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Abstract-A compact ultra-wideband (UWB) bandpass filter (BPF) with dual notch bands is presented using a tri-layer structure. In the design of UWB BPFs, it is desired to have a uniform 3.1 GHz to 10.6 GHz full-band transmission response. Dual notch bands are generated for filtering out the interferences caused by strong signals transmitted from WLAN and/or WiMAX systems at 5.8 GHz and 3.5 GHz, respectively. The sharp rejection of WiMAX signals is achieved by adding meander open-loop resonators on the middle layer. Another rejection of WLAN signals is introduced by adding a Cshaped resonator on the bottom layer. The proposed filter is not only realized theoretically but also verified by a full-wave electromagnetic simulation. The designed tri-layer UWB BPF with dual notch bands was fabricated by two FR4 printed circuit boards with the permittivity of 4.4 and the thickness of 0.8 mm. The total area is 11 mm × 10.5 mm.

The suppression at 5.8 GHz is larger than 15 dB. The proposed configuration is proved to be both simple and compact.

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New universal biquad ® lters using only two unity-gain cells RO-MIN WENG{{, JIUNN-RU LAI{ and MAW-HUEI LEE{New current-mode and voltage-mode universal biquad ® lters are presented using only two unity-gain cells (one current follower and one voltage follower) in each con® guration. The proposed ® lters employ one less follower than in the literature to date. The ® lters can realize highpass, bandpass, lowpass, notch and allpass responses without any changes in the circuit topology. The circuits enjoy the following advantages: minimum number of active elements, no componentmatching condition and low active and passive sensitivities.