Compact and high isolation microstrip diplexer for future radio science planetary applications

A novel electrically compact and high isolation microstrip diplexer is engineered for Radio Occultation (RO) System for future planetary systems. The radio occultation technique is being utilized extensively in examining properties of a planetary atmosphere. A detection of shift in microwave signal is primary method to measure the occultation. The On-board RO transmitter utilizes the frequency synthesizers at two distinct frequency bands. The proposed microstrip diplexer has self-symmetrical structure that permits reduction in the tradeoff between miniaturization and port isolation. The balanced geometry of two intrinsic filters permits several transmission zeros creating sharp edge, wider stopband and significant port isolation. The further tuning of the diplexer is possible without junction matching however; the insertion loss and isolation may vary based on the frequency shift. The electrical size of the proposed diplexer is 0.52 lambda x 0.625 lambda at lower frequency. The optimized structure provides fraction bandwidth of around 4.6% at 6.7 GHz and 4.34% at 8.4 GHz frequencies. The isolation is better than 27 dB for both frequencies. The validation of simulated results is carried out through measurements on fabricated prototype.