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A broadband microwave limiting amplifier

Neethling, M. (Marthinus) (2004-12)

Thesis (MScIng)--University of Stellenbosch, 2004.


ENGLISH ABSTRACT: Limiting amplifiers are employed in electronic warfare (EW) systems requiring a high measure of amplitude control. These EW systems employ sensitive signal processing components that are unable to accept the full dynamic range of input signals the system must face. The limiting amplifier, however, offers the unique capability of reducing the received signal spectrum to a suitable dynamic range. A typical application of the limiting amplifier is in the instantaneous frequency measurement (IFM) receiver where the limiting amplifier allows the receiver to accurately measure pulsed signals over a wide input dynamic range The aim of this study is the design and analysis of a broadband limiting amplifier. Focus is placed on the design of a socalled backbone limiting amplifier (BLA) which forms an integral part of a proposed modular design approach for realizing a design with improved input dynamic range. A designed BLA is discussed in this thesis while insight is given as to the intricacies associated with its mechanism of operation. Over its 45 dB (- 40 to + 5 dBm) input dynamic range, the designed 2-18 GHz limiting amplifier offers a typical saturated output power of 7.5 dBm while harmonic suppression of better than 8.6 dBc is achieved. The BLA design was based on an existing limiting amplifier design, the so-called baseline limiting amplifier, employing alternating amplifiers and attenuators. Evaluation of the baseline limiting amplifier design allowed for formulation of a design hypothesis for realizing the BLA design. Physical measurements on the BLA were then used to scrutinize and validate the formulated design hypothesis. The requirements for realizing the BLA design were the establishment of a thorough radio frequency (RF) amplifier design capability, an understanding of the nonlinear phenomena associated with the RF amplifier and the utilization and control thereof within the limiting amplifier. Different RF amplifier designs that were carried out are discussed in this thesis, while it is shown how they were used to further investigate important design considerations for application in the BLA design. The computer-aided design packages namely MultiMatch and Microwave Office (MWO) were successfully used in realizing the desired broadband RF amplifier designs and the eventual BLA design.

AFRIKAANSE OPSOMMING: Beperker versterkers word gebruik in elektroniese oorlogvoering (EO) stelsels waar ’n redelike mate van amplitude beheer noodsaaklik is. Sensitiewe seinverwerking komponente, wat nie die volle dinamiese bereik van intreeseine kan hanteer nie, maak deel uit van hierdie EO stelsels. Die beperker versterker bied egter die unieke eienskap om die ontvangde seinspektra te reduseer tot ’n gepaste dinamiese bereik. ’n Tipiese toepassing vir die beperker versterker is as deel van die oombliksfrekwensie- meting ontvanger waar die beperker versterker die ontvanger toelaat om akkurate meting van gepulsde seine te doen oor ’n wye intree dinamiese bereik. Die doel van hierdie studie is die ontwerp en analise van ’n wye-band beperker versterker. Fokus word geplaas op die ontwerp van ’n sogenaamde kruks beperker versterker wat ’n integrale deel uitmaak van ’n voorgestelde modulêre ontwerpsbenadering, wat ten doel het om ’n verbeterde intree dinamiese bereik daar te stel. Oor die 45 dB (- 40 tot + 5 dBm) intree dinamiese bereik, bied die ontwerpte 2-18 GHz beperker versterker ’n tipiese versadigde uittreedrywing van 7.5 dBm terwyl harmonieke onderdrukking van beter as 8.6 dBc verkry is. Die ontwerp van hierdie komponent word in hierdie tesis bespreek terwyl belangrike aspekte oor die werking daarvan uitgelig word. Die ontwerp van die kruks beperker versterker is gebaseer op ’n bestaande beperker versterker ontwerp, of sogenaamde basis ontwerp, wat gebruik maak van afwisselende versterkers en attenuators. Evaluering van die basis ontwerp het toegelaat vir die formulering van 'n ontwerpshipotese om die kruks beperker versterker te realiseer. Fisiese metings op die kruks beperker versterker is gebruik om die ontwerpshipotese krities te evalueer. Om die kruks beperker versterker te realiseer moes die nodige RF versterker ontwerpsvaardigheid daargestel word, ’n begrip vir die nie-liniêere verskynsels in die RF versterker en die gebruik en beheer daarvan in die beperker versterker moes daargestel word. Verskeie RF versterkers wat ontwerp is word in hierdie tesis bespreek, terwyl getoon word hoe hierdie ontwerpe gebruik is om belangrike ontwerpsaspekte te ondersoek wat uiteindelik toegepas is in die kruks beperker versterker ontwerp. Die ontwerpspakkette naamlik MultiMatch en Microwave Office is suksesvol gebruik vir die realisering van die nodige wye-band RF versterkers en die uiteindelike kruks beperker versterker ontwerp.

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