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In this brief, we proposed a switchable filtering circuit with single- and multi-channel operations. It is a six-port circuit, consisting of three sections, namely, a switchable single- and quad-channel filtering circuit, a reconfigurable impedance matching network (IMN), and a single-pole double-throw (SPDT) switch. Two of the ports can be switched to satisfy the requirement of a time division duplexer sub-system, while other four ports can be reconfigured to transmit or receive signals in one channel or four channels. The presented switchable circuit can be utilized as the feeding network of a switchable directive and omni-directional antenna systems by using only directive antennas, while the omni-directional antenna can be eliminated. The design methods and experimental results of the presented switchable filtering circuits are given to verify the proposed ideas.

This paper reports on the RF design of fully reconfigurable quasi-elliptic-type single- and multi-band microwave bandpass filters (BPFs) and duplexers. They are based on series-cascaded resonators and multi-resonant/multi-band cells that produce frequency-reconfigurable poles and transmission zeros (TZs). By appropriately tuning the resonant frequencies of their constituent resonators, multiple levels of transfer-function adaptivity can be obtained. These capabilities include center-frequency and bandwidth tuning, as well as intrinsic RF switching-off (i.e., without the use of RF switches). As opposed to conventional BPF tuning mechanisms, the aforementioned reconfiguration characteristics avoid the use of tunable couplings. The basic operating principles of the engineered resonator-cascade BPF concept are presented through a three-pole/two-TZ example. Afterward, methods for expanding the proposed filter design approach to higher order, multi-band, and multi-port (e.g., duplexers) realizations are explained through coupling-matrix-based analysis. For practical-demonstration purposes, four L-band tunable microstrip prototypes were developed and measured. They include: 1) a five-pole/four-TZ BPF; 2) a five-pole/two-TZ BPF; 3) a dual-band BPF with two three-pole/two-TZ passbands; and 4) an RF duplexer.

In this work, a design of BAW-like thin film resonator is presented and demonstrated with 15% Sc doped AlN piezoelectric material. Utilizing the thickness mode coupled with laterally propagated mode, the proposed coupled bulk acoustic resonator (CBAR) is able to achieve over 4 GHz resonant frequency with 400MHz lithographic tunability and a high effective coupling coefficient over 20%. Filters consisting of the proposed CBARs with different electrode pitches are fabricated on a single-chip. Measurement results show that two discrete filters can operate at 3.85GHz and 4.15GHz with 155MHz and 197MHz bandwidth, respectively. With the same material stack and adjacent operating frequency, these filters provide a promising single-chip duplexer solution for the high frequency filtering applications.

Applying the volumetric modular method to microwave devices provides for the compactness and modularity of their components. This article presents a duplexer (frequency-splitting device) built using the volumetric modular technology. The duplexer is designed to support the simultaneous operation of the receiving and transmitting microwave paths in communication systems, air traffic control systems, etc. It is applied when one antenna is used to simultaneously transmit and receive signals at different frequency ranges. A new method of designing a duplexer with the use of volumetric strip-slot transitions which couple to each other through the electromagnetic field of a slot resonator is considered. A layout for the volumetric strip-slot transitions, which provides a high level of electromagnetic isolation between the transmitting and receiving channels, is presented. The proposed layout provides preferable s-parameters for each channel. The results of an electrodynamics simulation are presented. The simulation results confirmed the legitimacy of the application of the presented layout to ensure the necessary isolation between channels.

