Based on the beamspace transform and the rank reduction theory (RARE), a fast direction of arrival (DOA) estimation algorithm in the presence of an unknown mutual coupling is proposed for uniform circular arrays (UCAs). Via relying on the circular symmetry and expand the mutual coupling into a limited number of phase modes, the azimuth estimates are able to be obtained without the exact knowledge of mutual coupling. Then, by using the special structure of mutual coupling matrix and the characteristic of mutual coupling coefficients, the elimination of spurious estimates and estimations of the mutual coupling coefficients are able to be handled simultaneously. The Propagator Method (PM) is used to avoid the eigenvalue decomposition and its corresponding RARE matrix allows decreasing the computation cost via using a well known identity for block matrices. Moreover, an implementation of rooting polynomial substitutes the one-dimension search. Therefore, the computation burden is greatly reduced. Numerical examples are presented to demonstrate the effectiveness of the proposed method.
Non-Cooperative Target Recognition (NCTR) of aircrafts from radar measurements is a formidable problem that has drawn the attention of engineers and scientists over the last years. NCTR techniques typically involve a database with a huge amount of information from different known targets and a reliable identification algorithm able to highlight the likeness between measured and stored data. This paper uses High Resolution Range Profiles produced with a high-frequency software tool to train Articial Neural Networks for distinguishing between different classes of aircrafts. Actual data from the ORFEO measurement campaign are used to assess the performance of the trained networks.
A design procedure for a dual-band CPW-fed linearly and circularly polarized (CP) antenna based on the L-shaped slot antenna is presented in this paper. The slot antenna and the feeding structure are fabricated on the same plane of the substrate so that circuit processes and position alignment can be simplified. By shortening the length of one arm of the L-slot, an additional mode with two orthogonal electrical fields with a phase difference of 90 degree is excited, so that the circularly polarized wave can also be excited. The enhancement of the resonant bandwidth is achieved by utilizing a stub-protruded feedline, adding one finger slit at the other arm slot, and tuning the dimension of the ground plane. A bandwidth of 22.0% (2.23-2.78 GHz) is achieved with an axial ratio < 3 dB for the optimized case.
This paper considers adaptive array beamforming using signal cyclostationarity. Due to the effect of using finite data samples, there exists an estimation error in computing the weight vector required by performing cyclic beamforming. To deal with this problem, we formulate a cost function consisting of a posteriori information of the received signal and a priori information regarding the probabilistic distribution of the error. By minimizing the cost function, we obtain a weight vector with a diagonal loading data covariance matrix under a white Gaussian estimation error. An analytical solution for determining the loading factor is further derived. Simulation results for showing the effectiveness of the proposed method are provided.
A planar W-band single balanced mixer is designed and measured in this paper. This mixer is realized by using two novel IF-block, a rat-race ring with the fifth port, two beamlead GaAs Schottky diodes and two RF chokes. The novel IF-block which designed the first time in W-band is employed to provide reflection points for IF signal and to provide low loss path in wide bandwidth for the RF and LO signals. To our knowledge, the mixer shows the best conversion loss at 95\,GHz and the highest 1\,dB power compression (P-1dB) point among the W-band planar hybrid microwave integrated circuit (HMIC) mixers.
Photonic wire lasers are compact light sources that are fabricated in high-index contrast waveguides (with typical widths of a few hundreds of nanometers). Because of their small footprints, they may become a basic laser component in future-generation of optical integrated circuits. Owing to having low optical volume by design, photonic wire lasers can only produce low output power that may not be adequate in many applications. A solution to this problem is to coherently combine the output power of different photonic wire lasers to produce larger output power. In this article, we analyze different ways to combine light coming out from photonic wire lasers and couple the combined power into a single-mode waveguide.
A planar monopole antenna with reconfigurable radiation patterns is demonstrated. The radiation pattern reconfigurability is realized straightforwardly with an employment of a detached magnetodielectric slab placed in the vicinity of the antenna structure. It is shown the radiation patterns can be easily reconfigured through the adjustment of the spacing between the slab and the antenna structure. Technically, the radiated fields are redistributed owing to the inclusion of the magnetodielectric slab, which is of high permittivity, as well as permeability. As a result, the planar monopole gain with the slab is increased up to 4 dBi while the antenna resonant frequency remains almost unchanged.
