A Novel UWB Pulse Expander Using an Integrated Microstrip Splitter, Delay Lines, and a Combiner

Passive pulse shaping at frequencies above 1 GHz is mainly achieved through frequency-domain processing using filters. Unfortunately, the conventional frequency domain approach does not allow precise control of the impulse response of the filter, therefore, setting limitations to the pulse shaping accuracy. Sub-nanosecond pulse expansion that preserves steep pulse transitions is one of the ultra-wideband (UWB) applications where frequency domain approaches do not provide satisfactory results. This paper proposes a highly innovative approach based on time-domain signal processing using a set of parallel microstrip delay lines connected in a network accompanied by a splitter at the input and a combiner at the output. The proposed design, analogous to finite impulse response (FIR) filters in digital signal processing (DSP), provides fine-grained control over time-domain characteristics and supports the implementation of complex functions, including pulse expansion. This paper presents a detailed analysis of previous work and theoretical considerations regarding the advantages and limitations of UWB pulse time-domain processing. Moreover, detailed HFSS simulations of components, such as a microstrip pulse splitter, delay lines, a combiner, and their combinations, are presented. Finally, the results of the experimental validation of the device, fabricated on an FR-4 substrate, are presented. Technology for effective implementation of a pulse splitter, delay lines, and a pulse combiner, as well as their matching, can be considered as key findings of the given research. Limitations associated with matching and delay estimation for pulsed UWB signals are highlighted.