Circular Substrate Integrated Waveguide Research Articles

Nanoarchitectonics of MXene-based sixteenth-mode flexible SIW antenna for conformal wireless applications

A miniaturized sixteenth-mode nanomaterial-based flexible substrate-integrated waveguide (SIW) antenna is demonstrated at an operating frequency of 3.5 GHz. The antenna is designed based on the one-sixteenth mode of a circular SIW cavity. The SIW in this instance is manufactured exclusively with flexible non-textile materials, which makes it unique and novel from the other reported works. The substrate of the proposed antenna is manufactured using PDMS by masking and laser cutting process. The patch on the substrate is made of a 2D nanomaterial MXene, whereas the ground at the bottom is created using copper tape. Vias connecting the patch and ground were filled with silver paste and dried at 80 °C in an oven. With a compact design and flexibility, the proposed flexible SIW antenna offers a unidirectional radiation pattern with a reasonable gain of −3.39 dBi at a 3.5 GHz resonant frequency. Additionally, the antenna is demonstrated for its flexible performance by straining it to the maximum extent without any structural damage. Consequently, the presented flexible SIW antenna can be well suited for conformal wireless applications.

Substrate integrated waveguide-based self-triplexing antenna-sensor

In this paper, a Substrate Integrated Waveguide (SIW) based self-triplexing antenna-sensor is introduced. The proposed structure can act as a sensor for concurrent detection of three chemical materials. Further, it can be used as a self-triplexing antenna for simultaneous operation at three different frequencies. To that end, initially, a half mode circular SIW cavity is designed. Then, it is divided into three parts. In each part, the position of maximum electric field is determined and subsequently, three holes are located in the positions for material insertion. Finally, considering the vacuum as the inserted material for each hole, each cavity is adjusted to operate at its operation frequency (4.8, 5.8, and 6.6 GHz). Altering the permittivity of the objects inserted in the holes, the resonant frequencies are changed and consequently the type of material is determined. The simulated and measured results validated the performance of proposed antenna-sensor as well. In all the frequency bands, the reflection coefficients as well as mutual coupling among ports are below −20 dB. It should also be expressed that such an SIW structure with the capability of sensing and propagation is provided for the first time.

Multilayer circular SIW cavity differential bandpass filter with wide‐stopband characteristics

AbstractIn this paper, a compact differential bandpass filter with wide‐stopband is presented. The proposed differential filter is designed using two circular substrate‐integrated waveguide (SIW) cavities coupled through a pair of symmetric coupling slots. The filter operates in TM110 mode of the circular SIW cavity. The degenerate TM110 mode is shifted to higher frequency by the introduction of two pairs of perturbation vias. The center frequency of the differential passband can be tuned by changing different design parameters such as location of perturbation vias and length of the slotlines. As a proof of the proposed concept, a second‐order differential bandpass filter is designed, fabricated, and measured. The measured results are in good agreement with the electromagnetic‐simulated ones.

Multilayer circular substrate-integrated waveguide cavity band-pass filters with ultrawide stopband characteristics

AbstractThis paper presents a methodology to design band-pass filters having ultrawide stopband characteristics using multilayer circular substrate-integrated waveguide (SIW) cavities. The orthogonal microstrip feedlines are used as input and output ports that are present at the top and bottom layers, while the middle layers are used to couple the SIW cavities. Higher-order spurious modes of the circular SIW cavity are suppressed by using orthogonal feeding mechanism and properly adjusting the arc-shaped slots between the cavities. To validate the present approach, two filters (second- and fourth-order) have been designed and fabricated and their characteristics are measured. The second-order filter exhibits a stopband rejection below 25 dB up to nearly 5.07f0, while the fourth-order filter has a stopband characteristic of nearly 5.05f0 with 20 dB rejection. The filters allow only TM010 mode propagation and attenuate the higher-order spurious modes of the cavity.

