This paper presents the performance of an Adaptive transmit beamspace beamformer (ATBBF) in a dynamic channel for Multiple input single output (MISO) per user wireless system. ATBBF consists of a of several transmit beamformers on the Transmit antenna array (TAA). The antenna weights of each Transmit beamformer (TB) are held constant while input to a TB is weighted by an adaptive beamspace weight. An algorithm that updates beamspace weights of all transmit beamformers of an ATBBF at the base station is described. It updates on the basis of a single feedback from the mobile. The feedback consists of one bit that indicates which of the two normalized perturbed beamspace weights that were time multiplexed onto the pilot signal from the base station delivered more power to the mobile. This algorithm is named Beamspace gradient sign feedback algorithm (BGSF) as its feedback mechanism is similar to that of Gradient sign feedback (GSF) algorithm that updates antenna weights of a TB. Performance metric of ATBBF is derived and analyzed in a dynamic channel undergoing Rayleigh fading. Performance comparison between an ATBBF with BGSF algorithm and a TB with GSF is made in terms of convergence and tracking of various slow and fast fading channels by simulations. Both full dimension (FD) and Reduced dimension (RD) ATBBF are considered. Comparisons show that FD ATBBF gives equivalent performance to that of TB and outperforms RD ATBBF.
A method for measuring the sensitivity of a capacitive proximity sensor and an application using the sensor as a proximity detector in mobile phone antennas is presented. 2D sensor data plots were physically more exact for tuning sensor placement. 3D sensor data plots were suitable for sensor intensity comparison, highlighting sensor differences in multiple sensor applications and effects in sensor`s output due to shadowing mechanical objects. The antenna proximity sensor was measured and optimised with sensitivity measurements. In a PIFA application the antenna load could be detected from both sides and from above the antenna on a scale o 4.03•10-14 F to 4.33•10-14 F. The cases present all possible positions of holding a phone used in either the ``calling'' or ``browsing'' mode. The method and the application emphasise the physical sensitivity and electrical fields of the sensor. The characteristics can be further improved by using other sensor types, sensor data fusion and advanced imitation of multisensory spatial interaction by humans and animals.
MVDR beamformer is one of the well-known adaptive beamforming techniques that offers the ability to resolve signals that are separated by a fraction of an antenna beamwidth. In an ideal scenario, the MVDR beamformer can not only minimize the array output power but also maintain a distortionless mainlobe response toward the desired signal. Unfortunately, the MVDR beamformer may have unacceptably low nulling level, which may lead to signicant performance degradation in the case of unexpected interfering signals. A new robust MVDR beamforming is presented to control the nulling level of adaptive antenna array. In this proposed approach, the beamforming optimization problem is formulated as a multi-parametric quadratic programming (mp-QP) problem such that the optimal weight vector can be easily obtained by real-valued computation. The presented method can guarantee that the nulling level are strictly below the prescribed threshold. Simulation results are presented to verify the efficiency of the proposed method.
This paper presents the development of a standard surface mountable ceramic ball grid array (CBGA) package with an integrated patch antenna in low temperature cofired ceramic (LTCC) technology for emerging single-chip 60-GHz radios. It addresses the challenges of low-loss wire bonding interconnections required between the chip and the antenna as well as the package to allow efficient utilization of available space for miniaturization. The compact package of size 12.5×8×1.265 mm3 achieves good electrical performance. For instance, the package part exhibits insertion loss <0.08 dB, return loss >22 dB, and attenuation rate <0.2 dB/cm below 5 GHz; while the antenna part demonstrates 8-GHz impedance bandwidth and 8±2 dBi peak realized gain at 60 GHz. Simulated and measured results are compared. They agree reasonably well, indicating the feasibility of designing and manufacturing the integrated antenna package in LTCC for millimeter-wave applications.
The Multilook Cross Correlation (MLCC) is one of the most reliable algorithms used for Doppler ambiguity number estimation of the Doppler centroid parameter. However, the existing MLCC algorithm is only suitable for low contrast scenes. In high contrast scenes, the estimated result is not reliable, and the error is unacceptable. Besides, the Doppler centroid estimation processing time is long and can only be used in offline processing. In this paper, we introduce a modified MLCC algorithm that has better sensitivity which is suitable not only for low contrast scenes, but also for high contrast scenes. In addition, the modified MLCC algorithm can be implemented on parallel signal processing units for better time efficiency. Experiments with RADARSAT-1 data show that the modified algorithm works well in both high and low contrast scenes.
This paper describes how the ionosphere reflected echoes observed by a high frequency surface wave radar (HFSWR) can be processed to extract information regarding the ionosphere sporadic E (Es) and F2 layers. It is shown that the range/time spectrum contains the data to estimate the occurring time and virtual heights of both the still and drifting Es layer clouds. In addition, for the drifting Es the data can be processed to extract the time-varying ranges and estimate virtual heights, horizontal drifting speeds. Information regarding the F2 layer such as the time-varying virtual heights can also be extracted. The time-frequency distributions (TFD) of the Es and F2 layer echoes calculated after the range migration compensation can be used to extract the intrinsic Doppler patterns. This is further used to obtain information on the internal nonuniform structures and disturbances such as the travelling ionospheric disturbances (TID) that are due to the acoustic gravity waves (AGW). Processing results of echo data collected by the portable HFSWR system named OSMAR-S demonstrate the validness of the above methods.
