Abstract: A novel microwave noninvasive planar sensor based on the complementary split ring resonator (CSRR) is proposed for an accurate measurement of the complex permittivity of materials. The CSRR is etched in the ground plane of the planar microstrip line. Two CSRRs of rectangular and circular cross-sections are chosen for the sensitivity analysis, where the later is found to possess higher sensitivity and hence appears to be more appropriate for the sensor design. At resonance, the electric field induced along the plane of CSRR is found to be quite sensitive for the characterization of specimen kept in contact with the sensor. A numerical model is developed here for the calculation of the complex permittivity as a function of resonant frequency and the quality factor data using the electromagnetic simulator, the Computer Simulation Technology. For practical applications, a detailed air gap analysis is carried out to consider the effect of any air gap present between the test sample and the CSRR. The designed sensor is fabricated and tested, and accordingly the numerically established relations are experimentally verified for various reference samples e.g., teflon, polyvinyl chloride, plexiglas, polyethylene, rubber, and wood. Experimentally, it is found that the permittivity measurement using the proposed sensor is possible with a typical error of 3%.

Abstract: Novel miniaturized two-layer electromagnetic band gap (EBG) structures are presented for reducing the electromagnetic coupling between closely spaced ultra wideband (UWB) planar monopoles on a common ground. The proposed EBG structures employ two closely coupled arrays, one comprising linear conducting patches and the other comprising apertures (slits) in the ground plane. The two arrays are printed on either side of a very thin dielectric layer ( $\bf{55}\;\upmu\mathrm{m}$ ) with a rotation between the elements to produce maximum coupling for miniaturizing. A microstrip line excitation is initially used for the efficient analysis and design of the slit–patch EBG structures, which are subsequently employed between two UWB printed monopoles. The proposed EBG structure has a small footprint and produces a significant reduction of the mutual coupling across the wide operating band of the UWB antennas. Simulated results and measurements of fabricated prototypes are presented.

Abstract: We present a dynamic metamaterial aperture for use in computational imaging schemes at microwave frequencies. The aperture consists of an array of complementary, resonant metamaterial elements patterned into the upper conductor of a microstrip line. Each metamaterial element contains two diodes connected to an external control circuit such that the resonance of the metamaterial element can be damped by application of a bias voltage. Through applying different voltages to the control circuit, select subsets of the elements can be switched on to create unique radiation patterns that illuminate the scene. Spatial information of an imaging domain can thus be encoded onto this set of radiation patterns, or measurements, which can be processed to reconstruct the targets in the scene using compressive sensing algorithms. We discuss the design and operation of a metamaterial imaging system and demonstrate reconstructed images with a 10:1 compression ratio. Dynamic metamaterial apertures can potentially be of benefit in microwave or millimeter wave systems such as those used in security screening and through-wall imaging. In addition, feature-specific or adaptive imaging can be facilitated through the use of the dynamic aperture.

Abstract: This paper presents the design and fabrication of a broadband microstrip attenuator, operating at 1–20 GHz, based on few layer graphene flakes. The RF performance of the attenuator has been analyzed in depth. In particular, the use of graphene as a variable resistor is discussed and experimentally characterized at microwave frequencies. The structure of the graphene-based attenuator integrates a micrometric layer of graphene flakes deposited on an air gap in a microstrip line. As highlighted in the experiments, the graphene film can range from being a discrete conductor to a highly resistive material, depending on the externally applied voltage. As experimental evidence, it is verified that the application of a proper voltage through two bias tees changes the surface resistivity of graphene, and induces a significant change of insertion loss of the microstrip attenuator.

Abstract: The utility model provides a co -planar waveguide feed broadband circular polarization microstrip antenna, including medium base plate, L type floor, L type ground connection microstrip strip and Y type microstrip feeder, the lower extreme of Y type microstrip feeder extends to the lower limb department formation feed end of medium base plate, be provided with the harmonious microstrip strip of rectangle on the lower extreme right side of Y type microstrip feeder, lower extreme right side at Y type microstrip feeder is equipped with the rectangle floor, the feed end is between L type floor and rectangle floor, be connected with the ground joint line between L type floor and rectangle floor, and at the left side of medium base plate edge, the upside is marginal and right side edge all is equipped with folding section, the both ends of L type ground connection microstrip strip are the both sides edge of perpendicular to place apex angle department respectively, and the folding section at left side edge is in the L in upper left corner type ground connection microstrip strip, and the folding section of right side edge is in the L in lower right corner type ground connection microstrip strip. This microstrip antenna is ensureing to possess less volume under the condition of bandwidth, and market perspective is better.

