Showing papers in "IEEE Transactions on Antennas and Propagation in 2001"
TL;DR: This paper presents a novel single-patch wide-band microstrip antenna: the E-shaped patch antenna, where two parallel slots are incorporated into the patch of a micro Strip antenna to expand it bandwidth.
Abstract: This paper presents a novel single-patch wide-band microstrip antenna: the E-shaped patch antenna. Two parallel slots are incorporated into the patch of a microstrip antenna to expand it bandwidth. The wide-band mechanism is explored by investigating the behavior of the currents on the patch. The slot length, width, and position are optimized to achieve a wide bandwidth. The validity of the design concept is demonstrated by two examples with 21.2% and 32.3% bandwidths. Finally, a 30.3% E-shaped patch antenna, resonating at wireless communication frequencies of 1.9 and 2.4 GHz, is designed, fabricated and measured. The radiation pattern and directivity are also presented.
989 citations
TL;DR: In this paper, a multilayer reflectarray composed of two stacked arrays with rectangular patches of variable size is demonstrated, and a progressive phase distribution on the reflector surface is achieved by adjusting the dimensions of the patches.
Abstract: A multilayer reflectarray composed of two stacked arrays with rectangular patches of variable size is demonstrated. A progressive phase distribution on the reflector surface is achieved by adjusting the dimensions of the patches. The phase of the reflection coefficient at each element is computed by the method of moments in the spectral domain, assuming local periodicity. A technique is presented for the design of dual polarization reflectarrays that yields all the dimensions for the photo-etching mask. A prototype has been design, built and measured, and a superior bandwidth performance has been verified, compared to conventional single layer reflectarrays.
613 citations
TL;DR: In this paper, a 1:1.5 VSWR was achieved at operating frequencies around 2 GHz, which is nearly ten times that of a conventional microstrip-line-fed printed wide-slot antenna.
Abstract: Printed wide-slot antennas fed by a microstrip line with a fork-like tuning stub for bandwidth enhancement are proposed and experimentally investigated. Both the impedance and radiation characteristics of this antenna are studied. Experimental results indicate that a 1:1.5 VSWR bandwidth of 1 GHz is achieved at operating frequencies around 2 GHz, which is nearly ten times that of a conventional microstrip-line-fed printed wide-slot antenna. It also achieved a 2-dB gain bandwidth of at least 0.5 GHz.
525 citations
TL;DR: In this article, the authors examined the antenna diversity configurations that improve the performance of handheld radios in line-of-sight (LOS) and obstructed outdoor and indoor multipath channels that experienced Ricean fading.
Abstract: This paper examines the antenna diversity configurations that improve the performance in handheld radios. Experiments using spatial, polarization, and pattern diversity were conducted for both line-of-sight (LOS) and obstructed outdoor and indoor multipath channels that experienced Ricean fading. Antenna separation, polarization, and pattern were varied independently to the extent possible. Envelope correlation, power imbalance, and diversity gain were calculated from the measurements. Diversity performance is measured by diversity gain, which is the difference in signal-to-noise ratio (SNR) between the output of a diversity combiner and the signal on a single branch, measured at a given probability level. Diversity gain increases with decreasing envelope correlation between the antenna diversity branches. However, diversity gain decreases as the power imbalance between diversity branches increases because a branch that has a weak signal has only a small contribution to the combined signal. Diversity gain values of 7-9 dB at the 99% reliability level were achieved in non-line-of-sight (NLOS) channels for all diversity configurations even with very small antenna spacings. The use of polarization diversity reduced polarization mismatches, improving SNR by up to 12 dB even in LOS channels.
465 citations
TL;DR: In this article, the authors present a model of the longwave atmospheric spectrum that improves in many respects widely used older models such as the microwave propagation model (MPM), since it is based on broadband measurements and calculations.
