Today’s data rates in wired networks can reach 100 Gbit/s using optical fiber while data rates in wireless networks are much lower - tens of Mbit/s for 3G mobile communication and 480 Mbit/s for ultra-wideband (UWB) short range wireless communications. This difference in data rates can mainly be explained by the limited allowed frequency spectrum, the nature of the radio signal and the high requirements imposed on all hardware designed for high speed and wideband wireless communications. However, the demand on wireless commercial applications at competitive costs is growing. The first step in regulations allowing higher data rates for wireless communications was taken in 2002, when the Federal Communication Commission (FCC) in USA released unlicensed the 3.1-10.6 GHz frequency band restricting only the power level (maximum mean equivalent isotropic radiated power density of a UWB transmitter is -41.3 dBm/MHz) in the band 3.1-10.6 GHz. But Europe, Japan and recently China have put additional restrictions on the 3.1-4.8 GHz band. The restrictions address the problems that have raised from the coexistence and colocation of the UWB systems with other narrowband wireless systems. Thus, the 6-9 GHz band combined with an increased modulation order scheme is of large interest.

Operating at higher frequency and wider bandwidth than today’s communication technologies, with the general task of maximizing the wireless data rate while keeping the power consumption low, requires new communication system solutions and new circuit design approaches. These new solutions also require understanding of many multi-disciplinary areas which until the recent past were not directly related: from classic analog circuit design to microwave design, from modulation techniques to radio system architecture.

In this thesis, new design techniques for wide bandwidth circuits above 3 GHz are presented. After focusing on ultra-wideband low-noise amplifier (UWB LNA) design for low-power and low-cost applications, the practical implementation and measurement of a 3.1-4.8 GHz UWB LNA is addressed. Passive distributed components of microstrip transmission lines are intensively used and their contribution to the UWB LNA performance is studied. In order to verify the design methodology while extending it to the UWB radio front-end,

the UWB LNA is integrated on the same substrate with a pre-selecting filter with the frequency multiplexing function. In this way, the concept of frequencytriplexed UWB front-end is demonstrated for the Mode 1 multi-band UWB bandwidth 3.1-4.8 GHz. Using the proposed receiver front-end topology, better receiver sensitivity and selective operation can be achieved.

The later part of the thesis investigates ultra-wideband 6-9 GHz receiver and transmitter front-end topologies for Gbit/s data rates and low power consumption. To capture the advantages offered by distributed passive components, both the transmitter and receiver use the six-port correlator as the core of a passive mixer. Modelling and design of the 6-9 GHz UWB front-end transceiver include different receiver topologies and different modulation schemes. Finally, the 7.5 GHz UWB transceiver front-end is implemented and evaluated. Measurement results confirm the large potential of the six-port UWB front-end to achieve multiple Gbit/s data rates. This may open for future solutions to meet the continuous challenge of modern communication systems: higher data rates at low power consumption and low cost.

Requirement for high speed wireless connectivity is propelling research in advanced communication systems. Low power and wide bandwidth of the ultra-wideband technology makes it a potential candidate for high speed data transmission. The six-port based radio systems and wideband antennas have been studied and presented in this dissertation for ultra-wideband applications.

The six-port modulator operation with carrier leakage suppression was demonstrated at a center frequency of 7.5 GHz. The six-port correlator utilizes a quarter wavelength transmission line for carrier leakage suppression, together with diodes or eld effect transistors as variable impedance terminations. Especially, a differential six-port modulator was designed and veried through simulation and measurement. The prototype shows its capability of carrier leakage suppression and high speed data transmission with 256-quadrature amplitude modulation at 50 Msymbol/s at the center frequency of 7.5 GHz. Furthermore, a differential six-port demodulator was demonstrated with the 16 quadrature amplitude modulation at a data rate of 0.8 Gbit/s at the center frequency of 7.5 GHz. It uses zero-bias anti-parallel Schottky diodes as power detectors.

Flexible antennas were designed such that they can be housed by folding it around in space limited environment with stable performance over a wide operation bandwidth. Measurement, on a exible dipole antenna with integrated balun, shows that it covers a frequency band from 6 to 11 GHz at a voltage standing wave ratio lower than 2.5 with the antenna eciency above 86%. A miniaturized monopole antenna that is not only capable of operating over an ultra-wideband but also for lower frequency bands was invented and veried. It covers a frequency range from 1.35 to 11.5 GHz. It gives a quasi-omnidirectional radiation pattern and high eciency. The antenna has a patent pending status with the United States Patent and Trademark Oce.