A highly miniaturized low-pass filter using microstrip open-loop and semi-hairpin resonators is designed and analyzed to enhance the bandwidth and further size reduction of this kind of elements. Initially, two microstrip open ring resonators and separately, two semi-hairpin resonators are arranged and attached back-to-back to each other respectively. A compact LPF is designed and simulated using these modified resonators. The size reduction of this proposed filter is reported about 65% with 190% enhancement of bandwidth in analogy with the conventional low-pass filters.
This paper presents a de-interleaved subsampling receiver architecture suitable for homodyne receivers. The proposed topology requires only a single branch to down-convert and extract the in-phase (I) and quadrature (Q) baseband signals. Using a single-branch receiver eliminates the I/Q mismatch issue of traditional direct down-conversion receivers. The simplicity of the proposed receiver architecture makes it an alternative solution for multi-band and multi-standard applications.
In this paper, a new technique that combines adaptive transmit antenna selection, transmit power allocation and iterative detection is introduced for the modified Turbo-BLAST system. At the transmitter, in order to minimize the BER performance of the overall system, an adaptive transmit antenna selection scheme is proposed to select the appropriate antenna subset for the actual transmission, and the proper power is allocated for the selected antennas subject to the total transmit power constraint. At the receiver the modified MMSE detector taking the imperfect CSI into account is used to remove the co-antenna interference. Finally the turbo principle is employed for iterative detection to further lower the BER results. Simulation results show that the introduced adaptive transmit antenna selection and power allocation algorithm can significantly improve the BER performance, and the iterative detection technique can further enhance the performance.
Radio over Fiber (RoF) system has attracted much industry and research interest to extend the wireless cell coverage and reduce the cost by using the distributed remote antenna units (RAUs). However, the effective transmission fiber length in the RoF systems would be limited due to the time division duplex (TDD) mode used in the practical WiMAX access. Here, we study the transmission limitations and performances of the standard WiMAX signal for RoF systems. The throughputs and packet-losses at different fiber lengths are also investigated and analyzed. Besides, in order to increase the emitting power of the RAUs, a robust TDD switching mechanism is proposed in each RAU for RoF system.
In traveling wave tube (TWT) amplifiers, an axial focusing magnetic field is required to keep electrons traveling in a narrow, pencil-like beam over the considerable length of the circuit. Conventionally, this focusing has been accomplished by using a periodic permanent magnet system housing axially polarized ring magnets. Making the structure to this point has been a complicated process consisting of brazing multiple metals together and honing the piece to the desired specifications. We present a new method of fabricating this housing structure monolithically using iron, developing magnetically oversaturated housing regions, and saving processing time and effort.
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% 10 dB impedance bandwidth at 2.5 GHz ISM band with a monopole area of 300 mils by 166 mils on a small circuit board and a backside ground plane 1500 mils by 600 mils. 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 ground plane area is characterized. The use of circuit ground as a part of an antenna should find useful applications in portable wireless systems. Good agreements are found between simulated and measured antenna gain patterns and return loss.
We previously analyzed the effects of trapezoidal tapered gratings on the dispersive bistable characteristics of a quarter wavelength phase-shifted distributed feedback semiconductor laser amplifier (QWS-DFB-SLA). In this paper, we analyze the effects of coupling coefficient on the static bistable characteristics of a QWS-DFB SLA with a tapered or a non-tapered grating. Simulation results show that any change in the coupling coefficient can change the characteristics such as the spectral range of low-threshold bistable switching and the on-off switching contrast.
This paper presents a dual-band dual-polarized antenna array design for WLAN applications. Four double-dipole elements are orthogonally interleaved to facilitate operation in both the standard WLAN frequency bands (IEEE 802.11b and IEEE 802.11a) simultaneously. The two linear polarizations have separate ports. The presented design is characterized by dual-band operation, reasonably good front-to-back ratios, average gains of 5.2 dBi and 6.2 dBi over the 2.4 and 5.2 GHz bands respectively, stable end-fire radiation patterns and very low cross-polarization levels.
