Wideband Tunable Filter Research Articles

Quasi-Elliptic Lossy Filter With Reconfigurable Bandwidth

This letter proposed a quasi-elliptic lossy filter with a wide tunable bandwidth and enhanced passband flatness. For adapting the limited circuit sizes, a new type of lossy technique named center-loaded resistive-cross-couplings (CLRCCs) is proposed. By loading resistor coupling at the centers of half-wavelength resonators, additional mid-passband losses can be introduced to flatten the passband. A bandwidth reconfigurable five-pole filter with a hybrid structure is developed for the examination. The measured promising results showed the superiority of the proposed novel lossy method for wideband tunable filters.

High-performance SH-SAW resonator using optimized 30° YX-LiNbO3/SiO2/Si

With the rapid development of 5G technology, acoustic wave filters with large bandwidths are urgently required to deal with the explosive increase in data traffic. Recently, there is extensive attention paid to shear-horizontal (SH) surface acoustic wave (SAW) resonators based on lithium niobate (LiNbO3) substrates, thanks to its large effective coupling coefficient (k2eff). However, because of the bulk acoustic wave (BAW) energy radiation into the LiNbO3 substrate, it is very challenging to obtain a high quality factor (Q) for SH-SAW resonators. In this study, a 30° YX-LiNbO3/SiO2/Si SAW resonator with the SH mode is proposed to achieve a large coupling and a high Q simultaneously. By bonding a LiNbO3 thin film onto a thermally oxidized Si(100) substrate, the velocity mismatch between the piezoelectric layer and the SiO2/Si substrate could significantly reduce the BAW energy leakage. Finite element method simulation is employed to optimize the cut angle of the LiNbO3 film and the thickness of each layer. The fabricated SH-SAW resonators with a resonant frequency of 924 MHz yield a k2eff of 24.8% and a maximum of Bode-Q (Bode-Qmax) of 1107. In comparison with the previously reported same-type SAW resonators, a higher Bode-Qmax is demonstrated in this work when their k2eff is larger than 20%, providing a potential solution to enable wideband tunable filters in the 5G communication system.

A Coupled Resonator for Highly Tunable and Amplified Mixer/Filter

We present an H-shaped resonator made of two clamped–clamped microbeams mechanically coupled at the middle with a strong coupler to achieve, in a single device, mechanical amplification of the response signal, filtering, and frequency conversion simultaneously. Usingmechanicalamplification combinedwith combination resonances generated from a mixed-frequency excitation, a wideband tunable filter, and a simultaneous frequency up and down convertors at multiple bands is demonstrated. The proposed coupled structure, when combined with the easy-to-implement technique of frequency mixing, is promising for applications in an RF chain.

Tunable 4-Pole Noncontiguous 0.7–2.1-GHz Bandpass Filters Based on Dual Zero-Value Couplings

This paper presents tunable 2- and 4-pole bandpass filters with a wide tuning range based on dual zero-value couplings. The zero-value coupling is achieved using a coupled line with two coupling paths. The proposed filter also has bandwidth tunability. Frequency and bandwidth tunings are achieved using silicon varactor diodes. Three types of tunable filters are designed and built on a substrate with ε r = 3.55 and h = 25 mil, two filters with two separate frequency bands (2- and 4-pole: Filter A) and one filter with contiguous frequency tuning (4-pole: Filter B). The 2-pole filter results in an insertion loss of 2.9-4.7 dB with a tuning range of 0.75-1.09 and 1.70-2.18 GHz. Filter A with a 4-pole response results in an insertion loss 3.7-7.9 dB and a -1-dB bandwidth of 68-87 MHz with a tuning ranges of 0.77-1.10 and 1.70-2.10 GHz. Filter B shows an insertion loss of 4.4-6.6 dB and a -1-dB bandwidth of 39-68 MHz with a tuning range of 0.70-1.44 GHz. The application areas are in wideband tunable filters requiring contiguous and noncontiguous frequency coverage with bandwidth tunability in separate bands.

All-optically reconfigurable and tunable fiber surface grating for in-fiber devices: a wideband tunable filter

A fiber surface grating (FSG) formed from a photosensitive liquid crystal hybrid (PLCH) film overlaid on a side-polished fiber (SPF) is studied and has been experimentally shown to be able to function as an all-optically reconfigurable and tunable fiber device. The device is all-optically configured to be a short period fiber surface grating (SPFSG) when a phase mask is used, and then reconfigured to be a long period FSG (LPFSG) when an amplitude mask is used. Experimental results show that both the short and long period FSGs can function as an optically tunable band-rejection filter and have different performances with different pump power and different configured period of the FSG. When configured as a SPFSG, the device can achieve a high extinction ratio (ER) of 21.5dB and a wideband tunability of 31nm are achieved. When configured as a LPFSG, the device can achieve an even higher ER of 23.4dB and a wider tunable bandwidth of 60nm. Besides these tunable performances of the device, its full width at half maximum (FWHM) can also be optically tuned. The reconfigurability and tunability of the fiber device open up possibilities for other all-optically programmable and tunable fiber devices.