Abstract: We present a model of the longwave atmospheric spectrum that improves in many respects widely used older models such as the microwave propagation model (MPM), since it is based on broadband measurements and calculations. According to our data, the model is fully applicable from 0 to 2 THz while including lines up to 10 THz. Its primary goal is to simulate the millimeter/submillimeter region accessible from the ground (frequencies up to /spl sim/2 THz at most, with a few windows between 1 and 2 THz accessible only under exceptional conditions at very dry sites). Line-by-line calculations of the absorption are performed using a line database generated from the latest available spectroscopic constants for all relevant atmospheric species. The collisional line widths are obtained from published laboratory data. The excess of absorption in the longwave range that cannot be explained by the line spectrum is modeled by introducing two different continuum-like terms based on FTS measurements between 170 and 1100 GHz: collision-induced absorption of the dry atmosphere due to transient dipoles in symmetric molecules (N/sub 2/ and O/sub 2/) and continuum-like water vapor opacity. All H/sub 2/O lines up to 10 THz are included in order to correctly account for the entire H/sub 2/O far-wing opacity below 2 THz for a given line-shape. Hence, this contribution does not need to be part of a pseudocontinuum term below that frequency cutoff (still necessary, as shown in this paper) in contrast to other models used to date. Phase delays near H/sub 2/O and O/sub 2/ resonances are also important for ground-based astronomy since they affect interferometric phase. The frequency-dependent dispersive phase delay function is formally related to the absorption line shape via the Kramers-Kronig dispersion theory, and this relation has been used for modeling those delays. Precise calculations of phase delays are essential for the future Atacama large millimeter array (ALMA) project. A software package called atmospheric transmission at microwaves (ATM) has been developed to provide the radioastronomy and aeronomy communities with an updated tool to compute the atmospheric spectrum in clear-sky conditions for various scientific applications. We use this model to provide detailed simulations of atmospheric transmission and phase dispersion for several sites suitable for submillimeter astronomy.
447 citations
TL;DR: In this paper, a broadband probe-fed rectangular patch antenna with a pair of wide slits is proposed and experimentally studied, and the proposed antenna can have an impedance bandwidth of about 24%.
Abstract: A new broad-band design of a probe-fed rectangular patch antenna with a pair of wide slits is proposed and experimentally studied. The proposed design is with an air substrate, and experimental results show that, simply by inserting a pair of wide slits at one of the radiating edges of the rectangular patch, good impedance matching over a wide bandwidth can easily be achieved for the proposed antenna. With an air substrate of thickness about 8% of the wavelength of the center operating frequency, the proposed antenna can have an impedance bandwidth of about 24%. For frequencies within the impedance bandwidth, good radiation characteristics are also observed, with a peak antenna gain of about 7.2 dBi.
303 citations
TL;DR: A compact integrated antenna that has two feed ports with more than 20 dB isolation between them that can be utilized in compact wireless communication handsets to provide diversity signals or act as a duplexer allowing the receive and transmit signals to be well isolated.
Abstract: We introduce a compact integrated antenna that has two feed ports with more than 20 dB isolation between them. The significance of the design is that it can be utilized in compact wireless communication handsets to provide diversity signals or act as a duplexer allowing the receive and transmit signals to be well isolated. The antenna design is based on merging two patch antennas together in combination with capacitive loading so that a compact design can be obtained. Justification for the design is provided by considering the mutual coupling using the reaction principle and finite-dimensional time-domain (FDTD) simulations. Experimental results are also presented for a design that operates in the 2100-2200 MHz band for possible application in forthcoming third-generation wireless systems. Results include radiation patterns, S-parameters, and signal correlations between ports so that the diversity performance and isolation characteristics of the antenna can be demonstrated. These show that in typical wireless environments envelope cross correlations of less than 0.1 between the ports are obtained.
267 citations
TL;DR: In this article, a compact circular-polarization (CP) operation of the square microstrip antenna with four slits and a pair of truncated corners is proposed and investigated.
Abstract: A novel compact circular-polarization (CP) operation of the square microstrip antenna with four slits and a pair of truncated corners is proposed and investigated. Experimental results show that the proposed compact CP design can have an antenna-size reduction of about 36% as compared to the conventional corner-truncated square microstrip antenna at a given operating frequency. Also, the required size of the truncated corners for CP operation is much greater than that for the conventional CP design using a simple square microstrip patch, providing a relaxed manufacturing tolerance for the proposed compact CP design. Details of the experimental results are presented and discussed.
