A half-moon antenna

This work presents a half-moon antenna (HMA), which is composed of two semi-circular top and bottom conducting plates joined by a rectangular conducting plate. The HMA has a wide radiation beam. Radiation in the y-z plane (in the E plane) is hemispherical with a half-power beam width (HPBW) of more than 200/spl deg/. Radiation in the x-y plane (in the H plane) forms a sector beam with an HPBW of more than 100/spl deg/. To reduce the backward radiation and improve the gain, chokes are added to the HMA. An increase in the gain of approximately 1 dB is obtained. In order to obtain a tilted beam, the radius of the bottom plate is reduced. The maximum beam direction of the tilted beam /spl theta//sub max/ is not sensitive to frequency. Within a frequency range of 11 to 14 GHz (24%), /spl theta//sub max/=167/spl deg//spl plusmn/2/spl deg/. The gain is found to be G=9.5/spl plusmn/0.5 dBi within this same frequency range.     

Printed figure-of-eight wire antenna for circular polarization

A new printed wire antenna with circular polarization properties is presented. The geometry of the printed wire which takes the form of a figure-of-eight has a total length of 1.3/spl lambda//sub o/ and serves as a nonresonant traveling-wave antenna. It is shown that a 3-dB axial ratio bandwidth of 15% can be achieved. The half-power and 3-dB axial ratio beamwidth is approximately /spl plusmn/45/spl deg/, while its gain is of the order of 6.5 dB.     

Composite right/left-handed transmission line based compact resonant antennas for RF module integration

Several electrically small resonant antennas employing the composite right/left-handed transmission line (CRLH-TL) are presented for integration with portable RF modules. The proposed antenna designs are based on the unique property of anti-parallel phase and group velocity of the CRLH-TL at its fundamental mode. In this mode, the propagation constant increases as the frequency decreases, therefore, a small guided wavelength can be obtained at a lower frequency to provide the small /spl lambda//sub g//2 resonant length used to realize a compact antenna design. Furthermore, the physical size and the operational frequency of the antenna depend on the unit cell size and the equivalent transmission line model parameters of the CRLH-TL, including series inductance, series capacitance, shunt inductance and shunt capacitance. Optimization of these parameters as well as miniaturization techniques of the physical size of unit cell is investigated. A four unit-cell resonant antenna is designed and tested at 1.06 GHz. The length, width and height of the proposed antenna are 1/19/spl lambda//sub 0/, 1/23/spl lambda//sub 0/ and 1/83/spl lambda//sub 0/, respectively. In addition, a compact antenna using a 2-D three by three mushroom like unit cell arrangement is developed at 1.17 GHz, showing that an increased gain of 0.6 dB and higher radiation efficiency can be achieved over the first prototype antenna. The same design is applied in the development of a circularly polarized antenna operating at 2.46 GHz. A 116/spl deg/ beamwidth with axial ratio better than 3 dB is observed. The physical size of the proposed mushroom type small antenna and the circularly polarized antenna is 1/14/spl lambda//sub 0/ by 1/14/spl lambda//sub 0/ by 1/39/spl lambda//sub 0/ and 1/10/spl lambda//sub 0/ by 1/10/spl lambda//sub 0/ by 1/36/spl lambda//sub 0/, respectively.     

Broad-band fragmented aperture phased array element design using genetic algorithms

In this paper, a synthesis procedure to design thin broad-band fragmented aperture array elements is described. The arrays are assumed to be infinite periodic and the elements consist of a conducting pattern etched on a dielectric backed by a groundplane. A genetic algorithm (GA) is used to design the conducting pattern, relative permittivity, and thickness of the dielectric substrate with respect to array scan and bandwidth performance. The fitness function in the GA is evaluated using a finite-difference time-domain code with periodic boundary conditions. For a substrate thicker than about 0.1 /spl lambda//sub L/ (/spl lambda//sub L/= wavelength at the lowest frequency in the frequency band investigated), it was found that a bandwidth of at least one octave can be obtained for arrays scanned within 45/spl deg/ from broadside.     

