Anders Ellgardt

A Circularly Polarized Cylindrical Dielectric Resonator Antenna Using a Helical Exciter

A novel circularly polarized cylindrical dielectric resonator antenna excited by an external tape helix is presented. The helix is fed by a coaxial line through a small hole on a finite size ground plane. The configuration offers a compact and easy to fabricate feeding network providing a 3 dB axial-ratio bandwidth of 6.4%. A prototype of the proposed configuration is fabricated and measured. Measured and simulated return loss, axial-ratio, radiation pattern, and realized gain are presented and discussed together with design guidelines.

A Scan Blindness Model for Single-Polarized Tapered-Slot Arrays in Triangular Grids

A simple model is presented that predicts scan blindness in the E-plane for single polarized tapered-slot arrays where the elements are positioned in a triangular grid. The blindness occurs when the phase progression along the dielectric substrates is equal to the phase progression of a leaky mode in the structure. A simple equation is presented that estimates the frequency at which the scan blindness occurs for a given angle in the E-plane. This equation is derived from a simple representation of the phased array antenna, but includes the dominant effect of this particular class of scan blindness. The method is shown to agree well with computed results obtained with two different numerical codes.

A Helix Excited Circularly Polarized Hollow Cylindrical Dielectric Resonator Antenna

In this letter, we use a helix to excite two orthogonal HE11δ modes in phase quadrature in a hollow cylindrical dielectric resonator antenna to generate circular polarization. As compared to our previous work, it is shown that replacing the cylindrical dielectric resonator antenna with a hollow cylindrical-shaped one leads to a significant enhancement in the 3-dB axial-ratio bandwidth. A design guideline is provided, and three design cases are presented. A prototype for one of the designs is fabricated and measured. Measured and simulated data are presented and discussed. It is shown that the 3-dB axial-ratio bandwidth increases as the wall thickness of the hollow cylindrical dielectric resonator decreases. Furthermore, a reduction in the wall thickness requires a longer helix exciter for similar performance .

A study of edge effects in triangular grid tapered-slot arrays using coupling coefficients

Edge effects for tapered-slot elements in triangular grid array antennas are studied by using finite difference time domain codes. The S parameters for finite-by-infinite arrays are computed and ev ...

Modeling Shielding Effectiveness for Composite Walls of Concrete and Carbon Filaments

Concrete walls reinforced with rebars have poor shielding efiectiveness for telecommunication frequencies (frequencies above 0.5GHz). An efiective method to increase the shielding efiectiveness of the walls is to increase the complex permittivity of the concrete. This can be done by mixing in thin fllaments of a material with high conductivity. One such material is carbon. In this paper the Maxwell Garnett mixing rule is used to model a concrete material with carbon fllaments. The shielding efiectiveness computed with the mixing rule is found to agree with previously published measurement results.

Comparing Analytical and Numerical Calculations of Shielding Effectiveness of Planar Metallic Meshes with Measurements in Cascaded Reverberation Chambers

Large electrical systems or facilities can be satisfactorily shielded by using low-cost meshed metallic nets. Here the shielding efiectiveness for two such planar meshes is calculated analytically and verifled both experimentally by using cascaded reverberation chambers as well as numerically with results computed using a full wave electromagnetic solver. It is shown that all three methods agree and, in addition, that non-square shaped aperture meshes can be handled with an equivalent square area shaped aperture.

A Single Polarized Triangular Grid Tapered-Slot Array Antenna

A triangular grid single polarized tapered-slot array antenna for radar applications is studied. Compared with a rectangular grid an equilateral triangular grid allows a larger unit cell without any onset of grating lobes. Since single polarized tapered-slots in triangular grids support guided modes, which cause scan blindness, the increase in unit cell size is smaller than the optimal 15%. The design presented in the paper is capable of scan angles out to 60° from broadside in the E and H planes. To improve the match over the radar band a local minimum in the active reflection coefficient is positioned at the most critical scan direction, resulting in a reflection coefficient that is less than -12 dB in the X-band. To reduce the radar cross section for the cross-polarization an absorbing layer is positioned above the ground plane, which affects some of the guided modes that lead to scan blindnesses. An experimental antenna with 16 × 16 elements was built, and it was found that the H-plane performance for large scan angles for the finite antenna deviates more than expected from the infinite array approximation. Otherwise both mutual coupling measurements and embedded element patterns agrees well with the numerical results.

Characteristics of a broad-band wide-scan fragmented aperture phased array antenna

In this paper a phased array antenna is described that is designed with the help of a genetic algorithm for scan angles out to 60° from broadside. The focus is on simplifying the manufacturing of the diagonally adjoining pixels and on numerical results for thin antennas. The effects of the corner to corner contacts are studied and results for two synthesized elements ar Test and measurement requirements on wireless devices

A comparison of a finite and an infinite antenna array with cylindrical dielectric resonator elements

In this paper we compare radiation patterns and mutual coupling in finite and infinite square lattice arrays of dielectric resonator antenna (DRA) elements. The array elements are cavity backed, slot fed cylindrical DRAs that utilizes the HE11δ mode. It is observed that the degree of the mutual coupling for non-edge elements is very close to the mutual coupling between the corresponding elements in the infinite array. However, a large difference is observed in the mutual coupling between the center element and the two corner elements in the finite array with respect to the corresponding elements in the infinite array. The coupling is strongest in the E-plane and it is shown how it changes the embedded element patterns in the array.