A tunable third‐order bandpass filter based on combining dual‐mode square‐shaped substrate integrated waveguide resonator with triangular‐shaped resonator

A frequency reconfigurable third‐order bandpass filter based on two substrate integrated waveguide (SIW) cavities is presented in this article. The purposed filter consists of a dual‐mode square‐shaped resonator and a triangular‐shaped resonator. In the square‐shaped cavity, four lumped capacitors are loaded as electrical tuning elements in the area where the electric fields of diagonal TE₂₀₁ and TE₁₀₂ modes are strongest. And an another capacitor is loaded at the suitable region of the triangular‐shaped cavity. Square‐shaped cavity introduces two transmission zeros and the triangular‐shaped cavity can suppress out‐of‐band spurious modes. The method that combines the resonators with different shapes and multiple modes into an organic whole cannot only achieve synchronous tuning but also have complementary advantages and improve out‐of‐band rejection. To verify its practicality, a SIW reconfigurable bandpass filter is simulated when the capacitance value varies from 0 to 1.4 pF and measured at 0.7, 0.8, and 0.9 pF, respectively. Measured results show that when the center frequency is tuned from 3.42 to 3.52 GHz, the proposed filter exhibits good tuning performance with insertion loss of less than 2.5 dB and return loss of better than 10 dB, which is suitable for fifth‐generation communication system.     

Study of the design of waveguide filters with improved suppression of modal interference through the cross‐shaped slot

In this article, a new method is suggested to improve the frequency responses of dual‐mode waveguide filters employing cross‐shaped slots. According to this method, regarding one cross‐shaped slot between two cavities, the horizontal (vertical) mode in one cavity influences the vertical (horizontal) mode in the other cavity to a much lesser extent. It enhances the overall performances. A 4^th‐order dual‐mode filter is used as an example and it validates the method. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 285–292, 2003.     

Design of high selectivity tri‐band bandpass filter with wide upper stopband

This article presents a dual‐plane structure high selectivity tri‐band bandpass filter (BPF) which consists of a pair of T‐shaped microstrip feed lines with capacitive source‐load coupling as well as spur lines embedded, and three resonators, i.e., a dual‐mode stub‐loaded stepped impedance resonator and two nested dual‐mode defected ground structure resonators. Using the intrinsic characteristics of the resonators and feed lines, nine transmission zeros near the passband edges and in the stopband can be generated to achieve high selectivity. An experimental tri‐band BPF located at 2.4/5.7 GHz [wireless local area networks (WLAN) application] and 3.5 GHz [worldwide interoperability for microwave access (WiMAX) application] has been simulated and fabricated. Good agreement between the simulated and measured results validates the design approach. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

A novel 3D cavity diplexer with compact size using LTCC technologies for V‐band wireless communication systems

In this article, a novel concept of 3D integrated V‐band diplexer, which permits the realization of compact size using a dual‐mode cavity and four single‐mode cavities, has been realized in low‐temperature cofired ceramic technologies. The dual‐mode cavity resonator acting as one resonator for both Rx and Tx filters is developed to generate two resonant modes (TE₁₀₂ and TE₁₀₃) at the center frequency of Rx (56.5–58.5 GHz) and Tx (64–66 GHz) channels, separately. Meanwhile, this dual‐mode cavity becomes the interconnect between Rx/Tx channels and help to realize good isolation without using conventional T‐junction. In the measurement, each filter designed for Rx and Tx channels exhibits excellent performance. Channel‐to‐channel isolations better than 35 dB across the Rx band and better than 32.5 dB across the Tx band are also obtained. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:141–145, 2015.     

A new dual‐band single‐ended‐to‐balanced filtering power divider

This article proposes a new dual‐band single‐ended‐to‐balanced (SETB) filtering power divider (FPD), which shows the excellent characteristics of wideband common‐mode (CM) suppression and good selectivity. By employing the structure of double‐sided parallel‐strip line with a mid‐inserted conductor and a T‐shaped defected ground structure etched in the mid‐inserted conductor, out‐of‐phase behavior and high CM suppression can be achieved successfully. Besides, to realize dual‐wideband filtering performance and high selectivity, two pairs of step impedance stubs (SIS) loaded quarter‐wavelength central line‐terminal‐shorted three parallel‐coupled microstrip lines structure are adopted. Meanwhile, two pairs of resistors are introduced so as to realize excellent isolation. To verify effectiveness of the design method, a prototype of dual‐band SETB FPD which operates at 3.2 and 4.9 GHz is designed, fabricated, and tested. Final results exhibit that the new dual‐band SETB FPD possess high selective dual‐band differential mode response, wideband CM suppression, and excellent isolation between the balanced output ports.     

