**5. Conclusion**

In this chapter, novel hardware components, algorithms, systems and possible approaches in the field of UWB radar and communications for biomedical applications have been presented.

Three novel UWB antenna concepts have been introduced targeting different tasks in the medical field. For communication purposes, a circular slot antenna excited with a dipole element has been presented. Its novel differential feeding concept suppresses parasitic radiation by cable currents on the feed lines. In a new concept for applications requiring directive antennas with small beamwidths, a dielectric rod has been added to the circular slot antenna, resulting in a compact and easy-to-fabricate antenna with a high mean gain of 8.7 dBi. Furthermore, a miniaturized UWB slot antenna, optimized for the radiation in human tissue has been designed.

A flexible, differential chipset using Si/SiGe HBT technology for IR-UWB applications has been presented. On the transmit side, a low power impulse generator based on cross-coupled LC oscillator is successfully realized. It generates ns-duration and stable impulses with a spectrum well fitting the FCC mask. This impulse generator has been successfully extended to include tunability to the FCC, ECC and Japanese UWB masks as well as a biphase modulation function. On the receive side, an energy detection receiver optimized for simple on-off keying communications and a correlation detection receiver for short range radar applications have been presented. Both receivers are based on a fully differential UWB low-noise amplifier and a four-quadrant RF multiplier which performs either squaring or multiplication operations.

Using the aforementioned components, two bistatic radar systems, a single-ended and a differential configuration, have been built. Their performance has been demonstrated in a setup for vital sign detection.

Regarding UWB communications, a proposal for a transmission scheme has been discussed, using a special spread spectrum method and energy detection combined with a comb filter, which improves the SNR and rejects narrowband interference. The robustness of this concept has been demonstrated for multipath propagation channels as well as for narrowband interference, noise, and synchronization errors. The approach fits well to medical applications, because small multipath delay spreading promises an easier realization of the analog time delay needed for the comb filter. A trade-off between the number of UWB impulses per symbol (bit) and the data rate requirement has to be made for different applications.

In addition, a new concept for an impulse-radio transmission based on code shift keying with a comb filter receiver has been introduced. In this concept, the delay of the analog delay element could be shorter than the channel impulse response. It has been shown and verified by simulation that the performance and the resistance against multipath propagation, noise, narrow band and multisensor/multiuser interference are the same as in the original approach with longer delays in the comb filter loop.

Simulation results have shown that particle filtering can improve the ranging and tracking performance of an impulse UWB radar substantially in scenarios with low signal-to-noise ratio and cluttering in comparison with more conventional methods. A trade-off between realization complexity and performance can be adjusted thanks to the flexibility of the proposed algorithm.

It has been shown practically that a non-coherent energy detector is a suitable receiver concept for UWB communication with implants. The energy detector operates without synchronization and is insusceptible to dispersive effects of the channel. Demonstrational measurements in tissue-mimicking liquid have been performed with a data rate of 100 Mbit/s meeting the requirements for modern medical devices.

A 3D surface estimation algorithm based on trilateration for ultra-wideband pulse radars has been presented and derived mathematically. Since this method needs no preprocessing of measurement data its implementation is very simple. In 3D surface measurements the performance of the proposed algorithm has been verified, and comparisons with established algorithms have shown a similar performance regarding estimation errors.

As a next step towards the targeted application of catheter tracking, a method for the localization of UWB transmitters buried in homogeneous dielectric media has been presented. With the aid of surface estimation algorithms a localization behind an arbitrarily shaped medium boundary is possible. For this purpose we have proposed a system consisting of an array of UWB radar sensors outside the medium and a beacon inside the medium transmitting a short UWB pulse. The external sensors serve for surface scanning and for measuring the time of arrival of the transmitted signal. The performance of the proposed localization algorithm has been verified using electromagnetic field simulations and measurements, in which a transmitter has been placed in tissue-mimicking liquid.
