Efficient design of SIW filters with knowledge‐embedded space mapping technique

This article presents an optimization technique for the design of substrate‐integrated waveguide (SIW) filters using knowledge‐embedded space mapping. An effective coarse model is proposed to represent the SIW filter. The proposed coarse model can be analyzed in the available commercial software ADS. The embedded knowledge includes not only formulas but also extracted design curves, which help to build the mapping between the coarse and fine models. The effectiveness of the proposed method is demonstrated through a design example of a six‐pole SIW filter. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Design and optimization of cross‐coupled substrate integrated waveguide filters using space mapping method

This work presents an efficient method for the design of substrate integrated waveguide (SIW) filters. The proposed design approach is based on a combined use of equivalent circuit model of a filter and a space mapping technique. A reduced number of full‐wave evaluations are needed, leading to a reduced optimization time. A novel SIW filter with improved stop‐band characteristic using cross‐coupling has been proposed. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:360–366, 2014.     

Substrate‐integrated waveguide band pass filters with frequency‐dependent coupling elements

An effective technique to improve the stop‐band frequency response of direct‐coupled resonators in substrate‐integrated waveguide (SIW) technology is introduced. Regular inductive‐iris filters in SIW technology are supplemented with H‐plane frequency‐dependent inverters which not only create transmission zeros but also serve as the proper impedance inverter. A synthesis technique is introduced to prescribe transmission zeros at finite frequencies on either side of the pass band, symmetrically or asymmetrically. Two different topologies of frequency‐dependent inverters for X‐band SIW band pass filters demonstrate that attenuation poles can be created on both side of the passband and significantly improve the filters' stop‐band performences. Measurements confirm the validity of the presented design approach. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:237–242, 2014.     

Neural network of calibrated coarse model and application to substrate integrated waveguide filter design

In this article, we propose a novel neural network of calibrated coarse model, which can obtain the optimal filter response with as little training data as possible to synthesize the entire substrate integrated waveguide (SIW) filter. By incorporating the knowledge of filter decomposition with the inverse neural network, we build a coarse model that can synthesize the dimensions of a SIW filter. However, the SIW structures are subject to a potential leakage problem due to the periodic gaps, the results of the coarse model are very different from the ideal response. We propose a novel calibrated neural network from the perspective of the coupling matrix to correct the errors generated in the coarse model. In addition, this article also proposes an equivalent de‐embedding technique, which is simpler than the thru‐reflect‐line calibration technique to accurately extract the scattering parameters of the SIW discontinuities. An H‐plane fifth order SIW filter is synthesized by the proposed model. The result shows that the SIW filter that is very close to the ideal response can be synthesized with only a few hundred training data.     

Low loss and broadband transition between substrate integrated waveguide and rectangular waveguide

In this article, a novel transition between substrate integrated waveguide (SIW) and rectangular waveguide is proposed. A pair of antipodal tapered probes is developed to convert the E‐field of SIW to that of waveguide, acting as an antipodal dipole antenna to improve the performance of the SIW‐to‐waveguide transition. A back‐to‐back prototype of the proposed transition is fabricated and measured, the results show that the transition achieve a bandwidth of 51.1% from 23.7 to 40 GHz, and a size reduction of 75.3% compared to the SIW‐to‐waveguide transition using antipodal fin‐line. A tolerance analysis is performed via the simulation to verify the reliability of this transition design. For further validation, the antipodal tapered probes are employed for the design of partially filled SIW‐to‐waveguide transition. From its experimental results, it demonstrates that the loss of a single SIW‐to‐waveguide is less than 0.26 dB over the frequency range of 24.9–40 GHz. In addition, such proposed SIW‐to‐waveguide transition is suitable for hermetic packaging due to the inherent property in transition structure. These results show that the proposed transition can offer the advantages of broad bandwidth, low loss, compact size, and stable performance at millimeter‐wave frequencies. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:54–61, 2016.     

