Tuneable Recursive Active Monolithic Microwave Integrated Circuit Filters

Sammanfattning: In this thesis tuneable recursive active monolithic microwave integrated circuit (MMIC) filters are studied theoretically and experimentally. A possible future application for such filters is, for example, the microwave receivers of adaptive radar antennas. Tuneable narrow-band active MMIC filters could be used there to realize more compact and less complex receiver architectures, thus making much more cost effective radar systems possible in the future. Active MMIC filters of the recursive type have, in contrast to most other known types of active MMIC filters, the advantage that they can be designed with a rather high gain without adding too much noise. Thus, narrow-band recursive active MMIC filters can be an interesting alternative to the classic combination of a low-noise amplifier and a bandpass filter possibly enabling an even higher level of integration. In this thesis we analyze important filter requirements that must be fulfilled if such filters are to be used in frequency-hopping radar systems. Examples of such filter requirements are a sufficiently high gain, dynamic range and center frequency tuning range in combination with a sufficiently low noise figure. It is also of great importance that the filters are not too sensitive to temperature variations.In this thesis we present for various topologies of recursive active filters a theoretical analysis of noise, large signal performance and temperature sensitivity. First, we present for different recursive active filter topologies analytical models of filter gain sensitivity to temperature drift or process parameter induced variations. The theoretical results obtained from these filter models are compared with experimental data of a recursive active MMIC filter and a good agreement between these results is found for low filter Q-factors or for small deviations in temperature. Based on the theoretical analysis two different methods of minimizing the filter gain sensitivity of recursive active MMIC filters are presented. Second, a theoretical analysis of the optimum filter noise figure that includes the effects of metallic and dielectric coupler losses is presented for two recursive active filter topologies. These coupler losses are found to be important factors that limit the optimum noise performance of recursive active MMIC filters. Consequently, such losses should be taken into account when we want to determine which recursive active filter topology is optimal with respect to minimum noise figure and minimum noise measure. Third, analytical models of filter intermodulation distortion are developed for the intended filter topologies. A method that significantly improves the third order intercept point and thereby the spurious-free dynamic range of recursive active MMIC filters with a given relative filter bandwidth is then proposed. Following this approach our theoretical results indicate that it should be possible to design a second order recursive active MMIC filter with a performance that is sufficiently good for future advanced radar applications. The theoretical results obtained from our noise and large signal models are compared with the corresponding experimental and simulated data of two recursive active MMIC-filters. An overall agreement between these resultsis generally found.Finally, we present a novel design of a tuneable recursive active MMIC filter based on the principles discussed above. The filter center frequency tuning range (8-10GHz) corresponds to the lower part of the X-band. The MMIC filter design has been sent to a commercial semiconductor foundry to be fabricated in a standard GaAs PHEMT process technology. Filter simulations using a commercially available microwave simulator together with foundry-provided circuit component libraries strongly indicate that it can achieve a performance adequate for frequency hopping X-band radar antennas.Our proposed MMIC filter has also been used in a first design of an 8-10 GHz frequency agile onchip X-band radar receiver front-end. The use of such compact MMIC front-ends is expected to result in a significant reduction of the size and cost of the microwave receiver modules in future advanced X-band radar systems.