Bandwidth-Controllable Third-Order Band Pass Filter Using Substrate-Integrated Full- and Semi-Circular Cavities

The article presents a novel circular substrate-integrated waveguide (SIW) bandpass filter (BPF) with controllable bandwidth. The proposed BPF was configured using two microstrip feed lines, semi-circular SIW cavities, capacitive slots, and inductive vias. The circular cavity was divided into two halves, and the two copies were cascaded. The resulting bisected and cascaded structures were then connected back-to-back. Finally, by introducing two inductive vias to the circular center cavity, a transmission zero was generated. In order to examine the design concept, a coupling matrix was generated. To demonstrate the theory, a third-order BPF was realized, fabricated, and experimentally validated. The BPF prototype features a wide passband of 8.7%, a low insertion loss of 1.1 dB, and a stopband of 1.5 f0 with a rejection level better than 20 dB, which makes it a potential candidate for microwave sensing and communication industries.

Realizing the High Q-Factor of a CSIW Microwave Resonator Based on an MDGS for Semisolid Material Characterization.

In this work, the high-quality factor (Q-factor) and high sensitivity of a circular substrate-integrated waveguide (CSIW) are proposed for the characterization of semisolid materials. The modeled sensor was designed based on the CSIW structure with a mill-shaped defective ground structure (MDGS) to improve measurement sensitivity. The designed sensor oscillates at a single frequency of 2.45 GHz, which was simulated using an Ansys HFSS simulator. Electromagnetic simulation explains the basis of the mode resonance of all two-port resonators. Six variations of the materials under test (SUTs) were simulated and measured, including air (without an SUT), Javanese turmeric, mango ginger, black turmeric, turmeric, and distilled water (DI). A detailed sensitivity calculation was performed for the resonance band at 2.45 GHz. The SUT test mechanism was performed using a polypropylene tube (PP). The samples of dielectric material were filled into the channels of the PP tube and loaded into the center hole of the MDGS. The E-fields around the sensor affect the relationship with the SUTs, resulting in a high Q-factor value. The final sensor had a Q-factor of 700 and a sensitivity of 2.864 at 2.45 GHz. Due to the high sensitivity of the presented sensor for characterization of various semisolid penetrations, the sensor is also of interest for accurate estimation of solute concentration in liquid media. Finally, the relationship between the loss tangent, permittivity, and Q-factor at the resonant frequency were derived and investigated. These results make the presented resonator ideal for the characterization of semisolid materials.

Semi‐circular mushroom resonator loaded substrate integrated waveguide cavity based compact triple‐band bandpass filter with high selectivity

Two cascaded semi-circular mushroom resonators (ScMRs) loaded to a circular substrate integrated waveguide (CSIW) is used to implement a triple-band bandpass filter of compact size and high selectivity with six transmission zeros (TZs). The ScMRs are coupled to each other along the linear edges of the metal patches and are loaded to the CSIW cavity. A distinctive modification in the schematic and the orientation of the loaded mushroom resonators is carried out along with the introduction of radial coupling slots into the CSIW cavity to generate the three passbands. The TM101 mode is responsible for the generation of first passband. The second and third passbands are formed due to the split odd and even modes of next higher order mode (TM201). An extracted pole is formed within the second passband that splits TM201 mode into odd and even modes. TM201 odd mode (TM201odd) and TM201 even mode (TM201even) are responsible for the generation of second and third passbands, respectively. Here, source-load coupling is employed within the proposed resonator to generate one TZ each at the lower stopband and upper stopband. Two cross-couplings of different modes between two loaded ScMRs are introduced to generate four transmission zeros (TZs) additionally to achieve high selectivity. The triple bandpass filter covering a compact volume of 0.0011 λg3 is fabricated and measured to validate the filter structure. The measured result agrees decently with the simulated one where the passband center frequencies (CFs) of first, second, and third passbands are measured at 1.9, 3.5, and 4.4 GHz with measured insertion losses of 1.5, 1.87, and 1.8 dB, respectively.

Miniaturized filtering rat‐race coupler based on hybrid circular substrate integrated waveguide and coplanar waveguide resonators

In this paper, an approach to designing filtering rat-race coupler (FRRC) with hybrid circular substrate integrated waveguide (CSIW) and coplanar waveguide (CPW) resonators is proposed. The FRRC is developed in a single CSIW cavity embedded with four CPW resonators and four feeding ports, featuring miniaturized size. The desired 0° and 180° phase characteristics of the RRC are realized by the inherent in-phase and out-of-phase electromagnetic fields of the dual-mode CSIW cavity. By properly arranging the sum, difference and other two output ports, the FRRC is exploited to achieve the desired properties of a RRC with bandpass filtering responses. In addition, transmission zeros are generated in the vicinity of the upper stopband. For validation and demonstration, a miniaturized FRRC utilizing hybrid CSIW and CPW resonators is synthesized, fabricated and experimented in a single-layered process. Comparisons with previously state-of-the-art research, the proposed FRRC prototype indicates the superiorities of miniaturized footprint, high-quality-factor, high-order filtering response and enhanced out-of-band rejection.

