15.2.13
job hunting website
monster.co.uk jobsite.co.uk jobs.ac.uk cwjobs.co.uk, linkedin.com reed.co.uk fish4.co.uk
14.11.12
Sidelobe control of a time-modulated reflector-array Sidelobe control of a time-modulated reflector-array Sidelobe control of time modulated reflector array
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
8.10.12
Is Time-Modulated Reflector Array with feed a challenge?
First of All, TMRA WITH FEED is really challenge.
1. Which feed should be use?In the conventional TMRA with plane wave. The source is a plane wave which is considered as radiation from infinite far-field. The electromagnetic waves arrive at the elements at the same time. Hence, a exact identical theory from Time Modulated Array can be applied to TMRA. Hence, to make things easier, it is best to use a feeding source similar to plane wave.Furthermore, the back radiation of the source should be very small.1) dipoledipole is easy to make and simulate. The numerical theory is considerably easy. However, the radiation pattern is omni-directional at the H-plane (normally horizontal cut). That means the back radiation or the radiation towards the bore-sight is high (we expect only scattering from TMRA elements at bore sight). NOT GOOD CHOICE2) Patch antennaPatch antenna is seldom known in the use of reflector antenna. Performance is not tested. However, according to my experience of patch antenna. The antenna gain is small. The profile of the antenna is big. Back radiation is small.3) Horn antennaHorn antenna is widely used to feed reflector arrays. The beam-width is fixable. The gain is flexible. Gain can be up to 20 dB. Low back radiation,2. How many elements should use?The number of elements is one of the parameter could be used in time-modulation theory. I would say the number of elements has the same functionality in conventional phased array.FOR a linear array, I would think one row of element is not enough. The scattering energy is comparably small thus the power from the feeding source domains. Hence, it is good to increasing the rows of element.A 2D array is good, elements are serial connected in column.3. How to deal with coupling?Theoretical analysis do not consider coupling at all. Simulation in CST do. Couplings can be divided into1) between ON element and OFF element2) between ON element and ON element3) between elements and feeding antenna4. Which is the best way to estimate the phase shifts of signals arrive at the elements?original phase start at the antenna+phase shifts due to propagation.
Fig. 1 Illustration of a TMRA with feed: feed is placed at distance of d at the bore-sight of TMRA; Ri is a relative path between the feed to the i-th element.
Fig 2. CST model of the feed (blue box: constructed in another file and imported as a field source) and the linear TMRA (8 element dipoles tested in previous research)
Fig. 3 The feed: a X-band Horn designed use Antenna Magus (high gain and wide beam-width)
Solo walk at Derwent dams Peak District
On a nice sunny Sunday, I went to Derwent dams for a 3 hours walk. The view is picturistic. Woods, water, breeze, sunshine and lovely people make the Sunday the day.
a view of Howden Dam (Upper Derwent)
The leaves are going red soon
Light and shadow (a drive way in the woods)
It says 'take time to look, to sit, to stare, allow these hills to ease your cares' on a bench.
Lockerbrook is a field of woods with amazing view of whole reservoir
Enjoy!
6.9.12
CST official tutorial for beginner: a patch antenna
This tutorial introduce a comprehensive procedure for a beginner to design, study, simulate and post-simulation analyse a patch antenna working at a frequency range of 3-8 GHz.
Note: I share the file ONLY for educational use and preview; I do not have the copyright of the tutorial, please contact the author for further information.
click this for DROPBOX link
if you can not see the link, you may enter: https://dl.dropbox.com/u/30481878/cst-patch_antenna-example.pdf
click this for DBank (Huawei cloud storage) link
file preview image
Note: I share the file ONLY for educational use and preview; I do not have the copyright of the tutorial, please contact the author for further information.
click this for DROPBOX link
if you can not see the link, you may enter: https://dl.dropbox.com/u/30481878/cst-patch_antenna-example.pdf
click this for DBank (Huawei cloud storage) link
file preview image
26.4.12
A time-switched reflector array
The ideal of time switched/modulated array has been introduction to add a new parameter to antenna array factor equations. As known to all, using periodical switching or modulating signal can generate harmonics onto fundamental carrier. A mathematical approach to explain it is Fourier series. In old time, harmonics are bad. Scientist nowadays try to persuade these bad boys to do good things. Using different switching sequences, a time switched array can mimic the beam scanning function of phased array or generate low sidelobe power pattern.
A time-switched reflector array is a reconfigurable reflector array which using periodical switching sequence to control elements.
You can find the full paper on:
Yang Wang; Tennant, A.; , "Time-modulated reflector array," Electronics Letters , vol.48, no.16, pp.972-974, August 2 2012
IEEE XPLORE LINK
For further analysis, please be free to contact me: yang.wang@sheffield.ac.uk
A time-switched reflector array is a reconfigurable reflector array which using periodical switching sequence to control elements.
You can find the full paper on:
Yang Wang; Tennant, A.; , "Time-modulated reflector array," Electronics Letters , vol.48, no.16, pp.972-974, August 2 2012
IEEE XPLORE LINK
For further analysis, please be free to contact me: yang.wang@sheffield.ac.uk
Fig. 1 Front view
of time modulated reflector array: 8 pin-diode loaded dipole reflector array.
Fig.
2 Time switching
sequence: elements are energised sequentially and progressively with 1/8 of cycle
Fig. 3 An ideal scattering pattern of time modulated reflector array from
isotropic element: fundamental and first positive and negative harmonics
Fig. 4 A scattering pattern of time modulated reflector array predicted from
dipole array:fundamental and first positive and negative harmonics
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