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.     

Design of wideband comb shape substrate integrated waveguide multimode resonator bandpass filter with high selectivity and improved upper stopband performance

In this article, a wideband bandpass filter (BPF) is designed using the comb slotted substrate integrated waveguide (SIW) cavities. The comb‐shaped slots engraved on the SIW cavity are used to constitute a novel multiple‐mode resonator (MMR) that accomplishes a wide passband of operation. Further, a Jerusalem cross defected ground structure (DGS) is introduced to miniaturize it and enhance filter performance in the pass band and stop band. The filter is fabricated on RT/Duroid 5880 having dielectric constant 2.2 and tested to prove the validity of design. The filter achieves 3 dB fractional bandwidth of 48%, return loss above 14 dB and insertion loss of 1.1 dB in the passband. Also, the proposed filter has steep selectivity and wide upper stopband with 25 dB attenuation from 16.7 to 24 GHz.     

Miniaturized substrate integrated waveguide filter using fractal open complementary split‐ring resonators

A miniaturized substrate integrated waveguide (SIW) bandpass filter using fractal open complementary split‐ring resonators (FOCSRRs) unit‐cell is proposed. The proposed structure is realized by etching the proposed FOCSRR unit‐cells on the top metal surface of the SIW structure. The working principle of the proposed filter is based on the evanescent‐mode propagation. The proposed FOCSRRs behave as an electric dipoles in condition of the appropriate stimulation, which are able to generate a forward‐wave passband region below the cutoff frequency of the waveguide structure. Since, the electrical size of the proposed FOCSRRs unit‐cell is larger than the conventional OCSRRs unit‐cell; therefore, the FOCSRR unit‐cell is a good candidate to miniaturize the SIW structure. The proposed filter represents high selectivity and compact size because of the utilization of the sub‐wavelength resonators. The introduced filter is simulated by a 3D electromagnetic simulator. In order to validate the ability of the proposed topology in size reduction, 1‐ and 2‐stage of the proposed filters have been fabricated based on the standard printed circuit board process. The measured S‐parameters of the fabricated filters are in a good agreement with the simulated ones. The proposed SIW filters have many advantages in term of compact size, low insertion loss, high return loss, easy fabrication and integration with other circuits. It is the first time that the FOCSRR unit‐cells were combined with the SIW structure for miniaturization of this structure. Furthermore, a wide upper‐stopband with the attenuation >20 dB in the range of 3–8 GHz is achieved. The results show that, a miniaturization factor about 75.5% has been obtained.     

Compact reconfigurable triple‐mode triple‐band substrate integrated waveguide bandpass filter

In this study, a reconfigurable triple‐band triple‐mode substrate integrated waveguide filter is designed and fabricated in the C‐band spectrum. A novel and simplified design procedure based on analytical equations is proposed. The filter design also benefits from a reconfigurable structure, using metallic via holes as perturbation, allowing wide‐band selectivity of the C‐band spectrum (from 4.4 to 6.9 GHz). Moreover, the filter benefits from a magnetic coupling solution between the resonators, which only couples the first three modes and rejects the next resonating modes. Therefore, a large bandgap in the spectrum is achieved. The proposed structure is fabricated and measured, and a high similarity between the simulation and fabrication is observed. The measured results show that the first band can be tuned in the frequency range of 4.4 to 7, the second band can be tuned in the range 5.8 to 7.7 GHz, and the third band from 5.8 to 7.7 GHz. The insertion loss 1.5 to 2.5 dB, 2 to 3 dB, and 2.5 to 3.5 dB for the first, second, and third bands, respectively.     

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.     

A bandpass filter using modified half mode substrate integrated waveguide technique

This article reports a novel bandpass filter using modified half mode substrate integrated waveguide technique. The via‐fences are deployed as impedance inverters for the proposed filter to reduce its footprints, which are extracted by using a full‐wave electromagnetic simulator HFSS for the filter design. Detailed design procedure is discussed. A bandpass filter having a center frequency of 10.03 GHz and a pass band from 9.78 to 10.3 GHz is designed for demonstration, and experiments are carried out for the validation. Good agreements between experiment and simulated results are obtained, which show that the proposed filter has a compact size, a low insertion loss, and a high selectivity. It is attractive for the radio communication system. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:277–281, 2015.     

Compact wideband microstrip bandpass filter with wide upper stopband based on coupled‐stub loaded resonator

A novel wideband microstrip bandpass filter (BPF) based on a coupled‐stub loaded resonator (CSLR) is presented in this article. The CSLR is constructed by attaching one short‐circuited parallel coupled microstrip line (PCML) in shunt to a high impedance microstrip line. The filter bandwidth can be conveniently controlled via reasonable adjusting of the impedance of PCML. Moreover, new defected microstrip structures (DMSs) introduced in the PCML functions as a means of adjusting the positions of transmission zeros, created by the PCML. The resonant mode and transmission zero chart are given, indicating that the higher modes could be suppressed by the transmission zeros. Finally, to validate the proposed method, two wideband BPF filters with and without DMSs centered at 3 GHz with 3 dB fractional bandwidth of 87% are designed and fabricated. The measured results show that both the return losses are better than 15.8 dB, while the BPF with DMSs has a ?19.4 dB isolation wideband from 1.57 to 4.23 . The measured results are in excellent agreement with full‐wave electromagnetic simulation results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:122–128, 2015.     

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.     

Dual‐passband bandpass‐filtering power divider using half‐mode substrate integrated waveguide resonator with high frequency selectivity

In this paper, a half‐mode substrate integrated waveguide (HMSIW) power divider with bandpass response and good frequency selectivity is proposed. The proposed power divider includes input/output microstrip lines, four HMSIW resonators, cross‐coupling circuits, and an isolation resistor. The dual‐band bandpass‐filtering response is obtained by using the dual‐mode slotted HMSIW. To get good frequency selectivity, the input/output cross‐coupling circuits have been used, and several transmission zeros can be observed. A dual‐band filtering‐response HMSIW power divider is designed, fabricated and measured. The total size of the fabricated power divider is 0.58λg × 0.45λg. The measured results show a reasonable agreement with the simulated ones. The measured central operating frequencies of the dual‐band HMSIW power divider are at 2.43 and 3.50 GHz, respectively. The measured 3‐dB fractional bandwidth is about 13.3% and 6.3% in the two passbands, and the measured output isolation is about 20 dB.     

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.     

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.     

A novel E‐plane substrate inserted bandpass filter with high selectivity and compact size

In this article, a novel E‐plane substrate inserted waveguide bandpass filter with high selectivity and compact size is proposed in Ka‐band. By integrating an extra resonator between two metal septa, the E‐plane waveguide filter is achieved with two transmission zeros at both sides of the passband which contribute to the high‐skirt selectivity. One sample is fabricated, whose total length is just 5 mm, namely, less than 0.5 and the minimum insertion loss is only about 0.3 dB. Good agreements between simulated and measured results are obtained. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:451–456, 2014.     

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.