Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This thesis addresses the complications that are encountered when characterising the performance of differential microwave LNAs. The predominant sources of noise in electronic circuits are introduced and equivalent two-port noise models for active devices are derived. Correlation between noise generators are defined by means of the noise correlation matrix and existing network theory is adapted to include noise analysis of twoport and multi-port networks. Mixed-mode scattering parameters are introduced in order to define the signal performance of differential and common-mode propagation in multi-port networks and, by applying the same theory, the mixed-mode correlation matrix for a three-port dLNA is derived. Furthermore, an expression is derived for de-embedding the differential noise figure of a three-port dLNA using two single ended measurements. Two dLNA designs, both incorporating wideband 180°-Hybrid ring couplers, are discussed and the differential signal and noise performance of the dLNAs are compared to that of their constituent single ended LNAs. / AFRIKAANSE OPSOMMING: Hierdie tesis behandel die komplikasies wat ontwerpers in die gesig staar tydens die karakterisering van mikrogolf differensiële laeruis versterkers. Die hoof ruisbronne in stroombane word bespreek en ekwivalente tweepoortnetwerkmodelle vir aktiewe toestelle word afgelei. Korrelasie tussen ruisbronne word gedefnieer deur middel van ruiskorrelasiematrikse en bestaande tweepoort- en multipoort-netwerkteorie word aangepas om ruismodelle in te sluit. Weens die feit dat differensiële- en gemene-wyse voortplanting van seine voorkom in multipoortnetwerke word gemengde-modus S-parameters behandel. Dieselfde teorie maak dit vervolgens moontlik om die gemengde-modus ruiskorrelasiematriks van ’n drie-poort differensiële laeruis versterker af te lei. Verder word daar ’n wyse voorgestel waarmee die differensiëleruissyfer van ’n drie-poort differensiële laeruis versterker vanuit twee enkel ruissyfermetings bereken kan word. Twee differensiële laeruis versterker ontwerpe, waarvan beide wyeband 180 -differensiaalkoppelaars implementeer, word bespreek en die differensiëlesein- asook die differensiëleruis-werking word vergelyk met die werking van die omsluite ongebalanseerde laeruis versterkers.