With the growing demand of compact radio transmitters, so do the need for silent and efficient thermal management systems. Given the restricted form-factor, ensuring robustness of a unit with a detachable fan tray imposes a challenge. In this thesis the authors were tasked with creating a new design solution where the robustness, thermal and noise performance of the cooling system is revised. The project was initiated with an investigation of the baseline product, the AIR5322, to identify areas of in need of improvement. The initial goal was to design an integrated fan tray that would not require in-field maintenance. A literature study was performed to evaluate common integrated cooling solutions in compact electronic devices, which was then followed by concept generation study. These were then ranked based on Pugh’s selection method. An integrated solution was deemed not feasible due to the average lifespan of common fans used in this type of product. A CAD model of said design was created, for which a prototype was manufactured by Ericsson. The final design consisted of a set of 80mm Noctua (NF-A8) fans in a new fan tray, retrofitted onto a modified stock AIR5322 heatsink. Experimental tests were conducted where heat dissipation, noise generation and mechanical robustness was tested. The results concluded that the prototype design managed to reduce the temperature of the entire unit, up to 17°C cooler and lower the sound levels by up to 18 dB. The prototype, despite halving the number of fans, retained the single fan failure redundancy, as running just one fan allowed for performance that was equal to or better than the reference solution at full capacity. The prototype was deemed robust enough to withstand the drop test, which was performed at −18°C. Additional work would include to incorporate fans with an appropriate IP rating and to fully complete the testing using a climate chamber and performing impact testing. / Med den växande efterfrågan på kompakta radiosändare ökar också behovet av tysta och effektiva kylsystem. Givet den begränsade formfaktorn innebär det en utmaning att säkerställa robustheten hos en enhet med en löstagbar fläktlåda. I denna avhandling fick författarna i uppdrag att skapa en ny designlösning där kylsystemets robusthet, termisk prestada och ljudprestanda revideras. Projektet inleddes med en undersökning av basprodukten, AIR5322, för att identifiera eventuella förbättringsområden. Det ursprungliga målet var att designa en integrerad fläktlåda som inte skulle kräva fältetunderhåll. En litteraturstudie genomfördes för att utvärdera vanliga integrerade kyllösningar i kompakta elektroniska enheter, som sedan följdes av konceptgenerering. Dessa utvärderades sedan och rangordnades utifrån Pughs urvalsmetod. En integrerad lösning ansågs inte möjlig på grund av den genomsnittliga livslängden för typiska fläktar som används i liknande produkter. En CAD-modell av denna design skapades, för vilken en prototyp tillverkades av Ericsson. Den slutliga designen bestod av en uppsättning 80 mm Noctua (NF-A8) fläktar i en ny fläktlåda som monterades i en modifierad kylfläns för AIR5322. Experimentella tester där värmeavledning, bullergenerering och mekanisk robusthet testades. Med resultaten kunde följande slutsats dras: prototypdesignen lyckades sänka temperaturen på hela enheten med upp till 17°C och sänka ljudnivåerna med upp till 18 dB. Prototypen visade sig ha en fläkt vara termiskt redundant, eftersom en fläkt igång resulterade i en prestanda som var lika med eller bättre än referenslösningen. Prototypen ansågs vara robust nog att motstå falltestet, som utfördes med prototypen nedkyld til −18°C. Ytterligare arbete som kan vara till nytta för detta projekt skulle vara att införliva fläktar med en lämplig IP-klassning och att fullständigt testa prototypen med klimattester och slagtester.

The random fluctuations of signal phase of an oscillator limit the precision of time and frequency measurements. The noise and long-term stability of the system’s oscillator or clock is of major importance in applications such as optical and wireless communications, high-speed digital electronics, radar, and astronomy. The Optoelectronic Oscillator (OE Oscillator), a new class of time delay oscillator with promise as a low-phase noise source of microwave carriers, was introduced by Steve Yao and Lute Malek in 1996. The OE Oscillator combines into a closed loop an RF photonic link and an RF chain. The RF photonic link consists of a laser, electro-optic modulator, optical fibre delay line, and a photo-receiver that together provide an RF delay. An RF chain consists of one or more amplifiers and a RF resonator that together provide the sustaining amplification and the frequency selectivity necessary for single mode oscillation of the loop. The low loss of optical fibres enables the attainment of delays that correspond to optical fibre lengths of several kilometers. It is the long delay, unattainable in an all electronic implementations that is responsible for the superior phase noise performance of an OE Oscillator. In this thesis the fundamental principles of operation of an OE Oscillator are described and the principal sources of in-loop phase fluctuations that are responsible for phase-noise identified. This lays the ground for an exposition of the mechanism that describes the perturbation of a time delay oscillator by injection into the loop of a carrier that is detuned in frequency from the natural frequency of the oscillator. For sufficiently small detuning the oscillator can become phase locked to the injected carrier. The model presented in the thesis generalises the traditional Yao-Maleki and Leeson model to include all the important features that describe the injection locking dynamics of an OE Oscillator. In particular the common assumptions of single mode oscillation and weak injection are removed. This is important to correctly predict the effect of injection locking on the spurious peaks in the phase noise spectrum corresponding to the side-modes of a time delay oscillator. Simulation results are presented in order to validate the dynamics of the oscillator under injection and analytic results on the lock-in range and phase noise spectrum. A 10 GHz OE Oscillator with a single 5km delay line is used as an example in the simulation illustration.