Compact SIW-Based Self-Quadruplexing Antenna for Wearable Transceivers

This letter proposes a low-profile substrate integrated waveguide (SIW) cavity backed self-quadruplexing antenna for wearable transceivers. The full-mode circular SIW cavity is split into four unequal quarter-mode SIW (QMSIW) cavities using the two slots on the upper layer of the cavity. The proposed antenna uses C-shaped and arc-shaped slots of different dimensions in each QMSIW resonator to operate at wireless local area network bands (3.5, 4.9, 5.4, and 5.8 GHz). The measured gains are 4.4, 5.07, 5.40, and 5.7 dBi at 3.5, 4.9, 5.4, and 5.8 GHz, respectively. The antenna is simulated and optimized inside a 48 $\times \text{76}\times$ 21 mm3 rectangular device by keeping the device on the chest of a realistic human model. The proposed antenna has unidirectional radiation patterns in all four operating bands with low backward radiations. Thus, it has low specific absorption rate at all four operating bands.

Dual band bandpass filter based on semi‐circular mushroom loaded substrate integrated waveguide

AbstractThis paper presents a dual band bandpass filter by loading two semi‐circular mushroom resonators (ScMRs) inside the cavity of a circular substrate integrated waveguide (SIW). TM101 and TM201 modes of the mushroom resonator loaded circular SIW cavity are excited to generate the first and second passbands respectively. As the proposed bandpass filter is based on circular SIW cavity, the passbands of the filter undergo relatively low insertion loss (IL) compared to other referred works. The selectivity is improved by generating four transmission zeros (TZs); two TZs are generated in between the two passbands by cross coupling the excited modes of the resonators and other two TZs are generated in lower and upper stopband by the source to load coupling. The passbands of the proposed filter are centred at 2.24 GHz and 4.35 GHz with 13% and 6.2% fractional bandwidth (FBW) respectively. A prototype of the proposed dual bandpass filter occupying a compact area of 0.3λ0 × 0.3λ0 is fabricated in Rogers RT/Duroid 5880. The measured minimum insertion losses for the first and second passbands are 0.9 dB and 1.1 dB respectively with a good agreement observed between simulated and measured results.

Simplified Approach to Detect Dielectric Constant Using a Low-Cost Microfluidic Quarter Mode Substrate-Integrated Waveguide.

Liquid materials’ characterization using commercial probes and radio frequency techniques is expensive and complex. This study proposes a compact and cost-effective radio frequency sensor system to measure the dielectric constant using a three-material calibration. The simplified approach measures reflection coefficient magnitudes for all four materials rather than the complex values in conventional permittivity detection systems. We employ a sensor module based on a circular substrate-integrated waveguide with measured unloaded quality factor = 910 to ensure measurement reliability. Miniaturized quarter-mode substrate-integrated waveguide resonators are integrated with four microfluidic channels containing three known materials and one unknown analyte. Step-wise measurement and linearity ensures maximum 4% error for the dielectric constant compared with results obtained using a high-performance commercial product.

Cavity Backed Circular Half Mode SIW Array for Microwave Communications

A two element array of circular shaped cavity backed substrate integrated waveguide (SIW) based antenna is proposed in this work. The elements are backed by a dielectric cavity of FR4 epoxy and fed by SIW slot coupling mechanism. Keeping the advantages of the conventional waveguides, the bandwidth of the radiation can be increased by choosing proper dimensions to the slots and circular patches. The two element array configuration in the design contributed to the comfortable uplift of the gain. The impedance matching is achieved by inserting a two arm power divider with pre-calculated dimensions. The accurate formulation of the electromagnetic problem of analyzing the SIW antenna is achieved by using integral equation based methods which can be solved numerically. The designed top layer of the antenna is analyzed with well known Method of Moments (MoM) and the results are compared. The functioning of the antenna is compared in terms of Return losses, radiation pattern and gain. The antenna exhibits 72% of bandwidth with peak gain of 4.2dB in the range of 4.4GHz to9.9GHz with the resonating frequency of 7.54GHz and well suited for C-band microwave communication applications.

