Robert P. Penno

On the lower bound of the radiation Q for electrically small antennas

The fundamental question of the lower bound on the radiation Q of an electrically small antenna is of practical importance because of its relationship to the antenna bandwidth. Previous works predict a lower bound on the radiation Q that is usually too low and, hence, a bandwidth that can be optimistically large. This paper addresses why this is so and offers a new prediction for a realizable lower bound on the radiation Q. This new prediction is based on the far-field pattern, in both the visible and invisible spatial regions, in contrast to previous works based upon a near-field modal approach. Results for a linear dipole, bow-tie, and end-loaded dipole are presented to illustrate the validity of the lower bound presented herein. Radiation Q can be related to bandwidth provided the Q is adequately large. Implicit is the presence of a matching network as a part of the antenna system. Both the losses in the antenna and the losses in the matching network have an effect on the system bandwidth, the system efficiency and the system Q, of which the radiation Q is a part. These various relationships are also discussed.

Theory of angle estimation using a multiarm spiral antenna

An analysis of angle estimation using a single aperture, multimode spiral is presented. It is demonstrated that in addition to the classical Comparison method, modern parameter estimation techniques such as Multiple Signal Classification (MUSIC) and MLM (Maximum Likelihood Method) can be applied to multimode antenna technology for angle estimation. These techniques, coupled with the advent of digital receivers make possible the elimination of the mode-forming network. Results of computer simulations show that these new approaches give lower bias and variance, and also extend coverage toward boresight compared with the traditional Comparison method.

Scattering from a perfectly conducting cube

The cube epitomizes the complex, three-dimensional scatterer with its multiple interactions and vertex diffraction playing a critical part in the far-field patterns of some bistatic planes. the results presented are for a cube on the order of 1.5-3 wavelengths on edge which is illuminated by a plane wave at broadside incidence. The method employed is the hybrid iterative method (HIM) which utilizes an initial approximation of the surface currents on the cube faces. These currents are inserted into the magnetic-field integral equation (MFIE) to produce improved or updated approximations to these surface currents. This process is repeated to convergence by the method of successive approximations. These currents are then used to find the bistatic radar cross section (RCS) for an arbitrary plane of measurement (emphasis has been placed upon the H-plane and the E-plane). Of particular interest is the development of cross-polarized currents, which are initially approximated by zero. As the iteration process progresses, it is seen that all physical scattering processes present in this body are introduced by enforcing the MFIE. >

A novel multi-mode interferometer system

In this paper we consider a new interferometer comprising wideband multi-mode antenna elements rather than conventional antenna elements. As a result, the phase ambiguities associated with the long baselines of the interferometer are resolved using the angle estimates provided by the multi-mode elements. This results in the elimination of the short baseline interferometers of the conventional five-element interferometer; the hybrid multimode interferometer needs only three elements. In addition, since the multi-mode elements are wide band, the hybrid multi-mode interferometer is capable of giving good performance over a wide bandwidth.

Broadband Microstrip Leaky Wave Antenna With Inhomogeneous Materials

Analytical solutions for the fields and propagation constant in an open microstrip line above an inhomogeneous substrate are derived and the finite element method (FEM) is used as a tool to validate the theory. Excellent agreement between theoretical and simulated results is obtained and the theory is used to determine the driving point impedances. The complex propagation constant corresponding to the leaky mode is derived from the fields computed using the FEM technique and compared to the values obtained using the transverse resonance method (TRM). It is demonstrated that by periodically loading the microstrip line with air gaps and keeping the period much less than a wavelength, it is possible to realize a leaky wave antenna with lower dielectric constant whose bandwidth is increased by a factor of approximately 50% or so. The proposed inhomogeneous LWA has been fabricated, and measured with results corroborating the theory shown here.

Simulation of the scattered EM fields from a rotating conducting cylinder

The effect of the acceleration on the signal scattered by a rotating, perfectly electrically conducting cylinder is investigated. This problem is discussed in terms of the Franklin transformation. However, the scattering of electromagnetic plane waves by a conducting cylinder in uniform rotation were investigated by many researchers in the past by using Galilean rotation. These discussions show that the effect of rotation is negligible in the case of a perfectly conducting cylinder. In this paper, we use the Franklin transformation to analyse the scattering of both types of electromagnetic waves (H-wave and E-wave) by a rotating circular very good conductor cylinder for a small angular velocity and we show that the rotation of a very good conducting cylinder generates a distortion that is evident on the scattering patterns. This distortion is more evident in the case of an incident time-harmonic plane H-wave (TE-mode). The results indicate that the magnitude and phase of the backscattered field of an H-wave by a rotating very good conducting cylinder is different from stationary one.

Finite element-boundary integral simulation of a conformal microstrip leaky-wave antenna

Microstrip leaky-wave antennas offer an attractive wide bandwidth alternative to microstrip patch antennas with the caveat involving pattern control. Leaky-wave antennas, by their nature, will steer the main-lobe of the radiation pattern as the operating frequency is changed. Therefore, although the bandwidth of leaky-wave antennas is attractive, ensuring a fixed angle of radiation independent of the operating frequency, within the leaky-wave region of operation, is challenging.This is especially true for microstrip leaky-wave antennas that are conformally mounted on a curved surface, such as a circular cylinder. In this paper, a microstrip leaky-wave antenna is investigated and particular attention is paid to the radiation properties of the antenna. The antenna is simulated with a finite element-boundary integral formulation that makes use of a dyadic Greens function for an infinite, metallic, right circular cylinder.

Mitigation of jamming of an angle estimation system using multi-mode antennas

The problem of obtaining accurate estimates of the angle of arrival (AOA) of an unknown source using a single aperture multi-mode antenna in the presence of a jamming signal is considered here. Two approaches, one based on maximum likelihood and the second based on a modified MUSIC algorithm are presented. A simulation study is carried out to test the efficacy of the algorithm. It is demonstrated that when the signal and jammer are uncorrelated and when they are not too close to each other in angle, good angle estimates are obtained even in the presence of powerful jamming.

An improved model for the phase of backscattered electromagnetic fields from a conducting rotating cylinder

The rotation or vibration of a complex scattering object induces frequency modulations on the scattered signal. This modulation during this rotation or vibration is referred to as the micro-Doppler effect. The Micro-Doppler effect was investigated by many researchers in the past for different types of rotating objects, such as propellers of a fixed wing aircraft and rotors of a helicopter. In this paper, we examine the time-frequency analysis of a rotating, very good conducting cylinder. The scattering of an electromagnetic H-wave by a rotating very good conducting cylinder is investigated using the Franklin transformation. Then, micro-Doppler effects can be extracted by using the short time, fast Fourier transform for scattered fields associated with the rotational motion. The simulated results confirm that the Franklin transformation gives a more accurate analysis for a rotating, very good conducting cylinder than Galilean transformation. Also the results demonstrate the difference between the stationary and rotating very good conducting cylinders in time frequency analysis. Finally, the simulation shows that this approach produces a different result than previous approaches such as the Chen model.

Bistatic aspect diversity for improved SAR target recognition

This paper analyzes the potential for improvement in the performance of automatic target recognition (ATR) for synthetic-aperture radar (SAR) with bistatic aspect diversity. Initial assessments using decision-level fusion of monostatic observations with bistatic observations provide promising results. Data was generated using three civilian vehicle facet files and an electromagnetic scattering simulator. Classification was performed using normalized cross-correlation template matching and majority voting. Results showed an increase in the probability of correct classification with decision-level fusion of bistatic observations over classification using single observations.