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This paper introduces a compact ultra-wideband (UWB) microstrip filter featuring both a fixed and an electronically tunable notch band. Operating within the frequency range of 3.27 GHz to 5.61 GHz, the filter incorporates a permanent notch at 4.08 GHz and a tunable notch at 4.88 GHz. Utilizing a traditional ground plane and a short-circuited transmission line, we develop a bandpass filter with a stable notch-band positioned and another tunable notch band. Systematic defects are made to the ground plane to increase the coupling between input and output ports leading to UWB response. The stable notch band is created using a rectangular slot resonator, while the tunable notch employs a varactor diode (NXP BB135 Varactor Diode) integrated into a rectangular stub. Operating in the even-mode with symmetrical current distribution, the filter exhibits a -3dB passband bandwidth of 740 MHz, 610 MHz, and 240 MHz across its respective passbands. Notch band attenuation measures at -10 dB and -9 dB, respectively. Experimental results from the prototype demonstrate excellent agreement with simulated results, confirming the efficacy of the design.

This letter presents a wideband bandpass filter (BPF) with a tunable and switchable in-band notch. This allows the RF front end to pass the signal of interest uninterrupted in the absence of an in-band interferer and reject part of the passband in case a narrowband interferer exists. The BPF is based on a two-path architecture, loaded with resonators on one of the paths to deliver an absorptive notch. The resonators are tuned with varactor diodes and are deactivated when the diodes are in forward bias. The implemented proof-of-concept hardware operates in the 4.8–7.8-GHz frequency range, with an in-band notch tunable between 5 and 6.25 GHz, when activated. The transmission lines were implemented as striplines, resulting in a measured insertion loss of 0.6 dB. [ABSTRACT FROM AUTHOR]

In this article, the working mechanism of a wideband absorber designed with an adjustable and highly selective notch band is studied, in which the narrow notch band is independently controlled by the lower lossless layer of the absorber, whereas the upper lossy layer loaded with lumped resistors realizes absorption. We present two instances with geometrically controlled and electrically controlled notch bands, respectively. Without decreasing absorption performance, the notch position can be flexibly adjusted throughout the entire frequency band by simply modifying the dimension of the lossless frequency-selective surface (FSS) or changing the capacitance of the varactor, i.e., using geometric control or electrical control. The narrow notch band allows two wide absorption bands to be retained on both sides; therefore, good stealth performance is still guaranteed. Equivalent circuit models (ECMs) are proposed to further explain the principle. The frequency-domain simulation, ECM, time-domain simulation, and experimental results are in good agreement and validate the adjustability and high selectivity of the notched absorbers. At the end of this article, an FSA-backed monopole antenna is simulated and measured, which clearly illustrates that these FSAs can serve as the ground plane for antennas and realize out-of-band RCS reduction. [ABSTRACT FROM AUTHOR]

ABSTRACT A tunable band-notch printed monopole antenna is presented, exhibiting a wide impedance bandwidth from 1.5 to 5.5 GHz with good impedance matching (VSWR ≤ 2) and a tunable rejected frequency band from 2.38 to 3.87 GHz. The band-notching is achieved by adding an inner chorded crescent element within a driven element of a similar shape. By varying the value of the varactor, which is placed between the inner and outer arcs, the desired variable rejected can be obtained. Simulated and measured results show wide impedance bandwidth with a tunable band notch, stable radiation patterns, and consistent nearly constant gain. The antenna is suitable for mobile and portable applications. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:403-412, 2015. [ABSTRACT FROM AUTHOR]

A simple technique to reconfigure a notch filter employing a 1-D electromagnetic bandgap (EBG) structure, which is capacitively coupled to a microstrip line, is presented in this letter. The resonant nature of the EBG creates a notch in the transmission band. The notch filter is made reconfigurable/tunable by introducing an additional capacitive structure to change the size (geometry) of the EBG unit cell. The structure is connected or disconnected to the main structure (unit cell) by means of a PIN diode or varactor diode. Its application in notched-band ultra wideband (UWB) filter is demonstrated. A 450 MHz change in notch frequency is observed using PIN diode, and 340 MHz tuning range is observed using varactor diode. [ABSTRACT FROM PUBLISHER]