Isolator is a non-reciprocal device that is an integral component of RF systems. This article details the design approach and simulation studies of a microstrip based drop in isolator at X band intended to be used in aerospace modules. Isolator design and realization is critical as it is sensitive to the choice of ferrite-dielectric assembly and magnetic bias. The design presented here operates at 8.2 GHz, offers an Insertion Loss better than 0.3 dB, Return Losses better than 23 dB and Isolation better than 20 dB over a relative bandwidth of 13%. It is designed using Yttrium-Calcium Garnet as the ferrite and Alumina as the dielectric substrate which are readily available and does not rely on access to specialty materials.