Arbitrary dual-band components using composite right/left-handed transmission lines

Arbitrary dual-band microstrip components using composite right/left-handed (CRLH) transmission lines (TLs) are presented. Theory, synthesis procedure, and implementation of the dual-band quarter-wave (/spl lambda//4) CRLH TL are presented. Arbitrary dual-band operation is achieved by the frequency offset and the phase slope of the CRLH TL. The frequency ratio of the two operating frequencies can be a noninteger. The dual-band /spl lambda//4 open/short-circuit stub, dual-band branch-line coupler (BLC), and dual-band rat-race coupler (RRC) are also demonstrated. The performances of these dual-band components are demonstrated by both simulated and measured results. Insertion loss is larger than 23 dB for the shunt /spl lambda//4 CRLH TL open-circuit stub and less than 0.25 dB for the shunt /spl lambda//4 CRLH TL short-circuit stub at each passband. The dual-band BLC exhibits S/sub 21/ and S/sub 31/ larger than -4.034 dB, return losses larger than 17 dB, isolations larger than 13 dB, phase differences 90/spl deg//spl plusmn/1.5/spl deg/, and gain imbalance less than 0.5 dB at each passband. The dual-band RRC exhibits S/sub 21/ and S/sub 31/ larger than -4.126 dB, return losses larger than 12 dB, isolations larger than 30 dB, phase difference 180/spl deg//spl plusmn/4/spl deg/, and gain imbalance less than 0.2 dB at each passband.     

Rhombus-like stripe BA InGaAs-AlGaAs-GaAs lasers

A 1.5-W continuous-wave power output in a beam pattern of 3/spl deg/ is obtained from a new designed rhombus-like stripe strained quantum-well diode laser (/spl lambda/=980 nm) with a 150-/spl mu/m-wide emission aperture grown by molecular beam epitaxy. The /spl eta//sub d/ is as high as 78%, and the maximum output power by the new stripe laser is 5.0 W for antireflection/high-reflection coated devices.     

The b-factor as a function of frequency and canopy type at H-polarization

For anticipated synergistic approaches of the L-band radiometer on the Soil Moisture and Ocean Salinity (SMOS) mission with higher frequency microwave radiometers such as the Advanced Microwave Scanning Radiometer (AMSR) (C-band), a reanalysis has been performed on the frequency dependence of the linear relationship between vegetation optical depth (/spl tau//sub o/) and vegetation water content (W), given by /spl tau//sub o/=b/spl middot/W. Insight into the frequency dependence of the b-factor is important for the retrieval of surface moisture from dual- or multifrequency microwave brightness temperature observations from space over vegetation-covered regions using model inversion techniques. The b-values presented in the literature are based on different methods and approaches. Therefore, a direct comparison is not straightforward and requires a critical analysis. This paper confirms that when a large frequency domain is considered, the b-factor is inversely proportional to the power of the wavelength b=c/(/spl lambda/)/sup x/, which is in line with theoretical considerations. It was found that different canopy types could be separated into different groups, each with a different combination of values for log(c) and x, which characterize the linearized relationship log(b)=log(c)-x/spl middot/log(/spl lambda/). A comparison of ratios b/sub C//b/sub L/ (with C and L denoting C- and L-band, respectively) also resulted in basically the same groups.     

A photonic-link millimeter-wave mixer using cascaded optical modulators and harmonic carrier generation

Efficient frequency conversion into and out of the millimeter wave frequency band has been demonstrated using photonic link signal mixing with cascaded optical modulators. By adjusting the modulator bias point and RF drive power to the modulator introducing the local oscillator signal at f/sub LO/=8.8 GHz, frequency conversions from f/sub s/ to f/sub LO//spl plusmn/f/sub s/, sf/sub LO//spl plusmn/f/sub s/, and 4f/sub LO//spl plusmn/f/sub s/ with respective losses of 4.8, 6.3, and 7.5 dB have been demonstrated. The direct phase noise measurement of the optical RF signal at 2f/sub LO/=17.6 GHz with 1 kHz offset shows -89 dBc/Hz, limited by the RF drive source.     