Compact filtering power divider based on corrugated third‐mode circular SIW cavities

AbstractIn this article, a compact single‐layer filtering power divider based on third‐mode circular substrate integrated waveguide (SIW) cavities is proposed. The third‐mode SIW technique is introduced to divide an SIW cavity into three cavities and get 66% size reduction. The proposed power divider is composed of three third‐mode circular SIW cavities within a circuit with the size of a circular SIW cavity. The power is coupled from the input cavity to two output cavities through the electric coupling, separately. To achieve a more size reduction, the designed cavities are corrugated along the cutting planes. By increasing the length of the corrugated edges, the center frequency can be easily shifted to lower frequencies. In order to prove the proposed design procedure, the presented power divider with a second‐order bandpass filtering response is designed and fabricated. Reasonable agreements between the measured and simulated results are found. The measured results show that the power divider achieves an insertion loss of 1.2 dB at 5.61 GHz, return loss of higher than 14 dB, and 3‐dB fractional bandwidth of 7.8%. The results show that this power divider has the advantages of the compact size, high selectivity, and single‐layer structure.

High‐selective triple‐mode SIW bandpass filter using higher‐order resonant modes

A novel high-selective triple-mode substrate integrated waveguide (SIW) bandpass filter using higher-order resonant modes is proposed in this Letter. The new triple-mode SIW resonator is realised by the second degenerate dual modes TM 210 and one perturbed higher-order mode TM 020 in a circular SIW cavity. The resonance of TM 020 mode can be independently moved to that of dual modes TM 210 by changing the size of a floating circular patch. The proposed triple-mode SIW filter can produce three finite-transmission zeros (FTZs), which can also be controlled well by the angle between two feeding lines. For the demonstration, a triple-mode SIW filter with the centre frequency of 13.5 GHz was designed, fabricated and measured. The proposed triple-mode circular SIW filter has the merits of the high-quality factor, high selectivity and controllable bandwidth as well as FTZs.

Tunable bandpass filter with wide tuning range of center frequency and bandwidth based on circular SIW

This paper presents a circular substrate integrated waveguide (SIW) bandpass filter (BPF) with wide tuning range of center frequency and bandwidth (BW). For designing such a filter, lumped varactors loaded at two metal posts are utilized to adjust the center frequency, and the bandwidth is tuned by varactors mounted between two SIW cavities. One transmission zero (TZ) can be located at the lower or upper stopband by controlling the mixed coupling between two resonators. The external coupling is changed by using two lumped varactors mounted between feedlines and resonators. Eventually, the BPF with tunable center frequency and bandwidth is designed, fabricated and measured. Measured results indicate the center frequency is tuned from 1.48 to 2.61 GHz (up to 55.3%) while maintaining a 3-dB absolute BW of 31 ± 2 MHz, and the 3-dB bandwidth is tuned from 29 to 250 MHz (up to 8.6). Insertion loss from 1.8 to 4.8 dB is observed within the wide tuning range.

A Compact Double-Folded Substrate Integrated Waveguide Re-Entrant Cavity for Highly Sensitive Humidity Sensing.

In this study, an ultra-compact humidity sensor based on a double-folded substrate integrated waveguide (SIW) re-entrant cavity was proposed and analyzed. By folding a circular re-entrant cavity twice along its two orthogonally symmetric planes, the designed structure achieved a remarkable size reduction (up to 85.9%) in comparison with a conventional TM010-mode circular SIW cavity. The operating principle of the humidity sensor is based on the resonant method, in other words, it utilizes the resonant properties of the sensor as signatures to detect the humidity condition of the ambient environment. To this end, a mathematical model quantitatively relating the resonant frequency of the sensor and the relative humidity (RH) level was established according to the cavity perturbation theory. The sensing performance of the sensor was experimentally validated in a RH range of 30%–80% by using a humidity chamber. The measured absolute sensitivity of the sensor was calculated to be 135.6 kHz/%RH, and the corresponding normalized sensitivity was 0.00627%/%RH. It was demonstrated that our proposed sensor not only has the merits of compact size and high sensitivity, but also benefits from a high Q-factor and ease of fabrication and integration. These advantages make it an excellent candidate for humidity sensing applications in various fields such as the agricultural, pharmaceutical, and food industries.

