KoREMA - Croatian Society for Communications, Computing, Electronics, Measurement and Control
Abstract
Twin slot antennas coupled to superconducting devices are currently being developed for terahertz mixers and direct detectors for astronomical observations. Although these mixers show promising performance in terms of noise temperature, they usually also show a considerable downward shift in the center frequency, especially when compared with calculations obtained with commonly used simplified models. This discrepancy is actually due to a variety of reasons. The effect of the bolometer-to-CPW transition, the RF choke filter and the radiation losses in the CPW line have been demonstrated in a recent study to be some of the most important reasons of the disagreement between calculations and measurements. In this paper we discuss these effects and other features, such as the silicon lens, obtaining a more robust model suitable not only for analysis but also for the synthesis of these circuits. A complete set of terahertz mixers at four different center frequencies, between 600 GHz and 2.5 THz, has been fabricated following the guidelines provided by our model and is currently being tested. The preliminary results of power coupling measured at 2.5 THz are still not as good as expected, however they show that our model is going in the right direction. With respect to previous designs, the new mixers have now a much better efficiency in terms of power coupling to the superconducting device and the center frequency shift is now decreased roughly from 30 % to 10 %.Dvostruka prorezna antena u koju su ugrađeni supravodljivi elektronički elementi trenutačno se razvija za terahercna mješala i detekore za primjenu u astronomskim promatranjima. Iako ta mješala imaju nisku temperaturu šuma, redovito se javlja značajan pomak središnje frekvencije na niže vrijednosti u usporebi s rezultatima proračuna dobivenih uobičajenim pojednostavljenim modelima. Ovo je odstupanje frekvencije posljedica više uzroka. Najnovija su istraživanja pokazala da su najvažniji uzroci ovog odstupanja prijelaz između bolometra i koplanarne prijenosne linije, filtar za potiskivanje radiofrekvencijskog signala i gubici zbog zračenja koplanarne linije. U ovom se radu razmatraju ovi uzroci te novi elementi, kao što je silicijska leća, da bi se dobio robustniji model pogodan ne samo za analizu već i za sintezu ovih sklopova. Koristeći ovaj model izrađeno je i ispitano više terahercnih mješala na četiri različite središnje frekvencije između 600 GHz i 2,5 THz. Preliminarni rezulati prijenosa snage na 2,5 THz još uvijek nisu u potpunosti zadovoljavajući, ali pokazuju da je predloženi model postavio dobre smjernice. U usporedbi s ranijim izvedbama, nova mješala imaju mnogo bolju djelotvornost prijenosa snage u supravodljive elektroničke elemente, a pomak središnje frekvencije se smanjio s 30 % na 10 %