Independently controllable dual‐band microstrip bandpass filter using quadruple‐mode stub‐loaded resonator

In this article, a quadruple‐mode stub‐loaded resonator (QM‐SLR) is introduced and its four modes are excited using a simple approach, which can provide a dual‐band behavior. By changing the length of the loaded stubs, independently tunable transmission characteristics of the proposed quadruple‐mode stub‐loaded resonator were extensively described for filter design. Moreover, microwave varactors were adopted to represent the length variation of the loaded stubs for the dual‐band tunability. The equivalent circuit modeling of the open stub with microwave varactor was given and discussed. Then, adopting the compact quadruple‐mode stub‐loaded resonator with three varactors, an independently controllable dual‐band bandpass filter (BPF) was designed, analyzed, and fabricated. Its separated bandwidths and transmission zeros can be tuned independently by changing the applying voltage of the microwave varactors. A good agreement between simulated and measured results verified the design methodology. The proposed filter possesses compact size, simple structure, and excellent dual‐band performances. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:602–608, 2016.     

Inter‐digital coupled dual‐mode patch resonator with crossed‐island configuration for tri‐band filter design

The miniaturized dual‐mode tri‐band band‐pass filters (BPF) using crossed‐island patch resonator is proposed in this article. The BPF is mainly formed by a square patch resonator in which a crossed‐island configuration is embedded in the patch. The patch size reduction with 74.4% is achieved. By the perturbation and the alternative inter‐digital coupling, the tri‐band responses are obtained. The proposed filter covers the required bandwidths for WLAN band (2.26–3.11 GHz and 5.02–6.0 GHz) and X‐band (7.58–8.41 GHz) applications. Five transmission zeros are placed between three pass‐bands and resulted in a good isolation. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:457–463, 2014.     

Design of dual‐mode dual‐band rectangular waveguide filtering antenna

A dual‐mode dual‐band rectangular waveguide filtering antenna with fourth‐order Chebyshev response is presented. First, design equations and processes of filtering networks are presented. Then, filtering antenna is constructed through cross‐shaped slot for radiation instead of the output port of filtering networks. A pair of degenerated modes are exploited in waveguide resonator design to miniaturize the whole size and form two passbands. In addition, the bandwidth can be adjusted flexibly in proper range. A prototype at C‐band is fabricated and measured, showing two operation channels of 5 to 5.05 GHz and 5.1 to 5.15 GHz with high rejection between two bands. Good agreement is achieved between the simulations and measurements, showing excellent performance in terms of filtering, out‐of‐band rejection, and gain in bands.     

Compact dual‐band bandpass filter and diplexer using hybrid resonant structure with independently controllable dual passbands

In this article, a compact dual‐band bandpass filter (BPF) is developed using a hybrid resonant structure, which consists of a microstrip stub‐loaded dual‐mode resonator and a slotline stub‐loaded dual‐mode resonator. These two resonators, both having two controllable resonant modes and one transmission zero (TZ), are analyzed and used to construct two desired passbands of a dual‐band BPF. Multiple TZs are generated by introducing a source‐load coupling, thus improving the selectivity of the passbands. Then, the dual‐band BPF is reshaped to configure a compact diplexer. The inherent TZs of the two proposed resonators are designed to improve the frequency property and port isolation of the diplexer. Finally, a dual‐band BPF and a diplexer with the lower and upper passbands centered at 2.45 and 3.45 GHz, respectively, are designed, fabricated, and measured to verify the proposed structure and method.     

Compact Dual‐/Tri‐/Quad‐Band banpass filters using shorted stub loaded stepped‐impedance resonator

In this article, the shorted stub loaded stepped‐impedance resonator (SSLSIR) with the individually tunable first even resonant mode and first odd resonant mode is applied to design dual‐, tri‐, and quad‐band bandpass filters (BPFs). The SSLSIR dual‐band BPF with asymmetrical coupling is realized using the first even resonant modes and the first odd resonant modes of a set of SSLSIRs. Then, the high‐impedance feeding lines of SSLSIR dual‐band BPF is modified to produce a new passband, and thus a new tri‐band BPF is realized. The proposed quad‐band BPF consists of two sets of SSLSIRs with symmetrical coupling. Each of the designed circuits occupies a very compact size and has a good in‐band out‐of‐band performance. Good agreements are observed between the simulated and measured results. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:601–609, 2015.     