253 citations
TL;DR: In this article, a single-feed dual-band circular polarization (CP) radiation was obtained by inserting four T-shaped slits at the patch edges of a square microstrip antenna.
Abstract: New designs of obtaining dual-band circular polarization (CP) radiation of a single-feed square microstrip antenna are proposed and experimentally studied. The proposed single-feed dual-band CP designs are achieved by inserting four T-shaped slits at the patch edges or four Y-shaped slits at the patch corners of a square microstrip antenna. From experiments conducted, a patch size reduction as large as 36% for the proposed design, compared to a conventional CP design without the inserted slits, has been obtained. Details of the design considerations of the proposed antennas are described, and experimental results of the obtained dual-band CP performances are presented and discussed.
237 citations
TL;DR: This paper describes the design and testing of a prototype dual-band dual-polarized planar array operating at L- and X-bands, featuring low mass, high efficiency, and limited beam scanning.
Abstract: This paper describes the design and testing of a prototype dual-band dual-polarized planar array operating at L- and X-bands. The primary objectives were to develop new antenna technology with dual-band and dual-polarization capability in a shared aperture, featuring low mass, high efficiency, and limited beam scanning. The design of a prototype planar microstrip array of 2/spl times/2 L-band elements interleaved with an array of 12/spl times/16 X-band elements that meets these requirements is discussed in detail and measured results are presented. The array is modular in form and can easily be scaled to larger aperture sizes.
200 citations
TL;DR: A direct data domain (D/sup 3/) least-squares space-time adaptive processing (STAP) approach is presented for adaptively enhancing signals in a nonhomogeneous environment to detect a Sabreliner in the presence of urban, land, and sea clutter.
Abstract: A direct data domain (D/sup 3/) least-squares space-time adaptive processing (STAP) approach is presented for adaptively enhancing signals in a nonhomogeneous environment. The nonhomogeneous environment may consist of nonstationary clutter and could include blinking jammers. The D/sup 3/ approach is applied to data collected by an antenna array utilizing space and in time (Doppler) diversity. Conventional STAP generally utilizes statistical methodologies based on estimating a covariance matrix of the interference using data from secondary range cells. As the results are derived from ensemble averages, one filter (optimum in a probabilistic sense) is obtained for the operational environment, assumed to be wide sense stationary. However for highly transient and inhomogeneous environments the conventional statistical methodology is difficult to apply. Hence, the D/sup 3/ method is presented as it analyzes the data in space and time over each range cell separately. The D/sup 3/ method is deterministic in approach. From an operational standpoint, an optimum method could be a combination of these two diverse methodologies. This paper represents several new D/sup 3/ approaches. One is based on the computation of a generalized eigenvalue for the signal strength and the others are based on the solution of a set of block Hankel matrix equations. Since the matrix of the system of equations to be solved has a block Hankel structure, the conjugate gradient method and the fast Fourier transform (FFT) can be utilized for efficient solution of the adaptive problem. Illustrative examples presented in this paper use measured data from the multichannel airborne radar measurements (MCARM) database to detect a Sabreliner in the presence of urban, land, and sea clutter. An added advantage for the D/sup 3/ method in solving real-life problems is that simultaneously many realizations can be obtained for the same solution for the signal of interest (SOI). The degree of variability amongst the different results can provide a confidence level of the processed results. The D/sup 3/ method may also be used for mobile communications.
TL;DR: In this article, the effects of geometric parameters on the characteristics of the L-probe patch antenna are extensively studied and the variation of input impedance at resonance with different geometric parameters is plotted on a Smith chart.
Abstract: In this paper, the finite-difference time-domain (FDTD) method is employed to analyze L-probe proximity-fed rectangular patch antennas. Numerical results for the input impedance, co- and cross-polarization radiation patterns are presented and compared with the measurements. Good agreement between the computed and measured results is obtained. The effects of geometric parameters on the characteristics of the L-probe patch antenna are extensively studied. For design purposes, the variation of input impedance at resonance with different geometric parameters is plotted on a Smith chart. Mutual coupling between two L-probe patch antennas is also investigated.
