Mark Kragalott

Design of a 5:1 bandwidth stripline notch array from FDTD analysis

A 5:1 bandwidth stripline notch array antenna is designed from parametric investigations of flare and feed dimensions. The finite-difference time-domain (FDTD) method is employed to perform the parametric studies. Both linear and planar single-polarization arrays are considered with half-wavelength element spacing at the highest frequency. The linear array elements depend upon E-plane element mutual coupling to achieve wideband behavior. Edge elements, which cannot benefit from full E-plane coupling, are shown to maintain good transmit performance with the application of amplitude tapering. The planar array is shown to have a scanability (active VSWR <2) averaging 51/spl deg/ off broadside in the E-plane and exceeding 60/spl deg/ in the H-plane. As an infinite planar array, the antenna is predicted to have a bandwidth exceeding 7:1 on broadside. Measurements are in good agreement with the computations.

Time-domain fields exterior to a two-dimensional FDTD space

A transformation algorithm for the near-zone and far-zone fields exterior to a two-dimensional (2-D) finite-difference time-domain (FDTD) field lattice has been developed entirely in the time domain. The fields are found from a surface integration of the convolution of the time derivative of equivalent currents and charges along a contour that encloses the scatterer or radiator of interest. The kernel of the convolution integral has a square-root singularity for which an efficient numerical integration rule is presented. Using this technique, a very accurate solution is obtained; however, convolution integrals are computationally expensive with or without singularities. As an alternative, a rapidly convergent approximate series expansion for the convolution integral is presented, which can be used both in the near and far zone. Results using the new 2-D transform are compared with analytical expressions for the fields generated by a modulated Gaussian pulse for TE and TM line sources. In addition, the 2-D transform solution for the near-zone fields scattered from an open-ended cavity for a TE incident modulated Gaussian pulse plane wave is compared against a full-grid FDTD solution for accuracy and efficiency. The 2-D transform far-zone fields are compared against an alternative technique, which uses a double Fourier transform to perform the convolution in the frequency domain.

Preliminary Investigations of a Low-Cost Ultrawideband Array Concept

A design concept is presented that achieves ultra wideband (UWB) array performance with significantly fewer elements than the traditional approach of using a single wideband antenna element type to fully populate the array. Starting from a conventional 8:1 bandwidth array design of a given aperture size, an array of equivalent aperture and bandwidth is created using scaled elements of three different sizes. This wavelength-scaled equivalent array has fewer than 18% of the original element count, i.e., roughly 6-times fewer elements, a similar reduction in weight, and most importantly, a significant reduction in electronics required to feed the array. If proven viable, array architectures of this type could make UWB arrays significantly more cost effective. In this preliminary numerical study, rigorous full-wave simulation tools are used to test the performance of small but informative wavelength-scaled array configurations of flared-notch radiators for the single-polarization case.

A wavelength-scaled ultra-wide bandwidth array

An ultra-wideband antenna array design concept is presented that achieves the same functionality of traditional single-element-based ultra-wideband arrays using multiple elements that are scaled in size from the base high-frequency element, resulting in significantly fewer elements overall. For an array with 8:1 bandwidth, a fully functional design can be achieved with fewer than 16% of the original element count - i.e. 6.4× fewer elements, and the need for only 11% of the original electronics - a reduction factor of 9.2×, while maintaining the same array footprint. This novel array design leads to a significant reduction in weight and most importantly - a significant reduction in the cost to construct hardware and electronics; all while maintaining the same performance capacity of a traditional wideband antenna array.

A Toolset Independent Hybrid Method for Calculating Antenna Coupling

Calculation of the electromagnetic interference (EMI) between electrically large antennas mounted on ships is important for a variety of Navy problems. This paper presents a toolset independent hybrid method for calculating the power at receive antenna terminals relative to the power incident on transmit antenna terminals. The hybrid method coupling results are validated against full-wave computational electromagnetic (CEM) simulations and measurements. An advantage of the proposed hybrid approach is that CEM calculations for antenna near-fields and propagation between antennas can be executed with user-preferred tools. In addition, transmit and receive antenna calculations are executed in transmit mode independent of ship structures. Thus, antenna calculations can be stored in a library for calculation reuse and optimization of antenna placement for EMI reduction.

