Henrik Holter

Experimental results of 144-element dual-polarized endfire tapered-slot phased arrays

Two 9/spl times/8/spl times/2 (144 element) dual-polarized endfire tapered-slot phased arrays have been built. Measured data for mutual coupling coefficients and scan-element patterns are presented. Also, element resonances, predicted by numerical infinite-array analysis are examined. The dimensions of the two arrays are identical. They differ in that plated-through vias have been repositioned to eliminate element resonances. One array was expected to operate from 1.0 to 4.6 GHz and the other from 1.0 to 5.9 GHz. It was found that, at low frequencies, the central elements are heavily affected by the finiteness of the arrays due to strong mutual coupling between array elements. Extrapolation of the observations indicates that a tapered-slot phased array, designed for wide-angle scanning, should be comprised of at least 30-40 rows and columns of elements to obtain low-frequency performance that is comparable to infinite-array predictions. In spite of the smallness of the array, predicted-element resonances could be identified by examination of the phase of the mutual coupling coefficients. Based on these observations, the plated-through vias are adequate to remove element resonances.

Elimination of impedance anomalies in single- and dual-polarized endfire tapered slot phased arrays

A method to eliminate bandwidth-limiting impedance anomalies or resonances in stripline-fed single- and dual-polarized tapered slot phased arrays is presented. For dual-polarized arrays, others have shown that the resonance with the lowest frequency is related to a cavity constituted by the dielectric region of the tapered slot element. Simulations have been performed to test if this cavity model also predicts the remaining resonances. It was found that the cavity model predicts some but not all of the resonances. However, it was found that all resonances in both single- and dual-polarized arrays have some dependence on the dielectric region. The resonances are effectively suppressed by introducing plated through vias in the element. The vias are positioned along the edges of the slotline, slotline cavity, stripline, and stripline stub. The analysis is performed with the finite-difference time-domain method by considering a unit cell in an infinite array.

Broad-band fragmented aperture phased array element design using genetic algorithms

In this paper, a synthesis procedure to design thin broad-band fragmented aperture array elements is described. The arrays are assumed to be infinite periodic and the elements consist of a conducting pattern etched on a dielectric backed by a groundplane. A genetic algorithm (GA) is used to design the conducting pattern, relative permittivity, and thickness of the dielectric substrate with respect to array scan and bandwidth performance. The fitness function in the GA is evaluated using a finite-difference time-domain code with periodic boundary conditions. For a substrate thicker than about 0.1 /spl lambda//sub L/ (/spl lambda//sub L/= wavelength at the lowest frequency in the frequency band investigated), it was found that a bandwidth of at least one octave can be obtained for arrays scanned within 45/spl deg/ from broadside.

Dual-Polarized Broadband Array Antenna With BOR-Elements, Mechanical Design and Measurements

A dual polarized broadband phased array antenna designed for the frequency range 6-18 GHz, a 45deg conical grating lobe free scan volume and equipped with BOR-elements developed by Saab is presented. The aim with this array element is to bring about a dual polarized broadband array antenna that is easy to assemble, disassemble and connect to active microwave modules. Disassembling may be important for maintenance and upgrade reasons. Mechanical design and electromagnetic performance in the form of active reflection coefficient, calculated from measured mutual coupling coefficients, and measured active gain element pattern for a central and an edge element is presented. Edge effects in the array, which may be severe in small broadband arrays, are considered in this paper

Spiral elements for broad-band phased arrays

In this paper, we present a numerical analysis of an infinite periodic array of planar spiral elements with octave bandwidth. For off-broadside scan the array is found to exhibit very narrow resonances, which are independent of scan angle. They occur when the spiral arms are multiples of half a wavelength, in which case the current forms a high amplitude standing wave along the spiral arms. The resonances are conveniently suppressed by making the arms unequally long. We also discuss the equivalent 3-port for this nonsymmetrical array element and evaluate the element polarization performance.

TSA element design for 500-1500 MHz array

The Square Kilometer Array (SKA) project is exploring issues pertinent to deployment of a radio telescope comprised of wide-band phased arrays with a total receiving area of 10/sup 6/ m/sup 2/. Present scenarios consider a large collecting area comprised of several large subarrays with thousands of elements each. The subarrays will be placed within an area extending a few hundred kilometers and interferometric beamforming techniques will be employed for scanning of multiple beams in the manner of a VLB array. The field of view of the subarrays will be at least 100/spl deg/. Although SKA will be dual-polarized to permit extraction of polarization information from the received signals, the THousand Element Array (THEA) demonstration project will be restricted to a single polarization. This paper describes the design and predicted performance of a tapered slot antenna array to fulfil the THEA requirements. Several relevant array specifications are listed.

An Approximate Method for Calculating the Near-Field Mutual Coupling Between Line-of-Sight Antennas on Vehicles

Calculating the mutual coupling between antennas on vehicles using full-wave simulations requires a vast amount of computer resources due to the electrical size of the structures. We therefore propose an alternative and approximate method to determine mutual coupling between antennas on vehicles for the case where there is line-of-sight (LOS) between the antennas. The proposed method is based on approximating the mutual coupling between LOS antennas on vehicles as near-field transmission between antennas in free space. We begin the analysis with a brief review of four methods for calculating the near-field free-space transmission. Of the investigated methods, we demonstrate that a nonsingular form of the near-field transmission integral originally proposed by Yaghjian (1982) is the most suitable for LOS antennas on vehicles. We introduce a modification to this method, in order to only use the antenna far-fields and geometrical separation to determine the mutual coupling. The comparison with full-wave simulations indicates that the proposed method has a good accuracy for LOS antennas. This paper ends with a full-scale mutual coupling calculation for two monopoles on an aircraft under LOS conditions, demonstrating a root mean square (rms) accuracy of 6 dB for frequencies up to 5 GHz, as compared with full-wave simulations.

On Mutual Coupling and Coupling Paths Between Antennas Using the Reaction Theorem

The reaction theorem is applied to antenna coupling problems. It is shown that the reaction theorem can be used to calculate the mutual impedance between antennas, when the electromagnetic fields are known on a plane that separates the antennas in two disjoint regions. We also show that coupling paths between the antennas can be visualized by using intermediate results from the reaction theorem. The coupling paths are visualized based on the fields generated by each of the two antennas, and only take into account the energy that is actually transferred between the antennas. The visualization of coupling paths is useful for understanding how the coupling between the antennas is distributed in space.