Center Frequency Tuning Range Research Articles

Ultra-Narrow Bandwidth Microwave Photonic Filter Implemented by Single Longitudinal Mode Parity Time Symmetry Brillouin Fiber Laser.

In this paper, a novel microwave photonic filter (MPF) based on a single longitudinal mode Brillouin laser achieved by parity time (PT) symmetry mode selection is proposed, and its unparalleled ultra-narrow bandwidth as low as to sub-kHz together with simple and agile tuning performance is experimentally verified. The Brillouin fiber laser ring resonator is cascaded with a PT symmetric system to achieve this MPF. Wherein, the Brillouin laser resonator is excited by a 5 km single mode fiber to generate Brillouin gain, and the PT symmetric system is configured with Polarization Beam Splitter (PBS) and polarization controller (PC) to achieve PT symmetry. Thanks to the significant enhancement of the gain difference between the main mode and the edge mode when the polarization state PT symmetry system breaks, a single mode oscillating Brillouin laser is generated. Through the selective amplification of sideband modulated signals by ultra-narrow linewidth Brillouin single mode laser gain, the MPF with ultra-narrow single passband performance is obtained. By simply tuning the central wavelength of the stimulated Brillouin scattering (SBS) pumped laser to adjust the Brillouin oscillation frequency, the gain position of the Brillouin laser can be shifted, thereby achieving flexible tunability. The experimental results indicate that the MPF proposed in this paper achieves a single pass band narrow to 72 Hz and the side mode rejection ratio of more than 18 dB, with a center frequency tuning range of 0-20 GHz in the testing range of vector network analysis, which means that the MPF possesses ultra high spectral resolution and enormous potential application value in the domain of ultra fine microwave spectrum filtering such as radar imaging and electronic countermeasures.

High-Q cascaded single-passband microwave photonic filter based on an optical-electrical feedback loop.

A cascaded microwave photonic filter refers to a microwave photonic filter (MPF) with higher performance obtained by cascading a MPF with two different structures. A high-Q cascaded single-passband MPF is proposed experimentally based on stimulated Brillouin scattering (SBS) and an optical-electrical feedback loop (OEFL). In this experiment, the pump light of SBS is provided by a tunable laser. The Brillouin gain spectrum generated by the pump light is used to amplify the phase modulation sideband, and the narrow linewidth OEFL is subsequently used to compress the passband width of the MPF. By carefully adjusting the pump wavelength and tuning the tunable optical delay line, stable tuning can be achieved for a cascaded single-passband MPF with a high-Q value. The results have demonstrated that the MPF has characteristics of high-frequency selectivity and a wide frequency tuning range. Meanwhile, the filtering bandwidth is up to 300kHz, the out-of-band suppression is more than 20dB, the maximum Q-value is 5.333×104, and the center frequency tuning range is 1-17GHz. The cascaded MPF proposed not only achieves a higher Q-value, but also has the advantages of tunability, a high out-of-band rejection ratio, and strong cascaded ability.

A Reconfigurable Pseudohairpin Filter Based on MEMS Switches

This work presents a bandpass-reconfigurable planar pseudohairpin filter based on RF-MEMS switches. Hairpin-line structures are preferred to design microstrip filters because this class of filters offers a more compact size, and, in general, hairpin filters do not need ground connections for resonators. In this work, the U-shape resonators are arranged to obtain an interdigit capacitor to improve the coupling between the resonators. RF-MEMS switches modify the lengths of coupled resonators by adding microstrip segments to control the filter bandwidth, moving the center frequency and the return loss. An experimental hairpin tunable filter prototype based on RF-MEMS has been designed, fabricated, numerically and experimentally assessed, and compared concerning its tunability, quality factor, and capability with standard tunable filters based on PIN diodes. In conclusion, the tunable hairpin filter based on RF-MEMS switches offers the best performance in center frequency tuning range, compactness, and power consumption regarding reconfigurable filters based on standard PIN diodes switches. The obtained results are appealing and demonstrate the capabilities and potentialities of RF-MEMS to operate with the new communication standards that work at high microwave frequency bands.