A balanced dual‐band bandpass filter with a wide stopband and controllable differential‐mode frequencies and fractional bandwidths

In this article, a balanced microstrip dual‐band bandpass filter (BPF) is designed. The proposed filter is achieved by employing a microstrip U‐shape half‐wavelength resonator, a folded stub‐loaded resonator and balanced microstrip/slotline transition structures. The center frequencies and the fractional bandwidths of the two differential‐mode (DM) passbands can be controlled independently by changing the physical lengths of the two resonators and the gaps between each resonator, respectively. The balanced microstrip/slotline transition structures can achieve a wideband common‐mode (CM) suppression. Meanwhile, the DM passbands are independent from the CM responses, which significantly simplify the design procedure. In addition, a wide DM stopband is also realized. In order to validate the design strategies, a balanced dual‐band BPF centered at 2.57 and 3.41 GHz was fabricated and a good agreement between the simulated and measured results is observed.     

Complementary metamaterial transmission line for monoband and dual‐band bandpass filters application

A novel composite right‐/left‐handed transmission line (CRLH TL) and its equivalent circuit model are proposed based on cascaded complementary single split ring resonator (CCSSRR). It features an intrinsically balanced wider band and an additional transmission zero above the right‐handed band relative to CRLH TL using complementary single split ring resonator and complementary split ring resonators. Moreover, two single negative (SN) metamaterial (MTM) TLs constructed by using complementary electric inductive‐capacitive resonator on the conductor strip and on the ground, respectively, are researched. Both SN MTM TLs exhibit electric resonance above the fundamental magnetic resonance. For application, a monoband (MB) bandpass filter (BPF) covered WLAN band, and a dual‐band (DB) BPF covered satellite DMB band and WiMAX band are designed, fabricated, and measured. The SN MTM TLs are adopted for the sake of deep and wide out‐of‐band suppression while CRLH MTM TLs using square‐shaped and Sierpinski‐shaped CCSSRR are critical factors of the MB and DB behavior. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Dual‐band dual‐polarized hybrid aperture‐cylindrical dielectric resonator antenna for wireless applications

A dual‐band dual‐polarized hybrid aperture‐cylindrical dielectric resonator antenna (CDRA) is examined in this article. Inverted regular pentagon shaped aperture is not only used to launch two radiating hybrid modes (HEM_11δ and HEM_12δ mode) in CDRA but also act as a radiator. Out of two frequency bands, the lower frequency band is linearly polarized while upper frequency band is the combination of both circular and linear polarization. A circular polarization (CP) characteristic in upper frequency band is created by loading quarter annular stub with microstrip line. LHCP/RHCP can easily be controlled by alternating the position of quarter annular stub. It is operating over two frequency ranges i.e. 2.48‐2.98 GHz and 4.66‐5.88 GHz with the fractional bandwidth 18.31% and 23.14% respectively. Axial ratio bandwidth (3‐dB) is approximately 8.78% (4.9‐5.35 GHz) in upper frequency band. The proposed antenna design is suitable WiMAX (2.5/5.5 GHz) and WLAN (2.5/5.5 GHz) applications.     

Dual‐mode resonator with modified dual‐square‐Loop for WLAN and WiMAX quad‐band filter design

We propose the improved configurations with dual‐mode dual‐square‐loop resonators (DMDSLR) for quad‐band bandpass filter (BPF) design. The modified DMDSLR filter employs two sets of the loops. The square loop is designed to operate at the first and third resonated frequencies (2.4/5.22 GHz) and the G‐shaped loop is employed at the second and fourth resonated frequencies (3.59/6.6 GHz). The resonant frequency equations of DMDSLR are introduced for simply designing quad‐band BPF. Resonant frequencies can be controlled by tuning the perimeter ratio of the square loops. A systematic design procedure with the design map is applied for accuracy design. To obtain lower insertion loss, higher out‐of‐band rejection level and wider bandwidth of quad‐band, the miniaturized DMDSLR with meander‐line technique is proposed. The proposed filters are successfully simulated and measured showing frequency responses and current distributions. It can be applied to WLAN and WiMAX quad‐band systems. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:332–340, 2014.     

An efficient dual‐band filter‐antenna design based on simplified integration methodology

In this article, a newly developed filter‐antenna synthesis and realization methodology is applied to design a planar dual‐band filtering antenna. The synthesis method is derived based on the filter synthesis theory. As a result, a coupling coefficient expression is formulized more precisely specially for the antenna matched to the filter, which is essentially different from that in filter coupling. The synthesized circuit is realized by an efficient parameters extraction process. A third‐order dual‐band filtering antenna integrated with two dual‐mode 8‐shaped resonators and a dual‐inverted‐L antenna is then implemented for example to illustrate the design procedure. The integration method facilitates an efficient and practical filter‐antenna design without complicated parameters evaluation process. Finally, the proposed filtering antenna with simple structure and controllable frequencies is developed with the use of the investigated formulations and extraction curves. The circuit is realized for 2.5/3.45‐GHz WiMAX‐band applications. The tested results agree well with the simulations, showing good passbands selectivity and out‐of‐band rejection are attained.     