A planar sleeve dipole array antenna is analyzed and successfully implemented. The proposed antenna is designed for operation at 1800/1900 MHz band of basic station applications. To achieve sufficient bandwidth for the requirement of the PCS 1800 MHz band (1710-1880 MHz) and 1900 MHz band (1880-1930 MHz) for DECT (Digital Enhanced Cordless Telecommunications), the proposed antenna comprises of a 1 × 5 coplanar back-to-back sleeve dipole elements, we adopt the microstrip line to balanced transmission line feeding technique in this design. This structure is easily constructed by printing on both sides of a dielectric (FR4) substrate. The measured -10 dB return loss (VSWR 2 : 1) impedance bandwidth is around 13.2% (1690-1930 MHz). A reflector is put behind the dipole array to obtain directional radiation and high gain, and the measured antenna gain for operating frequencies across the 1800/1900 MHz band is about 7.2-9.1 dBi. The measured results of radiation efficiency, radiation pattern, antenna gain and return loss show the sleeve dipole array antenna has a good performance.
This paper describes a high-gain CMOS low-noise amplifier (LNA) for 2.4/5.2-GHz WLAN applications. The cascode LNA uses an inductor at the common-gate transistor to increase its transconductance equivalently, and therefore it enhances the gain effectively with no additional power consumption. The LNA is matched concurrently at the two frequency bands, and the input/output matching networks are designed with two notch frequencies to shape the frequency response. The dual-band LNA with the common-gate inductor is designed, implemented, and verified in a standard 0.18-μm CMOS process. The fabricated LNA which consumes 7.2 mW features gains of 14.2 dB and 14.6 dB, and noise figures of 4.4 dB and 3.7 dB at the 2.4-GHz and 5.2-GHz frequency bands, respectively. The proposed LNA demonstrates a 4.9-7.8 dB gain enhancement compared to conventional cascode LNAs, and the chip size is 1.06 mm × 0.79 mm including all testing pads.
We experimentally investigate the properties of nonlinear pulses in coupled transmission lines with regularly spaced Schottky varactors. The c and π modes are different propagation modes that can be developed on a coupled line. Time-domain measurements show that both modes support soliton-like pulses due to the presence of the Schottky varactors; small c-mode pulses are generated by colliding two π-mode pulses traveling in opposite directions. Moreover, we discuss the relationship of the amplitude of the newly generated c-mode pulses with different bias voltages and π-mode-pulse amplitudes.
Two directional UWB monopole antennas are proposed. It is shown that a design methodology for omnidirectional UWB rectangular planar monopole antennas can be applied for directional ones. The directional features are taken by introducing a slanting angle between the radiator and the ground plane. The slanting angle also plays a role in the low cutoff frequency, and it is considered in a proposed equation to determine that frequency. For the two UWB antennas the radiators have a rectangular shape, and the bandwidth is extended by choosing beveling angle and an appropriate height-width ratio. The developed antennas have a bandwidth wider than 10 GHz for a reflection coefficient lower than -10 dB. The directional radiation pattern has an average gain of 5 dB.
An X-band active radial-waveguide pulsed power amplifier (PA) with high power and high power added efficiency (PAE) is designed, fabricated, and measured in this paper. A bandwidth of 1000 MHz with peak power level of 53.2 dBm at the frequency 9.85 GHz, under the condition of 4 KHz pulse repeat frequency (PRF) and 10% of duty cycle, has been obtained by five-way radial waveguide power combiner. Key features of this combined device are its maximum PAE (>43.6%) and combining efficiency (>92.8%). From 9.5 to 10.5 GHz, the pulsed solid-state power amplifier (PSSPA) can provide a minimum output power level 51.4 dBm, which operates on the repeat frequency 4 KHz, duty cycle 10%. The gain varied between 41.4 and 43.1 dB at the desired frequency range, with only less than ±0.9-dB gain variation, which displayed a flat gain ripple. The PAE of the active combiner fluctuated between 36.5% and 43.6% as frequency varied from 9.5 to 10.5 GHz.
This paper presents a new dual-mode stub-loaded resonator, which consists of a microstrip resonator with internal coupled lines and an open-circuit stub. Based on the odd- and even-mode equivalent circuits, the resonant characteristics of the proposed microstrip resonator are investigated. It is found that the fundamental even-mode resonant frequency of the proposed resonator can be flexibly controlled while the fundamental odd-mode resonant frequency remains unaffected. Then, based on the proposed resonator, three compact dual-mode bandpass filters, namely filer A, filter B and filter C, are designed, fabricated and measured to validate the design concept. Filters A and B demonstrate opposite asymmetric responses with two transmission poles in the passband and a transmission zero in the stopband. Filter C has three transmission poles in the passband and two transmission zeros respectively in the lower and upper stopbands to enhance selectivity. The experimental results show excellent agreement with the theoretical simulation results.
For a cellular mobile communication system in narrow streets of urban areas, blind spots caused by shadowing of high buildings are a significant problem. In this research, a new dual-antenna system (DAS) is proposed, including a power transmission network, a receiving and a reradiating antenna to realize a broad-angle beam control. An equivalent bi-static radar cross section (BRCS) is deduced to present a theoretical explanation to the operating principles of the DAS. The main advantage of this design over ordinary reflectarray antenna as a passive RF booster is its flexible beam control capabilities. The simulated BRCS of the proposed DAS, composed of a microstrip patch array and a planar Yagi-Uda antenna, is given along with that of a metal plate of identical dimensions for comparison. purposes.