This thesis explores a new range of electromagnetic structures made available by a subtle change in the interpretation of how resonators interact. The focus is on microwave filters and antennas that are essential to wireless communication. The standard interpretation is that filters and antennas are made from a series of intercoupled resonators, with multiple paths through the structure allowing transmission zeros that increase selectivity and isolation between ports. This thesis instead begins with the assumption that the resonators of multi-mode structures are more effectively interpreted as not interconnected at all, being perfectly orthogonal to each other. The resonators are now equivalent to the structure’s eigenmodes and couple only to the ports, in parallel, with the phase and amplitude relationships of these parallel external couplings allowing a generalised frequency response with maximum transmission zero flexibility. This thesis aims to improve the size, cost and performance of filters and antennas using parallel-coupled multi-mode resonating structures by contributing six novel implementations.The first contribution introduces a bandpass filter made from a parallel coupled, triple-mode, silver-plated, surface-mounted ceramic cube, with a novel coupling topology featuring over-coupled single-mode input/output quarter wave stripline resonators. A single cube achieves class leading ratio of quality factor to volume (Q/V), three flexibly placed transmission zeros and allows a simple cubic construction without the need for chamfers for inter-resonator coupling. To validate the proposed design and analysis method, multiple filters are designed and simulated. Moreover, two DCS-1800 Band-3 (utilized in mobile communications) single cube transmit filters are fabricated and measured.The second contribution is a duplexing filter with high isolation. The device is based on triple mode filters that are built using silver plated ceramic cubes. To create a six-pole, six-transmission zero filter in the DCS-1800 band, two cubes are cascaded. To improve spurious harmonics, low dielectric caps are placed on the cube faces. These caps push the first cube spurious up in frequency by around 340 MHz compared to the uncapped cuboid, allowing a 700 MHz spurious free window. To verify the design, a DCS-1800 duplexer with 75 MHz wide bands is built. It achieves around 1 dB of insertion loss for both the receive (Rx) and transmit (Tx) ports with around 70 dB of mutual isolation within only 20 MHz band separation, using a volume of only 30 cm3. It is estimated that a similarly specified coaxial cavity duplexer would need a volume of at least 300 cm3.The third contribution is a triple-mode silver-plated ceramic cavity bandpass filter with wide spurious-free response. It uses single mode ceramic slabs as interfacing resonators with the triple-mode cube to give wide spurious-free performance up to 4 GHz for an 1800 MHz base-station filter. Three square apertures at the slab-cube interface give simple and flexible control of transmission zero placement while maintaining low insertion loss. The parallel nature of the slab-to-cube coupling allows a simple cubic structure without chamfers or inter-mode coupling elements. A seven-pole filter in the DCS-1800 transmit band using a slab-slab-cube-slab-slab structure is built and measured. The filter achieves 1 dB of band edge insertion loss with more than 50 dB of attenuation, 20 MHz from the band edges, from an 11 cm3 package. The wideband response shows more than 40 dB of attenuation up to the frequency 3.7 GHz.The fourth contribution is a triple-mode band-stop ceramic cavity filter utilizing parallel-coupled resonators. A transmission line, etched onto the face of a silver-plated ceramic cube, couples to three modes in parallel, avoiding any inter-resonator coupling perturbations. By varying only a few structural parameters, the coupling strengths into each mode can be controlled, and highly flexible band-stop filtering functions are demonstrated. A 30 MHz band-stop filter at 1800 MHz, from a roughly 27 mm3 ceramic block mounted to a copper base, is fabricated and measured. It achieves 26 dB of attenuation, with less than 0.3 dB of insertion loss 20 MHz away from the stop-band, and less than 0.3 dB of reflection loss in the stop-band, closely matching the simulation.The fifth contribution demonstrates a generalised frequency response for cavity filters from six modes coupled in parallel. The six modes belong to two parallel-coupled triple-mode spheres and are coupled in parallel via two half-wavelength transmission line resonators. The theory of phase and amplitude control of parallel couplings into spherical cavities is introduced by way of coupled resonator models, and the structure of two combined spheres is detailed. The theory and simulations prove that multiple transmission zeros can be arbitrarily placed, including inside the passband to create multiple bands and beyond infinity (imaginary frequencies) for flattened group delay. Several design examples of two spheres in parallel are presented to demonstrate a high degree of flexibility of transmission zero placement, and one example is fabricated and successfully tested.The sixth contribution reinterprets the assumption that mutual coupling is the mechanism that leads to the degradation of isolation between the active ports of antenna arrays. It is shown that a coupled-resonator model with series-coupled mutual coupling breaks down when applied to multi-mode/multi-port antenna arrays and limits the achievable isolation. An improved model based on parallel-coupled modes is presented. This model suggests that poor isolation is more accurately caused by unbalanced antenna modes. Using this model, several novel examples of simple and compact dual- and triple-mode antennas show how to maximize isolation in multi-mode antennas by balancing the modes’ resonant frequencies and radiation bandwidths. For comparison, the mutually coupled assumption limits isolation to around 20 dB in the proposed novel structures whereas 40 to 70 dB is possible when parallel-coupled modes are considered. Based on the developed concept, a compact triple-mode two-pole-filtering antenna is fabricated at 3500 MHz with 160 MHz of bandwidth and more than 40 dB of isolation between the antenna ports.

In this paper, a compact microstrip duplexer with relatively close channels is proposed. The ring resonator and the orthogonal-feed are directly connected to form a band elimination filter. The band elimination filter is loaded with branches to realize the band-pass filter. The design of the duplexer in the article composed of two such band-pass filters. The design method of the duplexer is introduced in detail, and verified by the experimental results of the manufactured duplexer. The central frequency of the bandpass channels is 1.45Ghz and 1.75Ghz respectively. The measurement results show that the two channels of the duplexers are close to each other, with low insertion loss and high out-of-band rejection, which are in good agreement with the simulation results.

In this paper, a method is proposed to synthesize acoustic wave duplexers with asymmetric ladder-type channel filters. By relocating the finite transmission zeros based on the sensitivity matrix, all resonators satisfy the requirement of keff2 and no additional lumped elements are needed at the output ports for simple fabrication and integration. Our method is validated by the synthesis of a B2 duplexer prototype, where the Tx and Rx filters operate at 1.88 and 1.96 GHz both with the bandwidth of 60 MHz, respectively. The case of asymmetric filter topology without shunted elements at output ports shows almost the same frequency response as that of the case of symmetric topology with shunted elements.

This work aims to provide design rules for shunt-starting acoustic wave (AW) ladder filters concerning the input reflection phase. Thanks to a general synthesis methodology, the paper proves that when the first resonator is shunt the AW ladder can only implement a Chebyshev filter function if the input reflection phase is set appropriately, depending on the position of transmission zeros. For phases out of the correct range, inductive static branches appear at the first and last resonators. Moreover, if the filter is designed as part of a duplexer, the reflection phase to avoid loading effects requires two input reactive elements unless the resonance frequency of the first resonator is placed below the central frequency of the duplexer's counter band.

This paper explores how acoustic wave (AW) filters whose first resonator is in shunt configuration require particular phase conditions to ensure network feasibility. The position of the transmission zeros (TZs) might lead to non-feasible solutions with negative values of the static capacitance Co of the first and last resonators and, therefore, the role of the first TZ in this behaviour is investigated. A lowpass synthesis view of these issues is presented providing different approaches for designers to achieve feasible networks.

