Naftali Herscovici

Analysis of cylindrical array of infinitely-long slots fed by connected dipoles

We have developed an accurate analysis of a cylindrical array structure of long slots with connected dipole feeds, [1]. The array exhibits wide-band characteristics, about 3:1 frequency band at broadside scan. The code we generated could be used to accurately predict the impedance and radiation characteristics of the array.

A fragmented aperture-coupled microstrip antenna

This paper summarizes an effort to obtain a wideband aperture-coupled fragmented microstrip antenna. The antenna is modeled as a 2.5D structure, and is optimized using a genetic algorithm (GA). The realistic physical feed, a microstrip-fed slot, is also included in the optimization process.

Dyadic Green's function for an electric current source in the unit cell of a periodic structure

A dyadic Greens function for rectangular waveguides has been derived and discussed in [1–5]. None of these works, however, discusses the Greens function for a unit cell of a periodic structure. In this work the dyadic Greens function for an electric current source in a Floquet phase-shift-wall waveguide (unit cell) is derived using the magnetic vector potential. Complete solutions for the electric and magnetic fields in the unit cell, including the source region, are obtained in the form of known waveguide modes with periodic boundary conditions. To validate the theory the scattered field from an array of z-directed strips is computed using the new Greens function and compared with results obtained by the HFSS code. This dyadic Greens function can be used to analyze various periodic structures such as large array antennas and metamaterials.

An electrically-small multi-frequency genetic antenna immersed in a dielectric powder

In this paper, we investigate the performance of an electrically small genetic antenna, immersed in several different powders having relative dielectric constants as large as 12. Placing the antenna in a dielectric reduces its electrical size from about 1/20th of a wavelength in free space to less than 1/50th of a wavelength, in a powder having a dielectric constant of 12, even for a dielectric volume just slightly larger than the antenna. Although the bandwidth decreases as the electrical size of the antenna becomes smaller, it is shown that for each dielectric powder, there is a set of frequencies for which the antenna is operational. It is thus possible to efficiently operate the antenna at specific frequencies within a wide band.

Scanning characteristics of Aperture Coupled Fed Fragmented Microstrip arrays

The scanning characteristics of a certain class of Aperture Coupled Fed Fragmented Microstrip Antennas are presented. This type of antenna exhibits relatively wide-band performance and its scanning characteristics are investigated.

Considerations in the design of parallel plate lüneburg beamformers and cylindrical arrays

We present a new concept for a low-profile, low cost integrated multi-beam cylindrical array. It consists of a parallel plate 2D Luneburg beamformer feeding a cylindrical aperture. The concept incorporates a number of novel features, such as low profile, and highly directive excitations. All these features are introduced in order to reduce volume, weight and ultimately cost. The paper discusses the various challenges this concept presents, and ways to mitigate these difficulties.

A conformal rotman lens

One of the challenges of designing UAVs is the limited amount of interior space for components. The communication, navigation, and radar systems all compete for this limited space. Phased array antenna systems, in turn, save space, weight, and power by steering the antenna electrically versus mechanically. Rotman lens devices (Fig. 1) are a particularly efficient means providing the correct amplitude and phase waveform inputs to a phased array antenna to allow this steering. However, the elongated, flat shape of a Rotman lens makes it cumbersome to fit the confines of a UAV.

Considerations in the synthesis of elevation patterns in cylindrical parallel plate antennas

Cylindrical antennas and arrays are very useful when 360° coverage is required. Either a multibeam cylindrical narrow beam or an omnidirectional parallel plate based antenna can significantly benefit from an elevation pattern for either gain increase or specific angular coverage. The challenge is in the design of the geometry associated with the elevation pattern, so that performance is optimized for specific requirements while the volume is kept at a minimum. In this paper, a number of cylindrical antennas are presented. Two specific antenna types are addressed: the Corrugated Cylindrical Antenna and the Short-Backfire based Cylindrical Antenna.

A low-profile VHF dual band printed antenna

We present a new design of a low-profile small VHF dual-band omnidirectional antenna made on a compact ARLON board. The antenna was optimized using full-wave EM simulations to provide an omnidirectional radiation pattern. A reactive impedance matching circuit was synthesized to operate the antenna in two VHF bands around 150 and 450 MHz with high efficiency. Several prototypes of the antenna have been fabricated and tested.

Antennas operating in close proximity of textured surfaces

In this paper a new method to reduce the interaction between antennas and nearby objects is proposed. It involves the use of a thin textured surface similar to a high-impedance layer that is wrapped around the objects that are in close proximity of the antenna (ground planes, various platforms, etc.). The textured surface acts as a “diffuser” spreading the reflected fields from the close objects and thereby reducing the power otherwise directed in the specular reflections. This method allows reducing the profile of endfire antennas working in close proximity to various platforms.