The corrected dispersion relation governing the linear interaction of a TE mode in a circular cylindrical wave guide with an annular beam of gyrating electrons in a gyro-TWT configuration is derived. The derivation of the correct dispersion relation no longer involves any integration with respect to the radial coordinate ro. of the electron guiding center as the relevant equilibrium distribution function turns out to be independent of ro. When the cyclotron resonance condition is satisfied by the TE mode for a positive s-number, the small-signal theory is shown to predict an initial exponential growth of the mode with interaction length over a small but finite band of frequencies around the design frequency.
In this paper spatial-band pass filters consisting of frequency selective surfaces (FSSs) are designed in order to realize both the desired transfer function of the filter in the frequency domain and drastic size reduction. Each FSS is made of aperture elements and patch elements. In this design method, the shape of each FSS is designed by a genetic algorithm (GA) so that the resonant curve of each FSS fits to the resonant curve which can be obtained from an equivalent circuit approach. By locating these designed FSSs at the intervals of quarter wavelength a spatial band pass filter is realized. Furthermore, a technique which controls the frequency response of each FSS has been applied to reduce the longitudinal size of filter. By this technique the FSSs are located at the intervals which are much shorter than a quarter wavelength, keeping the desired transfer function. Through a designed example it is shown that the half longitudinal length of a typical spatial filter can be obtained without any additional structure. Magnetic type spectral domain dyadic Green's functions are derived, and the characteristics of a spatial band-pass filter are calculated by means of the coupled magnetic filed integral equation which accurately takes higher order mode interactions. Derived linear matrix equations are solved using method of moment (MoM). The effectiveness of the proposed structure and its performance are verified and validated by designing and simulating an equal ripple spatial band pass filter at X-band.
Recently, substrate integrated waveguide (SIW) technology attracts more and more attentions in the development of millimeter-wave integrated beamforming network (BFN) depending on its inherent advantages. However, the SIW-based BFN usually has a relative large circuit size. To overcome this weakness, we propose a novel multi-folded SIW Butler matrix at the center frequency of 60 GHz. Such a structure can reduce the circuit area more than 75% compared with the conventional single-layer version. Two different full-wave simulation tools are employed to validate our design. This folded BFN offers a number of benefits, such as highly compact configuration, low couplings between adjacent paths, and wide operation bandwidth. For convenient use, the SIW ports can be converted to the microstrip line ports arranged in order through a special broad-band two-layer transition network. Such a miniaturized SIW Butler matrix presents an excellent candidate in the development of compact intelligent millimeter-wave communication system.
A novel compact design of planar T-shaped monopole antenna with multi-band operation for WLAN/WiMAX system is proposed. By insetting a pair of mirrored L-shaped monopole strips, multi resonant modes close to 2.45/3.5/5.5 GHz band are excited to meet the specifications of WLAN/WiMAX system. And, the obtained impedance bandwidth across the operating bands can reach about 160/1100/2690 MHz for the 2.45/3.5/5.5 GHz bands, respectively. Only with the antenna size of 30×42×0.8 mm3, the proposed monopole antenna has the compact operation with more than 20% antenna size reduction. The measured peak gains and radiation efficiencies are about 3.2/3.5/5.4 dBi and 72/98/96% for the 2.45/3.5/5.5 GHz band, respectively, with nearly omni-directional pattern in the XY-plane.
In this paper, a novel maximum likelihood algorithm for joint angle and delay estimation is developed to identify the specular components of channel fading for uniform linear array based on the physical propagation channel model. Frequency domain presmoothing is applied to the structured frequency transfer matrix before the estimation procedure in order to utilize substantial observations. Iterative Gauss-Newton method is used to solve the multidimensional optimization problem, and a new compact matrix form is presented. Further simplification of the iteration is derived based on the assumption of independent channel parameters. Both simulations and measurement results are investigated for performance analysis. The simulations reveal that the proposed algorithm leads to higher performance with appropriate complexity. Also, a comparison with other algorithms is carried out to validate the accuracy of algorithm by using the power delay profile measured in a real environment, and the results show the proposed algorithm performs well.
We investigate numerically the collision of nonlinear envelope pulses in composite right- and left-handed transmission lines with regularly spaced Schottky varactors. Because of the nonlinearity caused by the Schottky varactors, the dispersive distortion of envelope pulses is well compensated. We find that when two nonlinear envelope pulses traveling in the opposite directions collide, two envelope pulses are newly developed. The carrier wave frequency of the newly developed pulse is the harmonic of the colliding pulses that satisfies the phase-matching condition.