Compact bandpass filter based on SIW loaded by open complementary split‐ring resonators

A compact substrate integrated waveguide (SIW) with open complementary split‐ring resonators (OCSRRs) loaded on the waveguide surface is proposed. The OCSRRs can be interpreted in terms of electric dipoles and they are good candidates to behave as electric scatterers. By loading OCSRRs on the waveguide surface, a forward‐wave pass‐band propagating below the waveguide cutoff frequency is generated. The resonance frequency of the OCSRRs is approximately half of the resonance frequency of the complementary split ring resonator (CSRR). Therefore, the electrical size of this particle is larger than the CSRRs and the OCSRRs are more appropriate for the SIW miniaturization. A bandpass response with a sharp rejection frequency band is obtained by properly manipulating the structure of the elements. By changing the orientation of the OCSRRs, two types of unit cell are proposed. Moreover, by resizing the OCSRRs, resonance frequency can be easily moved and the bandwidth can be tuned by the coupling between two OCSRRs. Compared with some other reported bandpass filters (BPFs) with SIW technique, the presented BPF has great improvements on size reduction and selectivity. To verify the methodology, two filters with center frequency of 5.5 GHz are designed and measured. The measured results are in good agreement with the simulated ones. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:674–682, 2016.     

A novel super compact half‐mode substrate‐integrated waveguide filter using modified complementary split‐ring resonator

A novel super compact filter based on half‐mode substrate‐integrated waveguide (HMSIW) technology loaded by the modified complementary split‐ring resonator (MCSRR) is proposed. The working principle of the proposed filter is based on the evanescent‐mode propagation technique. According to this technique, by loading the complementary split‐ring resonator (CSRR) on the metal surface of the substrate‐integrated waveguide (SIW) structure, an additional passband below the SIW cutoff frequency can be obtained. In order to miniaturize the physical size of the conventional CSRR, a new method is introduced. In the proposed MCSRR unit‐cell, the meander slots are carved inside all of the interior space of the ring. Accordingly, the length of the slot is increased which leads to an increase in the inductor and capacitor of the proposed structure without occupying the extra space. Therefore, the electrical size of the proposed MCSRR unit‐cell is reduced. Consequently, the resonance frequency of the proposed MCSRR unit‐cell is decreased compared to the conventional CSRR with the same sizes. Namely, the lower resonance frequencies can be achieved by using this technique without increasing the size of the unit‐cell. In order to confirm the miniaturization technique, two HMSIW filters loaded by the proposed MCSRR unit‐cell are designed, fabricated, and experimental verifications are provided. The results show that a miniaturization about 67% is achieved.     

Half mode substrate‐integrated waveguide‐loaded evanescent‐mode bandpass filter

In this article, a filter size reduction of 46% is achieved by reducing a substrate‐integrated waveguide (SIW)‐loaded evanescent‐mode bandpass filter to a half‐mode SIW (HMSIW) structure. SIW and HMSIW filters with 1.7 GHz center frequency and 0.2 GHz bandwidth were designed and implemented. Simulation and measurements of the proposed filters utilizing combline resonators have served to prove the underlying principles. SIW and HMSIW filter cavity areas are 11.4 and 6.2 cm², respectively. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Compact metamaterial unit‐cell based on stepped‐impedance resonator technique and its application to miniaturize substrate integrated waveguide filter and diplexer

In this article, a new miniaturized metamaterial unit‐cell using stepped‐impedance resonator technique is proposed. The proposed unit‐cell is used to miniaturize the physical size of the conventional complementary split‐ring resonators (CSRRs). In the proposed unit‐cell which is called complementary G‐shaped resonator (CGR), the slot line in the conventional circular CSRR is replaced with the stepped‐impedance slot line. As well as, by carving two trapezoidal shapes inside the inner ring, the resonance frequency of the proposed CGR unit‐cell has been more decreased. Compared to the conventional circular CSRR structure, the electrical size of the proposed CGR is decreased and miniaturization is occurred. To investigate the performance of the proposed CGR unit‐cell in the size reduction, two substrate integrated waveguide filters and a diplexer are designed. To validate the proposed miniaturization technique, the designed filters and diplexer loaded by the CGR unit‐cell are fabricated and measured. The measured results are in a good agreement with the simulated ones. The results shows that, a miniaturization factor about 0.69 is achieved.     

