The current paper describes the design of a fourth-order compact narrow-band hairpin-line bandpass filter centered at 2.5 GHz and enhanced stopband suppression ~38 dB required for wireless local area network (IEEE802.11b). The size reduction of 24% has been achieved for a conventional hairpin-line filter with a second-order inward folding of the open-end arms with an improvement in the skirt characteristics. However, the folding mechanism has been overshadowed by the presence of spurious harmonics with an attenuation level of <10 dB. Subsequently, L-shaped spurlines with optimum dimensions have been incorporated in the coupled arms of the folded hairpin-line cells. Three fourth-order filters have been designed with the incorporation of spurlines in different coupling regions, fabricated, and tested experimentally. Accordingly, an extended stopband with a rejection level of 38 dB up to 4.48f0 and a size reduction of 18% over the conventional hairpin-line filter has been achieved.

In this paper, a novel microwave oscillator incorporating miniaturized nested split-ring resonators is proposed. The high-quality (Q) factor and wide spurious-free band of the NSRR contribute to low-phase noise and high-harmonic suppression of the proposed oscillator circuits. In addition, the NSRR is featured by compact size of 0.12λg × 0.12λg, where λg is the guided wavelength of resonance frequency. The fabricated 2.4 GHz oscillator has an output power of 11.7 dBm with 5 V DC supply and 10 mA current consumption. The second harmonic suppression is −45.49 dBc, the phase noise is −110 dBc/Hz @100 kHz, and the DC–RF conversion efficiency is measured as 30%.