Design of compact microstrip lowpass filters using coupled half-circle defected ground structures (DGSs)

Microstrip filter with defected ground structure: a close perspective

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Fig. 2.Different DGS geometries: (a) dumbbell-shaped [17, 18], (b) circular head dumbbell, (c) arrow head dumbbell [42], (d) U-shaped [21, 43], (e) H-shaped [22], (f) square heads connected with U-slots [21], (g) square slots connected with narrow slot at edge [44], (h) cross-shaped [22, 23], (i) inter-digital [45], (j) Fractal [27], (k) open loop dumbbell [17], (l) L-shaped [46], (m) meander lines [44, 47], (n) U-head dumbbell [44], (o) double equilateral U [48], (p) V-shaped [21], (q) split-ring resonators [25, 26], (r) concentric ring shaped [24], (s) half-circle [49], and (t) spiral-shaped [20].

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Compact tunable U-Hi-Lo low pass filter using quasi C-shaped stubs

“…All previous demands make the RF filters compatible with the modern wireless technologies [1,2]. There is an enormous demand for designing and implementing a low pass filter with a pass-band covering the L-band (1-2 GHz), S-band (2-4 GHz), and C-band (4)(5)(6)(7)(8). Microstrip low pass filters with advanced features have been widely utilized in various technological aspects and due to their importance; many techniques have been used to obtain the required features.…”

“…One of the techniques used was cascaded technique where resonators are placed in horizontal or vertical topology, but it needs a larger occupied area in addition to larger coupling between resonators is occurred [3,4]. Other techniques can also be used to improve the behaviour of the low pass filter such as stepped-impendence resonators (SIR) [5,6], defected ground-plane structures (DGS) [7][8][9][10], combination of DGS and DMS [11], interdigital line resonator (ILR) [12], and meander-loop resonator [13], meander inductor [14,15], complementary split-ring resonator (CSRR) [16], and combination of SIR and DGS [17].…”