Thin film bulk acoustic resonator (FBAR) plays a very important role in radio frequency (RF) filters used in cell phone and other wireless systems. Although FBAR is commercialized, the design/process interactions on the frequency response variation in FBAR device are still lacking. Design and fabrication are two crucial aspects affecting FBAR device performance. In this report, various solidly mounted resonators (SMR) were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. As a key process step for SMR FBAR, the optimization process of Mg-doped ZnO piezoelectric thin film deposition was studied by varying thin film sputtering conditions using various sputtering targets and by post annealing treatment after the deposition. The quality of this crucial layer was verified by XRD on its (0 0 2) crystallization and wafer-level FBAR RF characterization. FBAR devices with high quality were fabricated with an excellent resonant behavior near 2 GHz and a maximum return loss of −15 to 25 dB. Quality factor Q ranges from 400 to 800, with a coupling coefficient keff2 of 1.5–3%. Wafer-level and wafer-to-wafer variation of central frequency are within 1.8–2.1 GHz. Computer simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm. Process control on this piezoelectric thin film is essential to maintaining the resonator frequency-controlled value when building duplexer RF circuits. The dependency of RF performance on FBAR size, density and orientation is not obvious, compared to that of the wafer-level FBAR device variation on fabrication process. Regarding to the Mg-doping effect in MgxZn1-xO piezoelectric film, the amount of Mg in MgxZn1-xO film during the sputtering process must be properly controlled within 30% to keep the piezoelectric quality. The average acoustic speed of the Mg-doped ZnO film is 6870 m/s with the estimated range of 5760–7980 m/s, which is better than that of pure ZnO film (6330 m/s).

A microwave duplexer with high isolation is presented in this paper. The device is based on triple-mode filters that are built using silver-plated ceramic cuboids. To create a six-pole, six-transmission-zero filter in the DCS-1800 band, which is utilized in mobile communications, two cuboids are cascaded. To shift spurious harmonics, low dielectric caps are placed on the cuboid faces. These caps push the first cuboid spurious up in frequency by around 340 MHz compared to the uncapped cuboid, allowing a 700-MHz spurious free window. To verify the design, a DCS-1800 duplexer with 75-MHz widebands is built. It achieves around 1 dB of insertion loss for both the receive and transmit ports with around 70 dB of mutual isolation within only 20-MHz band separation, using a volume of only 30 cm3 .

A novel concept for the two-in-one design with the integration of filters and antennas, using a single cavity, is presented in this communication. Basically, a triple-mode resonator (TMR) is utilized as a common feeder to achieve filtering and radiating functions at three different frequency bands. Each of the three bands adopts one of the three fundamental modes, namely, TE011, TE101, and TM110, in a single TMR to realize the relevant functions. Owing to the modal orthogonality of these fundamental modes, high isolation can be effectively realized among these three channels. Based on the proposed TMR, three different prototypes are designed for different applications. For the first prototype, the structure of a dual-band filter plus an antenna is presented using a second-order TMR. Based on the combination of a duplexer plus an antenna, the second prototype is attained. To further explore the function of the proposed TMR, the structure of a filter plus a dual-polarization antenna is depicted as the third prototype. For verification, the third prototype is fabricated and tested. Good agreement between the simulated and the measured results is achieved, which proves the feasibility of the proposed design methodology.

In a scenario where the segment of wireless communication systems are allocated in an ever more crowded frequency spectrum, the design of filtering structures, stand-alone, duplexers, or multiplexers, become a challenging task. Moreover, filters based on acoustic wave resonators are the more suitable technology in this context due to the small size and the exhibited outstanding performance. However, to accommodate the technological requirements to the mask fulfillment is not straightforward unless a systematic synthesis methodology is used. Taking advantage on the nodal approach, the general synthesis methodology for ladder-type filters based on acoustic wave resonators is presented in this paper. This is a very fast procedure, which allow a better understanding of the interaction between technological constraints and filter performance. An experimental validation is proposed for a B28Rx band filter.

The quasi-elliptic multi-mode bandpass cavity filters and duplexer with slot mixed-coupling structure are proposed in this paper. A single metal cavity embedded with a rectangular- shaped slot-cut metal plate is utilized to constitute a multi-mode bandpass filter with a few features including wide passband, low profile and controllable transmission zeros (TZs). In this paper, the slot-cut metal plane serves as the multi-mode resonators. In detail, the slot on the metal plane functions as the circuit element to move the higher order modes within the reasonable frequency-band, while serving as a mixed-coupling structure to generate out-of-band transmission zeros. To demonstrate the multiple-mode capability in filter design, the dual-mode, triple-mode, and quadruple-mode filters are developed by appropriately allocating a few TZs in the upper stopbands using the proposed slot mixed-coupling approach, namely, Type-I filters. Next, a quadruple-mode cavity filter with both lower and higher TZs is designed, namely, Type-II filter, which is further applied for the exploration of a duplexer. Finally, the filter and duplexer prototypes are fabricated and measured. The measurement results are found in good agreement with the simulated ones.

This paper proposes an adaptive RF front-end (RFFE) architecture that uses an electrical-balance duplexer (EBD) and tuned surface acoustic wave (SAW) resonators to enable adaptive dual-frequency isolation suited for LTE’s frequency-division duplex (FDD) mode of operation. Alternatively, in the in-band full-duplex (IBFD) mode, the EBD cancels the in-band TX self-interference directly at RF for increased channel capacity. Furthermore, the EBD’s balance network is optimized to reduce the TX insertion loss (IL) below the nominal 3-dB limit in the FDD mode. A 0.18- $\mu \text{m}$ SOI CMOS prototype implements the EBD, low-noise amplifier, and SAW-tuning capacitor banks. The chip is mounted to a module substrate together with the SAWs and matching components. The RFFE achieves >50-dB dual-frequency isolation and 2.6–3.4-dB TX IL in FDD mode, has +58/+42-dBm TX/RX-path IIP3 for an increased IBFD-link budget and handles up to +27.5-dBm TX power in both modes.

