A band-rejection type RF switch, which has very high offstate isolation, low on-state insertion loss, and adjustable bandwidth, is proposed using a dual-mode ring resonator and two PIN diodes. To enable sharp band stop and dual-mode transmission, the ring resonator is directly fed using nonorthogonal feeding. Two PIN diodes are mounted in shunt after a quarter-wavelength transmission line from each feeding point, to turn the switch on and off and to reduce the size of the ring resonator. To estimate the practicable transmission characteristics of the proposed switch in relation to the angle of feeding and the wire-bonded PIN diodes, a lossy transmission-line equivalent circuit model is proposed, and even-odd mode analysis is carried out. The calculated frequency response shows good agreement with the measurement. The fabricated switch exhibits off-state isolation of 43.08 dB, and on-state insertion loss of 0.74 dB, within the range of 2.298-2.401 GHz.ABSTRACT: A band notched CPW UWB filter backed by rectangular rings is proposed. Initially, cascading of aperture-backed second-order microstrip filters is done to achieve the UWB passband. Later, to take advantage of the CPW geometry, the filter is converted to CPW configuration with rings at the back to achieve sharp cutoff characteristics and a notch at 5.1 GHz.

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For the size reduction and sharp attenuation of the low‐pass filter in lower RF frequency range, a semilumped elliptic‐function low‐pass filter was proposed using microstrip meander line, chip capacitor, and radial stubs. To estimate more accurate inductance of microstrip meander line, it was modeled in an inhomogeneous dielectric environment, and then the calculated inductance was compared with the conventional case. To provide an additional attenuation pole in stop‐band, radial stubs were added to the proposed structure. The 3‐order low‐pass filter has a cutoff frequency of 1GHz and dimension of 14.6 × 16.3 mm2 on the substrate with a relative dielectric constant of 3.38. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1777–1779, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22545