| Summary: | Thesis (PhD)--Stellenbosch University, 2013. === ENGLISH ABSTRACT: The triple layer pillbox antenna is an antenna topology well suited for use as a stackable "plank" element in radar applications. Its suitability arises from the folding which makes it compact,
and from the layered nature which can be exploited for low cost manufacture. Existing designs of these "cheese" antennas, whether two or three layers, suff er from two drawbacks: a) The bend or fold between layers introduces undesirable reflections and b) Due to their parabolic sector geometry virtually no pattern control is available to the designer. This work addresses both of these shortcomings.
A low reflection transition is realized by introducing simple compensating elements into the
design which, with minimal manufacturing complexity, off er high performance over a broad
frequency and incidence angle range. To cater for pattern control the concept of "dual shaped
reflectors" is borrowed from the high performance dish antenna literature and implemented in
the pillbox geometry. This shaping off ers limited but useful control of the aperture distribution
and thus indirectly over the radiation pattern.
To test these innovations three X-band antennas have been designed, built and measured. An
initial unshaped geometry is used for the fi rst design to show the fold or bend performance. This
antenna has a simulated and measured 2GHz usable bandwidth, with a reflection coeffi cient
below -10dB and side-lobes below -27dB over a bandwidth in excess of 20%. Shaping is then
added to show how either side-lobe levels can be lowered to below -32dB, or the gain enhanced
by 2dB. The enhanced designs have been built and experimentally veri fied. === AFRIKAANSE OPSOMMING: Die drie-dubbel gevoude pildoos antenna is `n antenna topologie wat goed gepas is vir die gebruik
as `n stapelbare "plank" element vir radar aanwending. Sy geskiktheid kom vanwee die vou van
die struktuur wat dit meer kompak maak sowel as die konstruksie moontlik goedkoper maak.
Huidige ontwerpe van die antenna strukture, hetsy twee of drie lae, ly aan twee tekortkominge:
a) Die buiging of vou tussen die lae veroorsaak ongewensde weerkaatsings en b) Weens hul
paraboliese meetkunde is feitlik geen beheer oor die stralings patroon beskikbaar nie. Hierdie
werk spreek beide hierdie tekortkominge aan.
`n Lae weerkaatsing by die oorgang is verkry deur eenvoudige kompenserende elemente by die
ontwerp in te voeg wat, met minimale vervaardigings kompleksiteit, hoë werkverrigting lewer oor `n breë frekwensie en invals hoek spektrum. Om patroon beheer te voorsien is die konsep van "dubbele gevormende weerkaatsers" geleen vanaf die hoë verkverrigting skottel antenna literatuur en in die pildoos meetkunde ingestel. Hierdie vorming lewer beperkte dog nuttige beheer oor die
openings verspreiding en dus indirek oor die stralings patroon.
Om hierdie nuwighede te toets is drie X-band antennas ontwerp wat gebou en gemeet is. 'n
Aanvanklike ongevormende meetkunde is gebruik vir die eerste ontwerp om die vou of buiging
se werksverrigting te bewys. Hierdie antenna het `n gesimuleerde en gemete 2GHz bruikbare
bandwydte met `n weerkaatsings kwosiënt onder -10dB en sylobbe van minder as -27dB oor
`n bandwydte van meer as 20%. Vorming is dan bygevoeg om te bewys dat of verlaagde sylobbe
van onder -32dB of verhoogde aanwins met 2dB verkrygbaar is. Die verbeterde ontwerpe is
gebou en eksperimenteel bewys.
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