This paper presents a novel technique to improve the cross-polarization and the beam efficiency of an offset parabolic reflector antenna used for space borne radiometric applications. A special multi-mode primary feed (tri-mode conjugate matched feed) is used to illuminate the offset parabolic reflector antenna. The simulated data on the radiation characteristics of the offset parabolic reflector antenna with a matched feed has been compared with that of a conventional Potter horn. It is observed that the tri-mode feed suppress the unwanted high cross-polarization of an offset reflector antenna and improves the beam efficiency.
This paper shows that an optimal antenna pattern for active phased array synthetic aperture radar (SAR) has been synthesized to meet the best performances based on particle swarm optimization (PSO) and adaptively selected weighting factors. Because the antenna radiation pattern has a very close relation with the performance of an active phased array SAR system, the authors derived the multi-objective cost functions on the basis of the system performance measures such as the range-to-ambiguity ratio, noise equivalent sigma zero, and radiometric accuracy. The antenna mask templates were derived from the SAR system design parameters in order to optimize the system requirements. To effectively minimize the cost functions and to search for the amplitude and phase excitations of an active phase array SAR antenna, the authors applied the PSO technique to SAR antenna pattern design and also carefully selected weighting factors to improve the fitness of the cost functions on the basis of the SAR performance.
A hybrid electromagnetic-network analysis of the antennas-channel multiple input multiple output (MIMO) communication subsystem is presented. The analysis is based on the antenna effective and realized effective length matrices, which relate in a compact mathematical way the radiated and received electric field intensities to the network characteristics of actual and coupled transmitting (Tx) and receiving (Rx) multi-element antenna (MEA) systems. The effective length matrices are calculated via the active power gain and phase antenna patterns obtained by means of any full wave computational electromagnetics (CEM) field solver. It is shown that the realized effective length matrix is suitable for the S-parameter analysis of a MIMO communication link, while the effective length matrix is convenient for its Z-parameter analysis. The effective length matrix framework is applied to a free space 2x2 coupled dipoles MIMO system and its results are in excellent agreement to those obtained by a Method of Moments (MoM) based field solver.
A novel wideband multilayered microstrip antennas with shorting pins and arc-shaped apertures loaded is designed and fabricated. The antenna consists of two dielectric substrates and a quasi H-shaped circular patch with five shorting pins and four arc-shaped apertures loaded on the upper layer. Multiple layers are employed to achieve wide bandwidth by stacked electromagnetic coupling. The arc-shaped apertures and shorting pins are used to excite multiple modes, which can change the cavity's electromagnetism characteristic with influencing the series-parallel connection inductance, so that the wide bandwidth is obtained. Effects of the key parameters on the wideband performance are also studied, and a set of optimum values is chosen for the antenna design. The impedance bandwidth (VSWR < 2.0) of the proposed antenna reaches 2.59 GHz with the measured results, which means the relative impedance bandwidth is expanded up to 34.7% across 6.17 to 8.76 GHz. Simulation results agree well with measured ones.
A compact CPW-fed slot antenna is proposed for dual-band wireless local area network (WLAN) operations. In this letter, electromagnetic band gap (EBG) structures with square-shaped lattices have been incorporated into the feed network for harmonic suppression. Experimental results show that EBG structures not only exhibit well-behaved band stop characteristics, but also enhance the bandwidth of the proposed antennas. For the proposed antenna with square-shaped lattices, the -10 dB return loss bandwidth could reach about 38.4% for the 2.4 GHz band and 23.8% for the 5 GHz band, which meet the required bandwidth specification of 2.4/5 GHz WLAN standard.
A novel approach of left-handed (LH) structures is introduced to reduce the size of microwave components by combining a loaded coupled transmission lines and complementary split ring resonators (CSRRs). The performance of the loaded part of the proposed model is equal by two cascaded unit elements. The equivalent circuit model and subsequently, the left and right handed transmission frequencies of the proposed structure are presented. A highly miniaturized dual-band branch-line coupler (BLC) is analyzed, designed, tested and proposed by this technique. The size reduction is reported about 75% in analogy with the conventional ones. The measurement results are in good agreement with the theoretical ones.