Miniaturized rectangular waveguide filters

Two types of miniaturized rectangular waveguide filters are presented. Miniaturization is achieved using the slow‐wave effect of electromagnetic bandgap (EBG) surfaces and the left‐handed properties of split ring resonators (SRRs). The proposed EBG waveguide bandpass filter performs passband in the frequency range, which corresponds to the waveguide with the lower recommended operating band consequently enabling significant miniaturization of the structure. The SRR‐loaded bandstop filter makes use of the effect imposed by left‐handed medium (LHM), which is created by a combination of SRRs and wireline on the dielectric slab. Both filters are designed, simulated, and tested. Experimental results of the SRR‐loaded bandstop filter are presented to demonstrate feasibility of the proposed structures. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Miniaturized substrate integrated waveguide 5G LTCC bandpass filter exploiting capacitive loaded cavities

In this article, a compact bandpass filter with a pair of transmission zeros exploiting capacitive loaded cavities is presented. The proposed filter structure is mainly composed of coplanar waveguide (CPW) feeding structures and four substrate integrated waveguide (SIW) resonators. The size of the filter has been greatly reduced due to the capacitive loaded circle metallic septum and the vertical coupling of stacked cavities in three dimensional structures by low temperature co‐fired ceramic technology. The filter not only achieves the advantages of high‐selectivity, a much wider upper stopband bandwidth, but also realizes a miniaturized volume of 3.35 × 2.10 × 0.66 mm³. The simulated and measured results show the bandpass filter achieves a center frequency of 28 GHz with 3 dB fractional bandwidth of 8%. The filter is suitable for application in 5G wireless communication.     

Enhanced waveguide bandpass filters using S‐shaped resonators

This article presents a new solution for stopband performance improvement of rectangular waveguide bandpass filters using S‐shaped resonator loaded waveguide configurations at microwave and millimeter‐wave frequencies. The proposed filter structure is compact in size when comparing with the standard E‐plane counterpart. Compactness is achieved by taking advantage of the properties of slow wave effect in half wavelength resonators. Periodicity is readily imposed upon cascading the S‐shaped resonators within the rectangular waveguide. The structure is simple and compatible with E‐plane technology. This type of bandpass filters can be easily realized with a single metallo‐dielectric insert within a standard rectangular waveguide. Simulation and experimental results are presented to validate the argument along with some design guidelines. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2009.     

A novel bandpass filter based on TEM‐SIW cavity

A novel microstrip filter based on transverse electromagnetic (TEM)‐substrate integrated waveguide (SIW) cavities is firstly proposed in this letter. Compared to the traditional SIW cavities, the TEM‐SIW cavities have more compact size and higher Q value. Then, two bandpass filter adopting TEM‐SIW cavities is designed and one of it is fabricated. Both simulated and measured results are presented. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Compact substrate integrated waveguide rat‐race filtering couplers with arbitrary angular interval between ports

A new type of compact filtering rat‐race couplers with arbitrary port direction based on different shape substrate integrated waveguide (SIW) cavity are first proposed in this paper. Different shaped SIW resonators can be combined together to achieve better performance and flexible topology. Resonant frequencies of fan‐shaped SIW cavity with various central angles have been derived to construct the resonant cells and obtain different topological structures. Moreover, interdigital capacitor SIW unit loaded on the common wall between cavities is used to achieve negative coupling structure. The detailed analysis and the design method have been introduced to realize a filtering rat‐race coupler based on substrate integrated fan‐shaped cavity (SIFC) and rectangular cavity. In particular, the combination of different shaped resonators can be selected according to the requirement of port angle interval. In order to further verify the method, the other filtering rat‐race coupler is fabricated using four SIFCs to achieve more available port angle intervals. Compared with other filtering couplers, the proposed designs exhibit good filtering responses, high Q factor, amplitude balance, as well as 0° and 180° phase differences. Furthermore, various angular intervals for input/output ports are convenience to meet the requirement of system topology and interconnect.     

Dual‐band ridge waveguide filters for high‐selectivity wireless base station applications

Dual‐band filters simplify the system architecture considerably by replacing doubly multiplexed filters. This is especially important in base stations for wireless communications, where high‐selective filtering functions are required, with very stringent requirements in size and insertion losses. For this goal, compact dual‐band filters realized in air‐filled metallic ridge waveguides are proposed. The dual‐band approach shown in this article allows fulfilling the stringent insertion loss specifications of very selective filtering functions. The ridge waveguide resonators are placed in a canonical folded top‐bottom structure layout. Coupling sections that provide cross‐couplings are realized by irises opened in the intermediate wall. Given the high‐order of the dual‐band filter required for actual wireless applications, an efficient modeling by the mode‐matching method is used. A complete challenging filter prototype with 16 poles and 10 transmission zeros with specifications of typical wireless transceivers is built and tested for verification. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:703–712, 2016.     

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.     