Abstract: The active impedance of each element in a phased array changes substantially with scan angle due to mutual coupling. Therefore, a key challenge in the design of wide-angle scanning phased array is to achieve wide-angle impedance matching (WAIM). In this communication, an efficient decoupling network is developed to reduce the mutual coupling between adjacent elements for this purpose. A complete scattering matrix analysis of the decoupling network is given and the design procedure is summarized. A ${1} \times {16}$ linear microstrip phased array has been designed and fabricated for experimental verification. Good agreement is obtained between measured and simulated results. The measured mutual coupling between adjacent elements is reduced to lower than $- {35}\; \text{dB}$ at the center frequency. Due to the reduced mutual coupling, the array can experimentally scan to 66° with a gain reduction of only 3.04 dB.

Abstract: This paper addresses the exploitation of signal-interference concepts for the realization of single/multi-frequency Wilkinson-type filtering power dividers in planar/lumped-element technologies. By embedding transversal signal-interference filtering sections into the arms of conventional Wilkinson-type power-divider topologies, RF/microwave power-distribution actions with intrinsic mono/multi-band bandpass filtering capabilities can be obtained. Analytical equations and rules for the theoretical synthesis of this dual-function device are derived. The generalization of the approach to multi-stage schemes for enhanced-performance designs or for the shaping of frequency-asymmetrical responses is also discussed. Furthermore, for practical demonstration, three prototypes are developed and characterized. They are a microstrip quad-band circuit for the 1–5 GHz range, a dual-band lumped-element device for the band of 0.2–0.6 GHz, and a new type of two-branch channelized active bandpass filter at 3 GHz that makes use of single-band versions of this dual-behavior component as signal-division/combination blocks.

Abstract: An original and simple approach to the design of fully reconfigurable multi-band microwave bandpass filters (BPFs) with an arbitrary number of passbands is reported in this paper. It exploits the use of an innovative quasi-BPF configuration made up of different sets of controllable mono-frequency resonators to separately shape each tunable passband. Thus, high-selectivity multi-band bandpass filtering transfer functions exhibiting independent control in terms of center frequency, bandwidth, and transmission zeros can be synthesized. Furthermore, as an unprecedented frequency-agility feature of the proposed reconfigurable multi-band BPF structure when compared to the state-of-the-art, its passbands can be merged together to form broader, and for certain realizations, higher order transmission bands. This allows even more degrees of reconfiguration to be achieved in the devised circuit, which can also operate as ultra-wideband BPF with flexible in-band notches or self-equalized flat-group-delay quasi-elliptic-type BPF. The theoretical foundations of the described reconfigurable multi-band BPF scheme, along with guidelines for its design and a triple-passband filter synthesis example based on the coupled-node formalism, are expounded. In addition, as an experimental proof-of-concept, two microstrip prototypes with high- $Q$ tuning implemented through mechanically variable capacitors are manufactured and tested. They are a wideband dual-band BPF and a quadruple-band BPF with narrow-bandwidth passbands.

Abstract: This letter presents a novel substrate integrated waveguide (SIW) resonator sensor that is specifically designed to measure the complex permittivity of liquids. The resonant characteristics of the sensor are influenced by liquids through a slot opened on the top plane. The inverse problem of obtaining permittivity is solved with artificial neural network. Experiments were performed with an SIW resonator sensor designed at C band. Experimental data were reported and they agreed well to the reference values. The sensor is simple and low cost, which may be applied to permittivity measurements in applications at the industrial, scientific and medical (ISM) frequencies.

Abstract: With the development of wireless communication technology, radiofrequency (RF) circuits and integrated circuits are becoming more complex and packing more functionality and signals into an ever closer space, with a high level of electromagnetic interaction between circuit nodes and interference/crosstalk from substrate coupling and free space [1]. Balanced/differential circuit technology has become more important in modern communication systems because of good commonmode rejection that leads to relatively high immunity to environmental noise when compared with the single-ended technology [1]-[3], as shown in Figure 1(a) and (b). For balanced circuits, the differential mode should have excellent out-of-band rejection and high selectivity for the desired frequency band, while the common mode should be suppressed over a wider frequency band. In the past few years, many microstrip balanced filters for single band and dual band with common-mode suppression have been realized [4]-[10], with different balanced networks, balanced driven antennas, balanced amplifiers, and mixers [11]-[18].

