This paper demonstrates the initial stage of developing a 1-18GHz five port frequency multiplexer. The design details of 1-6GHz and 6-10GHz bandpass filters are discussed along with their results. Modified optimum short-circuited stub technique is used for designing a 1-6GHz bandpass filter and cascading high pass filter with low pass filter is used for the design of a 6-10GHz bandpass filter. Both filters achieve a passband return loss <-15dB, passband insertion loss <2dB and stopband attenuation > 50 dB. © 2023 IEEE.