Analysis of two aperture-coupled cavity-backed antennas

The feasibility and performance of an aperture-coupled cavity-fed microstrip patch antenna and an aperture-coupled cavity antenna are demonstrated using reciprocity and moment method analyses, followed by practical design guidelines and equivalent circuit models. Each antenna incorporates a thick ground plane that can be useful as a heat sink for active MMIC circuitry and as structural support for thin substrates. Prototype antennas show good experimental agreement with the analyses in each case. The resonators of the aperture-coupled cavity-fed patch antenna are optimized to achieve a prototype having a measured 2:1 bandwidth of 26%. The size of the aperture-coupled cavity antenna can be easily reduced for array applications by filling the cavity with a dielectric material     

Surface-wave effect in a wideband aperture-coupled stackedmicrostrip antenna array

A wide band aperture coupled stacked microstrip antenna at the Ku band is described. The stacked element design achieves bandwidths in excess of 20%, but when incorporated into an array the gain bandwidth is reduced owing to surface wave excitation. Studying the nature of the surface wave interference can help reduce its impact, thereby retaining almost the full bandwidth of the single element     

A dual-band circularly polarized aperture-coupled stackedmicrostrip antenna for global positioning satellite

This paper describes the design and testing of an aperture-coupled circularly polarized antenna for Global Positioning System (GPS) applications. The antenna operates at both the L1 and L2 frequencies of 1575 and 1227 MHz, which is required for differential GPS systems in order to provide maximum positioning accuracy. Electrical performance, low-profile, and cost were equally important requirements for this antenna. The design procedure is discussed, and measured results are presented. Results from a manufacturing sensitivity analysis are also included     

Input impedance of aperture-coupled dielectric resonator antennas

Dielectric resonator antennas (DRAs) excited by a narrow-slot aperture in a conducting ground plane are analyzed using a numerical technique based upon a surface-integral equation formulation for bodies of revolution (BORs) coupled to non-BOR geometries. An efficient matrix-solution algorithm, together with a simple microstrip transmission-line model or a delta-source model are used to compute the antenna input impedance. Input impedances obtained with this technique show favorable agreement to those obtained via another numerical technique, as well as to those obtained by measurement     

Optically fed aperture-coupled microstrip patch antennas

Several techniques are presented for feeding microstrip antennas with RF-modulated lightwave signals via an optical fiber. Lightwave-to-RF conversion is performed in a module containing a photodiode, RF circuitry, and a microstrip antenna element. Three different transmitting configurations at microwave frequencies were designed and tested: passive matching, matching with amplification, and an injection-locked oscillator. In each case, the only connections to the antenna modules were an optical fiber and DC bias lines     

Performance of aperture-coupled dual-patch microstrip phased arrays

This paper presents an analysis of infinite phased arrays of aperture-coupled two-layer dual-patch microstrip antennas. The substrate layers for supporting the patches have the same dielectric constant and are separated by an airgap. The numerical model is based on the spectral-domain method of moments together with the Floquet theorem. Calculated results predict a 2:1 standing-wave ratio (SWR) bandwidth of 30-40% in a ±60° scan cone for arrays operating at around 4 GHz. Measured results from a waveguide simulator are obtained to verify the theoretical prediction     

Dielectric reflector backed aperture-coupled antennas for reduced back radiation

A new design using a dielectric reflector to reduce the back radiation of aperture coupled antennas is proposed and developed in this paper. To validate the proposed design, a concise theory analysis is first conducted and then the proposed design is analyzed in a modified aperture coupled microstrip antenna. In this design, a radiating patch and a microstrip feed line are both etched on the same side of a top substrate and a coupled slot is etched on the opposite side of this substrate. To examine the effect of the dielectric reflector on the antenna performance, theoretical simulations and experimental investigations were carried out, and a good agreement between the theoretical expectation and the measured results validates the proposed design. The measured radiation patterns show that the proposed structure can offer a high radiation efficiency, a high front to back radiation ratio, and a high co-cross polarization ratio. With these features, the proposed design is significant in the electromagnetic interference and electromagnetic compatibility (EMI/EMC) designs for reduced undesirable radiation.     

Design of aperture-coupled annular-ring microstrip antennas for circular polarization

The design of an aperture-coupled annular-ring microstrip antenna for circular polarization (CP) is presented. The CP radiation of the annular-ring microstrip antenna is achieved by a series microstrip-line-feed configuration through the coupling of a ring slot in the ground plane. The key parameters of the proposed design are investigated using a commercial simulation software based on the Method of Moments to show how to obtain the 50 /spl Omega/ input impedance and optimum axial ratio. The proposed design can be applied to the annular-ring microstrip antennas with different inner radii and substrate thickness, and several antenna prototypes are constructed and measured. Details of the experimental results of the CP performance are presented and discussed.     

