Dan S. Janning

Effects of surface waves on the currents of truncated periodic arrays

The behavior of surface waves in truncated periodic arrays is examined through analysis of the currents. The surface waves to be studied are guided by the perfectly conducting elements of the array itself and are to be distinguished from the dielectric slab-guided surface waves encountered elsewhere in the literature. The conditions under which surface waves may arise are given. The surface wave currents are extracted from the method of moments solution for the finite by an infinite array using a least squares algorithm. Surface wave excitation and reflection coefficients are then be determined from the data and compared with the semi-infinite array solution.

Scattering from surface waves on finite FSS

This paper discusses the presence of surface waves on periodic structures in general and on frequency selective surfaces (FSS) in particular. While certain types of surface waves can exist on infinite as well as finite periodic structures, this investigation centers around the types that can exist only on finite FSS. Radiation caused by these surface waves may lead to a significant scattering increase in the backscatter as well as the bistatic directions. Thus, this paper is of both theoretical and practical interest.

FE-BI analysis of a leaky-wave antenna with resistive sheet termination

Printed leaky-wave antennas offer the potential for a low-profile, wide-bandwidth antenna element that can be arrayed if desired. Microstrip leaky-wave antennas rely on the suppression of the familiar EH/sub 0/ mode and the propagation of the radiating EH/sub 1/ mode. It is well-known that above a critical frequency, this leaky-wave will propagate with little attenuation and that the phase difference between the two radiating edges of the microstrip leads to radiation. However, due to the limits of installation area, such antennas must be terminated in a manner that reduces back reflection. If this is not done, a standing wave is established on the antenna limiting its utility as a leaky-wave antenna in terms of front-to-back ratio and bandwidth. In this paper, the hybrid finite element-boundary integral method is used to investigate an antenna termination scheme involving the use of resistive sheet extensions to the antenna. It was shown that such a termination increases the front-to-back ratio and usable bandwidth of the antenna as compared to an antenna without such termination.

The design of wideband arrays of closely-spaced wire and slot elements

The quest for wide band operation of antenna arrays, for example reaching 10 to 1 or more, has led to the consideration of many different types of elements. Spirals and other wide band elements have been tried as one alternative, but this leads to large elements with wide interelement spacing that results in grating lobes at high frequencies. Munk [1, 2] has shown that simple dipoles and slots can be effectively used to achieve wide band widths without grating lobes by the effective use and control of element to element coupling and wide band matching techniques. This paper outlines the logic of this array design procedure. Many impedance calculations used in planar wideband array design are made using the Periodic Moment Method code [3]. The theory behind PMM is based on a plane wave expansion technique [4], and yields the analysis of infinite, periodic, and planar arrays of scattering elements (wires or slots). Semi-infinite calculations are made using a code referred to as SPLAT [5, 6].

Analysis of arrays of microstrip half-width leaky wave antennas

The research described in this paper continues that work by analyzing two four-element arrays of microstrip half-width leaky wave antennas of different element lengths. The experimental results are compared with calculations made using the commercial software CST Microwave Studio.

Wave guidance between pairs of periodic surfaces

Fourier analysis of the currents on one of a pair of periodic surfaces is used to show the presence of quasi-waveguide modes and array-guided surface waves. Several distinctions are drawn between these two mechanisms as well as trapped grating lobes which can occur if dielectric slabs are present.

Dual-Function 3-D Heatsink Antenna for High-Density 3-D Integration

Radiation from heatsinks is typically undesirable and should be minimized to reduce electromagnetic interference (EMI). However, in certain applications such as high-power transmitters where both a heatsink and an antenna are required it can be advantageous to maximize the radiation from a heatsink by using the heatsink as the antenna. In this case, not only is the total component count in the transmitter reduced, but the heatsink can be beneficial to the antenna performance. A 2.4 GHz heatsink antenna based on a microstrip patch antenna design shows improved radiation efficiency and broader bandwidth. Also, the peak antenna gain is increased. This presentation reviews the idea of the heatsink antenna and how the heatsink can be exploited for improved antenna performance.

On finite frequency selective surfaces

It is customary to approximate finite periodic structures by considering infinite surfaces. While this approach works under many circumstances, there are cases where strong surface waves are excited that cannot be accounted for by the infinite array approach An explanation of this phenomenon is shown.