TL;DR: In this article, the authors used the finite difference time-domain (FDTD) method to calculate the electric field distribution in the slot cut in the outer conductor of the coaxial cable.
Abstract: Frequency band and coupling loss are the two important parameters of leaky coaxial cables with periodic slots. The frequency band can be predicted by analyzing the arrangement of the slots on the outer shield of the cable, but the coupling loss is not so easy to determine by classical methods. In this paper, the finite-difference time-domain (FDTD) method is used to calculate the electric field distribution in the slot cut in the outer conductor of the coaxial cable. The dyadic Green's function is then used to calculate the radiation field of the equivalent surface magnetic current densities. By these two methods, the coupling losses of the leaky coaxial cables with different periods, sizes and shapes of the slots can be accurately obtained. Some results in this paper were verified by the experimental results of leaky coaxial cables designed for railway mobile communications with a frequency band of 100-500 MHz.
TL;DR: In this paper, the authors defined the characteristics of wideband indoor radio channel at 5.3 GHz based on an extensive measurement campaign using a wideband channel sounder with 19 ns delay resolution.
Abstract: Characteristics of wideband indoor radio channel at 5.3 GHz were defined based on an extensive measurement campaign using a wideband channel sounder with 19 ns delay resolution. Pathloss exponents were 1.3-1.5 in LOS and 2.9-4.8 in non-line of sight (NLOS). Large difference in NLOS exponents was due to different dominating propagation mechanisms in different types of building structures. The delay dispersion was characterized by cumulative distribution functions (CDF) of the RMS delay spreads, the values for CDF=0.9 varied from 20 to 180 ns in different setups in an office building and large hall environments. The correlation functions of the radio channel in spatial and frequency domains were extracted. Small scale models for five typical indoor scenarios were developed using tapped delay lines.
TL;DR: In this paper, a perfectly matched layer (PML) medium with complex frequency shifted (CFS) constitutive parameters is introduced for the three-dimensional alternating direction implicit (ADI) formulation of the finite-difference time-domain (FDTD) method.
Abstract: A perfectly matched layer (PML) medium with complex frequency shifted (CFS) constitutive parameters is introduced for the three-dimensional alternating direction implicit (ADI) formulation of the finite-difference time-domain (FDTD) method. The absorbing boundary is implemented using the convolutional PML (CPML) approach. It is demonstrated that the resulting ADI-CPML scheme is unconditionally stable. The effectiveness of the absorbing medium as a function of the time step is also demonstrated. The proposed method has the advantage that it allows the application of the ADI method to low-frequency analysis.
TL;DR: In this paper, a GA with adaptive cost function is implemented to obtain the optimal design of a non-uniform Luneburg (1964) lens antenna, where the GA optimizer simultaneously determines the optimal material and its thickness for each shell by controlling the gain and sidelobes envelope of the radiation pattern.
Abstract: Design optimization of radially nonuniform spherical lens antennas is the focus of this paper. In particular, special attention is given to the optimal design of nonuniform Luneburg (1964) lens antennas. One of the important engineering objectives of designing an optimal Luneburg lens antenna is to use as small number of shells as possible while maintaining an acceptable gain and sidelobe performance. In a typical radially uniform design, by reducing the number of shells, the gain is decreased and the grating lobes are increased. This deficiency in the radiation performance of the uniform lens antenna can be overcome by designing the nonuniform lens antenna. This necessitates the optimum selection of each layer thickness and permittivity. A genetic algorithm (GA) optimizer with adaptive cost function is implemented to obtain the optimal design. In this manner, the GA optimizer simultaneously determines the optimal material and its thickness for each shell by controlling the gain and sidelobes envelope of the radiation pattern. Various lens geometries, including air gaps and feed offset from the lens surface, are analyzed by using the dyadic Green's functions of the multilayered dielectric sphere. Many useful engineering design guidelines have been suggested for the optimum construction of the lens. The results have been satisfactory and demonstrate the utility of the GA/adaptive cost-function algorithm. Additionally, the radiation characteristics of a novel two-shell lens antenna have been studied, and its performance is compared to the Luneburg lens.