Abstract: In this paper, a balanced-to-unbalanced microstrip power divider based on branch lines with several stubs and one resistor is proposed. The functions of power dividing, frequency selectivity, isolation between output ports, and common-mode suppression can be realized at the same time. The even–odd-mode equivalent circuits combining with the standard S-parameters and the mixed-mode S-parameters are adopted to derive the analytical equations at the center frequency. One or two transmission zeros can be achieved to enhance the out-of-band suppression. The center frequency, bandwidth, isolation, common-mode suppression, and the frequencies of transmission zeros can be controlled by the design procedure. To verify the theoretical prediction, two fabricated prototypes are designed and compared. One gets 7.7% 1-dB bandwidth with 0.6-dB insertion loss and one transmission zero. The other gets 1-dB bandwidth of 5% with 0.7-dB insertion loss and two transmission zeros. The isolation and common-mode suppression for both prototypes are better than 15 and 20 dB within the whole passband, respectively.

Abstract: This letter presents a new design of a multiband microstrip antenna with a proximity-coupled feed for operating in the LTE2300 (2300–2400 MHz), Bluetooth (2400–2485 MHz), WiMAX (3.3–3.7 GHz), and WLAN (5.15–5.35 GHz, 5.725–5.825 GHz) bands. In addition, it also covers 6-dB impedance bandwidth across the UMTS (1920–2170 MHz) band. The proposed antenna consists of a corner-truncated rectangular patch with a rectangular slot, meandered microstrip feed, and defected ground plane. The antenna is fabricated using 0.8-mm-thick FR4 substrate with a dielectric constant of 4.4 and has a small size of only $27\times 24~\hbox{mm}^{2}$ . The antenna shows a stable gain over the operating bands and good radiation characteristics. The simulated and measured results are shown to have good agreements.

Abstract: A low radar cross section (RCS) microstrip antenna is proposed and investigated in this letter. This design is based on implementation of frequency-selective surfaces (FSSs) and microstrip resonators. By using the FSS ground instead of the solid metal ground, out-of-band RCS reduction can be realized. Moreover, in-band RCS reduction can be obtained by loading microstrip resonators. Significant RCS reduction has been accomplished in the frequency ranges of 3-10 GHz. Compared with the reference antenna, the simulation results show that RCS reduction of the proposed antenna in and out of the operation band is as much as 13 and 17 dB, respectively. Measured results satisfactorily agree with the simulated ones. Radiation performance of the proposed antenna is preserved compared with the reference antenna.

Abstract: Half-width microstrip leaky-wave antennas (HW-MLWAs) are generally single band. Here, we present a new method to achieve dual-band operation from an HW-MLWA by periodically loading the antenna with U-shaped slots. These dual-band MLWAs are able to steer the beam in forward directions in one band and in backward directions in the other band. One of the antenna designs was prototyped and tested, and excellent agreement between the predicted and measured results were observed. The measured 10-dB return loss bandwidth of the first and second bands are $19.5 \% $ (5.24–6.37 GHz) and $13.2 \% $ (7.9–9.02 GHz), respectively. The antenna can steer the main beam from $30^\circ $ to $65^\circ $ in the first band and from $-46^\circ $ to $-10^\circ$ in the second band by sweeping the frequency from 5.25 to 6.25 GHz and 7.75 to 9 GHz, respectively. The measured peak gain of the antenna is 12.2 and 14.1 dBi in the first and second bands, respectively. Although the antenna parameters are optimized for dual-band operation, the radiation properties in another higher frequency band (third band) are also explored. In the third band, the antenna beam continuously scans from backward to forward direction as frequency increases. Moreover, this U-slot loaded single-layer half-width LWA is easy to fabricate.

Abstract: This work demonstrates the viability of Ground-backed Complementary Split-Ring Resonator (G-CSRR) arrays with significant power conversion efficiency and bandwidth enhancement in comparison to the technology used in current electromagnetic energy harvesting systems. Through numerical full-wave analysis, we demonstrated correlation between either the resonance frequency or the input impedance of G-CSRR cells with the periodicity of the array. A comparative study of power harvesting efficiency through numerical analysis and laboratory measurement was presented where an array of G-CSRRs is compared to an array of microstrip patch antennas. We demonstrated that a G-CSRR array yields power conversion efficiency of 92%, which represents a significant improvement in comparison to the single G-CSRR reported in our earlier work.