Leaky CPW-based slot antenna arrays for millimeter-wave applications

A uniplanar leaky-wave antenna (LWA) suitable for operation at millimeter-wave frequencies is introduced. Both unidirectional and bidirectional versions of the antenna are presented. The proposed structure consists of a coplanar waveguide fed linear array of closely spaced capacitive transverse slots. This configuration results in a fast-wave structure in which the n=0 spatial harmonic radiates in the forward direction. Since the distance, d, between adjacent elements of the array is small d/spl Lt//spl lambda//sub o/, the slot array essentially becomes a uniform LWA. A comprehensive transmission line model is developed based upon the theory of truncated periodic transmission lines to explain the operation of the antenna and provide a tool for its design. Measured and simulated radiation patterns, directivity, gain, and an associated loss budget are presented for a 32-element antenna operating at 30 GHz. The uniplanar nature of the structure makes the antenna appropriate for integration of shunt variable capacitors such as diode or micro-electromechanical system varactors for fixed frequency beam steering at low-bias voltages.     

A slotted post-wall waveguide array with interdigital structure for 45/spl deg/ linear and dual polarization

This work proposes a dual-polarized planar antenna; two post-wall slotted waveguide arrays with orthogonal 45/spl deg/ linearly-polarized waves interdigitally share the aperture on a single layer substrate. Uniform excitation of the two-dimensional slot array is confirmed by experiment in the 25 GHz band. The isolation between two slot arrays is also investigated in terms of the relative displacement along the radiation waveguide axis in the interdigital structure. The isolation is 33.0 dB when the relative shift of slot position between the two arrays is -0.5/spl lambda//sub g/, while it is only 12.8 dB when there is no shift. The cross-polarization level in the far field is -25.2 dB for a -0.5/spl lambda//sub g/ shift, which is almost equal to that of the isolated single polarization array. It is degraded down to -9.6 dB when there is no shift.     

A 16-element two-dimensional active self-steering array using self-oscillating mixers

A 16-element two-dimensional (2-D) retrodirective array using self-oscillating mixers (SOMs) is presented. SOMs allow for easier implementation of larger 2-D arrays by eliminating the complex local-oscillator (LO) feed structure. A 4 /spl times/ 4 element retrodirective array using SOMs is demonstrated at an LO frequency of 7.68 GHz. Each element is phased locked at the LO frequency with an accompanying RF frequency isolation of 17.9 dB between adjacent horizontal elements and 22.2 dB between adjacent vertical elements. A -10-dBm external injection-locking signal is applied to reduce the phase noise of the 16-element array to -68.2 dBc/Hz at 10-kHz offset. Retrodirectivity is observed in the /spl phi/=0/spl deg/, /spl phi/=-45/spl deg/, and /spl phi/=-90 plane for scattering angles of /spl theta/=-15/spl deg/, /spl theta/=0/spl deg/, and /spl theta/=+30/spl deg/.     

InGaAs/InP DHBTs with 120-nm collector having simultaneously high f/sub /spl tau//, f/sub max//spl ges/450 GHz

InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors (DHBT) have been designed for increased bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 450 GHz f/sub /spl tau// and 490 GHz f/sub max/, which is the highest simultaneous f/sub /spl tau// and f/sub max/ for any HBT. The devices have been scaled vertically for reduced electron collector transit time and aggressively scaled laterally to minimize the base-collector capacitance associated with thinner collectors. The dc current gain /spl beta/ is /spl ap/ 40 and V/sub BR,CEO/=3.9 V. The devices operate up to 25 mW//spl mu/m/sup 2/ dissipation (failing at J/sub e/=10 mA//spl mu/m/sup 2/, V/sub ce/=2.5 V, /spl Delta/T/sub failure/=301 K) and there is no evidence of current blocking up to J/sub e//spl ges/12 mA//spl mu/m/sup 2/ at V/sub ce/=2.0 V from the base-collector grade. The devices reported here employ a 30-nm highly doped InGaAs base, and a 120-nm collector containing an InGaAs/InAlAs superlattice grade at the base-collector junction.     

