Missile base mounted microstrip antennas

Proof of the feasibility of aft mounting low-profile antennas on reentry vehicles is presented. This is an application of state of the art antenna hardware. Aft mounting presents the best reentry environment to antenna hardware, and its practicality has been demonstrated. Microstrip antenna principles can be used to produce very rugged antennas. Their low profile reduces many interface, mechanical, and survival problems. The pattern coverage for these vehicles must be toward the fore direction. This type of pattern requires an interaction between the vehicle and the antenna when the antenna is effectively shadowed from that direction. This paper describes the results obtained by actual experimental hardware. Contoured elements were used, as were foreshortened elements. These elements demonstrated ability to be fit around other aft equipment. The versatility of these elements were further demonstrated by tailoring them for two different types of coverage to accommodate different vehicle operational requirements.     

Hybrid-coupled shorted rectangular microstrip antennas

Hybrid-coupled (both gap and direct) shorted rectangular microstrip antennas have been investigated. Only one patch is fed and the other patch is parasitically coupled along the radiating and the non-radiating edges, respectively. Dual frequency and broadband operation has been obtained by optimising the coupling between the two patches through a copper strip     

H-plane coupling between rectangular microstrip antennas

A new model that theoretically characterises mutual coupling effects between two rectangular microstrip antennas is presented. Numerical S-parameter results exhibiting mutual coupling effects are reported.     

Mutual coupling between cylindrical rectangular microstrip antennas

The effect of curvature and separation on the mutual coupling between probe feed rectangular microstrip antennas printed on a cylindrical surface is studied theoretically and experimentally. To incorporate the interactions between patches through the space wave as well as the surface wave, the rigorous spectral domain approach is adopted. The experiment is performed for the purpose of validation of the theoretical results     

Surface wave losses of rectangular microstrip antennas

A closed-form expression is presented for the space wave efficiency of rectangular microstrip antennas. This expression is derived from and compared to numerical results available in the literature. The expression is useful for substrates with relative permittivities between 1 and 12.8 and for the complete range of thicknesses normally used.<>     

E-plane coupling between two rectangular microstrip antennas

A model which theoretically characterises end coupling (E-plane coupling) between two rectangular microstrip antennas is discussed. Computer generated S-parameter results for this particular type of mutual coupling are presented.     

A reciprocity approach for calculating radiation patterns of arbitrarily shaped microstrip antennas mounted on circularly cylindrical platforms

The paper presents a convenient and efficient approach, based on the reciprocity theorem, for calculating the radiation patterns of arbitrarily shaped microstrip antennas with dielectric substrate and superstrate layers mounted on circularly cylindrical platforms. A detailed theoretical development followed by examples with numerical and graphical results illustrate the versatility of the technique. The reciprocity approach presented is very flexible and may be used in conjunction with any of the commonly employed computational electromagnetics modeling approaches such as the method of moments, finite-element methods, and finite-difference time-domain techniques.     

Radiation patterns in far field from two H-plane coupled rectangular microstrip antennas

Numerically determined far-field radiation patterns are found for H-plane mutual coupling between two rectangular microstrip antennas. A simple closed-form radiation model is used in the analysis.     

An experimental investigation of electrically thick rectangular microstrip antennas

The electromagnetic properties of electrically thick rectangular microstrip antennas were investigated experimentally. Antennas were fabricated with different patch sizes and with electrical thicknesses ranging from 0.03 to 0.23 wavelengths in the dielectric substrate. The resonant frequencies were measured and compared to existing formulas. The bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured.     

Input impedance and mutual coupling of rectangular microstrip antennas

A moment method solution to the problem of input impedance and mutual coupling of rectangular microstrip antenna elements is presented. The formulation uses the grounded dielectric slab Green's function to account rigorously for the presence of the substrate and surface waves. Both entire basis (EB) and piecewise sinosoidal (PWS) expansion modes are used, and their relative advantages are noted. Calculations of input impedance and mutual coupling are compared with measured data and other calculatious.     

A transmission line model for arrays of rectangular microstrip antennas

A very efficient transmission line model for the analysis of arrays of rectangular microstrip antennas is presented. The structure of the model is discussed, and its validity is proved. This is done for the isolated microstrip antenna as well as for the coupling between antennas. Then follows a discussion of the numerical efficiency. And finally a numerical example shows the effect of mutual coupling on the impedance and radiation pattern of a 21 element Chebyshev array at different scanangles.     

Analysis of dielectric covered infinite array of rectangular microstrip antennas

A method is presented to determine the active input impedance of an infinite array of rectangular patches embedded in a dielectric layer. The reaction integral equation is used to include details of feed structure into the formulation. The matching performance over wide scan angles of the printed antenna with a dielectric cover is studied. The results obtained by the present method are compared with the theoretical and experimental results reported earlier, for an array without a cover layer.     

