# A Novel UWB Pulse Expander Using an Integrated Microstrip Splitter, Delay Lines, and a Combiner
## 4 Conclusions  
This research focuses on integrating a microstrip splitter delay lines, and a combiner into a single electrical scheme, capable of expanding the duration of picosecond-range electrical pulses without significant distortion of the rising and falling edges of the pulses.  
We present initial considerations, Ansys HFSS simulations, and experimental validation of the designed pulse expander and its components. The design was fabricated and tested by capturing and analyzing signal waveforms on the DSO. The main novelty of this research is the concept of splitting a pulse into multiple pulses using a custom-designed microstrip pulse splitter and shifting these pulses in time before summing them together by using a pulse combiner. This paper proposes that--contrary to the theory of branch-line power dividers--isolation resistors in the pulse splitter can be omitted to achieve a larger pulse amplitude at its output if mutual isolation between the output ports is optional for the desired application.  
The pulse expander proposed in this paper can expand an input Gaussian pulse with a duration of 210 ps up to about 455 ps with an acceptable pulse shape and amplitude.  
This research presents an innovative solution to the actual problem of ultra-short pulse expansion in UWB communications systems. The proposed ideas can be further explored and the designs refined to achieve better matching between the components of the expander, reduce its size, and enhance spectral characteristics.  
In this work, a low-cost FR-4 substrate was used for the expander design and fabrication. This substrate exhibits frequency-dependent variations in its dielectric constant and loss tangent within the critical frequency band for the expander, along with significantly higher losses compared to more expensive substrates. Future work will involve designing and fabricating the expander using a higher-quality substrate. This will also provide an opportunity to evaluate the trade-off between using a lower-cost, lower-quality substrate and a higher-cost, higher-quality one.  
The given design can be employed for a broad range of applications that require time domain processing at microwave frequencies. This includes pulse sequence generation, shaping, pulse suppression, and matched filtering. For instance, the proposed design can be directly employed for cost-efficient and power-efficient generation and detection of pseudo-noise (PN) sequences in UWB communication and radar applications.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app142411641/s1](https://www.mdpi.com/article/10.3390/app142411641/s1)]([https://www.mdpi.com/article/10.3390/app142411641/s1](https://www.mdpi.com/article/10.3390/app142411641/s1)).  
Conceptualization, J.S., T.S. and A.A.; methodology, T.S.; software, T.S. and N.T.; validation, S.M., N.T., T.S., D.C., S.S. and K.R.; formal analysis, J.S. and T.S.; investigation, S.M., T.S. and D.C.; resources, A.A. and S.S.; data curation, T.S., S.M., N.T. and K.R.; writing--original draft preparation, J.S. and T.S.; writing--review and editing, A.A., S.M., N.T., D.C. and S.S.; visualization, N.T.; supervision, A.A.; project administration, A.A.; funding acquisition, A.A. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Latvian Council of Science, grant no. lzp-2021/1-0475, \"Picosecond-resolution pulse position modulation for beyond-the-limits energy efficiency of communications\".  
Not applicable.  
Data Availability Statement: Data are contained within the article and Supplementary Materials. The data used to support the findings of this study are available from the corresponding author upon request.  
The authors declare no conflicts of interest.