Low profile high gain circular SIW antenna for L and S band applications

AbstractIn this article, a circular substrate integrated waveguide (CSIW) antenna is proposed. Conventional log‐periodic antenna offers unidirectional and bidirectional radiation patterns that are used in two‐way communications provide moderate gain. The proposed antenna has the advantages of high gain, compact size, low loss, easy to integrate the high frequency components, and it also operates at L band and S band frequencies. To improve the gain and radiation characteristics, circular SIW is introduced and integrated with log‐periodic antenna. The comparison between simulated and measured results shows that the proposed antenna used for wireless communications both in L (1‐2 GHz) and in S (2‐4 GHz) frequency bands. It provides the bandwidth of 9.1%, 10%, 21.6%, and 11.03% and also the realized gain of 6.62 dB, 15.8 dB, 3.9 dB, and 8.3 dB is obtained in 1.2 GHz, 1.6 GHz, 2.4 GHz, and 2.9 GHz, respectively.

Microfluidic biochemical sensor based on circular SIW‐DMS approach for dielectric characterization application

This work proposes an advancement of microwave planar resonator sensor with high sensitivity for microfluidic dielectric characterization. The physical design was employed based on circular substrate integrated waveguide (CSIW) with an integration of defected microstrip structure (DMS). This approach can be applied to accelerate the dielectric detection, structure miniaturization and material differentiation. The presented sensor operates based on variations in the dielectric properties of solvents in the vicinity of a planar open-ended microstrip resonator device. Further analysis in volume and concentration were performed to validate the reliability of the sensor. Validation and functionality of the sensor were investigated by experimental and results comparison. A mathematical model was developed to determine the dielectric constant and the loss tangent of the microfluidic samples. The average error detection has a lower percentage value of 0.11% by comparison to the commercial and ideal dielectric properties of the aqueous samples. The maximum relative error detection, ±0.37% implied better accuracy compared to the existing resonator sensors with more than 400 of the Q-factor. The proposed CSIW-DMS sensor was found to give higher accuracy and detection response; besides easier to fabricate, and compatible for integration with other electronic components in an RF sensor for variety of applications.

Real Time Microwave Biochemical Sensor Based on Circular SIW Approach for Aqueous Dielectric Detection

In this study, a critical evaluation of analyte dielectric properties in a microvolume was undertaken, using a microwave biochemical sensor based on a circular substrate integrated waveguide (CSIW) topology. These dielectric properties were numerically investigated based on the resonant perturbation method, as this method provides the best sensing performance as a real-time biochemical detector. To validate these findings, shifts of the resonant frequency in the presence of aqueous solvents were compared with an ideal permittivity. The sensor prototype required a 2.5 µL volume of the liquid sample each time, which still offered an overall accuracy of better than 99.06%, with an average error measurement of ±0.44%, compared with the commercial and ideal permittivity values. The unloaded Qu factor of the circular substrate-integrated waveguide (CSIW) sensor achieved more than 400 to ensure a precise measurement. At 4.4 GHz, a good agreement was observed between simulated and measured results within a broad frequency range, from 1 to 6 GHz. The proposed sensor, therefore, offers high sensitivity detection, a simple structural design, a fast-sensing response, and cost-effectiveness. The proposed sensor in this study will facilitate real improvements in any material characterization applications such as pharmaceutical, bio-sensing, and food processing applications.

A Simple and Accurate Method for Extracting Super Wideband Electrical Properties of the Printed Circuit Board

In order to accurately design microwave, millimeter-wave components and circuits, a simple and accurate method for extracting extremely wideband characteristics of the printed circuit board (PCB), including relative dielectric constant, dielectric loss tangent, and equivalent copper conductivity, is proposed and validated in this paper. By properly selecting wideband distribution of multiple TMmn0 modes in the designed circular substrate integrated waveguide (CSIW) cavities, extremely broadband properties of PCB can theoretically be extracted with only one pair of CSIW cavities. The proposed method overcomes the limitations of conventional methods that only support narrowband applications, require a large number of cavities, and have relatively large errors. The experiments show that the proposed method is able to extract, accurately and efficiently, 8-110 GHz characteristics of a TLY-5Z substrate-based PCB and the extracted results are verified by designing and measuring the fourth-order Chebyshev filter at X-band.