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The effect of the human body on wearable off-body communication antennas is studied in the frequency range from 100 MHz to 2.5 GHz. Special emphasis is on single-layer structures, with metallisation in one layer only. In particular, the effect of the antenna--body-separation distance is studied extensively. The results are based on measurements of fabricated antennas worn by human subjects, as well as measurement and simulation results available in the literature. A transition region is found between 200 and 500 MHz. Below this region, the posture and size of the human body are the key parameters to determine the resonant frequency of the antenna. Because the body is thin compared to the penetration depth, the radiation pattern of a body-worn antenna can be omnidirectional since the body does not shadow the backwards radiation. Above the transition region, the body size and posture and the placement of the antenna on the body do not affect the input impedance or the resonant frequency, but the key parameter to determine the performance is the antenna--body-separation. The radiation pattern always includes a deep null because the radiation cannot penetrate the body. To ease the comparison of different wearable antenna structures, new figures of merit are proposed: Detuning percentage gives the relative difference of the centre frequencies between the body-worn and the free-space case. Usable bandwidth describes the frequency band that fulfills certain specifications in all use conditions. Crossover distance indicates the distance where the forward gain on-body equals the free-space gain--a small crossover distance indicates that the antenna is well suited for body-worn use. As a rule of thumb, the user should be kept at a minimum distance of wavelength/(2*pi) from a wearable single-layer antenna. At this distance, the input impedance and forward gain equal their free-space values, and the body-worn efficiency is between 60% and 80%. The reflection from the body can be utilised to increase the forward gain especially above 2 GHz. Single-layer topologies with quickly decaying near-fields should be preferred to dipole-like structures. It is concluded that, contrary to common belief, both single- and multilayer antenna topologies are feasible as wearable antennas. Both approaches should be considered when the antenna topology for a wearable system is selected. Single-layer antennas are especially useful in situations where the size of the antenna is restricted.

This thesis covers various methods to measure phase noise of oscillators. The main goal is to build a working phase noise measurement system for the Department of Electronics, Tampere University of Technology. The current facilities have limitations which restrict the measurements. Phase noise of oscillators can be measured for example with the following methods: phase locked loop (PLL) method, delay line discriminator method, and cross correlation method. In addition to these basic methods, some commercial phase noise measurement systems will be covered. Phase noise of two-ports can be measured with a residual method, and this will be covered shortly. The phase locked loop method is chosen for closer investigations. A measurement system based on that method is built and all related properties are introduced. Most of the required components were readily available, but two filters and a low noise amplifier for 0–100 kHz bandwidth was built and their performance verified during this project. The design and building process of those components is covered, and the performance of all the components used is verified with measurements. The measurement process and set-ups used are introduced. The measurement system built during this project can be used to measure phase noise of oscillators, as shown in this thesis. Measuring phase noise of low noise oscillators is not an easy task, but it can be done without expensive commercial phase noise measurement systems using only commonly available equipment. This thesis shows how that can be done. /Kir10 Tässä työssä paneudutaan oskillaattorien vaihekohinaan ja sen mittaamiseen käytettyihin menetelmiin. Päällimmäisenä tarkoituksena on kehittää toimiva vaihekohinan mittausjärjestelmä Tampereen teknillisen yliopiston elektroniikan laitokselle. Laitoksen RFLaboratoriossa tällä hetkellä käytetty menetelmä ei mahdollista useimpien oskillaattorien vaihekohinan mittaamista, koska järjestelmän rajat tulevat nopeasti vastaan. Oskillaattorien vaihekohinaa voidaan mitata esimerkiksi seuraavilla menetelmillä: vaihelukkomenetelmä (PLL-menetelmä), viivelinjadiskriminaattorimenetelmä ja ristikorrelaatiomenetelmä. Näiden lisäksi käsitellään kaupallisia toteutuksia ja vaihekohinan mittaamista suoraan spektrianalysaattorilla. Kaksiporttien vaihekohina saadaan mitattua esimerkiksi residuaalimenetelmällä, joka esitellään lyhyesti. Mittausmenetelmistä tarkimmin paneudutaan vaihelukkomenetelmään. Sen ympärille rakennetun mittausjärjestelmän ominaisuudet esitellään ja kerrotaan eri komponenttien vaatimuksista. Suurin osa järjestelmän vaatimista komponenteista löytyi laboratoriosta valmiina, mutta kaksi suodatinta sekä pienikohinainen vahvistin 0–100 kHz taajuuskaistalle täytyi rakentaa. Noiden komponenttien suunnittelu ja rakentaminen käydään läpi riittävällä tarkkuudella. Käytettyjen komponenttien ominaisuudet mitattiin niiltä osin kuin ne vaikuttavat käytettyyn mittausjärjestelmään. Näistä tuloksista ja mittauksista käydään läpi järjestelmän suorituskyvylle kriittiset alueet. Projektin aikana rakennettu mittausjärjestelmä todettiin toimivaksi tavaksi mitata vaihekohinaa. Pienikohinaisten oskillaattorien vaihekohinan mittaaminen on varsin vaativa tehtävä, mutta tämän työn perusteella se on mahdollista tehdä ilman erityisiä kaupallisia vaihekohinamittalaitteita käyttäen hyväksi RF-laboratoriosta todennäkoisesti löytyviä laitteita.