Tunable Bandpass Filter Design Based on External Quality Factor Tuning and Multiple Mode Resonators for Wideband Applications

In this paper, a tunable bandpass filter using cross-shaped multiple mode resonators (MMRs) and N:1 transformer based external quality factor tuning structures is proposed. The use of a cross-shaped MMR simplifies inter-resonators control while two Qe tuning structures are investigated and incorporated with the MMR to implement simultaneous center frequency agility and narrow and wide bandwidth tuning. Compared with traditional tunable filters, the proposed architecture requires less tuning elements and is easier to realize wideband and high-order tunable filters. Two examples (Filter I and II) are presented to validate the design. Both filters use a single MMR and six tuning elements to achieve a third-order wideband tunable filter. Filter I reports 58% center frequency tuning with constant bandwidth and 14%-64.4% fractional bandwidth (FBW) tuning when center frequency locates at 1 GHz. Filter II achieves larger frequency agility and wider FBW tuning of 82.9% and 95%, respectively, for the same bandwidth and center frequency of Filter I.

Tunable filter with a complex coefficient based on polarization controller

A wideband tunable filter with a complex coefficient is proposed and demonstrated. The output of a polarization modulator is filtered by the optical bandpass filter, an optical single sideband modulation will be generated. When it passes through a polarization controller and a polarizer, a complex coefficient will be achieved by tuning the angle of the polarization controller before the polarizer, and the real coefficients are controlled by the optical power of the lasers. As the real coefficients and complex coefficient can be tuned, a two-taps incoherent photonic microwave filter with a tunable range over the entire full free spectral range is realized by adjusting the polarization angle from −90 deg to 90 deg while the shape of filter remains unchanged.

Wideband tunable Love wave filter using electrostatically actuated MEMS variable capacitors integrated on lithium niobate

A tunable bandpass filters with low insertion loss, sharp cut-off characteristics, wide bandwidth and wide tunability is strongly expected for future reconfigurable and cognitive wireless systems. In this study, a wideband tunable filter with the center frequency of 1.08GHz was fabricated by directly integrating Love wave resonators and electrostatically actuated MEMS variable capacitors on a 15° Y LiNbO3 wafer. The Love wave resonators have an extremely large electromechanical coupling coefficient (k2∼30%), providing wide bandwidth and wide tuning range. The 3dB bandwidth was tuned from 146MHz to 130MHz by applying 15V to one of the MEMS variable capacitors.

A zipper RF MEMS tunable capacitor with interdigitated RF and actuation electrodes

This paper presents a new RF MEMS tunable capacitor based on the zipper principle and with interdigitated RF and actuation electrodes. The electrode configuration prevents dielectric charging under high actuation voltages. It also increases the capacitance ratio and the tunable analog range. The effect of the residual stress on the capacitance tunability is also investigated. Two devices with different interdigital RF and actuation electrodes are fabricated on an alumina substrate and result in a capacitance ratio around 3.0 (Cmin = 70–90 fF, Cmax = 240–270 fF) and with a Q > 100 at 3 GHz. This design can be used in wideband tunable filters and matching networks.

Tunable Filters With Nonuniform Microstrip Coupled Lines

A basic wideband tunable filter design based on combline topology is presented. At the presence of the parasitic effects, the structure of the filter must be modified by introducing additional degrees of freedom to the geometry of the coupled line segment. A design procedure involving iterative steps will be described. This procedure is used to design two bandpass filters with more than one octave tuning range in the UHF band. The experimental results are presented for the filter prototypes implemented using printed circuit boards and PIN diodes.

A 12-18-GHz three-pole RF MEMS tunable filter

This paper presents a state-of-the-art RF microelectromechanical systems (MEMS) wide-band tunable filter designed for the 12-18-GHz frequency range. The coplanar-waveguide filter, fabricated on a glass substrate using loaded resonators with RF MEMS capacitive switches, results in a tuning range of 40% with very fine resolution, and return loss better than 10 dB for the whole tuning range. The relative bandwidth of the filter is 5.7/spl plusmn/0.4% over the tuning range and the size of the filter is 8 mm/spl times/4 mm. The insertion loss is 5.5 and 8.2 dB at 17.8 and 12.2 GHz, respectively, for a 2-k/spl Omega//sq bias line. The loss improves to 4.5 and 6.8 dB at 17.8 and 12.2 GHz, respectively, if the bias line resistance is increased to 20 k/spl Omega//sq. The measured IIP/sub 3/ level is >37 dBm for /spl Delta/f>200 kHz. To our knowledge, this is the widest band planar tunable filter to date.