical results.
We investigate experimentally and theoretically Ultra-Wideband (UWB) wireless transmission in different WPAN scenarios. Short-range UWB wireless link (wireless fire-wire) have been studied theoretically and experimentally. Different mutual positions and distances between the antennas have been investigated. It was found that the reactive antenna coupling might decrease power budget as much as 15 dB by an antenna separation of 5 mm.
A compact double-balanced monolithic star mixer for Ka-band applications using 0.25 μm GaAs pHEMT process is presented. With multi-coupled lines technology, the proposed dual 180° hybrid is produced and applied to a star mixer successfully. The proposed hybrid adopts the power divider and two types of multi-coupled lines to improve the return loss and isolation at the balance outputs of a traditional dual Marchand balun. Output ports are allowed to locate arbitrarily, eliminating a complex layout while the dual 180° hybrid is applied to double balanced star mixers. As the measurement results show, the proposed mixer achieves an operation bandwidth of 27 to 36 GHz with the best conversion loss of 6.3 dB at 28 GHz. In addition, the chip dimension can be manufactured as small as 0.81 mm2.
In the future, mobile handsets might incorporate more than 20 separate radios, creating a difficult antenna design problem due to the sever space restrictions. This paper proposes a reconfigurable wideband antenna, for use within clamshell mobile handsets. The impedance bandwidth of the new antenna was selected in order to meet current and future demands within the industry. It has been suggested that a portable Cognitive Radio must be capable of simultaneous communication (via a narrowband antenna) and spectrum sensing (via a wideband antenna). For this reason a narrowband slot antenna has also been integrated within the wideband radiator.
A novel dual-mode double square loop resonator (DMDSLR) for dual-band band-pass filter (BPF) is presented in this paper. The simple meander loop in DMDSLR is studied to improve the performance of the conventional DMDSLR. Significant size reductions over 33% are achieved. In addition, the designed meander-loop DMDSLR filter shows lower insertion loss (2.24 and 2.28 dB), higher rejection level (28/56 dB and 53/36 dB), wider bandwidth (about 8.5% and 28%) at the 2.47 and 5.47 GHz bands, respectively. Two transmission zeros are placed between the two pass-bands and result in a good isolation.
In this paper, the self-complementary principle has been applied to develop the traditional planar monopole antenna into a dipole antenna whose frequency range exceeds UWB requirements. The proposed design has compact, planar, and simple shape arranged in self-complementary manner connected to the (SMA) connector via rectangular microstrip line. The self-complementary structure offers better reduction of the imaginary part of antenna impedance, which allows matching on a wider band of frequencies. The proposed antenna showed -10 dB return loss bandwidth extending from 1.86 GHz up to 17.7 GHz. Moreover, this antenna has a simple shape as compared with complicated and irregular shapes with curves, slots or parasitic elements. The proposed design is validated by experimental measurements. The phase of the return loss is investigated for more insight into antenna matching.
A compact symmetrical band-pass filter design using coupled microstrip line is presented in this paper. The microstrip line sections connected to the two input and output ports of the filter structure are printed over the Defected Ground Structure (DGS). The proposed symmetrical structure offers a simple and compact design and exhibits improved stop-band characteristics in comparison to the conventional coupled microstrip line filter structure. The prototype model of the proposed filter structure is developed and tested. The measured results are found to be in good agreement with the simulation results.
Japanese terrestrial broadcasting was completely converted to digital television (DTV) broadcasting on 470--710\,MHz as of July 2011. However, fading phenomenon resulting from standing waves is a factor in quality deterioration in TV and mobile communication technologies. Suppression of this is needed for many kinds of technologies. A broadband single-feed planar antenna composed of two antenna components, a Broadband Planar Monopole Antenna (B-PMA) and a Broadband Planar Slot Antenna (B-PSA), is proposed for reducing deterioration of reception due to the fading across the DTV band. Reflection coefficients and radiation patterns analyzed by the Finite Difference Time Domain (FDTD) method and compared with measured results indicate that the proposed antenna is broadband compared with a conventional antenna studied previously. A field experiment is conducted in the DTV band. The results of the field experiment indicate clearly that the proposed antenna efficiently suppresses fading resulting from standing waves across the band.