A compact dual‐band superconducting filter with fine‐tuning coupling structure

A novel dual‐mode optimized patch capacitor loaded T‐type resonator is proposed for the design of a dual‐band filter (DBF). The resonator has its lowest even‐ and odd‐mode at the two expected passband frequencies and the first spurious mode far away from the passbands. For tuning of the two sets of coupling strengths for both passbands, open/shorted secondary coupling structures are introduced as a fine‐tuning coupling structure to increase/decrease the primary coupling strength. A four‐pole DBF with passbands centered at 2450 and 3500 MHz, respectively, is proposed and fabricated using the HTS material. The measured results of the filter indicate superior performance and good fitting with the simulation results. The return losses of both passbands and the insertion losses obtained by measurements are greater than 14 dB and less than 0.3 dB, respectively. The stopband rejection exceeds 50 dB up to 8.0 GHz.     

Miniaturized dual‐band dielectric resonator antenna for IEEE 802.16d fixed WiMAX applications

A miniaturized dual‐band C‐shaped dielectric resonator antenna (DRA) with partial ground plane is presented for IEEE 802.16d fixed WiMAX applications at 3.5 and 5.8 GHz. The design starts with dimensioning a single band cylindrical DRA, which has been transferred to get a dual‐band ring‐shaped DRA. One portion of the ring‐shaped DRA is removed for forming a C‐shaped DRA to get a more compact antenna. For easy fabrication, the compact DRA dimensioned as 60 × 50 × 6.6 mm³ is excited by a microstrip line feeding. The design parameters are inner and outer radii of the C‐shaped antenna and air gap (between DR and ground) to control both the resonating frequency and the quality factor. The result shows peak gain around 3.26 and 5.55 dBi at 3.5 and 5.8 GHz, respectively. The obtained results indicate very good agreement between the simulated and measured results. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22: 682–689, 2012.     

Dual‐band differential bandpass filter using stepped impedance resonators

In this article, a novel dual‐band differential bandpass filter using (SIRs) is designed. To demonstrate the design ideas, the differential and common mode equivalent half circuits are built and studied. Two resistors are connected between the two ends of the SIRs to consume the power in common mode. A capacitor is connected between the Ground and Center of the SIR to adjust the spurious frequencies, also strength the coupling of the two SIRs. The theoretical analysis shows the second band can be obtained by the proper impedance ratios of the resonances and the capacitor connected to the resonator. Two through ground vias (TGVs) connecting the top and bottom sides of the SIR filter, are used to realize the common mode rejection. To investigate the proposed filter in detail, a set of design equations are derived based on the circuit theory and transmission line theory. A phototype dual‐band differential filter operating at 1.5 and 2.75 GHz has been realized to validate the proposed concept and theory. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:468–473, 2015.     

Dual‐band dielectric resonator bandstop filters

This article presents the design and implementation of a new asymmetric dual‐band bandstop filter using TE01δ mode dielectric resonator (DR) technology. The coupling matrix is generated by frequency transformation technique applied to advance filtering functions for direct‐coupled asymmetric dual‐band bandstop filter in cul‐de‐sac configuration. The proposed approach provides control of all the major parameters such as center frequencies, intercavity couplings, and input/output couplings of filter independently in both the designated bands. The dual‐band DR filters (2 × 2) pole, with return loss = 15 dB and percentage rejection bandwidth of 1.6 and 0.6% in two bands, at 9.96 and 10.15 GHz, respectively, are designed, built, and tested. The measured and simulated results are in good agreement over the desired band. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:282–288, 2015.     

Dual‐band rotary standing‐wave voltage‐controlled oscillator

In this article, a dual‐band rotary standing‐wave oscillator (RSWO) is introduced that generates sinusoidal signals by the formation of a standing wave on a ring (closed‐loop)‐distributed composite right/left‐handed (CRL) Inductor‐Capacitor (LC) transmission line network. The LC network consists of four unit cells of CRL LC resonator stacked in series, and two pairs of cross‐coupled transistors are used to compensate for the loss of LC resonator. Varactors are used as the control to switch on/off the high‐ or low‐frequency bands. In the fundamental mode, the RSWO operates at the high‐frequency band. In the harmonic mode, the oscillator provides low‐frequency band outputs. The dual‐band function exploits the multiple oscillation modes of the CRL RSWO. The proposed RSWO has been implemented with the Taiwan Semiconductor Manufacturing Company, Limited (TSMC) 0.18‐μm SiGe BiCMOS technology. It can generate differential signals in the high‐band frequency range of 6.73–8.60 GHz and in the low‐band frequency range of 3.68–3.73 GHz. The die area of the RSWO is 1.123 × 1.123 mm². © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:536–543, 2014.