TL;DR: In this article, a circular microstrip antenna with dual capacitively coupled feeds for broad-band circular polarization radiation is presented, which can provide an impedance bandwidth (VSWR /spl les/2) of about 49% and a 3-dB axial-ratio bandwidth of about 35%.
Abstract: New design of a circular microstrip antenna with dual capacitively coupled feeds for broad-band circular polarization radiation is presented. The dual feeds are with a small top-loaded disk and are connected to a Wilkinson power divider with a 90/spl deg/ phase shift between its two output feedlines. The radiating circular patch, printed on a thin substrate, is supported by nonconducting posts on a conducting ground plane and is excited capacitively through the dual feeds. With a distance less than 10% times the center operating wavelength between the circular patch and the ground plane, the present proposed antenna can provide an impedance bandwidth (VSWR /spl les/2) of about 49% and a 3-dB axial-ratio bandwidth of about 35%. The antenna gain bandwidth, defined to be within 1-dB gain variation in the axial-ratio bandwidth, is as large as 28%, with the antenna gain level at about 7.0 dBi.
TL;DR: In this paper, the impedance of a rectangular patch antenna fed by an inset microstrip transmission line was measured for various feed positions and the dependence found was then compared to theoretical predictions both for this geometry and for the similar case of an INSET coaxial probe feed.
Abstract: The impedance of a rectangular patch antenna fed by an inset microstrip transmission line was measured for various feed positions. The dependence found was then compared to theoretical predictions both for this geometry and for the similar case of an inset coaxial probe feed.
TL;DR: In this article, an improved analytical model is presented for calculating the resonant frequency of circular microstrip antennas with and without air gaps, which is widely applicable to all patch diameters-from very large to very small compared to the height of the dielectric medium below the patch.
Abstract: An improved analytical model is presented for calculating the resonant frequency of circular microstrip antennas with and without air gaps. Unlike the previous models, the present one is widely applicable to all patch diameters-from very large to very small compared to the height of the dielectric medium below the patch and also to the substrates covering the entire range of dielectric constants. The computed results for different antenna dimensions and modes of resonance are compared with the experimental values.
TL;DR: In this article, a new set of fractal multiband antennas called mod-p Sierpinski gaskets is presented, which derive from the Pascal triangle and present a log-periodic behavior, which is a consequence of their selfsimilarity properties.
Abstract: A new set of fractal multiband antennas called mod-p Sierpinski gaskets is presented. Mod-p Sierpinski fractal antennas derive from the Pascal triangle and present a log-periodic behavior, which is a consequence of their self-similarity properties. Mod-p Sierpinski fractal antennas constitute a generalization of the classical Sierpinski antenna.
TL;DR: The simultaneous optimization of the partition in subarrays and the subarray weights is reported, which allows the same array also to generate a difference pattern, with minimal alteration of the signal feed circuitry.
Abstract: Given a linear antenna array with an excitation distribution affording a sum pattern, subarray weighting allows the same array also to generate a difference pattern, with minimal alteration of the signal feed circuitry. Previous implementations of this approach have optimized the weights of given subarrays. Here we report the simultaneous optimization of the partition in subarrays and the subarray weights.
TL;DR: In this article, a relatively fast and simple method utilizing Gaussian beams (GBs) is developed which requires only a few seconds on a workstation to compute the near/far fields of electrically large reflector antennas when they are illuminated by a feed with a known radiation pattern.
Abstract: A relatively fast and simple method utilizing Gaussian beams (GBs) is developed which requires only a few seconds on a workstation to compute the near/far fields of electrically large reflector antennas when they are illuminated by a feed with a known radiation pattern. This GB technique is fast, because it completely avoids any numerical integration on the large reflector surface which is required in the conventional physical optics (PO) analysis of such antennas and which could take several hours on a workstation. Specifically, the known feed radiation field is represented by a set of relatively few, rotationally symmetric GBs that are launched radially out from the feed plane and with almost identical interbeam angular spacing. These GBs strike the reflector surface from where they are reflected, and also diffracted by the reflector edge; the expressions for the fields reflected and diffracted by the reflector illuminated with a general astigmatic incident GB from an arbitrary direction (but not close to grazing on the reflector) have been developed in Chou and Pathak (1997) and utilized in this work. Numerical results are presented to illustrate the versatility, accuracy, and efficiency of this GB method when it is used for analyzing general offset parabolic reflectors with a single feed or an array feed, as well as for analyzing nonparabolic reflectors such as those described by ellipsoidal and even general shaped surfaces.