Novel Passive Vector-Sum Amplitude-Variable Phase Shifter With Integrated Reconfigurable Filtering Function

In this article, a novel passive vector-sum amplitude-variable phase shifter with integrated reconfigurable filtering function is proposed for the first time. It is constructed using conventional trisection filtering topology, with all the couplings between adjacent resonators being implemented with controllable mixed electric&#x2013;magnetic couplings. This not only achieves a reconfigurable filtering response but also forms an intrinsic <inline-formula> <tex-math notation="LaTeX">$I/Q$ </tex-math></inline-formula> signal generator inside the filter, which can be directly utilized to achieve continuous phase control based on the vector-sum mechanism. In such a manner, an integrated filtering phase shifter (FPS) without the need for an extra <inline-formula> <tex-math notation="LaTeX">$I/Q$ </tex-math></inline-formula> generation network and individual filtering device is obtained. By properly choosing the coupling types and coupling strengths between adjacent resonators, a continuous phase control from 0&#x00B0; to 360&#x00B0;, covering the full four quadrants, is successfully realized. Closed-form equations associating the circuit parameters and insertion phase at center frequency are deduced, providing a quantitative theoretical guideline for determining the parameters of the FPS. Subsequently, a novel tuning mechanism for independent <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula>-factor and resonant frequency control of the resonator is proposed and applied in the circuit to further exploit the amplitude control ability of the phase shifter. Measured results show that the proposed amplitude-variable FPS is capable of achieving a continuous phase control range of 360&#x00B0; and an amplitude control range of 10 dB within a center frequency tuning range of 0.75&#x2013;0.95 GHz. The measured root-mean-square (rms) amplitude error and the rms phase error are less than 2.58 dB and 8.45&#x00B0;, respectively.

A 10.23–15.7-GHz Varactor-Tuned Microstrip Bandpass Filter With Highly Flexible Reconfigurability

This article demonstrates a 10.23–15.7-GHz varactor-tuned microstrip bandpass filter (BPF) with fully controllable center frequency, bandwidth, and transmission zeros. The concept of cascading a tunable low-pass unit together with a tunable high-pass unit is adopted to achieve the reconfigurable BPF. A comprehensive loss analysis is carried out to determine the preferable circuit topologies for low-pass filter (LPF) and high-pass filter (HPF), respectively. This not only overcomes the limitation of low quality factor of varactor at high frequency, but also contributes to a highly flexible reconfigurability of the BPF. A reconfigurable LPF using defected ground structure (DGS) and a quasi-elliptic HPF using microstrip technology are then proposed to demonstrate the improved BPF performance at high frequency. The measured results show that the designed BPF is capable of operating in five working modes, with a center frequency tuning range from 10.23 to 15.7 GHz and a fractional bandwidth (FBW) tuning range from 32.48% to 95.76%. The minimum in-band insertion loss reaches 2.55 dB. A steep cutoff characteristic and ultrawide stopband with high rejection level are successfully achieved and are well preserved during the whole tuning process, demonstrating the superiority of the designed BPF.

Multifunctional photonic broadband RF memory for complex electronic jamming

A multifunctional photonic broadband RF memory structure is presented to adapt to more and more complex electronic jamming scenarios. Based on precise sequence control of the structure with integration of switching and amplification functions at the output end, the response time of the structure is greatly reduced to 30 ns. Moreover, multiple jamming modes including reconfiguration of Doppler frequency shift (DFS), instantaneous bandwidth (IBW), center frequency, pulse width, storage time and pulse number are realized based on a coherent DFS structure with tunable optical filter and a memory structure with Vernier effect. The tuning range of DFS is greater than ±9 MHz, the reconfiguration range of IBW is 1.5 GHz–11 GHz, the tuning range of center frequency is 6.5 GHz–17 GHz, the maximum storage time of 100 ns–10 µs RF pulse signals is 750 µs, and the maximum number of stored RF pulses is 2500.

Fully tunable filter with cross coupling and reconfigurable transmission zero

In this article, a novel coupling structure is proposed. The surface voltage and current distribution on this structure can be tuned by changing the ratio of the two capacitances so that the central frequency and coupling coefficient can be tuned. The coupling structure can also be tuned to change the sign of coupling coefficient, which is utilized to control the transmission zero of cross coupled tunable bandpass filter. A second order bandpass filter with tunable central frequency and bandwidth is designed and measured. The measurement shows that the central frequency tuning range is 0.768 to 1.512 GHz and the fractional bandwidth tuning range is 0.052 to 0.18 at 1.14 GHz. It shows that the filter can also be tuned with constant fractional bandwidth or constant absolute bandwidth. A tunable cascaded triple bandpass filter with tunable central frequency and bandwidth is designed and measured, as well. The cross‐coupled transmission zero can be configured to locate at either high side or low side of the passband by changing the coupling type of the filter topology.