A novel ultra-wideband (UWB) pulse synthesizer is proposed, which uses a distributed amplifier to combine Gaussian pulses of different polarities, amplitudes and delays. The center frequency and bandwidth of the synthesized pulse can be adjusted by varying the number of the Gaussian pulses and the delays between them. Compared to other UWB pulse generators, the present synthesizer is capable of higher voltages and higher efficiencies. Using 0.25-μm pHEMTs, a prototype synthesizer has been designed and fabricated with a center frequency of 4.0 GHz and a bandwidth of 1.9 GHz. Under a Gaussian input pulse of 1.5 V and 100 ps, the synthesizer outputs into 50 Ω a pulse of 4.5 V and 1 ns. At a pulse-repetition frequency of 10 MHz, the synthesizer consumes 1 mA at 3 V with 17% efficiency. Approaches to maintain high efficiency by scaling the supply voltage for different input amplitudes and pulse-repetition frequencies have also been verified experimentally.
A novel resonate-type composite right/left handed transmission line (CRLH TL) is presented based on a high-low impedance section and a capacitive gap on the conductor strip, and a Minkowski-loop-shaped complementary split ring resonators (ML-CSRRs) etched on the ground plane. Influence of different iteration orders on the performance of novel CRLH TL and miniaturization mechanism are investigated in depth by electrical simulation (an analysis of circuit model) together with planar electromagnetic (EM) simulation. The close-form results of negative refractive index and complex propagation constant are provided by constitutive parameters retrieval method. For application, a compact branch-line coupler (BLC) centered at 0.88GHz (GSM band) is designed, fabricated and measured. The upper signal line of CRLH impedance transformer is constructed as Koch curves of first order to facilitate further integration of the BLC. Exact design method for fractal implementation is involved. Measurement results indicate that the proposed coupler achieves a comparable 81% size reduction and good in-band performance with regard to already covered ones. The concept, validated by consistent measurement data, is of practical value for other components design.
This paper demonstrates the exhibition of pulse compression from an electronic circuit with negative group delay (NGD). This circuit consists of a field effect transistor (FET) cascaded with shunt RLC network. Theoretic and experimental investigations have proved that, at its resonance frequency, the group delay of this circuit is always negative. The present study shows that around this resonance, it presents a gain form enabling to generate pulse compression. To validate this concept, as proof-of-principle, devices with one- and two-stages FET were implemented and tested. Measurements of the one-stage test device evidenced an NGD of about -2.5 ns and simultaneously with 2 dB amplification operating at 622 MHz resonance frequency. In the frequency domain, in the case of a Gaussian input pulse with 40\,MHz frequency standard deviation, this resulted in 125% expansion of pulse width compared to the input one. In time domain, simulations showed that the compression was about 80% in the case of an input Gaussian pulse with 4 ns standard deviation. With the other prototype comprised of two-stage NGD cell, the use of a sine carrier of about 1.03 GHz allowed to achieve 87% pulse width compression.
This paper presents a novel frequency selective window for waveguide filters. It has a resonant characteristic with two attenuation poles on both sides of a passband, that is, a dual-behavior resonance. Such frequency selective windows make it possible to construct a compact bandpass filter having multiple attenuation poles without any additional coupling structures. As design examples, we show 3-pole Chebyshev waveguide filters with six attenuation poles in both the microwave and the millimeter-wave regions. The validity of the present filters is proven by the comparison of the frequency characteristics between the calculated and the measured results.
A simple low-cost Y-branch plastic optical fiber (POF) coupler which can be assembled easily by the end users has been developed. The acrylic-based Y-Branch POF coupler consists of input POF fiber, a middle high index contrast waveguide taper and output POF fibers. The optical device is based on a 1x2 Y-branch coupler design with a middle high index contrast waveguide taper. Non-sequential ray tracing has been performed on the device giving an insertion loss of 4.68 dB and coupling ratio of 50:50. The middle waveguide taper region is constructed on the acrylic block itself without using any additional optical waveguiding medium injected into the engraved taper region. Fabrication of the devices is done by producing the device structures on an acrylic block using high speed CNC machining tool. Input and output POF fibers are inserted in to this device structure in such a way that they are passively aligned to the middle waveguide taper structure. The first prototype device shows an insertion loss of 7.5 dB and a splitting ratio of 50:50. A second prototype device which includes additional U-groove slots for the jacketed fibers shows an insertion loss of 5.9 dB and a splitting ratio of 50:50.
