A low cost electrically tunable bandpass filter with constant absolute bandwidth (original) (raw)
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2006
Stepped impedance resonator with harmonic suppression and capability of frequency tuning have been incorporated into a bandpass filter design. A tapped-in U-shaped feed structure is introduced in the design to suppress harmonic and to reduce the passband insertion losses. The passband flexibility is accomplished by using a pair of tuning varactors. A simple method to implant a zero in the frequency response is also studied herein to further deepen the pass-band skirt. A 163% (4 GHz) stopband bandwidth is observed under over 20 dB band rejection. A measured minimum insertion loss of 1.27 dB is observed for the circuit with absence of the tuning varactors. Using the varactors, this filter has achieved a 21.9% frequency tuning range with all the insertion losses less than 5 dB.
2015
This paper presents two types of microstrip bandpass<br> filter (BPF) at microwave frequencies. The first one is a tunable BPF<br> using planar patch resonators based on a varactor diode. The filter is<br> formed by a triple mode circular patch resonator with two pairs of<br> slots, in which the varactor diodes are connected. Indeed, this filter is<br> initially centered at 2.4 GHz; the center frequency of the tunable<br> patch filter could be tuned up to 1.8 GHz simultaneously with the<br> bandwidth, reaching high tuning ranges. Lossless simulations were<br> compared to those considering the substrate dielectric, conductor<br> losses and the equivalent electrical circuit model of the tuning<br> element in order to assess their effects. Within these variations,<br> simulation results showed insertion loss better than 2 dB and return<br> loss better than 10 dB over the passband. The second structure is a<br>...
Antennas and Propagation Conference 2019 (APC-2019), 2019
This paper presents a compact planar tunable filter covering the 2.5 to 3.8 GHz spectrum for 4G and 5G wireless communications using a new hybrid technique open-circuited stubs. The coupling between the resonators is adjusted to tune the centre frequency with Butterworth characteristics. The proposed bandpass filter (BPF) is designed on a Rogers RO3010 substrate with a relative dielectric constant of 10.2 and a compact size of 13×8×0.81 mm 3. The coupling coefficients between the adjacent resonators, external quality factors, varactor diodes and biasing circuit are designed to resonate the tunable filter at 3.5 GHz. The bandwidth is adjustable between 90 and 110 MHz with return losses between 15 to 25 dB and insertion loss around 0.8 dB. Computer simulation technology (CST) software is used to simulate and optimize the designed tunable filter, with hybrid co-simulation between CST MWS and CST DS is used to implement the structure, taking into account the SPICE model for the varactor diodes and the effect of the biasing circuit.
Open-loop tunable resonators and filters with constant bandwidth
2012
This study presents a compact novel design for achieving constant bandwidth tunable filters with wide tuning range. A method for linearising the Q-factor against frequency is proposed. A modified coupling structure is introduced to compensate for variations in filtering characteristic across the theoretical 50% tuning range of the filter. Filter design equations are provided for designing Butterworth or Chebyshev filters. An experimental second-order filter is demonstrated with 22.5% pass-band shift with only 3% bandwidth variation and insertion loss better than 3 dB. Furthermore, a third-order tunable bandpass filter with tuning range of 45% and less than 5% bandwidth variation is illustrated through simulation and modelling to show feasibility with higher filter orders. There is very good agreement between the theoretical and experimental results.
IEEE Access, 2021
In this study, defected ground structures (DGSs) are applied in the coupling schemes of a planar tunable filter to achieve constant absolute bandwidth (CAB). The filter consists of parallel-coupled quarter-wavelength resonators loaded with varactor diodes, and the DGSs are implemented to enhance the coupling at a certain part. This method enables controlling the ratio between electric coupling and magnetic coupling and makes the total coupling coefficient inversely proportional to frequency, as required to achieve CAB. With the DGSs, the tunable resonators can be equalized to stepped-impedance tunable resonators, which bring wider-frequency tuning range. Moreover, due to the help of the DGS in adjusting the coupling coefficient curve versus frequency, the resonators maintain their universal widths and are coupled at full length. Thus, the tunable filter is as compact as a traditional combline filter. Meanwhile, each external coupling scheme contains a series capacitor and a short-ended stub that is parallel coupled to the first or last resonator, resulting in external Q factor being proportional to frequency. A second-order tunable filter is designed and measured, and a wide tuning range from 0.63 GHz to 1.09 GHz together with a constant bandwidth of 65±4 MHz are achieved. Besides, a transmission zero generated by coupling zero of the DGS-loaded coupling structure can be observed at the high stopband. The total dimension of the filter is 0.05 λ g * 0.15λ g , which is more compact than solutions with partial-length coupling schemes. Owing to the simple structures of the resonators and coupling schemes, the filter solution has the potential to design high-order tunable filters with CAB, and a compact fourth-order tunable filter with ABC is given with simulation results. INDEX TERMS Tunable filter, defected ground structure, constant absolute bandwidth.