In this paper, two architectures for tunable duplexers are presented. The tuning is accomplished through variable capacitance and resistance. The architectures are based on a three element series-parallel resonator, with one pass and one stop frequency. Both architectures rely on filtering as well as cancellation for good Tx to Rx isolation while maintaining low insertion loss. The first architecture, the filtered transformer balanced (FTB) isolator, has single ended transmit and antenna ports and a differential receive port. The second architecture, the cross coupled filtering (CCF) isolator, is fully differential. For a resonator $Q$ of 50, the impedance ratio of the resonator at pass and stop frequencies is 18.5 dB for 3GPP band-I. In the FTB isolator, this results in 1.65-dB Tx and 2.14-dB Rx insertion loss, and 53 dB isolation for a 20-MHz channel bandwidth. In the CCF isolator, this results in 1.9-dB Tx and 1.9-dB Rx insertion loss, and 59-dB isolation for a 20-MHz channel bandwidth. These figures are obtained with a 20% resistive mismatch, showing feasibility of good performance in an environment with changing impedance. As the operating frequencies of cellular systems increase, these structures will become fully integratable due to the reduced sizes of inductors and transformers.

The compact duplexer using the symmetric stripline and containing the fifth-order comb filters in transmit channel TX (2300–2370 MHz) and receive channel RX (2510–2580 MHz) is constructed, and the characteristics of obtained duplexer are measured. This duplexer is built using dielectric material Al2O3 (Alumina, polikor) with high thermal conductivity that makes it possible to use the operating power of 10Wat small dimensions 57-11.8-4 mm. The losses in bandpass of TX and RX filters did not exceed 3 dB during the filter attenuation at adjacent channel frequencies of no less than 60 dB. It is shown that the selection of the width of metallized strip at the base of quarter-wave resonators makes it possible to change the duplexer width for attaining the required value. The circuit of coupling of resonators with loads used in this design made it possible to obtain a sufficiently high level of isolation from each other for RX and TX channels of duplexer. This level does not exceed 60 dB. The finite thickness of internal conductors of stripline amounting to 16 μm is taken into account while building the duplexer that results in good agreement between the simulation and measurement results.

To develop the high-performance filters and duplexers required for recent long-term evolution frequency bands in mobile handsets, a surface acoustic wave (SAW) resonator is needed that has a higher quality (Q) and a lower temperature coefficient of frequency (TCF). To achieve this, the authors focused on acoustic energy confinement in the depth direction for a rotated Y-X LiTaO3 (LT) substrate. Characteristics of multilayered substrates with low-impedance and high-impedance layers under LT layer were studied numerically in terms of acoustic energy distribution, phase velocity, coupling coefficient, and temperature characteristics employing a finite-element method simulation. After several calculations, a novel multilayered structure was developed that uses SiO2 for a low-impedance layer and AlN for a high-impedance layer under the thin LT layer. A one-port resonator using the new substrate was fabricated, and its experimental results showed that the developed resonator had a Bode-Q over 4000 and TCF of −8 ppm/°C, which are four times higher than and one-fifth as small as those of a conventional 4° YX-LT SAW resonator, respectively. By applying this technology, a band 25 duplexer with very narrow duplex gap was successfully developed, which shows extremely low insertion loss, steep cutoff characteristics, and stable temperature characteristics.

Relentless pressure to reduce the size of filters, duplexers and multiplexers in mobile phone RF front end modules requires close packing of the filters and any associated PCB or SMT inductors. In these multiplexers, however, every Tx filter has to reject every Rx frequency and vice versa, while TDD bands/filters must be rejected by and reject nearly every other band -60 dB typical with -55 dB guaranteed. These seemingly contradictory requirements can both be satisfied if we reduce the magnitude of the grounding inductors of the filters to a point that their mutual inductance is not significantly degrading isolation. The Band 25 duplexer described is 1.5 mm x 1.1 mm x 0.6 mm.

A switchable and tunable bulk acoustic wave (BAW) duplexer for RF applications is presented in this paper. The fabricated BAW duplexer was built on sapphire substrate using solidly mounted resonators. A metal-organic solution deposition technique was used to form resonators with barium strontium titanate (BST) thin film and six layers of silicon dioxide and tantalum oxide as Bragg reflector. By applying dc bias, the BST thin film shows an electrostrictive effect, and the two filter paths of the BAW duplexer switch to a bandpass response with center frequencies at 4.635 and 4.878 GHz, showing a bandwidth of 119 and 154 MHz for the transmitting (Tx) and receiving (Rx) filters, respectively. Further, the BAW duplexer was simulated using the circuit, Butterworth-van-Dyke, and electromagnetic models. The simulated results are in agreement with the measurements and show the response of bandpass filters at center frequencies of 4.633 and 4.876 GHz for Tx and Rx, respectively.

A class of frequency-agile planar duplexers with independently controllable channels in terms of center frequency, passband-width, out-of-band power-attenuation characteristics, and tune-all transfer-function capabilities is reported. Each channel filter is made up of frequency-reconfigurable resonators that are coupled to its direct input-to-output electrical path through static impedance inverters and generate power transmission zeros (TZs). Thus, the duplexer channels are exclusively reconfigured by means of dynamic TZ allocation. Furthermore, the channel filters can be intrinsically switched-OFF by incorporating a bandstop-filtering function into them. The operational principles of this spectrally adaptive duplexer concept are expounded and experimentally demonstrated through the manufacturing and characterization of a microstrip prototype in the UHF range.