Abstract: A broadband microstrip reflectarray with five parallel dipole elements is proposed. Based on the operating mechanisms and the reflection phase characteristics of the five-dipole elements, the elements for the broadband reflectarray are designed. The radiation patterns of the five-dipole element reflectarray with the design frequency of ${f_0} = 15~\hbox{GHz}$ are measured, and 1-dB gain bandwidth of 33.52% is achieved. The measured peak gain at ${f_0} = 15~\hbox{GHz}$ is 31.4 dBi, which corresponds to the high aperture efficiency of 64.1%.

Abstract: Inductance of superconducting thin-film inductors and structures with linewidth down to 250 nm has been experimentally evaluated. The inductors include various striplines and microstrips, their 90° bends and meanders, interlayer vias, etc., typically used in superconducting digital circuits. The circuits have been fabricated by a fully planarized process with 8 niobium layers, developed at MIT Lincoln Laboratory for very-large-scale superconducting integrated circuits. Excellent run-to-run reproducibility and inductance uniformity of better than 1% across 200-mm wafers have been found. It has been found that the inductance per unit length of stripline and microstrip line inductors continues to grow as the inductor linewidth is reduced deep into the submicron range to the widths comparable to the film thickness and magnetic field penetration depth. It is shown that the linewidth reduction does not lead to widening of the parameter spread due to diminishing sensitivity of the inductance to the linewidth and dielectric thickness. The experimental results were compared with numeric inductance extraction using commercial software and freeware, and a good agreement was found for 3-D inductance extractors. Methods of further miniaturization of circuit inductors for achieving circuit densities> 10 6 Josephson junctions per cm 2 are discussed.

Abstract: A four-way microstrip power divider is designed with bandpass filtering response The synthesized inline filter has a generalized Chebyshev response, where frequency-dependent couplings are utilized All of the critical parameters, including the characteristic impedances and electrical lengths, can be determined by our derived closed-form formulas By extending the inline filter, the configuration of four-way power divider is obtained Then, three isolation resistors are properly selected according to the even-/odd-mode analysis The proposed four-way filtering power divider has low in-band insertion loss and high frequency selectivity It can provide the in-band return loss and isolation between outputs better than 167 and 175 dB, respectively

Abstract: 3-D printing is enabling next generation manufacturing of RF and microwave circuits but little work has been done to demonstrate the true potential of this approach. This study shows that transmission lines fabricated using 3-D printing equipment are comparable in performance to traditionally-made versions. Basic transmission line parameters such as characteristic impedance, effective dielectric constant, dielectric loss, and conductor loss are modeled and measured for a variety of materials and types of transmission lines at frequencies up to 10 GHz. Data are given for use in future 3-D printed RF designs.

Abstract: A simple rectangular microstrip antenna on slot-type defected ground plane is proposed for reduced cross-polarized (XP) radiation and justified theoretically. This will reduce the XP radiation field compared to a conventional microstrip antenna without affecting its copolarized (CP) radiation characteristics.

Abstract: -A microstrip diplexer consisting of two new types of ring filters is presented in this letter The proposed ring filter is able to move one of transmission zeros closer to its passband corner by connecting the feeding capacitors at the different locations of the resonant ring Thus, a diplexer implemented by connecting two kinds of ring filters with different feeding features can achieve the required isolation for the small channel separation Then an open-stub is added at the common input port of the channel filters to achieve the required input matching at the two passbands of the diplexer A diplexer prototype with two passbands at 175 GHz and 185 GHz with a channel separation 40 MHz was fabricated The measured insertion losses in the pass bands are all less than 21 dB The isolation between the two channels is greater than 20 dB and the input return losses of the three ports are about 20 dB

Abstract: A new concept of planar magneto-electro-dielectric waveguided metamaterials (MED-WG-MTM) is proposed to manipulate the effective permeability ${\mu_{\mathrm {eff}}}$ and the effective permittivity ${\varepsilon_{\mathrm {eff}}}$ . The MED-WG-MTM cell consists of an electric complementary spiral ring resonator (CSR) in the upper metallic plane and a magnetic embedded Hilbert-line (EHL) in the ground plane. The characterizations and working mechanisms are investigated in depth through eletromagnetic (EM) simulation, circuit model calculation and effective material parameters analysis. Numerical results show that the MED-WG-MTM can be manipulated with a larger refractive index for miniaturization and a larger wave impedance for bandwidth (BW) enhancement. For demonstration and potential applications, a microstrip patch antenna working at 3.5 GHz and occupying an area of only ${0.20 \lambda _0 \times 0.20 \lambda _0}$ is designed by using the derived flexible three-step frequency tuning method. A good agreement of results between the simulations and measurements suggests that the designed antenna advances in many aspects such as compact dimensions with a 42.53% miniaturization, broad operation band with a 207% impedance BW enhancement, and comparable radiation performances relative to its conventional counterparts.