Design of varactor tuned bandpass filter
2015 Conference on Microwave Techniques (COMITE), 2015
The tunable bandpass filter is presented. The filter is realized in microstrip technology employing two steppedimpedance resonators tuned with varactor diodes. The filter has constant absolute bandwidth of 30 MHz in the frequency range from 380 MHz to 920 MHz. The insertion loss is lower than 5 dB and return loss higher than 17 dB in the full tuning range. The out of band attenuation is higher than 40 dB at frequencies below the passband and is higher than 50 dB at frequencies above the passband. The first spurious modes are observed at 3 GHz. Absolute bandwidth and the time delay in the full tuning range change by 33% only while center frequency changes 242%.
A Compact Switchable and Tunable Bandpass Filter
Progress In Electromagnetics Research M
In this paper, an integrated switchable and tunable bandpass filter is designed, simulated, and fabricated. This integrated bandpass filter is able to switch as well as tune in the ultra-wideband (UWB) as well as 2.4 GHz band. At first, a UWB bandpass filter is developed which consists of two bent shorted quarter-wavelength stubs and a connecting half-wavelength stub. Subsequently, a 2.4 GHz bandpass filter is realized by connecting another half-wavelength stub on top of the UWB filter. RF pin-diodes are used for switching the bands between UWB and 2.4 GHz bandpass filter. The switchable bandpass filter converts into a tunable filter by changing the inductance or the length of shorted stubs through the pin diodes. A detailed parametric analysis is done for calculating different stubs lengths of the UWB as well 2.4 GHz bandpass filter. The simulation results show a high rejection level of > 40 dB at the lower frequency and a low insertion loss of 0.8 dB in the passband for UWB filter. For 2.4 GHz bandpass filter, the simulation results show an insertion loss of 0.42 dB and a 3 dB bandwidth of 796 MHz. The filter is fabricated on a Rogers 4003 substrate, and the measurement results of the switchable filter in the UWB band show an insertion loss of 2.1 dB and a 3 dB bandwidth of 7 GHz. In the case of 2.4 GHz bandpass filter, the insertion loss is 0.78 dB.
Compact tunable lowpass filter with sharp roll-off and low insertion loss
Microwave and Optical Technology Letters, 2017
A novel continuously tunable lowpass filter (LPF) with compact size, sharp roll-off and low insertion loss is presented in this paper. The filter employs two varactor diodes, a pair of open-ended coupled lines and a U-shape step impedance line (SIL) with an open-ended stub loaded at the centre of the SIL to form a very compact layout. The odd-and evenmode analysis and equivalent circuit model are demonstrated for estimation of the transmission characteristics. Tuning the DC voltage applied on the varactor diodes, the varactor capacitance accordingly changes leading to a varying cutoff frequency f c. The measured results show that the achieved 3-dB f c tuning range is 60.6% (1.15 to 2.15 GHz). The measured insertion loss (IL) and roll-off rate are 0.2-0.4 dB and 50-73 dB/GHz, respectively. The overall size of the LPF is only 0.005λ g 2 , which shows a competitive advantage comparing with the state-of-the-art work.
A 1.3-V 5-mW fully integrated tunable bandpass filter at 2.1 GHz in 0.35-μm CMOS
IEEE Journal of Solid-State Circuits, 2003
A 2.1-GHz 1.3-V 5-mW fully integrated-enhancement LC bandpass biquad programmable in , , and peak gain is implemented in 0.35m standard CMOS technology. The filter uses a resonator built with spiral inductors and inversion-mode pMOS capacitors that provide frequency tuning. The tuning is through an adjustable negative-conductance generator, whereas the peak gain is tuned through an input stage. Noise and nonlinearity analyses presented demonstrate the design tradeoffs involved. Measured frequency tuning range around 2.1 GHz is 13%. Spiral inductors with of 2 at 2.1 GHz limit the spurious-free dynamic range (SFDR) at 31-34 dB within the frequency tuning range. Measurements show that the peak gain can be tuned within a range of around two octaves. The filter sinks 4 mA from a 1.3-V supply providing a of 40 at 2.19 GHz with a 1-dB compression point dynamic range of 35 dB. The circuit operates with supply voltages ranging from 1.2 to 3 V. The silicon area is 0.1 mm 2. Index Terms-LC bandpass filter, radio-frequency (RF) CMOS, tunable filter.