Electromagnetic metamaterials are periodic or nonperiodic artificial structures comprising basic elements in subwavelength scales. They can be used to control electromagnetic waves by designing the basic elements and their spatial arrangements. Metamaterial has been a research hotspot in physical and information sciences. In this review, I present the history and main progresses achieved in metamaterial studies conducted in the State Key Laboratory of Millimeter Waves at Southeast University, which were performed in three stages. In the first stage, we improved the developments in effective-medium metamaterials. In particular, we proposed a general theory to accurately describe the effective permittivity and permeability of metamaterials. Based on the general theory, we designed and realized a three-dimensional (3D) wideband ground-plane invisibility cloak, free-space electrostatic invisibility cloak, electromagnetic black hole, electromagnetic illusions, and radially anisotropic zero-index metamaterial for omni-directional radiations and nearly perfect power combinations of source arrays. Moreover, we undertook significant efforts in engineering applications of microwave metamaterials, such as broadband and low-loss 3D transformation-optic lens for wide-angle scanning, 3D planar gradient-index lens for high-gain radiations, and random metasurfaces to reduce radar cross sections. In the second stage, we opened up a new direction of plasmonic metamaterials from the viewpoint of microwave transmission lines. We proposed an ultrathin, narrow, and flexible corrugated metallic strip to guide spoof surface plasmon polaritons (SPPs) with small bending and radiation losses, based on which we designed and realized a series of passive SPP devices (such as power divider, coupler, filter, and resonator), active SPP devices (such as amplifier and duplexer) and SPP antennas in the microwave bands. We demonstrated a significant feature of the ultrathin SPP transmission line in overcoming challenges of signal integrity existing in the traditional integrated devices and circuits. We built up a full-SPP wireless communication system with unique properties to remotely transmit two movies in two deep-subwavelength-distance channels exhibiting excellent performance. In the third stage, we established a new area of metamaterial-information metamaterial. We proposed to describe the metamaterial using digital coding from the information science viewpoint, which directly resulted in a new kind of metamaterial-digital coding metamaterial. We theoretically and experimentally illustrated that the digital coding metamaterials comprising digital units can be controlled using different coding sequences to achieve different functions. When the digital state of the coding unit was controlled using a field programmable gate array (FPGA), we realized a field programmable metamaterial that can manipulate electromagnetic waves in real time and generate numerous different functions using a single piece of hardware. The digital coding metamaterial provides a platform to establish a digital space on the physical space and enriches the methodology and theory of metamaterials. We proposed measuring the information capacity of metamaterials using Shannon entropy and presented the convolution and addition theorems on metamaterial platforms, which can be used to simultaneously control the physical properties and digital information. Based on information metamaterials, we established new-architecture microwave imaging systems, wireless communication systems, and other intelligent information systems.

This paper reports on a simple RF design methodology for the realization of RF duplexers with quasi-elliptic-type filtering channels. It is based on Nth-order in-line bandpass filters (BPF) that are connected to the duplexer input through a multi-resonant junction that introduces three additional transmission zeros (TZs) and two in-band poles. Whereas the TZs are present in both channels, the poles are shared between them. As such, a quasi-elliptic-type BPF response is obtained in each channel that is shaped by N+1 poles and three TZs. As an important advantage to be highlighted, the aforementioned response is obtained without the use of cross couplings. For practical validation, a third-order (N=2) microstrip prototype with channels set at 2.14 and 2.84 GHz was designed, manufactured, and measured.

This paper performs a comprehensive nonlinear modeling of a Bulk Acoustic Wave (BAW) duplexer operating at the band 7 of the LTE wireless communication standard. The modeling starts by an accurate characterization of the resonators forming the filters by performing measurements of the second harmonic (H2). The modeling of individual resonators has then been used to predict second order nonlinear manifestations occurring in a real duplexer. These are H2, second order intermodulation products (IMD2), for the case where a jamming signal is set to low frequencies (IMD2-Low) and when the jamming signal is set to high frequencies (IMD2-High). Predicted results are then validated with real measurements. The authors would like to thank Qorvo Inc. for providing the on-wafer measurements that appear in this article. Work supported in part through grants TEC2017-84817-C2-2-R, TEC2017-88343-C4-2-R and 2017 SGR 813

In this paper, a dual-polarisation shared-aperture duplex antenna is presented for satellite communications at the standard microwave Ku-band, based on the integrated filtering-antenna concept and co-design approach. The design relies on the use of resonators coupled to the radiating dual-band dual-polarisation antenna. The resonant patch antenna forms one pole of each channel filter, resulting in a third-order filter in the Rx channel and a second-order filter in the Tx channel. The Rx and Tx ports of the antenna take in horizontal and vertical linear polarisations, respectively. The integrated duplexer helps to increase the isolation between the ports and the selectivity of each channel. The integration between the filter and the antenna is achieved by electromagnetic coupling, without the need of external matching circuits. Thus it attains a compact footprint. The operation frequencies of the demonstrated duplexantenna are from 11 to 12.5 GHz (12.8%) for the downlink to the Rx port, and from 13 to 14.4 GHz (10.2%) for the uplink at the Tx port. High port-to-port isolation of over 40 dB is realized to reduce channel interference. Flat in-band average gains are achieved to be 8.3 and 8.6 dBi, for the low- and high-bands, respectively.