Tunable bandpass filter with wide tuning range of center frequency and bandwidth based on circular SIW

This paper presents a circular substrate integrated waveguide (SIW) bandpass filter (BPF) with wide tuning range of center frequency and bandwidth (BW). For designing such a filter, lumped varactors loaded at two metal posts are utilized to adjust the center frequency, and the bandwidth is tuned by varactors mounted between two SIW cavities. One transmission zero (TZ) can be located at the lower or upper stopband by controlling the mixed coupling between two resonators. The external coupling is changed by using two lumped varactors mounted between feedlines and resonators. Eventually, the BPF with tunable center frequency and bandwidth is designed, fabricated and measured. Measured results indicate the center frequency is tuned from 1.48 to 2.61 GHz (up to 55.3%) while maintaining a 3-dB absolute BW of 31 ± 2 MHz, and the 3-dB bandwidth is tuned from 29 to 250 MHz (up to 8.6). Insertion loss from 1.8 to 4.8 dB is observed within the wide tuning range.

Advanced Synthesis of Wide-Tuning-Range Frequency-Adaptive Bandpass Filter With Constant Absolute Bandwidth

This article proposes an advanced synthesis of the frequency-adaptive bandpass filter (FA-BPF) with constant absolute bandwidth (ABW). The proposed synthesis is based on the element-variable coupling matrix (EVCM), which is directly extracted from the classical filter polynomials. The extraction method is presented, investigated in detail, and confirmed by a set of numerical simulations. All frequency-dependent couplings between the resonators in an FA-BPF are uniquely modeled by the new coupling matrix, and the element variation of the EVCM directly accounts for the frequency tuning behavior of an FA-BPF. This one-to-one correspondence tackles the difficulty of the FA-BPF synthesis and design with a different center frequency tuning range (FTR), a different bandwidth (BW), and a different BW variation rate. This article also proposes the predefined coupling technique in the new synthesis. It allows both nonfrequency-dependent matrix and frequency-dependent matrix in an EVCM to be separately implemented in practice. For experimental demonstration, two four-pole/four-transmission zero (TZ) FA-BPFs with identical passband and constant ABW are implemented and then constitute a frequency-adaptive bandpass diplexer (FA-BPD) with two tunable channels that have identical passband and constant ABW. The measurement results exhibited performance superiority of the design and validated the proposed design method.

Reconfigurable BPF With Constant Center Frequency and Wide Tuning Range of Bandwidth

A reconfigurable bandpass filter (BPF) with constant centre frequency and wide tuning range of bandwidth is presented. The proposed filter is based on the novel configuration of two modified asymmetrical $\pi $ -sections with folded shorted stubs loaded on a ring resonator. The novel topology allows the implementation of three reconfigurable passband states. A detailed theoretical analysis for calculating the transmission zeros using ABCD parameters is shown, and the design approach of implementing the random offset–x-, asymmetrical $\pi $ -sections with the folded stubs to get the bandwidth reconfigurability is thoroughly explained. PIN diodes are utilized as switching elements to achieve narrowband/mediumband/wideband response. The measured results indicate an absolute bandwidth tuning range of 1.3 GHz, whereas the −3 dB fractional bandwidth (FBW) can be varied from 37% to 92% while the centre frequency remains constant at 2.4 GHz. The fabricated prototype reconfigurable BPF demonstrates one of the widest 3-dB FBW tuning ranges and one of the highest absolute tuning ranges with a sharp-skirt characteristic. It has also more than 20 dB attenuation in the upper stopband which is extended to 2.7 times the centre frequency.

Design and fabrication of a miniaturized lowpass-bandpass diplexer with wide tuning range and high isolation

ABSTRACTIn this article, a compact lowpass-bandpass (LP-BP) diplexer with high isolation for wireless telecommunication applications is presented. The −3 dB cut-off frequency of the lowpass filter (LPF) is equal to 1 GHz. The roll-off-rate (ROF or ζ) parameter is sharp and equal to 108.8 dB/GHz, and the rejection level in the stopband is 20 dB. The center frequency of bandpass filter (BPF) is 2.4 GHz. The tuning range of −3 dB cut-off frequency of the LPF is wide and ranges from 0.3 to 0.89 GHz. The tuning range of center frequency of the BPF is wide and ranges from 2.65 to 3.1 GHz. The obtained isolation between the two output ports is better than 30 dB. The proposed tunable LP-BP diplexer is designed, simulated, fabricated and measured. The results of measurement and simulation are in good agreement with each other. The proposed diplexer has a compact size of 64 × 38 mm2.