Abstract: This work demonstrates the viability of wideband Ground-backed Complementary Split-Ring Resonator (WG-CSRR) arrays with significant power conversion efficiency and bandwidth enhancement in comparison to the technology used in current electromagnetic energy harvesting systems. Through numerical full-wave analysis, we demonstrated the correlation between the topology of the WG-CSRR patch and the electric current distribution over the patch at different frequencies. A comparative study of power harvesting efficiency and frequency bandwidth through numerical analysis was presented where an array of WG-CSRRs is compared to an array of G-CSRRs and an array of microstrip patch antennas. A significant improvement in bandwidth is achieved in comparison to the G-CSRR array reported in earlier work.

Abstract: The paper describes the design methodology, experimental validation, and practical considerations of two millimeter-wave wideband vertical transitions from two gap waveguide versions (inverted microstrip gap waveguide, and microstrip packaged by using gap waveguide) to standard WR-15 rectangular waveguide. The experimental results show $S_{11}$ smaller than $-{\hbox{10 dB}}$ over relative bandwidths larger than 25% and 26.6% when Rogers RO3003 and RO4003 materials are used, respectively. The vertical transition from standard microstrip line packaged by a lid of pins to WR-15 shows measured return loss better than 15 dB over 13.8% relative bandwidth. The new transitions can be used as interfaces between gap waveguide feed networks for 60-GHz antenna systems, testing equipment (like vector network analyzers), and components with WR-15 ports, such as transmitting–receiving amplifiers. Moreover, the paper documents the losses of different gap waveguide prototypes compared with unpackaged microstrip line and substrate integrated waveguide (SIW). This investigation shows that in $V$ -band, the lowest losses are achieved with inverted microstrip gap waveguide.

Abstract: We have investigated the fundamental and high-order spoof localized surface plasmons (LSPs) modes in the proposed corrugated ring resonator printed on a thin dielectric substrate with or without ground plane. An efficient and ease-of-integration method to excite spoof LSPs in the textured ring resonator has been adopted to suppress unwanted high-order modes and enhance fundamental modes. A multi-band-pass filter has been proposed and numerically demonstrated. Experimental results at the microwave frequencies verify the high performances of the corrugated ring resonator and the filter, showing great agreements with the simulation results. We have also shown that the fabricated device is sensitive to the variation of the refraction index of materials under test, even when the material is as thin as paper.

Abstract: A high selectivity bandpass filter loaded with open stubs using dual-mode ring resonator is presented in this letter. Sixth-order passband with six transmission zeros close to the passband is realized with two open stubs and open/shorted coupled lines. The transmission zeros near the passband can be adjusted conveniently by only changing the characteristic impedances of the coupled lines. For demonstration, a planar bandpass filter (3 dB bandwidth 20.6%) is designed and fabricated. Good filtering performance and high selectivity for the filter are realized and experimentally verified.

Abstract: A methodology based on Gaussian process regression (GPR) for accurately modeling the resonant frequencies of dual-band microstrip antennas is presented. Two kinds of dual-band antennas were considered, namely a U-slot patch and a patch with a center square slot. Predictive results of high accuracy were achieved (normalized root-mean-square errors of below 0.6% in all cases), even for the square-slot patch modeling problem where all antenna dimensions and parameters were allowed to vary, resulting in a seven-dimensional input space. Training data requirements for achieving these accuracies were relatively modest. Furthermore, the automatic relevance determination property of GPR provided (at no additional cost) a mechanism for enhancing qualitative understanding of the antennas’ resonance characteristics—a facility not offered by neural network-based strategies used in related studies.

Abstract: A novel non-uniform sinusoidally modulated half-mode microstrip structure with application to near-field focused leaky-wave radiation in the backward Fresnel zone is proposed First, it is presented a dispersion analysis of the constituent backward leaky wave in the sinusoidally modulated unit cell in half-width microstrip technology This information is then used to design a finite non-uniform line that focuses the radiated fields at the desired point Finally, eight similar line sources are arranged in a radial array to generate a three-dimensional focused spot located at the desired focal length over the simple central coaxial feeding Simulated and experimental results are presented to validate the proposed simple approach