Broadband 180/spl deg/ bit phase shifter using a /spl lambda//2 coupled line and parallel /spl lambda//8 stubs

In this paper, a broadband 180/spl deg/ bit phase shifter using a new switched-network was presented. The new network is composed of a /spl lambda//2 coupled line and parallel /spl lambda//8 open and short stubs, which are shunted at the edge points of a coupled line, respectively. According to a desired phase shift, it provides a controllable phase dispersive characteristic by the proper determination of Z/sub m/,Z/sub s/, and R values. The 180/spl deg/ bit phase shifter operated at 3 GHz was fabricated and experimented using design graphs which provide the required Z/sub m/,Z/sub s/ values, and I/O match and phase bandwidths. The experimental performances showed broadband characteristics.     

4H-SiC power bipolar junction transistor with a very low specific ON-resistance of 2.9 m/spl Omega//spl middot/cm/sup 2/

This letter reports a newly achieved best result on the specific ON-resistance (R/sub SP/spl I.bar/ON/) of power 4H-SiC bipolar junction transistors (BJTs). A 4H-SiC BJT based on a 12-/spl mu/m drift layer shows a record-low specific-ON resistance of only 2.9 m/spl Omega//spl middot/cm/sup 2/, with an open-base collector-to-emitter blocking voltage (V/sub ceo/) of 757 V, and a current gain of 18.8. The active area of this 4H-SiC BJT is 0.61 mm/sup 2/, and it has a fully interdigitated design. This high-performance 4H-SiC BJT conducts up to 5.24 A at a forward voltage drop of V/sub CE/=2.5 V, corresponding to a low R/sub SP-ON/ of 2.9 m/spl Omega//spl middot/cm/sup 2/ up to J/sub c/=859 A/cm/sup 2/. This is the lowest specific ON-resistance ever reported for high-power 4H-SiC BJTs.     

Development and analysis of a folded shorted-patch antenna with reduced size

The length of a wall-shorted rectangular patch antenna can be reduced from /spl sim//spl lambda//sub 0//4 to /spl sim//spl lambda//sub 0//8 by a simple folding operation, which results in a stacked shorted-patch (S-P) structure with a resonant frequency that can be controlled by modifying the distance between the stacked (lower and upper) shorted-patches. A theoretical analysis based on a simple transmission-line model is presented and compared with numerical simulations, showing good agreement if the height of the folded patch is much smaller than the patch length. The physical insight of the variation of the resonant frequency for this reduced-size antenna can be understood by considering the antenna as a shorted patch loaded with a capacitor. An experimental verification is carried out for a 15 mm/spl times/15 mm/spl times/6 mm folded S-P antenna prototype designed for the 2.4 GHz ISM band that can achieve a 10-dB return loss bandwidth of 4% and results in a nearly omni-directional radiation pattern.     

Entropy and the law of small numbers

Two new information-theoretic methods are introduced for establishing Poisson approximation inequalities. First, using only elementary information-theoretic techniques it is shown that, when S/sub n/=/spl Sigma//sub i=1//sup n/X/sub i/ is the sum of the (possibly dependent) binary random variables X/sub 1/,X/sub 2/,...,X/sub n/, with E(X/sub i/)=p/sub i/ and E(S/sub n/)=/spl lambda/, then D(P(S/sub n/)/spl par/Po(/spl lambda/)) /spl les//spl Sigma//sub i=1//sup n/p/sub i//sup 2/+[/spl Sigma//sub i=1//sup n/H(X/sub i/)-H(X/sub 1/,X/sub 2/,...,X/sub n/)] where D(P(S/sub n/)/spl par/Po(/spl lambda/)) is the relative entropy between the distribution of S/sub n/ and the Poisson (/spl lambda/) distribution. The first term in this bound measures the individual smallness of the X/sub i/ and the second term measures their dependence. A general method is outlined for obtaining corresponding bounds when approximating the distribution of a sum of general discrete random variables by an infinitely divisible distribution. Second, in the particular case when the X/sub i/ are independent, the following sharper bound is established: D(P(S/sub n/)/spl par/Po(/spl lambda/))/spl les/1//spl lambda/ /spl Sigma//sub i=1//sup n/ ((p/sub i//sup 3/)/(1-p/sub i/)) and it is also generalized to the case when the X/sub i/ are general integer-valued random variables. Its proof is based on the derivation of a subadditivity property for a new discrete version of the Fisher information, and uses a recent logarithmic Sobolev inequality for the Poisson distribution.     