This paper presents an UWB antenna concept adapted for a potential application of RFID in a severe multi-paths environment for European regulation (UWB-LDR 6--8.5 GHz). The UWB provides theoretically the signal integrity and designing the UWB antenna is compatible with low size, cost and low complexity consideration. Under the hypothesis of using the same antenna at both transmitting or receiving states, the 1/f2 effect of free space attenuation can be minimised by a pre-emphasis included in the antenna design, that is to say an ``f-gain" antennas at both transmitting (Tx) and receiving (Rx) parts. As a result, the printed antennas described are neither constant aperture nor constant gain type.
The design and manufacture of a circular polarized aperture stacked patch circular microstrip patch antenna (CPASPA) at L-band is presented. The Wilkinson power divider is used to excite the stacked circular patches by two orthogonal $H$-shape slots, which can improve the operation bandwidth and circularly polarized performance. The design is optimized by a series of parametric study of the input impedance for the antenna. The measurements show that the CPASPA has a 3-dB axial ratio (AR) bandwidth of 55.0% and a 10-dB return loss (RL) bandwidth of 47.0%. The measured gain is more than 0 dBic over the bandwidth of 42.5%, in which the maximum is 9.4 dBic. The measurements agree very well with the simulation results.
In this paper, a general design of an equal-split N-way power divider, similar to Bagley polygon power divider, but with an even number of output ports is proposed. A circularshaped 4-way divider is designed and simulated using two different full-wave simulators. Very good matching at the input port is achieved, and good transmission parameters are obtained. After that, the same circular-shaped divider is redrawn in a rectangular form to save more circuit area, and to align the four output ports together. For verification purposes, the 4-way rectangular-shaped Bagley power divider is simulated, fabricated and measured. Both simulation and measurement results prove the validity of the design.
In this paper, different topologies of dual-frequency modified 3-way Bagley polygon power dividers are designed and analyzed. Equal split power division is achieved at arbitrary design frequencies. In the first structure, two-section transmission line transformer is used to realize the dual-frequency operation. In the second and third structures, dual-frequency T-shaped and π-shaped matching networks are used. For the sake of simplicity, closed form design equations are presented for each matching network. To validate the design procedure, three examples are designed, simulated, and fabricated. The three matching networks are explored through these three examples. The design frequencies are chosen to be 0.5 GHz and 1 GHz.
The broadband microstrip antenna is realized by cutting the slot inside the patch. The slot introduces a resonant mode near the fundamental resonance frequency of the antenna and realizes broadband response. The compact variations of circular microstrip antenna are realized by placing the shorting posts along the zero field line at the fundamental mode. These shortened antennas have narrower bandwidth. In this paper, a compact half U-slot cut shorted sectoral microstrip antenna is proposed. The detailed analysis has been carried out to study the effect of the slot on various modes of the Sectoral patch. It has been observed that the half U-slot does not introduce any additional mode, but reduces the resonance frequency of the higher order mode of the shorted Sectoral patch and along with its fundamental mode realizes broader bandwidth. The bandwidth of more than 700 MHz, at the center frequency of approximately 2700 MHz, has been realized.
Great accuracy and reasonable computational time are desirable in a deterministic ray tracing model for an efficient radio frequency planning. An algorithm to speed up a ray tracing engine is described which allows to select arbitrary areas around transmitters and receivers by dividing the scene in a voxel chessboard. The reliability of the algorithm has been evaluated by comparing measured and predicted path losses in real urban scenarios while the algorithm performance is expressed in terms of computational time reduction.
The planar metal particles, consisting of a multi-turn spirals, are studied with the aim of using them to realize high impedance surfaces or as an elementary cell to create an artificial material. These spirals present a resonant behaviour in a certain frequency band. To obtain miniature devices, a compromise between the surface and the efficiency of the resonance must be found. The compactness of the particles can be increased by using s spirals. However, the accuracy on resonant frequency of existing models is not sufficient for our applications. We present a simple analytical model that determines the resonant frequency from the geometric dimensions of the approximated model. This model is verified by electromagnetic simulations and by measurements.
A novel compact multi-band design of planar C-shaped monopole antenna with inverted L-shaped parasitic strip is proposed for IEEE 802.16m WiMAX system. The obtained impedance bandwidth across the 2.6/3.5/5.5 GHz operating bands can reach about 240/570/4470 MHz, respectively. Only with the antenna size of 15×30×0.8 mm3, the proposed monopole antenna has the compact operation with more than 50% antenna size reduction. The measured peak gains and radiation efficiencies are about 2.1/2.2/2.9 dBi and 91/96/94% for the 2.6/3.5/5.5 GHz operating band, respectively, with nearly omni-directional pattern in the XY-plane.
This paper presents an optimal power pattern synthesis procedure able to tackle the mutual coupling and platform effiects even for electrically large arrays. The novelty of the approach is due to its capability to account in the synthesis procedure for two different aspects at the same time: the coupling between the array radiating elements and the coupling between these elements and the array platform. The mutual coupling evaluation is based on the active element pattern method, and the active element pattern is numerically computed. The kind of synthesis problems here addressed belongs to the class of convex optimization problems. Therefore, the solution is found by means of very efficient convex programming tools, without requiring global optimization schemes, thus saving time and costs. The extension of the overall tool to adaptive arrays is also considered.
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