A Miniaturized Eighth-Mode Substrate-Integrated Waveguide Filter With Both Tunable Center Frequency and Bandwidth

This letter presents a miniaturized eighth-mode substrate-integrated waveguide (EMSIW) filter with tunable center frequency and variable bandwidth. The filter uses a stub-capacitor-loaded EMSIW structure which not only achieves miniaturization but also tunes the center frequency. The edge electrical coupling strength between the two resonators can be adjusted by loading varactor to achieve the bandwidth tunability. In addition, two transmission zeros are introduced to improve the upper stopband rejection. Both the simulated and measured results show a center frequency tuning range of 2.17–2.72 GHz, as well as demonstrate a 3-dB BW tuning range of 140–208 MHz around 2.17 GHz, 231–355 MHz around 2.45 GHz, and 314–435 MHz around 2.72 GHz. The measured insertion loss is 1.7–4.8 dB, and the return loss is better than 10 dB for all tuning ranges.

A fully reconfigurable bandpass-to-bandpass-with-embedded-stopband filter with an ultra-wide 0.09–1.41 GHz bandwidth tuning range

AbstractA varactor-based fully reconfigurable microstrip bandpass-to-bandpass-with-embedded-stopband filter is presented in this paper. This filter offers wide center frequency and bandwidth tuning flexibility under both bandpass mode and bandpass-with-embedded-stopband mode. The entire tuning ability is based on multiple mode resonator theory and external quality factor tuning structure for bandpass mode and the introduction of transmission zeros (TZs) for bandpass-with-embedded-stopband mode. Under the bandpass mode, the center frequency tuning range is 0.96–1.45 GHz and the bandwidth can be tuned from 0.09 to 1.41 GHz with a fixed center frequency at 1.22 GHz. Under bandpass-with-embedded-stopband mode, the center frequency and bandwidth can be tuned from 0.94 to 1.61 GHz and 0.2–0.33 GHz, respectively. Good agreements are shown between simulated and measured results.

A fully reconfigurable bandpass‐to‐notch filter with wide bandwidth tuning range based on external quality factor tuning and multiple‐mode resonator

AbstractA fully reconfigurable microstrip bandpass‐to‐notch filter based on varactors is presented in this article. This filter offers wide center frequency and bandwidth tuning flexibility under bandpass mode and wide notch tuning range under notch mode. The entire tuning ability is based on multiple‐mode resonator (MMR) theory and tunable external quality factor for bandpass mode and the introduction of transmission zero (TZ) for notch mode. Under the bandpass mode, the center frequency tuning range is 0.9 to 1.42 GHz, and the bandwidth can be tuned from 0.09 to 1.44 GHz at a fixed center frequency 1.28 GHz. Under notch mode, the notch can be tuned from 0.98 to 2.02GHz. Good agreement can be observed between simulated and measured results.

Fully‐differential second‐order tunable bandstop filter based on source follower

A new design method for a second-order bandstop filter is presented. The proposed filter is based on the source follower configuration with a partial positive feedback. The positive feedback is used to increase the quality factor of the filter, and the feed-forward paths are used to create complex zeros. The proposed bandstop filter has electronically tunable centre frequency, bandwidth and attenuation with low power consumption. The proposed design has been simulated in TSMC 180 nm CMOS technology. The filter achieves 5.8 nV / Hz input-referred noise density. For a 2 GHz input signal, the filter achieves a signal-to-noise ratio of 60 dB for 238 mV 0 − P , diff input signal amplitude. The simulated results show that the centre frequency tuning range is between 1.6 and 3 GHz and the bandwidth is tunable from 0.6 to 1 GHz. The filter consumes about 2.5 mW for a supply voltage of 1.8 V at a centre frequency of 2.3 GHz.

A 0.61‐2.39 GHz fully tunable bandpass filter with minimum number of loaded varactors

AbstractA 2‐pole fully tunable bandpass filter (BPF) with only two varactors implemented is proposed in this paper. The ultra‐wide center frequency (CF) tuning range is built on short‐ended stepped‐impedance resonators (SIRs). Two varactors are placed at the symmetrical plane of the filter in series and shunt configurations, according to the odd‐even mode analysis the CF and bandwidth (BW) of the passband can be tuned independently without adding any redundant tuning elements. The CF of the proposed filter can be tuned from 0.61 to 2.39 GHz. The 3 dB BW tuning range is 150‐260 MHz at the lower side and 290‐520 MHz at the upper side of the entire passband tuning range. Good agreement is observed between simulated and measured results.