High gain substrate integrated waveguide beam scanning antenna with sub‐array elements

A method to enhance the gain of substrate integrated waveguide (SIW) beam scanning antenna is proposed in this article. 2 × 2 SIW cavity‐backed sub‐arrays are employed in array design. The antenna is constructed on two layers. The top layer places four SIW cavity‐backed sub‐arrays as radiating elements and the bottom layer is an SIW transmission line to feed the sub‐arrays. Beam scanning feature can be obtained due to the frequency dispersion. Moreover, through separating radiators to the other layer and using 2 × 2 SIW cavity‐backed sub‐arrays as radiating parts, the antenna gain is improved significantly. For a linear array, 4.1 to 6.8 dB gain enhancement is achieved compared to a conventional SIW beam scanning antenna with the same length. Then, the linear array is expanded to form a planar array for further gain improvement. A 64‐element planar beam scanning array is designed, fabricated, and tested. Experimental results show that the proposed planar array has a bandwidth from 18.5 GHz to 21. 5 GHz with beam scanning angle from ?5° to 11.5° and gain in the range of 20.5 to 21.8 dBi. The proposed high gain beam scanning antennas have potential applications in radar detection and imaging.     

Accurate and efficient design technique for wideband substrate integrated waveguide directional couplers

In this article, we present an efficient technique for the accurate design of wideband substrate integrate waveguide directional couplers. By tapering the coupling section, the bandwidth of substrate integrated waveguide (SIW) directional couplers can be enlarged. Two design aspects are involved in this approach. First, the even‐mode propagation constant in the tapered coupling section is accurately extracted with the help of a numerical thru‐reflect‐line calibration technique. Then, it is fitted into the model of a uniform dielectric‐filled rectangular waveguide and thereafter extrapolated to the operation range of the odd mode. Second, equivalent circuit models of the waveguide bifurcation effects are also presented together with parametric values. Based on the results of extraction, a 90° 3‐dB directional coupler is developed to validate the proposed design approach. To achieve the reverse phasing at two output ports, the prototyped 90° 3‐dB directional coupler is subsequently integrated with a novel broadband fixed phase shifter developed with the SIW technology, of which a systematic synthesis procedure has been proposed in this article. Measured performance of both 90° and 180° 3‐dB couplers confirms the accuracy of our proposed design approach. This kind of wide‐band directional coupler can find applications in wideband power dividing/combining circuits within a single‐layer platform. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Low‐profile substrate integrated waveguide (SIW) cavity‐backed self‐triplexed slot antenna

A low‐profile self‐triplexed slot antenna is proposed for multiple system integrations. The antenna comprises of hybrid substrate integrated waveguide (SIW) cavity (a combination of a half‐mode circular and half‐mode rectangular SIW), radiating slot, and feeding network. A slot is imprinted on the upper metal‐layer of the SIW which splits the cavity into three radiating sections. It offers tri‐frequency bands when each section is excited separately. By finely tuning the antenna dimensions, it produces three frequency‐bands around 5.57, 7.17, and 7.65 GHz simultaneously utilizes a single slot with maintaining the intrinsic input‐port isolation better than 20 dB. This property helps to introduce the self‐triplexing phenomenon. Compared with the conventional multiband antennas that use an extra circuitry to ensure the port isolations, this design preserves compactness and easy to integrate with planar circuits Moreover, the proposed antenna is fabricated and the measured results mutually agreed with the simulated counterparts. The proposed design can be a feasible option for mobile transceiver applications.     

Miniaturized planar ferrite junction circulator in the form of substrate‐integrated waveguide

The theoretical analysis and engineering implementation of the planar substrate‐integrated waveguide (SIW) ferrite junction circulator have been proposed in this article. The ferrite junction circulator is implemented in the form of SIW, taking the features of low profile, small volume and easy integration with other planar circuits. The design strategies of the device have been introduced, including the design consideration of the microstrip transition. One C‐band prototype of SIW ferrite junction circulator has been fabricated and measured. The experimental results indicate the bandwidth is about 33% at −15 dB isolation and the maximum isolation is near 40 dB. However, the insertion loss is a little big, owing to the imperfect dielectric material and fabrication inaccuracy. The SIW ferrite junction circulator and the microstrip transition are integrated into a same substrate, resulting in a very compact planar ferrite junction circulator and indicating potential applications in integrated communication and radar systems. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Compact planar substrate‐integrated waveguide diplexers with wide‐stopband characteristics