A hybrid formulation for the probe-to-patch attachment-mode currentfor rectangular microstrip antennas

We present a hybrid representation for the attachment-mode current existing on the surface of a coaxially fed rectangular microstrip patch antenna. The hybrid representation consists of a one- or two-term residue and an eigenfunction series which gives the attachment-mode current at all points on the patch surface, including the probe-to-patch junction. It is numerically demonstrated that the residue and eigenfunction series blend smoothly in the close vicinity of the Stokes region which includes the probe-to-patch junction. The Stokes region is a very narrow region over which the attachment-mode current changes rapidly. The residue and eigenfunction series are used outside and within this Stokes region, respectively. This hybrid representation can be used in either spectral- or space-domain techniques for a full-wave solution to the microstrip antenna problem. The residue series is obtained by using an equivalent contour integral representation of the infinite eigenfunction series, which subsequently reduces to the Watson transform under the assumption of a slightly lossy substrate. At or near the Stokes regions the residue series is inadequate, as it cannot model the rapidly varying junction currents there. Examination of the residue series shows that the attachment mode is a superposition of exponentially attenuated, leaky, surface-traveling modes. This hybrid representation is expected to provide the optimum trade-off between speed and accuracy for computations involving electrically large finite arrays     

Spectral analysis of microstrip antennas with CG-FFT:two-dimensional results

Theoretical expressions for the currents excited on the top and bottom surfaces of a coaxial-probe-fed patch antenna are derived. Exact expressions for the far-zone field in terms of the total current on the patch are found. The analysis is specialized to a two-dimensional case. Detailed results for current, far-zone fields, and radiating-aperture admittance have been computed for this two-dimensional antenna model using the conjugate-gradient-fast Fourier transform (CG-FFT) technique. For a thick-substrate antenna it is found that the upper surface current on the patch is significant. Under this condition the traditional approximation of the total current by the bottom surface current alone may be in considerable error     

Resonant frequencies of rectangular microstrip antennas with flushand spaced dielectric superstrates

This paper presents a predictive model for the resonant frequencies of rectangular microstrip antennas with flush and spaced superstrates. This closed-form model is suitable for CAD and is directly applicable for the integration of microstrip antennas beneath plastic covers or protective dielectric superstrates in portable wireless equipment. The model utilizes conformal mapping and the concept of equivalent capacitance to determine the effective permittivity of a covered microstrip structure. A comparison between calculated and measured resonant frequencies demonstrates that the model provides less than 1% errors for structures with low relative permittivities (ε _r<3) and slightly higher errors for structures that contain higher permittivity materials. Generally, the model predicts the resonant frequency of a spaced superstrate structure as accurately as possible within the tolerance range of the structure's electrical and physical parameters     

Analysis and design of broad-band single-layer rectangular U-slot microstrip patch antennas

A wide operating bandwidth for a single-layer coaxially fed rectangular microstrip patch antenna can be obtained by cutting a U-shaped slot on the patch. This antenna structure has recently been found experimentally to provide impedance bandwidths of 10%-40%, even with nonair substrates. However, design rules for this antenna have not yet been presented. This paper develops principle design procedures through examination of the structure's multiple resonant frequencies as well as the radiation and impedance properties of different antenna geometries. The approximate design rules are derived by analysis of former experiments, method of moments (MoM) simulations, and measurement results. Simulations and measurements of several antennas designed using these new rules are presented and directions for further study are discussed.     

Multiport network model and transmission characteristics oftwo-port rectangular microstrip patch antennas

A multiport network model for two-port rectangular microstrip patch antennas is introduced. This model is capable of accounting for the feedline-patch junction reactances as well as for the mutual coupling among the edges of the patch, and is used to evaluate two-port transmission characteristics of rectangular patches. The proposed model has been applied to the analysis of rectangular patches used as elements of series-fed microstrip arrays. Results presented show that it is possible to match a two-port patch at the input port and, at the same time, to achieve a specified transmission coefficient to the other port to taper the amplitude distribution of the array appropriately. These experimental results verify the validity of the proposed model and the method of analysis used     

Efficient analysis of input impedance and mutual coupling of microstrip antennas mounted on large coated cylinders

An efficient and accurate hybrid method, based on the combination of the method of moments (MoM) with a special Green's function in the space domain is presented to analyze antennas and array elements conformal to electrically large material coated circular cylinders. The efficiency and accuracy of the method depend strongly on the computation of the Green's function, which is the kernel of the integral equation that is solved via MoM for the unknown equivalent currents representing only the antenna elements. Three types of space-domain Green's function representations are used, each accurate and computationally efficient in a given region of space. Consequently, a computationally optimized analysis tool for conformal microstrip antennas is obtained. Input impedance of various microstrip antennas and mutual coupling between two identical antennas are calculated and compared with published results to assess the accuracy of this hybrid method.     

Improved cavity model parameters for calculation of resonantfrequency of rectangular microstrip antennas

Models for the resonant frequency proposed by other authors are shown to produce misleading results for frequencies greater than about 3 GHz. However, a cavity model with a novel empirically determined edge extension parameter provides calculated frequencies within 2% of measurements for antennas operating between 600 MHz and 5 GHz