A comprehensive study is performed to investigate the performance of a non-uniform circular array interferometer in a real time 3-dimensional direction finder. The angular range of view is supposed to be 65 degrees vertically and 120 degrees horizontally, which is suitable for airborne applications. Interferometer is designed to work in the S, C and X bands. Regarding optimization process, the interferometer employs an eight element non-uniform circular array along with a phase reference antenna at the center of the array. Several quantities and parameters are studied, e.g., frequency behavior, origins of phase measurement errors, Signal to Noise Ratio (SNR) effect on phase measurement, and the effect of the phase measurement error on direction finding performance. The proposed interferometer is able to tolerate at least 35 degrees of phase measurement error. Radius of the array is determined to be 22 cm in order to have good frequency response in the desired frequency band. Both Generalized Regression Neural Network (GRNN) and Maximum Likelihood (ML) estimation are applied for mapping the phase relationships between antennas to the Direction of Arrival (DoA). The results of two methods are well matched, and therefore validation is performed.
A novel compact printed antenna for dual band applications is presented. The antenna consists of two monopole elements and operates within the ISM 2.4 GHz and 5.2/5.8 GHz frequency bands. The proposed antenna provides a bandwidth of 403 MHz (2.184 GHz-2.587 GHz) in the lower frequency band and 4004 MHz (3.880 GHz-7.884 GHz) in the upper frequency band, respectively. Thus, it can cover multiple standards such as: HIPERLAN, 5.5 GHz WiMAX, and 2.4/5.2/5.8 GHz WLAN. Moreover, the lower resonant frequency of the proposed antenna can be easily tuned within 2.15 GHz to 3.22 GHz with almost no effect on the upper resonance. Additionally, the small ground plane size of the proposed antenna makes it suitable for almost any portable device.
A compact planar 4 x 4 microstrip Butler matrix is proposed in this paper. It is a wideband beam-forming network with the advantages of compact size, low cost and ease of fabrication. Three-branch line couplers with lumped-distributed elements are adopted to reduce the size, and multi-U-shaped coupled-line Schiffman phase shifters are designed to get good transmission and phase performances. The Butler matrix is fabricated and measured, and a good agreement is found between the simulated and measured results, which makes it very attractive for wideband multi-beam antenna applications.
A novel indoor positioning system based on received signal strength (RSS) in wireless networks with high accuracy is presented in this paper. The three improvement mechanisms, called signal strength filter, user location filter and path tracking assistance, are employed to improve the positioning accuracy of the system. The comprehensive performance of the proposed system is analyzed in detail and compared with the Radar system. Experimental results demonstrate that the proposed system in this paper can improve 80% accuracy in 3 meters of Radar system to 93% in typical office building testbed. Therefore, the indoor positioning system presented in this paper has the advantages of high accuracy, low cost and easy expansibility, and it can be used to locate people and assets in the fields of logistics, healthcare, and manufacturing.
In many cases, the study of DOA estimation techniques is developed based on ideal condition of signal sources and array sensor antennas. But, there are much more errors as a result of signal shadow effects from noise contribution and interference of installation environment in real system. In this paper, the DOA estimation algorithm using the de-noising pre-processing based on time-frequency conversion analysis was proposed, and the performance was analyzed. This is focused on the improvement of DOA estimation at a lower SNR and interference environment.
An experimental Unmanned Aerial Vehicle (UAV) Synthetic Aperture Radar (SAR) Sensor has been designed and developed at Multimedia University, Malaysia. This airborne system is an inexpensive C-band, single polarisation, linear FM airborne radar sensor. The system will be used for monitoring and management of earth resources such as paddy fields, oil palm plantation and soil surface. A series of field measurements and flight test has been conducted to verify the performance of the RF transceiver. This paper highlights the design and development of the SAR RF transceiver, as well as its evaluation result.