Due to the recent increase of traffic, miniaturization of cellular phone base stations has been strongly expected. Small base stations called Remote Radio Head (RRH) are being installed for advanced small cell. Since the filter duplexer occupies about half of the volume of RRH, miniaturization of the filter is very important. One of the approaches is use of multimode resonator. In this paper, a cavity-type quadrupole-mode resonator with rectangular-shape is investigated. Adjustment mechanisms for resonance frequency and coupling are studied.

In this paper, a multi-function duplexer using the varactor-loaded stepped-impedance resonators (SIRs) is proposed. Such duplexer utilizes two sets of SIRs to construct the two channels. Meanwhile, loaded-varactors are tapped at the SIRs for adjusting the frequency response. Besides, the varactor is embedded in each pair of SIRs for further enhancing the passband performance. Moreover, the T-junction is introduced to achieve higher output isolation. Thus, a multi-function duplexer is fabricated and measured. The measured tuning range of the dual channel is 2.7-3 GHz and 3.5-3.8 GHz, respectively, with an output isolation greater than 48 dB.

This paper reports on the RF design of planar RF duplexers with unprecedented levels of transfer-function adaptivity. These reconfiguration capabilities include center-frequency tuning, bandwidth (BW) tuning, and intrinsic RF switching-off. The proposed RF duplexer concept is based on the connection of two three-pole/two-transmission-zero (TZ) bandpass filters (BPFs) that exhibit fully-reconfigurable quasi-elliptic-type transfer functions, so that they can be exploited for the independent control of its transmit and receive channels. For experimental-validation purposes, a microstrip RF duplexer prototype was designed, manufactured, and measured in the 1.4-2 GHz band. Its channels show center-frequency tuning ratio of 1.3:1, BW tuning ratio of 5:1, and can be intrinsically switched-off in an independent way.

We designed a compact high-temperature superconductor (HTS) duplexer on a substrate. The duplexer consists of a T-junction with discontinuous impedance and two cascaded quadruplet (CQ) filters with a bandwidth of 20 MHz centered at 5.0 and 5.1 GHz, respectively. The unloaded quality factor Q u of the proposed resonator used for the CQ filter was about 98000, and the smallest line and gap width were 10 μm. We applied a CQ structure to the bandpass filter with one pair of transmission zeros. The isolation of the HTS duplexer could be designed at less than 35 dB. We fabricated the HTS duplexer by using a 300-nm single-sided YBCO film deposited on a sapphire substrate 10 mm × 10 mm in size. We measured the frequency response of the duplexer between 4.8 and 5.15 GHz. We found a separation of the two passbands and sharp out-of-band rejection with the pair of transmission zeros. The isolation between the two filters was better than 32 dB. However, it was necessary to adjust the measured center frequency shifts about 150 MHz to the low-frequency side from the design results. Through this method, we were able to fabricate a miniaturized HTS duplexer with high selectivity.

Commercial markets desire integrated multifrequency band-select duplexer and diplexer filters with a wide fractional bandwidth and steep roll-off to satisfy the ever-increasing demand for spectrum. In this paper, we discuss the fabrication and design of lithium niobate (LN) thin-film S0 Lamb-wave resonators on a piezoelectric-on-piezoelectric platform. Filters using these resonators have the potential to fulfill all the above requirements. In particular, we demonstrated one-port high-order S0 Lamb-wave resonators with resonant frequencies from $\sim 400$ MHz to $\sim 1$ GHz on a black rotated y-136 cut LN thin film. The effective electromechanical coupling factor ( $k_{eff}^{2}$ ) ranges from 7% to 12%, while the measured quality factor ranges from 600 to 3300. The highest $k_{eff}^{2} \times Q$ achieved on this chip is 194, significantly surpassing contour mode resonators manufactured in other technologies. [2014-0280]

This article proposes a novel design of a compact single-aperture dual circular polarization (CP) antenna with integrated duplexing functions using a phase controllable coupled resonator structure. To the best of the authors’ knowledge, this is the first report of a multifunctional CP antenna with integrated duplexing performance and dual polarizations. The two orthogonal CPs are realized for the two respective filtering channels. Each channel contains a phased filtering power divider forming the dual-feed to a patch to achieve right-hand or left-hand CP (RHCP or LHCP). The required output phases of the dividers are realized by varied configurations of the coupled k/2resonator pairs. A duplex-CP-antenna with RHCP/ LHCP at the downlink/uplink (2.45/2.7 GHz) is designed, fabricated, and measured. It achieved a 3dB AR bandwidth of 3.2/7.7% at the downlink/uplink and an isolation better than 20 dB. Meanwhile, the antenna showed expected second-order filtering characteristics at both channels.

Factors limiting the isolation of conventional miniaturized filters and duplexers have been considered in the literature. They can be classified into two types of signal leakage: one occurs via the main signal path due to the finite impedance of the RX filter in the TX band in a duplexer; the second one is due to electromagnetic feedthrough (EMF), electromagnetic couplings or imperfect grounding. Because of the existence of these leakages, the isolation of usual duplexers is limited to about 50 to 55 dB.