Switched parasitic antenna on a finite ground plane with conductive sleeve

A switched parasitic monopole antenna on a finite ground structure with a conductive sleeve attached to a small, circular ground plane controls the vertical radiation direction. The antenna was designed using a genetic algorithm and finite element (FEM) solver. At 1.575 GHz, the constructed antenna exhibited a front to back ratio of 10.7 dB and gain of 6.4 dBi with no elevation from the horizontal. The switched parasitic nature of the antenna allowed it to steer a directional beam through 5 locations in the azimuth. Incremented from 0/spl lambda/ to 0.45/spl lambda/, the sleeve was observed to linearly depress the main lobe elevation with little influence on other antenna characteristics such as gain and S/sub 11/.     

High-responsivity high-gain In/sub 0.53/Ga/sub 0.47/As-InP quantum-well infrared photodetectors grown using metal-organic vapor phase epitaxy

We report the growth and fabrication of bound-to-bound In/sub 0.53/Ga/sub 0.47/As-InP quantum-well infrared photodetectors using metal-organic vapor phase epitaxy. These detectors have a peak detection wavelength of 8.5 /spl mu/m. The peak responsivities are extremely large with R/sub pk/=6.9 A/W at bias voltage V/sub b/=3.4 V and temperature T=10 K. These large responsivities arise from large detector gain that was found to be g/sub n/=82 at V/sub b/=3.8 V from dark current noise measurements at T=77 K and g/sub p/=18.4 at V/sub b/=3.4 V from photoresponse data at T=10 K. The background-limited temperature with F/1.2 optics is T/sub BLIP/=65 K for 0相似文献   

High responsivity InP-InGaAs quantum-well infrared photodetectors: characteristics and focal plane array performance

We report the detailed characteristics of long-wavelength infrared InP-In/sub 0.53/Ga/sub 0.47/As quantum-well infrared photodetectors (QWIPs) and 640/spl times/512 focal plane array (FPA) grown by molecular beam epitaxy. For reliable assessment of the detector performance, characterization was performed on test detectors of the same size and structure with the FPA pixels. Al/sub 0.27/Ga/sub 0.73/As-GaAs QWIPs with similar spectral response (/spl lambda//sub p/=/spl sim/7.8 /spl mu/m) were also fabricated and characterized for comparison. InP-InGaAs QWIPs (20-period) yielded quantum efficiency-gain product as high as 0.46 under -3-V bias with a 77-K peak detectivity above 1/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W. At 70 K, the detector performance is background limited with f/2 aperture up to /spl sim/ 3-V bias where the peak responsivity (2.9 A/W) is an order of magnitude higher than that of the AlGaAs-GaAs QWIP. The results show that impact ionization in similar InP-InGaAs QWIPs does not start until the average electric-field reaches /spl sim/25 kV/cm, and the detectivity remains high under moderately large bias, which yields high responsivity due to large photoconductive gain. The InP-InGaAs QWIP FPA offers reasonably low noise equivalent temperature difference (NETD) even with very short integration times (/spl tau/).70 K NETD values of the FPA with f/1.5 optics are 36 and 64 mK under bias voltages of -0.5 V (/spl tau/=11 ms) and -2 V (/spl tau/=650 /spl mu/s), respectively. The results clearly show the potential of InP-InGaAs QWIPs for thermal imaging applications requiring high responsivity and short integration times.