Compact planar substrate‐integrated waveguide (SIW) diplexers with wide‐stopband characteristics are presented for the first time based on collaborative multispurious mode suppression techniques including the harmonic staggered technique, centered coupling windows, and offset‐centered output ports. The coupling scheme using common dual‐mode resonator coupled with multiple single‐mode resonators is adopted here to eliminate the T‐junctions for size and loss reduction, and the dual‐mode coupling controlling technique we previously proposed is also employed to allocate the fractional bandwidths (FBWs) of the two channels flexibly based on the FBW design graph. Additionally, by combining the harmonic staggered technique, centered coupling windows, and offset‐centered output ports, good out‐of‐band rejections can be achieved and excellent wide‐stopband characteristics have been implemented intrinsically. Two prototypes including second‐order and third‐order SIW diplexers are synthesized, designed, fabricated, and tested as demonstrations, extending the stopbands to 1.78f₁ and 2.04f₁ with the rejection levels better than 17.5 and 20 dB, respectively.     

A new design of substrate integrated waveguide diplexer using complementary split ring resonators

Design method for achieving the acceptable electrical responses (isolation and impedance matching) of a mixer in two‐close frequency with substrate integrated waveguide (SIW) is presented. SIW diplexer with complementary split ring resonators and an open stub is proposed. The SIW loaded diplexer is operated below the cutoff frequency of the equivalent waveguide for SIW; therefore, the size of the structure is compacted. Input and output ports matching are realized in the light of open microstrip stub. The diplexer with optimum dimensions is designed and fabricated. The measurement results verified the design procedures. They also show that operation frequencies are very close together, and also the proposed structure is suitable for long term evolution frequency bands.     

Multilayered substrate integrated waveguide 4 × 4 butler matrix

In this article, a multilayered substrate integrated waveguide (SIW) Butler matrix beam‐forming network is proposed, designed, and demonstrated at 24 GHz for automotive radar system applications. The proposed low‐cost SIW structure can be used to develop a highly integrated multibeam antenna platform in automotive radar systems and other applications. In this structure, an SIW H‐plane coupler is optimized with an H‐plane slit to provide the required phase shift. A class of SIW E‐plane 3‐dB couplers in doubled layer substrate are studied and designed as the fundamental building blocks to avoid crossovers usually required in the construction of a Butler matrix. A 4 × 4 matrix is investigated and designed, which shows excellent performance over 22–26 GHz frequency band. Two types of antenna are tested with the proposed matrix scheme. First, an antipodal linearly tapered slot antenna (ALTSA) is incorporated into the Butler matrix to verify the broadband performances. Second, a longitudinal slotted waveguide antenna array is examined to generate radiation patterns in the broadside direction. Measured results agree well with simulated counterparts, thus validating the proposed multilayer SIW design concepts. In the next sections, the use as feeding networks for providing the reconfigurability operation of an antenna will be illustrated. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2012.     

Computer aided equivalent circuit model of SIW cavity backed triple band slot antenna

In this article, a study of planar triple band unidirectional Substrate Integrated Waveguide (SIW) cavity backed slot antenna using equivalent circuit model is presented. The proposed antenna uses a modified dumbbell shaped slot of much larger length placed in a planar SIW cavity to excite three closely spaced SIW cavity hybrid modes which help the slot to radiate into free space. The design is analyzed with the help of equivalent circuit model to predict the resonant frequencies of the design and also to explain the excitation mechanism of the proposed slot antenna. The proposed circuit model is validated by comparing its performance with the simulation model for a wide range of parametric variation. The relationship between modification in design dimension with the variation of coupling between feed line and cavity modes is studied which gives a design guideline for the proposed antenna. The fabricated prototype of the antenna resonates at 7.39, 9.43, and 14.79 GHz with a gain of 3.2, 4.9, 4.7 dBi and front‐to‐back ratio (FTBR) of 10 dB, respectively, at three resonant frequencies which makes it suitable for C (4–8 GHz), X (8–12 GHz), and Ku (12–18 GHz) band applications.     