Broadband dual-polarized aperture-coupled patch antennas withmodified H-shaped coupling slots

This paper presents a new design of aperture-coupled patch antennas with modified H-shaped coupling slots for achieving dual-polarization radiation with high isolation over a wide bandwidth. By using the proposed coupling slots, whose two upper side arms are bent inward with a proper angle, the isolation between the two feeding ports of the patch antenna can. greatly be improved, compared to the case with conventional H-shaped coupling slots. Also, when using a pair of modified H-shaped coupling slots for each feeding port, the isolation can further be improved; a high degree of isolation (< -34 dB) over the entire impedance bandwidth greater than 15% and good cross-polarization level (> 20 dB) for the two polarizations can be achieved. Details of the proposed design and experimental results are presented and discussed     

Theory of aperture-coupled hemispherical dielectric resonator antennas with radiating elements

A new approach based on hybrid volume-surface integral equation (VSIE) formulation in combination with spherical dyadic Green's function (DGF) is presented in this paper to analyze aperture-coupled multilayer hemispherical dielectric resonator antennas (DRA) with conformal conducting patches. Hybrid VSIE is used for the planar part of the structure and is solved with the aid of spatial-domain method of moments (MoM) in order to compute magnetic surface current in a slot cut in a finite planar perfect electric conductor (PEC) sheet. Multilayer spherical electromagnetic DGFs are used to compute loading effects of hemispherical dielectric resonators and conformal patches on antenna characteristics. The effects of variation in some parameters of the structure on the return loss of the antenna are studied. Accuracy of the presented method is validated by comparing the results obtained from the proposed method with those of CAD simulations.     

对数周期偶极天线扇形阵的分析

采用矩量法对对数周期偶极天线扇形阵进行理论分析，在计算广义阻抗矩阵元素时，利用矩阵的互易性、天线阵的结构对称性和对数周期天线的工作原理进行了算法简化，从而在保证计算精度的前提下，大大提高了计算速度。     

Analysis and design of aperture-coupled microstrip patch antennasand arrays fed by dielectric image line

This paper presents the analysis and design of aperture-coupled microstrip patch antennas and arrays fed by an dielectric image line. A theory based on the cavity model of the microstrip patch antenna and the change in the modal voltage of the image line at the aperture was developed to analyze the single element aperture-coupled microstrip patch antenna. The theory developed was combined with the array theory to design linear traveling wave arrays at X-band and Ka-band frequencies. The required taper in the excitations of the individual patches of the array was achieved by varying the aperture dimensions. Experiments show very good results for the antennas and the arrays     

Structure of arrays of ultrawideband combined antennas

The results of experimental investigations and calculations of the energy characteristics of four-element arrays of combined antennas excited by a single generator of bipolar voltage pulses with a duration of 1 ns through a power divider are presented. Based on the proposed criteria, the optimum structure of arrays is determined.     

Influence of residual air gaps on characteristics of circularly polarised aperture-coupled millimetre-wave microstrip antennas

The influence of residual air gaps located between the two substrates of aperture-coupled printed antennas is investigated theoretically and experimentally in the 60 GHz band. It is shown that the input impedance and the axial ratio of thin-film circular polarisation patches and arrays are strongly altered by small gaps a few micrometres thick. An alternative configuration, comprising two ground planes and compatible with photolithographic processes, is then proposed to overcome this drawback.     

Microstrip antennas and arrays on chiral substrates

Results are presented for isolated microstrip antennas and infinite arrays of microstrip antennas printed on chiral substrates, computed from full-wave spectral domain moment method solutions. Data for resonant length, impedance, directivity, efficiency, cross-polarization level, and scan performance are compared to results obtained for a dielectric substrate of the same thickness and permittivity. It is concluded that, from the point of view of antenna characteristics, there does not seem to be any advantage to using chiral antenna substrates, while there are disadvantages in terms of increased cross-polarization levels and losses due to surface wave excitation     

Conformal microstrip antennas and microstrip phased arrays

A new class of antennas using microstrips to form the feed networks and radiators is presented in this communication. These antennas have four distinct advantages: 1) cost, 2) performance, 3) ease of installation, and 4) the low profile conformal design. The application of these antennas is limited to small bandwidths. Phased arrays using these techniques are also discussed.     

Constrained beam scanning for linear arrays of antennas

A method to scan the radiation pattern of a linear array, simultaneously reducing the pattern amplitude in constant directions, is described. The scanning process is obtained by phase control of the array excitations and, if necessary, by amplitude perturbations not exceeding a small threshold.     

Supergain antennas and the Yagi and circular arrays

The characteristics of endfire, Yagi, and circular arrays of dipoles are reviewed with special reference to their directional properties and the possibility of supergain. The quantum-mechanical analog that suggested the investigation is described. The critical newly emphasized feature is the high-Q property of a correctly designed closed loop of coplanar dipoles when only one element is driven and all dimensions (the length of the elements, their cross-sectional size and shape, the number of elements, and the circumference of the closed loop array) are correctly chosen so that the entire array is adjusted to resonance. An immediate application to beam scanning is described     

Analysis of aperture-coupled microstrip antenna using cavity method

Presents an original analysis of aperture coupling of a microstrip antenna. The theory is based on the cavity model, and results are compared with the moment method and measurement.<>     

Mutual coupling in phased arrays of randomly spaced antennas

Mutual coupling effects in phased arrays with randomly located elements are studied. The network formulation of antenna arrays is found to be a convenient and useful approximation. Two main effects of coupling are separately considered. The first is the increase in the sidelobe level. A new solution for the distribution of sidelobe level has been obtained which is applicable even for small arrays. It is found that the increase in sidelobe level is noticeable only for small average spacing (e.g., less than 2.5 wavelengths). The second effect of coupling is that it causes the fluctuation of main-beam amplitude as a function of the scan angle. The probabilistic properties of these fluctuations are studied. In the uniformly spaced arrays the accumulation of coupling effects may cause "blind angles". In random arrays this accumulation is highly improbable. This method of removing blind angles is further illustrated by an experiment on diffraction gratings where Wood's anomalies and blind angles are recognized as identical phenomena. Finally, an important contribution of this investigation is the analysis by various methods of the radiation pattern of random array. The results obtained by these methods agree remarkably well with the Monte Carlo simulations.