Small sized surface acoustic wave (SAW) devices with high performances have been strongly demanded. In order to fulfill these requirements, we have developed a small sized temperature compensated SAW (TC-SAW) duplexer. The die size of current SAW devices highly depends on the size of interdigital transducers (IDTs) which is proportional to the acoustic velocity of the SAW. Therefore, we tried to lower the acoustic velocity of the Rayleigh SAW on LiNbO3 (LN) substrates, which is widely used for TC-SAW devices. In order to lower the acoustic velocity, we adopted multi layered IDT electrodes of Pt and Al, and increased the thickness of the Pt layer. From both several calculations and experimental results of one port resonators, the thickness of the Pt layer where the target acoustic velocity can be derived was determined, and the cut angle of LN substrates was optimized so as to minimize a spurious response. Moreover, good characteristics of high quality factor (Q-factor) and small temperature coefficient of frequency (TCF) were experimentally confirmed. Finally, by using this low acoustic velocity Rayleigh SAW, we successfully realized a small sized SAW duplexer for Band 20, which is 19 % smaller than the conventional one, maintaining high performances.

Measurements of the intermodulation products with frequency 2ƒ 1 −ƒ 2 (ƒ 1 - transmitter frequency, ƒ 2 - antenna frequency) for a W-CDMA professional duplexer filter are presented. It is proved that the 2ƒ 1 signal and the intermodulation product are generated in this power BAW filter, despite its careful design.

Band 28 has wide bandwidth of 45MHz and narrow duplex gap of 10MHz in 700MHz band, and since digital terrestrial TV channels in some countries are overlapped with lower frequency range of the uplink band, two types of duplexer which have slightly shifted passbands need to be used. This paper describes a novel switchable SAW duplexer which can cover both bands in one duplexer. By using a filter design technique with unique switching circuit, and wideband and low temperature drift SAW resonator technology, high performance such as 2.6/3.0dB insertion loss and 55dB isolation have been achieved, in addition to more than 13/16dB near point attenuation only 5/8MHz apart from the passband edge. The developed switchable duplexer can lead the reduction of 40% in mounting area on RF front-end circuit of mobile terminals.

This Paper presents the design of interdigital filters for the application of duplexer. The Design is Based on the coupling between the micro strip resonators of Quarter Wavelength Long. The designed filters are of seventh order Chebyshev type with a passband ripple of 0.2dB and FBWs of 6.2% and 5.7%. The structure is simulated in the electromagnetic simulation tool such as ADS. The results achieved are of insertion loss S(2,1) around 2dB, Return Loss S(1,1) is of around 17dB and the stop band attenuation of 30dB. The Alumina substrate with an height of 1.27mm and Dielectric Constant of 9.8 is used to reduce the size of the filters. The Designed filters can be used for the Development of Duplexer by increasing the Stopband attenuation to more than 50dB.

A 0.7–1GHz tunable front-end module (FEM) is presented for frequency-division duplexing and in-band full-duplex. It combines an electrical-balance duplexer (EBD) and tunable surface-acoustic wave resonators, demonstrating for the first time that these techniques are compatible and can be tuned independently. The EBD is integrated with a low-noise amplifier (LNA) in 0.18μm SOI CMOS and can operate with any antenna with a VSWR less than 2.3:1. The tunable FEM achieves more than 50dB dual-frequency isolation prior to the LNA, 2.6–3.4dB TX insertion loss and +58/+42dBm TX/RX-path out-of-band-IIP 3 , respectively. It has

A balanced RF duplexer with low interference in an extremely narrow bandgap is proposed. The Long-Term Evolution band-7 duplexer should be designed to prevent the co-existence problem with the WiFi band, whose fractional bandgap corresponds to only 0.7%. By implementing a hybrid bulk acoustic wave (BAW) structure, the temperature coefficient of frequency (TCF) value of the duplexer is successfully reduced and the suppressed interference for the narrow bandgap is performed. To achieve an RF duplexer with balanced Rx output topology, we also propose a novel balanced BAW Rx topology and RF circuit block. The novel balanced Rx filter is designed with both lattice- and ladder-type configurations to ensure excellent attenuation. The RF circuit block, which is located between the antenna and the Rx filter, is developed to simultaneously function as a balance-tounbalance transformer and a phase shift network. The size of the fabricated duplexer is as small as . The maximum insertion loss of the duplexer is as low as 2.4 dB in the Tx band, and the minimum attenuation in the WiFi band is as high as 36.8 dB. The TCF value is considerably lowered to .

Design and implementation of a low-loss K-band duplexer consisting of two narrow bandpass filters with low-impedance open-loop resonators (OLRs) is presented. Narrow bandpass filters of 4%-7% bandwidth were often implemented with OLRs, but previous designs used OLRs mostly with 50 Ω linewidth. The design process was complicated due to multiple coupling mechanisms and multiple spurious response frequencies, often resulting in excessive insertion loss, especially at higher center frequencies. With the proposed design procedure for OLR filters, the values of the low-impedance line (less than 50 Ω) and proper coupling spacing are determined in the process of optimizing the filter performance, resulting in low insertion loss up to above K-band frequencies. The size of the proposed filter is also reduced to 64% of the conventional OLR filters. As an example of the proposed design method, a duplexer consisting of 4% narrow bandpass filters centered at 18.7 GHz and 22.5 GHz was implemented and measured, and the maximum insertion loss in each passband was 1.2 dB, which is much less than those of the previous design approaches.

Ceramic dielectric waveguide duplexer was developed. Duplexer was designed in order to minimize the muture interferences between transmission port and receive port of bandpass filter. The design method for antenna port was determined by the transmission loss and calibrated the length of resonator of recriving filter. We used the ceramic powder of dielectric constant 9.46 and installed SMD type on PCB board.