Ultrahigh-Q and tunable single-passband microwave photonic filter based on stimulated Brillouin scattering and a fiber ring resonator.

A scheme to perform ultrahigh-Q and single passband microwave photonic filter (MPF) with tunability is proposed and experimentally demonstrated. The single passband of the MPF is implemented by the stimulated Brillouin scattering (SBS) in an optical fiber. The ultrahigh-Q of the MPF is realized due to the ultra-narrow resonant linewidth of the fiber ring resonator, which compresses the bandwidth of the SBS dramatically. A MPF with a single passband and an ultra-narrow 3dB bandwidth of 825±125 kHz over the wide center frequency tuning range of 2-16GHz are achieved. The MPF also shows high out-of-band suppression exceeding 25dB and small amplitude fluctuation of ±1.8 dB within the tuning range. The maximum Q-factor of the MPF is 17778. To the best of our knowledge, this is the highest Q single-passband MPF reported to date, with wide tunability, high out-of-band suppression, and a simple structure.

A Frequency Tunable Quadrature Coupler With Wide Tuning Range of Center Frequency and Wide Operating Bandwidth

To solve the problems of existing frequency tunable quadrature couplers with limited tuning range and narrow bandwidth, a frequency tunable 3-dB quadrature coupler with wide tuning range and wide bandwidth is proposed and is based on the vertically installed planar (VIP) structure. Varactor diodes are loaded between vertical patches to achieve frequency tuning. Due to the strong coupling characteristics of the VIP structure, broad bandwidth is maintained during the frequency tuning process. For validation, a frequency tunable coupler is designed, fabricated, and measured. The center frequency of the designed coupler can be varied from 1.3 GHz to 2.7 GHz covering a frequency range of 70%. For each operating mode, more than 40% bandwidth defined by 1 dB amplitude imbalance between output ports, 10 dB return loss and isolation, and phase variation of 5°, can be achieved.

The novel reconfigurable double-layer half-mode SIW filter with tunable DMS structure

ABSTRACTThe contribution of this paper is to present a reconfigurable double-layer half-mode substrate integrated waveguide (HMSIW) bandpass filter with continuous center frequency and 3 dB bandwidth (BW) tuning capabilities. The double-layer rectangular HMSIW is subjected to vertical electrical coupling and magnetic coupling through the proposed semicircle aperture and rectangular slot etched on the middle metal layer. Due to this mixed electric and magnetic coupling structure, the 3 dB BW can be tuned and one adjustable transmission zero (TZ1) is introduced. Varactors (CV2) are used to adjust the center frequency. The parasitic passband produced by the higher-order mode TE102 can be suppressed, thanks to the proposed T-shapes defected microstrip structure. Compared with the conventional horizontal coupling SIW filters, the proposed HMSIW filter also shows a compact physical area. To demonstrate the proposed design method, a double-layer HMSIW bandpass filter is fabricated and measured. Both the simulation and measured results show a center frequency tuning range of 1.21–1.72 GHz, as well as demonstrate a 3 dB BW tuning range of 62–101 MHz around 1.21 GHz, 97–213 MHz around 1.45 GHz, 225–310 MHz around 1.72 GHz. The insertion loss ranges from 1.18 to 6.32 dB. Furthermore, simulated and measured results also show a good agreement.

Ultranarrow-bandwidth filter based on a thermal EIT medium

We present high-contrast electromagnetically-induced-transparency (EIT) spectra in a heated vapor cell of single isotope 87Rb atoms. The EIT spectrum has both high resonant transmission up to 67% and narrow linewidth of 1.1 MHz. We get rid of the possible amplification resulted from the effects of amplification without population inversion and four-wave mixing. Therefore, this high transmitted light is not artificial. The theoretical prediction of the probe transmission agrees well with the data and the experimental parameters can be derived reasonably from the model. Such narrow and high-contrast spectral profile can be employed as a high precision bandpass filter, which provides a significant advantage in terms of stability and tunability. The central frequency tuning range of the filter is larger than 100 MHz with out-of-band blocking ≥15 dB. This bandpass filter can effectively produce light fields with subnatural linewidth. Nonlinearity associating with the narrow-linewidth and high-contrast EIT profile can be very useful in the applications utilizing the EIT effect.