High‐isolation multiway power dividing/combining network implemented by broadside‐coupling SIW directional couplers

One kind of novel microwave planar power dividing/combining network based on substrate‐integrated waveguide (SIW) directional couplers is proposed and investigated. The design strategies of the broadside‐coupling SIW directional coupler are introduced, the series connection of several directional couplers with different coupling ratio then result in a multiway power dividing/combining network. One three‐way power dividing/combining network is designed and fabricated to demonstrate the validity of the proposed work, high isolation among the ports is observed. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

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.     

Design and optimization of a planar folded substrate integrated waveguide bandpass filter exploiting aggressive space mapping

Substrate integrated waveguide (SIW) is a new structure for microwave transmission. In this paper, a planar folded sixth‐order SIW filter is designed with aggressive space mapping (ASM) algorithm. Its center frequency is 22 GHz, 3 dB bandwidth 1 GHz, and in‐band return loss 22 dB. The filter satisfies design specifications after four iterations, and is fabricated using micro‐electro‐mechanical systems (MEMS) technology with a chip size of 7.5 mm × 8.5 mm × 0.4 mm. Measurement results show that the center frequency of the filter measures at 22.2 GHz, 3 dB bandwidth at 1 GHz, insertion loss at 3.57 dB, return loss at 22 dB and out‐of‐band rejection at 40 dB.     

A novel substrate integrated waveguide cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic

This article presented a substrate integrated waveguide (SIW) cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic. The proposed array consists of 16 SIW cavity‐backed slot antennas. The SIW cavity‐backed slot antenna can be fed by two separate ports to resonate at two different frequencies and achieve high isolation better than 20 dB between two input ports. The proposed element is a typical self‐diplexing antenna. These cavity‐backed slot antennas are shunt‐fed by a compact 1 to 16 SIW power divider and series‐fed by a set of microstrip lines, respectively. As a result, this array achieves an unidirectional radiation pattern at 10.2 GHz with high gain of 15.10 dBi, and a frequency beam scanning characteristic from 7.0 to 9.0 GHz ranging from ?50° to 46°.     

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.     

Substrate integrated waveguide dual‐frequency dual‐sense circularly polarized cavity‐backed slot antenna

A novel design of dual‐frequency dual‐sense circularly polarized (CP) substrate integrated waveguide (SIW) cavity‐backed slot antenna is presented for dual‐band wireless communication systems. The proposed antenna consists of square SIW cavity, asymmetrical bow‐tie‐shaped cross slot and probe feed. Due to use of asymmetrical bow‐tie‐shaped cross slot, circularly polarized wave radiates at two different frequencies with opposite sense of polarizations. The RHCP radiation occurs at (10.45‐10.54) GHz (Lower band) and LHCP occurs at (11.26‐11.34) GHz (Upper band). Moreover, in each band, sense of polarization can be change by changing the feed position. The front to back radiation ratio (FTBRR) is more than 10.5 dB and cross polarization level is lower than ?20 dB in both the bands.     

Eighth‐mode SIW based compact high gain leaky‐wave antenna

In this article, a novel electrically small eighth‐mode substrate integrated waveguide (EMSIW) based leaky‐wave antenna (LWA) in planar environment is presented. The proposed antenna uses 1/8th mode SIW resonator which helps to improve compactness of the design while maintaining high gain and increased scanning angle. The proposed SIW cavity is excited by a 50 Ω microstrip line feeding to resonate at dominant TE₁₁₀ mode in X‐band. The dimensions of the resonators are adjusted to keep resonant mode at same frequency. The fabricated prototype is approximately 5λ₀ long. Measured results show that the proposed leaky‐wave antenna is able to operate within frequency range of 8‐10 GHz with beam scanning range of 51° and maximum gain of 13.31 dBi.