Diplexers are three-port filtering devices with a junction connecting two channel filters; the common port connects to an antenna which serves the two channel filters bearing the second and the third port. Conventionally, diplexers are designed using transmission line based junctions or circulators, but recently a new approach of designing diplexers with resonant junctions was introduced and this led to a reduction in the total number of components needed in the system or reduction in size. Such techniques are reported in [1] where two novel multiplexer topologies based on all-resonator structures were implemented at X-band using waveguide technology. In [2], a diplexer with a resonant star-junction and a triplexer with a non-resonant node star-junction were presented using synthesis approach. [3] presented a diplexer with asplit-ring resonator (SRR) as a common resonator and signal splitter. In [4], an FDD diplexer with a T-shaped junction resonator was presented. This work presents a diplexer that uses a SRR as a common resonator to connect two channel filters. The SRR comprises two nested open-loop resonators resonating at different frequencies corresponding to the two passbands of the diplexer. This differs with [3] in that the nested resonators are synchronously tuned in [3], whereas these are asynchronously tuned in this work resulting in more widely separated channels. The two channels at 2 GHz and 3 GHz each with a 4% fractional bandwidth were separately designed and joined together using the SRR. The SRR was used to replace the first resonator of each filter, resulting in reduced circuit size. Fig. 1(a) illustrates the coupling topology of the SRR where the resonator 1 and 2 represents the resonator of low and high frequency respectively. Resonator 2 is nested in resonator 1 thereby allowing all external couplings to be made with resonator 1. Fig. 1(b) illustrates the coupling topology of the proposed diplexer.