A Novel Defected Microstip Structure (DMS) for Microstrip Gaps

Microstrip gap is a common discontinuity in planar structures. Circuit modeling of gap as capacitances convert microstrip line to a high pass transmission line. Novel defected microstrip structure (DMS) is presented to model gap discontinuity. 3D full wave simulations show the presented model is valid up to near 30GHz until higher order modes features will appear. Planar structures have found useful various applications in microwave instruments fabrication and generally microwave engineering. Producing difierent types of antennas, fllters, couplers and etc are simple models of this increas- ing interest. One of bold features of these structures is Flexibility and using changes in their structures to achieve better performance. In this regard, new structures such as defected ground structures (DGS), coupled resonators, defected microstrip structures (DMS) and etc have been developed. Microwave discontinuity like gap, T-shape, bend, step and etc. are some common changes that apply to microwave structures for leading to speciflc design performances. In this paper, gap structure studying in microstrip and presenting new structure using defected mirostrip structures (DMS) has been discussed. 2. MICROSTRIP GAP A microstrip line can generally be assumed as transmission line. transmission lines are low pass fllters that their cutofi frequencies are much higher than our common frequencies. This cut ofi frequency is limited by higher order modes (non Qausi-TEM). Two general circuit models were presented for microstrip gap (1,7). Equivalent line length ¢lg of Fig. 3 may be calculated as (1)