In this article, a narrow-bandwidth duplexer with a triple-split ring resonator (T-SRR) using mu-negative metamaterial is presented. The T-SRR not only has negative permeability at the operating frequency band but also flexibility in size adjustment. The experimental results for insertion and return losses are 1.33 and 16.1 dB with a bandwidth of 10% at a RX center frequency of 8 GHz, and they are 1.27 and 16.8 dB at the same bandwidth at a TX center frequency of 10 GHz, respectively. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1537–1540, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27656

High Q and low TCF are elemental characteristics for SAW resonator, in order to realize high performance filters and duplexers coping with new LTE frequency bands. Authors focus on the acoustic energy confinement in SAW propagation surface and electrical characteristics have been investigated theoretically and experimentally. A new multi-layered structure substrate have realized incredible high performances such as both three times Q and one fifth TCF compared with conventional structure. Band25 duplexer using the new structure has been developed successfully with low loss and good temperature stability.

This paper deals with a design of a frequency duplexer based on a cavity resonator for a primary surveillance radar. The duplexer in this radar system for receiving of two different frequencies is used. Using of two different frequencies allows us achieve a greater system reliability. The proposal of frequency duplexer is based on a cavity resonator. Design and optimization of the duplexer was performed in a CST Microwave Studio. After designing and optimizing, the final circuit was fabricated and required parameters were verified by a measurement.

Magnet-less Non-reciprocal Metamaterial (MNM) was presented as an counterpart to biased ferrite in 2011. MNM is an electromagnetic metamaterial technology, where the rotating magnetic dipole moments is synthesised by the combination of its metal ring resonator structure and transistors as an unilateral component, precisely corresponds to the feasible components in integrated circuits. In this paper, recent two footprint reduction by figure of eight resonator which requires half number of active components, and beam steerable non-reciprocal leaky-wave antenna are introduced. Figure of eight resonator structure provides higher isolation compared to two isolated ring pair even though half number of active component requirement. Leaky wave antenna structure exhibits unique duplexer and diplexer operation as same as ferrite implementation in addition to voltage beam scanning.

A novel tunable quad-band duplexer using short-ended stub-loaded stepped impedance resonator (SSSIR) is presented in this paper. The SSSIR is composed of a folded SIR and a short-ended stub with a varactor loaded at the center of SIR. As the bias voltage across the varactor increases, the equivalent length of the stub decreases, which leads to a tunable even-mode resonant frequency while a fixed odd-mode frequency. Two tunable dual-band filters are realized by a pair of SSSIRs and then combined to form a compact quad-band duplexer with tunable first/third passbands and fixed second/fourth passbands. Finally, a tunable quad-band duplexer is well designed and fabricated. The measured results show a good agreement with the simulations.

Requirements for radio frequency (RF) devices in mobile phones have been getting more stringent, especially in multiband / carrier aggregation systems constructing many RF components. In this paper, we discuss two important items for RF acoustic devices developed by our team. First, we introduce the heat radiation effect and temperature compensation technology to suppress the temperature drift of acoustic devices for lower insertion loss. Heat sink effect of substrates and package, and temperature compensated film bulk acoustic resonator (FBAR) devices employing SiOF is introduced. Then, how to suppress the signal leakage from transmission (Tx) to reception (Rx) of the duplexer using signal cancellation technique is discussed, and SAW Band 8 duplexer is demonstrated as an example.

In recent years, the mobile data traffic is increasing and many more frequency bands have been employed in cellular handsets. A simple π type tunable band elimination filter (BEF) with switching function has been developed using a wideband tunable surface acoustic wave (SAW) resonator circuit. The frequency of BEF is tuned approximately 31% by variable capacitors without spurious. In LTE low band, the arrangement of TX and RX frequencies is to be reversed in Band 13, 14 and 20 compared with the other bands. The steep edge slopes of the developed filter can be exchanged according to the resonance condition and switching. With combining the TX and RX tunable BEFs and the small sized broadband circulator, a new tunable duplexer has been fabricated, and its TX-RX isolation is proved to be more than 50dB in LTE low band operations.

High-Q resonators may be used to synthesize selective bandpass filters. Many commercial radio-frequency filters are based on coupled-resonators and realized in surface and bulk acoustic wave technologies due to the high quality factor and compact size of acoustic resonators. In this paper, it is shown that discrete-time equivalent of coupled-resonator bandpass filters may be realized using passive switched-capacitor circuits. The center frequency and the bandwidth are determined by the frequency of the switch driving signals and the capacitor values. The proposed passive filters can be linear, low noise, and compact. To further enhance the in-band linearity, an RF bootstrapping technique is proposed. Design and experimental verification of a forth-order RF BPF and a duplexer, realized in a 65nm CMOS technology, are reported.

This paper presents the design, fabrication, and performance of a high-temperature superconductor (HTS) duplexer sub-system at L-band. The HTS duplexer sub-system contains a low noise amplifier (LNA) and an HTS duplexer. The HTS duplexer consists of a T-junction and two eight-pole filters with a bandwidth of 40 MHz centered at 1245 MHz and 1305 MHz, respectively. A novel, compact, and low radiation stepped impedance resonator was developed to reduce the parasitical coupling of the filters. The HTS duplexer was fabricated on a LaAlO3 substrate. The insertion loss of the duplexer is 0.2 dB, and the 60/3 dB shape factor is better than 1.4:1. The out-of-band rejection and the isolation between the two channels of the duplexer are better than 60 dB. The noise figure of the HTS duplexer sub-system is 0.3 dB at 80 K.