Experimental validation of the FETI-DPEM algorithm for simulating phased-array antennas

The electromagnetic dual-primal finite element tearing and interconnecting (FETI-DPEM) method is a non-overlapping domain decomposition method developed for the finite element analysis of large-scale electromagnetic problems. The method is particularly suitable for simulating large finite arrays because the geometrical repetitions of an array structure can be exploited to further enhance the computation performance. The method has been applied to the simulation of phased-array antennas in addition to other finite array structures. This paper presents the first experimental validation of this method for the simulation of a highly complicated realistic phased-array antenna. The antenna geometry is described in detail and the comparison between the simulated solution and experimental measurement is presented.

Analysis of electrically large patch phased arrays via CFDTD

To validate the CFDTD code, analysis was first carried out on a smaller array with 64 elements. The structure was built up with elements identical to those used in the 10,000-element array. Models of the validation array were constructed using both CFDTD and XFDTD. The array radiation patterns were shown for 0deg, 30deg, 45deg, and 60deg scan angles at the center frequency of 1.75 GHz. The beam was scanned in the Phi = 90deg plane. The solid lines represent CFDTD data while the dotted lines indicate the corresponding XFDTD set. As the beam is steered away from boresight, the 3-dB beamwidth increases from 12.9deg at boresight to 26.2deg at the 60deg scan angle. The first sidelobe level is about 13 dB below the peak when the main beam is pointed at boresight. The total change in peak sidelobe level is 4.0 dB as the beam is scanned from boresight to 60deg. The array directivity calculated with CFDTD is 23.0 dB, which is within 0.2 dB of the value given by XFDTD. Furthermore, the scan loss from 0deg to 60deg is observed to be 3.0 dB with CFDTD and 2.8 dB with XFDTD. These values are consistent with expectations for a well behaved array with 0.5lambda element spacing

Coupling between planar microstrip patches in an array environment

In this paper, we utilize a conformal finite difference time domain (CFDTD) code to predict the coupling between two coplanar radiators with complete feed circuits. The CFDTD has been parallelized to operate on a Linux cluster, allowing rapid simulation of large, complex problems. A wide variety of antenna configurations have been analyzed, and two representative examples are discussed herein. The first consists of circular microstrip patches operating at C-band, while the second is comprised of rectangular Ka-band patches. Numerical coupling data are compared against both measurements and theory. Input impedance characteristics are also evaluated to determine the radiation efficiency.

Impact of mounting on UHF LOS antenna system

Shipboard line of sight (LOS) communication systems commonly rely on monopole and dipole antennas. When constructed out of segmented wires, the free space performance for these antenna types are well understood. This paper presents the results from a numerical study of deck proximity and mounting effects on the performance of a complex ultra high frequency (UHF) LOS antenna based on the multifunction electromagnetic radiating system (MERS) concept.

The Role of Mutual Coupling in A 5:1 Bandwidth Stripline Notch Array

The bandwidth broadening effects of time-domain mutual coupling from adjacent elements in a linear array of stripline notch elements was briefly described in previous papers1, 2, 3. The array was designed at the Naval Research Laboratory (NRL) to demonstrate the feasibility of 5:1 bandwidth wide-scan angle arrays with one-half wavelength spacing at the highest operational frequency. This paper presents an expanded examination of the role of mutual coupling in pulse-excited linear and planar single polarization arrays as well as in a planar dual polarization array. When viewed in the time domain, inspection of mutual coupling leads to a physical understanding of the cause of the ultrawideband (UWB) behavior of the NRL arrays. The finite-difference time-domain (FDTD) method4,5 is employed to perform the studies, and measurements verify some of the calculations.