Bandwidth Improvement in Large Reflectarrays by Using True-Time Delay

Abstract

Abstract-A significant improvement in the bandwidth of large reflectarrays is demonstrated using elements which allow true-time delay. Two identical, large reflectarrays have been designed using different phase distributions to generate a collimated beam. In the former, the phase distribution is truncated to 360° as is usual in reflectarray antennas, while in the second, the true phase delay is maintained (three cycles of 360°). The chosen phase-shifter elements are based on previously measured and validated patches aperture-coupled to delay lines. The radiation patterns for both reflectarrays have been computed at several frequencies and the gain is represented as a function of frequency for both cases. Bandwidth curves are presented as a function of the reflectarray size.

Demonstration of a Shaped Beam Reflectarray Using Aperture-Coupled Delay Lines for LMDS Central Station Antenna

“…Besides, the effect of the differential spatial phase delay [10] is reduced through the introduction of a physical path that produces true-time delay (TTD) without phase limitation [11]. This compensation avoids the reduction in gain for pencil-beam reflectarrays [12] and the shape distortion for contoured beam reflectarrays [3], especially in large antennas. Reflectarray elements based on aperture-coupled patches with lines of variable length have previously been designed, manufactured and measured, showing a wide range of phase delay, low reflection losses and good element bandwidth [11].…”

Principles of Ideal Wideband Reflectarray Antennas

“…This is because the frequency slope of RAA cells, dφmn df , is inherently negative [2][3][4][5][6][7][8][9][10][11][12][13][14]. Figure 2 illustrates the required phase-frequency response of the mn-th cell of a wideband RRA with center frequency of f 0 and bandwidth from f l to f u .…”

“…So far, several solutions have been proposed to increase the bandwidth of RAAs, such as using a thick substrate, multiple stacked patches [2,3], phase-delay lines [4], aperture-coupled patches to delay lines [5], an artificial impedance surface [6], and true time delay [7]. Almost all the proposed solutions have been based on linearization of the phase variation of the cells with respect to frequency.…”

Modified Phasing Element for Broadband Reflectarray Antennas

“…Elements with linear phase response can be used to improve the antenna bandwidth. Linearization of phase response can be done in several ways including a thick substrate, multiple stacked patches, and phase-delay lines [1][2][3]. Among these methods, elements with attached phase-delay lines are a good choice because of their low manufacturing cost relative to the other methods.…”