A compact and wideband array antenna with efficient hybrid feed network

This study presents a high‐efficient, compact, and broadband microstrip patch antennas (MPAs) based on substrate‐integrated waveguide (SIW) for X‐band applications. The proposed array consists of three stacked layers from top to bottom, including one layer as the antenna layer and two SIW layers as a feeding network. The performance was focused on improving the impedance bandwidth and radiation efficiency by mitigating the loss from the feed network while also maintaining the compact design. To this end, the SIW feeding network was designed to feed the MPA to save the physical aperture size which resulted in a more compact and efficient radiating structure. The overall size of the proposed array is compact and extra surface area around the radiation aperture has not been occupied. The measured ?10 dB impedance bandwidth span is from 8.9 to 10.9 GHz (20.2%). The maximum measured gain at 10.6 GHz is 10.6 dBi. The results show that the simulated radiation efficiency and the measured aperture efficiency are more than 75% and 50%, respectively. The fabricated array exhibits great advantages such as wide operating bandwidth, lightweight, low‐cost, high aperture efficiency, high radiation efficiency, and compactness which make it a good candidate for X‐band applications.     

Wideband bandpass filter based on U‐slotted SW‐HMSIW cavities

A wideband bandpass filter (BPF) is designed based on U‐slotted slow wave half mode substrate integrated waveguide (SW‐HMSIW) cavities. Similar to the substrate integrated waveguide (SIW), the SW‐HMSIW can also achieve a highpass characteristic while the lateral dimensions can be reduced by about 50%. By etching a U‐shape slot on the SW‐HMSIW cavity, a multiple‐mode resonator (MMR) can be realized, which can achieve a wide passband response and make the overall dimension of the filter much more compact. A wide passband, covering from 6.0 GHz to 10.65 GHz with a FBW about 58.13% is achieved. The measured minimum insertion losses including the losses from SMA connectors are 1.1 dB and return losses are better than 10 dB. Besides, the group delay varies between 0.2 and 0.5 ns within the passband. To validate its practicability, a wideband SW‐HMSIW BPF fabricated on a double‐layer printed circuit board (PCB) is designed and examined. The proposed filter has a more than 54% size reduction compared to the other designs reported in open literatures. The measured results have a good agreement with the simulated results. The effective size of the fabricated filter is about 27 mm × 8.55 mm.     

New multi‐standard dual‐wideband and quad‐wideband asymmetric step impedance resonator filters with wide stop band restriction

New multi‐standard wide band filters with compact sizes are designed for wireless communication devices. The proposed structures realize dual‐wideband and quad‐wideband characteristics by using a new skew‐symmetrical coupled pair of asymmetric stepped impedance resonators, combined with other structures. The first and second dual‐wideband filters realize fractional bandwidths (FBW) of 43.2%/31.9% at the central frequencies (CF) of 1.875/1.63 GHz, and second bandwidths of 580 MHz/1.75 GHz at CF of 5.52/4.46 GHz, respectively. The proposed quad‐band filter realizes its first/second/third/fourth pass bands at CF 2.13/5.25/7.685/9.31 GHz with FBW of 46.0%/11.4%/4.6% and 5.4%, respectively. The wide pass bands are attributed to the mutual coupling of the modified ASIR resonators and their bandwidths are controllable by tuning relative parameters while the wide stop band performance is optimized by the novel interdigital cross coupled line structure and parallel uncoupled microstrip line structure. Moreover, the quad band is generated by introducing the novel defected rectangle structure. These multi‐standard filters are simulated, fabricated and measured, and measured results agree well with both simulated results and theory predictions. The good in‐band and out‐of‐band performances, the miniaturized sizes and simple structures of the proposed filters make them very promising for applications in future multi‐standard wireless communication.     

Simple,compact and broadband right‐angle transition between substrate integrated waveguide and rectangular waveguide at Ka‐band

In this article, a simple compact broadband right‐angle transition between substrate integrated waveguide (SIW) and rectangular waveguide (RWG) working at Ka‐band is proposed. Three coupling slots etched on the interface are developed to couple the electromagnetic field from SIW to RWG. A metallic via is introduced into the end slot to enhance the inductance and all the slots are developed in different dimensions for multi‐resonance. By proper optimizing, three resonances are obtained which broadens the impedance matching effectively. All details of the transition are designed on the SIW part for the purpose of simple and compact. Two back‐to‐back prototypes working at Ka‐band are designed, fabricated and measured. The measured results show that the mean value of insertion loss for a single transition is about 0.51 dB and the return loss is better than 15 dB over the full Ka‐band. The proposed right‐angle transition has advantages of simple assembly, compact size and broadband characteristics and it can be a good candidate for millimeter‐wave applications.     

Design of a compact dual‐band folded‐waveguide bandpass filter using multilayer waveguide resonators

A novel compact dual‐band bandpass filter based on multilayer folded‐waveguide (FWG) structure is presented in this article.In this design, slots are used to realize direct coupling between adjacent resonators and apertures are adopted to implement cross coupling between non‐adjacent resonators.A new technique of external quality factor of FWG resonator and coupling coefficients between different resonators are studied using full‐wave simulator. In order to demonstrate the proposed technique, a four‐pole dual‐band bandpass filter is designed, fabricated and measured using vector network analyzer. Measurement results which are well agreed with simulation results are presented. Moreover, four‐pole substrate integrated folded waveguide SIFW dual‐band bandpass filter, using two layers of slotted folded waveguide resonators, is demonstrated. The proposed filter has a compact size and it is excellent candidate for the application of wireless communication systems. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:780–788, 2015.     

