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In this Letter, a new design of dual-band patch filter is proposed with greatly improved bandwidth and miniaturised size based on one single modified circular patch resonator. In this design,… Click to show full abstract
In this Letter, a new design of dual-band patch filter is proposed with greatly improved bandwidth and miniaturised size based on one single modified circular patch resonator. In this design, a metallic via is introduced in the centre region of the patch to develop the modified resonant TM01 mode (TM′01 mode), while two types of slot perturbations are adopted to separate a pair of degenerate modes of TM11 (TM11A and TM11B) and control another pair of degenerate modes of TM21 (TM21A and TM21B), respectively. Thus, two passbands with one transmission zero (TZ) can be attained by elaborately exploring these resonant modes (the TM′01 and TM11A modes form up the lower passband while TM11B and TM11A modes constitute the upper passband, and TM21B mode is responsible for the TZ). For verification, one prototype is implemented. Results indicate that the novel dual-band filter (centred at 3.7 and 5.3 GHz) exhibits not only relative compact size (0.36 λ g × 0.36 λ g), but also much larger 3-dB fractional bandwidths (27 and 13%), nice return loss (better than 21 dB) and insertion loss (better than 1.0 dB), compared with other reported patch filters.