An internal shorted patch antenna integrated with a RF/battery shielding metal case for application in a UMTS mobile phone is presented. The shorted patch antenna is mounted at the dented portion of the shielding metal case, with the top patch flushed with the top surface of the shielding metal case. This configuration shows no protruded portions, which makes the antenna very suitable to be integrated in a UMTS mobile phone as an internal antenna. With the integrated design, which provides a coupling-free region for the nearby electronic components or conducting elements in the mobile phone, possible coupling between the antenna and associated components can be avoided. Details of the proposed design showing a wide bandwidth for UMTS (Universal Mobile Telecommunication System, 1920 ~ 2170 MHz) operation are demonstrated, and effects of the dimensions of the RF/battery shielding metal case are presented and discussed.
A Sub Harmonically Pumped (SHP) mixer suitable for direct conversion receiver in 3G mobile frequency band is presented. This mixer is realized with N anti-parallel diode pairs (APDPs) and designed in self-biased structure to obtain minimum noise figure and conversion loss. In this paper, a simultaneous signal and noise analysis CAD routine to analyze a circuit consists of Arbitrary Number of anti-parallel diode pairs in self-biased structure is proposed. Then the results of this CAD routine are confirmed with other method. The mixer is optimized to obtain a maximally flat conversion gain and minimum Noise Figure over various LO powers. The proposed CAD is used to obtain the optimum number of APDPs. Also the optimum self-biased resistance and output load are calculated.
A novel circuit structure of dual-band bandstop filters is proposed in this paper. This structure comprises two shunt-connected tri-section stepped impedance resonators with a transmission line in between. Theoretical analysis and design procedures are described. The derived synthesis equations have two degrees of freedom which provide more design flexibility in filter synthesis. Notably, three advantages of the proposed filter structure lie in the fact of its increased nonuniform impedances, resulting in a compact size, wide range of realizable frequency ratio, and more realizable impedances. Three experimental dual-band bandstop filters with various frequency ratios were fabricated to demonstrate the feasibility of the new filter structure.
Based on swept frequency RCS measurements system, foam column and proper data processing procedure, the resonance curves of conducting spheres with RCS below -32.95 dBsm are achieved in a single reflector Compact Antenna Test Range (CATR), with measurement errors within 1.0 dB over most of the measurement frequencies. Nine spheres down to -49.01 dBsm are clearly imaged with Range-Doppler (R-D) method and pointwise vector background subtraction technique.
The design, simulation and performance enhancement of a new structure for X-band high-power, low-loss, low-bias, triangular-ferrite waveguide circulator are presented. Dual circulation property is obtained by triangular shape of ferrite post. The effects of circulator's structure parameters, such as ferrite parameters and magnetic DC bias, on isolation, insertion loss and return loss of circulator are discussed. The HFSS software is used for simulating the circulators. Final dual band designs with 20 dB return loss, 20 dB isolation and 0:1 dB insertion loss in dual frequency in X-band (8:2 GHz and 10:4 GHz) with only a magnetic bias of 10 Oe are obtained.
Multiple-input multiple-output (MIMO) systems play a vital role in fourth generation wireless systems to provide advanced data rate. In this paper, a better performance and reduced complexity channel estimation method is proposed for MIMO systems based on matrix factorization. This technique is applied on training based least squares (LS) channel estimation for performance improvement. Experimentation results indicate that the proposed method not only alleviates the performance of MIMO channel estimation but also significantly reduces the complexity caused by matrix inversion. The performance evaluations are validated through computer simulations using MATLAB® 7.0 in terms of bit error rate (BER). Simulation results show that the BER performance and complexity of the proposed method clearly outperforms the conventional LS channel estimation method.