TL;DR: In this article, the surface wave properties of printed circuit antennas on planar artificial periodic (photonic bandgap) structures were investigated and an integral-equation moment method in conjunction with an analytical array scanning scheme was applied to the boundary value problem associated with source interaction with infinite periodic structures.
Abstract: The characteristics of surface waves from a Hertzian (elementary) dipole on a multilayer structure with planar periodic material elements are investigated. An integral-equation moment method in conjunction with an analytical array scanning scheme is applied to the boundary-value problem associated with source interaction with infinite periodic structures. A pole-extraction technique and the saddle-point method are applied to find the far-zone periodic surface waves due to a current source. The investigation provides a fundamental study of surface wave properties of printed circuit antennas on planar artificial periodic (photonic bandgap) structures. It is found from the power patterns that surface waves are suppressed in the directions with wave bandgap and greatly enhanced in the directions just outside the bandgap zones. The surface wave pattern may be highly directive and the beam angle varies with frequencies. The finding suggests possible frequency-space selection devices. Experiments are carried out to validate the surface wave bandgap phenomenon and the beam angle frequency-selection property.
TL;DR: In this article, a new method to determine the reflection of substrate modes in finite substrate planar circuits is proposed, where the perfectly matched layer (PML) concept is used to transform the open problem into a closed one and the discrete set of substrate, evanescent, and Berenger modes of the resulting anisotropic waveguides are then used in a mode-matching scheme to deduce the scattering coefficients of the substrate modes for oblique incidence on the edge of substrate.
Abstract: A new method to determine the reflection of substrate modes in finite substrate planar circuits is proposed. The perfectly matched layer (PML) concept is used to transform the open problem into a closed one. The discrete set of substrate, evanescent, and Berenger modes of the resulting anisotropic waveguides are then used in a mode-matching scheme to deduce the scattering coefficients of the substrate modes for oblique incidence on the edge of the substrate. We show results for single- and double-layered substrates and compare with finite-difference time-domain (FDTD) results. The combined perfectly matched layer (PML) mode-matching technique turns out to be very efficient.
TL;DR: In this paper, a simple diffuse scattering model based on a ray approach suitable for urban radio propagation is presented, arranged so that the main parameters, having precise physical meaning, can be easily tuned using measurement results.
Abstract: A novel, simple diffuse scattering model based on a ray approach suitable for urban radio propagation is presented. The scattering model is arranged so that the main parameters, having a precise physical meaning, can be easily tuned using measurement results. The model is tested against 900-MHz measurements and the scattering contribution is shown to be important for both received power and channel dispersion in a typical microcellular case.
TL;DR: In this paper, the authors describe the development and performance of a wideband dual linear polarization microstrip antenna array used in the Danish high-resolution airborne multifrequency polarimetric synthetic aperture radar, EMISAR.
Abstract: This paper describes the development and performance of a wideband dual linear polarization microstrip antenna array used in the Danish high-resolution airborne multifrequency polarimetric synthetic aperture radar, EMISAR. The antenna was designed for an operating frequency of 1.25 GHz/spl plusmn/50 MHz and was built as an array of 8/spl times/2 probe-fed stacked microstrip patches. The feeding network is constructed in microstrip and is capable of handling 6 kW of peak input-power at an altitude of 45000 ft (unpressurized). The impedance bandwidth (return loss better than -14 dB) of the antenna is 10%, the isolation between the horizontal and the vertical ports of the array is 50 dB and the cross-polarization suppression is 40 dB. A new design principle for simultaneously achieving very low cross-polarization and low side lobes in dual linear polarization antenna arrays has been applied.