Compact,dual-band,and hybrid filter based on combline and substrate integrated waveguide resonators

A novel compact hybrid dual-band bandpass filter based on combline and substrate integrated waveguide (SIW) resonators is proposed. By exploring an SIW-based hybrid cavity structure, a controllable dual-band response is achieved. The low-frequency passband is obtained by the combline, or mushroom resonators and the high-frequency passband is formed by the TE₁₀₁ and TE₃₀₁ modes. Unlike other designs that use the main mode and the high-order mode of the same resonator, we innovative use the TE301 mode of the rectangular cavity and cleverly divide this rectangular cavity into two small cavities, and use its TE101 mode to form the second passband with the TE301 mode of the large cavity. To improve the selectivity and out-of-band suppression, three transmission zeros are configured in this design. In order to verify the proposed design concept, a compact dual-band filter using this hybrid resonance structure is fabricated and measured. It demonstrates good filtering performance, including a compact size of 0.45 × 1.09 λ₀, a low insertion loss of 0.57 and 1.67 dB in the two bands, and a high-design flexibility.     

A novel wideband bandpass filter based on CSRR‐loaded substrate integrated folded waveguide

A novel wideband bandpass filter based on folded substrate integrated waveguide (FSIW) is presented in the article. Five square complementary split‐ring resonators (CSRRs) are etched in the middle layer of the FSIW. By adjusting the physical size of the CSRR structure, the resonant frequency of the CSRRs can be tuned at the same time and the stopband performance can be changed. As transverse electromagnetic (TEM) mode can be transmitted in the stripline, FSIW excited by stripline shows wider passband than that excited by microstrip line directly. To achieve perfect impedance matching, two microstrip lines to stripline transitions are added in two ports of the filter. The proposed bandpass filter exhibits compact size, high selectivity, good stopband rejection, lower radiation loss, and wideband performances. The measured results show that the fractional bandwidth of the filter is about 35.5%. The measured return loss is better than 15 dB from 4.84 GHz to 6.90 GHz, and the insertion loss is less than 1.2 dB. The comparison between the simulated results and the measured ones validate the possibility of the technology that combines the FSIW and CSRR.     

Ultracompact two‐way and four‐way SIW/HMSIW power dividers loaded by complementary split‐ring resonators

In this paper, two ultracompact power dividers based on the substrate integrated waveguide (SIW) and half‐mode SIW (HMSIW) technologies loaded by complementary split‐ring resonators (CSRRs) are presented. The presented structures are designed based on the theory of evanescent mode propagation. To obtain a size reduction, the CSRR unit cells are etched on the metallic surface of the SIW and HMSIW structures. First, a two‐way HMSIW power divider is reported. In this circuit, the concept of HMSIW is utilized aiming at a further size reduction in addition to the size reduction by the CSRR unit cells. Then, a four‐way SIW power divider is designed so that the direct coaxial feed is used for the input port and microstrip transmission lines are used for the output ports. Both two‐way and four‐way SIW/HMSIW power dividers at 5.8 GHz covering WLAN are designed, fabricated, and measured. They respectively have 0.18 × 0.21 λg² and 0.38 × 0.21 λg² total size. A fair agreement between simulated and measured results is achieved. The measured insertion losses are 0.5 ± 0.5 and 0.6 ± 0.5 dB for the two‐way and four‐way SIW/HMSIW power dividers, respectively, in the operating band of interest.     

An SIW antenna utilizing odd‐mode spoof surface plasmon polaritons for broadside radiation

In this article, a substrate integrated waveguide (SIW) antenna utilizing odd‐mode spoof surface plasmon polariton (SSPP) for broadside radiation is proposed. Double gratings are etched on the top surface of SIW and the SSPP odd‐mode is excited on this hybrid SIW‐SSPP structure. The proposed SIW antenna has open‐circuit termination and can realize broadside radiation. A prototype of the SIW‐based odd‐mode antenna is fabricated. Reasonable accordance is achieved between measured results and simulated results. The antenna impedance bandwidth is about 5.5% (12.4~13.1 GHz) with |S₁₁| < ?10 dB. Stable broadside radiation is also realized within the operating band of 12.3~13.3 GHz and the measured gain varies from 5.66 to 6.34 dB in the frequency band. The proposed broadside radiation antenna is suitable for wireless communication systems due to its compact structure and good radiation performances.