A compact modal filter (MF), based on a modified microstrip line, is being developed to protect radio-electronic equipment from the destructive effects of ultra-short pulses. To improve noise suppression and reduce dimensions, FSD1020T high-frequency ceramic laminate was selected as the substrate. Based on this material, the MF cross-section was optimized within a range of parameters. As a result of this optimization, an input pulse with a duration of 150 ps and an amplitude of 2 V was attenuated 20.4 times. For comparison, on a 125-mm-long prototype made of FR4 fiberglass laminate, the attenuation was 7.8 times. The difference in the per-unit-length modal delays for this new configuration was 2.2 ns/m, which allows for the design of a 68-mm-long filter for protection against 150-picosecond pulses, almost half the length of the previously manufactured prototype. Additionally, a configuration with a maximum modal delay difference of 5.040 ns/m was found, which theoretically allows for a length reduction to 30 mm. Furthermore, the influence of cross-section parameters on the MF bandwidth was investigated. As a result of the simulation, the maximum bandwidth of the MF was 133 MHz. For an MF with parameters providing the maximum attenuation (a factor of 20.4), the bandwidth was 14.4 MHz. The possibility of increasing the bandwidth by reducing the electrical length of the filter was demonstrated: for an MF with a length of 68 mm, the bandwidth was 1.2 GHz. Thus, this study demonstrates the feasibility of creating highly efficient and compact MFs.