TL;DR: In this article, a hybridization of the finite element and boundary integral methods is presented for an efficient and accurate numerical analysis of electromagnetic scattering and radiation problems, which is free of interior resonance and produces a purely sparse system matrix, which can be solved very efficiently.
Abstract: A novel hybridization of the finite element (FE) and boundary integral methods is presented for an efficient and accurate numerical analysis of electromagnetic scattering and radiation problems. The proposed method derives an adaptive numerical absorbing boundary condition (ABC) for the finite element solution based on boundary integral equations. Unlike the standard finite element-boundary integral approach, the proposed method is free of interior resonance and produces a purely sparse system matrix, which can be solved very efficiently. Unlike the traditional finite element-absorbing boundary condition approach, the proposed method uses an arbitrarily shaped truncation boundary placed very close to the scatterer/radiator to minimize the computational domain; and more importantly, the method produces a solution that converges to the true solution of the problem. To demonstrate its great potential, the proposed method is implemented using higher order curvilinear vector elements. A mixed functional is designed to yield both electric and magnetic fields on an integration surface, without numerical differentiation, to be used in the calculation of the adaptive ABC. The required evaluation of boundary integrals is carried out using the multilevel fast multipole algorithm, which greatly reduces both the memory requirement and CPU time. The finite element equations are solved efficiently using the multifrontal algorithm. A mathematical analysis is conducted to study the convergence of the method. Finally, a number of numerical examples are given to illustrate its accuracy and efficiency.
TL;DR: In this article, a maximum likelihood algorithm is used to minimize the number of measurements, thus reducing the impact on the system and shifting the overhead to a remote site, which reduces the overhead.
Abstract: Calibration of a phased array antenna while the antenna is in service can be a complex and time-consuming procedure that affects use of the antenna and imposes an unacceptable overhead on the system. The procedure described herein uses a maximum likelihood algorithm to minimize the number of measurements, thus reducing the impact on the system and shifting the overhead to a remote site.
TL;DR: In this article, the authors examined the performance of an electromagnetic band-gap structure (also known as photonic bandgap), which is purely metallic and infinitely periodic in two dimensions with a finite periodicity in the third dimension.
Abstract: This paper examines the performance of an electromagnetic band-gap structure (also known as photonic band-gap). The structure is purely metallic and infinitely periodic in two dimensions with a finite periodicity in the third dimension. An effective band-gap exists when within a certain frequency range, the reflection is 100% for all angles of incidence and all polarizations. The performance of the structure is explained from a physical point of view by isolating the effects of each parameter of the structure. Cascading two periodic arrays with a very small separation distance gives a capacitance effect for the overlap region. The capacitance is shown to control the lower edge of the band-gap. Cascading more closely coupled periodic arrays gives a rejection band, with the separation controlling the upper edge of the band. An effective band-gap is shown to exist when different layers are connected with vias. The structure examined in this paper has an effective band-gap from 30 GHz to 100 GHz. The calculations are performed using the method of moments (MoM) to solve an integral equation with the periodic Green's function as its kernel. The computations are extensive because they involve double infinite summations. A customized Z-matrix interpolation scheme is, therefore, used to speed the total calculation time, without sacrificing accuracy.
TL;DR: In this paper, the effect of etched grooves around a patch element has been studied for performance improvement, and effective dielectric constant curves for the shielded micromachined substrates are provided for accurate design of patch antennas.
Abstract: Silicon micromachining has been used to demonstrate the possibility of building high performance microwave and millimeter-wave antennas. To suppress higher order substrate modes and increase the bandwidth of a patch antenna, silicon substrate has been used and material has been selectively removed under the patch area. In addition, the effect of etched grooves around a patch element has been studied for performance improvement, it has been shown that micromachined substrate structure can effectively suppress unwanted surface wave modes resulting in improved radiation efficiency. Moreover, effective dielectric constant curves for the shielded micromachined substrates are provided for accurate design of patch antennas. We have demonstrated that mutual coupling between the radiating patch elements due to surface waves can be controlled using various micromachined substrate configurations.