Introduction
The concept of a time-modulated reflector array (TMRA)
is introduced and investigated. A TMRA is proposed as a variant of a
conventional time-modulated array. TMRAs are
potentially simpler to implement in hardware as it does not require a complex
feed structure. A simple 8-element TMRA is analysed using both array-factor
theory and full-wave electromagnetic simulation software. The switching
sequence applied to the TMRA is configured to produce radiation patterns with
low sidelobe levels. The performance of the TMRA consisting of ideal, isotropic
elements is compared to that of the TMRA
consisting of diode controlled dipole elements.
The TMRA concept and
description
TMRA consists of a grid of scattering elements which are
illuminated by a feed. In TMRA pattern control is achieved by controlling the
active scattering (or reflecting) time of the elements. The elements are
assumed be switchable between highly reflecting (ON) and non-reflecting
(OFF) states.
Fig. 1 TMRA consisting of
pin diode loaded dipole elements
Let the i-th element (i=1,N) be
periodically switched on and off at times defined
by tion and tioff . Under these conditions, the TMRA
will generate far-field scattering pattern at the fundamental
frequency given by
Hence, we can directly apply an amplitude weighting
function to the element energisation times
Fig. 2 The TMRA element switching sequence: 8 elements are
energised with time periods which correspond to a -30 dB Chebyshev weighting
Results
Fig.
3 Scattering patterns for the time-modulated reflector
array at the fundamental frequency (non-suppressed and suppressed by -30dB
Chebyshev weighting), calculated using isotropic element patterns and without
mutual coupling
Fig. 4 Scattering patterns
for the time-modulated dipole reflector array at the fundamental frequency
(non-suppressed and suppressed with -30 dB Chebyshev weighting), calculated
using the embedded element pattern
