Double-sided Parallel-strip Line Research Articles

Permittivity measurement of high-frequency substrate based on the double-sided parallel-strip line resonator method

With the development of 5G technology, the accurate measurement of the complex permittivity of a printed circuit board (PCB) in the wide frequency range is crucial for the design of high-frequency circuits. In this paper, a microwave measurement device and method based on the double-sided parallel-strip line (DSPSL) resonator have been developed to measure the complex permittivity of typical PCBs in the vertical direction. The device includes the DSPSL resonator, the DSPSL coupling probe, a pressure monitor, a Farran C4209 vector network analyzer (100 K to 9 GHz), and a FEV-10-PR-0006 frequency multiplier (75–110 GHz). Based on transmission line theory, the physical model of the DSPSL resonator was established, and the relative permittivity and loss angle tangent value of the dielectric substrate were calculated using conformal transformation. To excite the resonator, the DSPSL coupling probe with a good transmission effect was designed, which consists of DSPSL microstrip line (MSL) transition structure and an MSL-WR10 rectangular waveguide converter. To reduce the air gap between the sample and the metal guide band and dielectric support block, and to improve test accuracy, a mechanical pressure device is added to the top of the DSPSL resonator. Based on the DSPSL resonator, we have used the device to test four typical PCBs, namely, polytetrafluoroethylene, Rogers RT/duroid®5880, Rogers RO3006®, and Rogers RO3010®. The results show that the maximum error of the relative permittivity is less than 3.05%, and the maximum error of the loss angle tangent is less than 1.27 × 10−4.

A compact differential branch‐line coupler using folded substrate integrated suspended parallel strip line

AbstractThis letter presents a compact fully differential branch‐line coupler. It is composed of folded substrate integrated suspended parallel strip line (SISPSL), which can generate slow‐wave effect and help reduce the circuit size. The used SISPSL type line is a fusion of double‐sided parallel‐strip line (DSPSL) and substrate integrated suspended line (SISL), which has the advantage of self‐packaging as compared with traditional DSPSL exposed to air. A DC to 30‐GHz differential transition from grounded coplanar waveguide (GCPW) to SISPSL is designed to test the SISPSL differential coupler. The implemented SISPSL branch‐line coupler has a compact size of 0.056 λg × 0.05 λg.

Wideband Vertically Polarized Planar Endfire Antenna Based on Spoof Surface Plasmon Polaritons

A novel wideband vertically polarized planar end-fire antenna based on the first and the second high-order modes of Spoof Surface Plasmon Polaritons (SSPPs) is proposed in this letter. A double-sided SSPP transmission line (TL) is used to produce vertically polarized radiation. By replacing the uniform stub in the conventional SSPP cells with a step-impedance-resonator (SIR) shaped stub, the bandgap between the first and the second high-order modes is eliminated. The double-sided SIR-shaped SSPP cells are tilted to make the maximum radiation point in the end-fire direction. Dielectric covers perforated with air vias are added to the top and bottom surfaces of the SSPP TL to generate end-fire radiation and enhance antenna gain. A grounded coplanar waveguide to double-sided parallel-strip line transition is designed to feed the radiator. A prototype of the proposed antenna has been fabricated and measured. The proposed antenna achieves a fractional bandwidth of 91.6% from 12.9 GHz to 34.6 GHz and a peak gain of 17.3 dBi.

Ku/Ka-Band Dual-Frequency Shared-Aperture Antenna Array With High Isolation Using Frequency Selective Surface

In this letter, a high-gain, high-efficiency, and high-isolation Ku/Ka-band dual-frequency shared-aperture antenna array using frequency selective surface (FSS) is investigated. The antenna consists of an 8×8 Ka-band and a 4×4 Ku-band printed double-sided dipole arrays in the upper and lower substrate layers, respectively. To realize high efficiency, the feeding networks are realized with double-sided parallel striplines. A low-pass FSS structure, sandwiched by the Ku-band array and the Ka-band array, works as the ground plane of the Ka-band array and is transparent to the Ku-band array, and it can also isolate the two antenna arrays for high isolations. In addition, a third-order impedance transform filter is integrated into the feed network of the Ka-band array. Ultimately, the antenna array has -10 dB impedance bandwidths of 14.47–17.52 GHz (19.07%) and 30.19–38.29 GHz (23.66%) with the peak antenna gain of 18.9 dBi at 16 GHz and 24.85 dBi at 35 GHz, respectively. High aperture efficiencies of 79% and 65% are realized. Meanwhile, the isolations between the two ports are better than 20 dB in low band and 30 dB in high band. For verification, a prototype is fabricated, and the measured results agree with the simulated ones.

Ultra-broadband direct dielectric spectroscopy of liquids using a calibrated Microwave-Fluidic vertical Two-Wire sensor with Bi-Material 3D printed chamber

A novel ultra-broadband dielectric spectroscopy technique for liquids is introduced. A two-wire transmission line sensor is employed in which the liquid-under-test comprises fully the propagation medium ensuring high sensitivity and direct permittivity measurement. A vertical wire arrangement is exploited fed by a double-sided parallel stripline with a microstrip interface and no bandwidth-limiting impedance transformation. A seal-integrated flex-rigid 3D-printed liquid container is developed for robust assembly. A raw measured propagation constant correction is proposed through setup calibration using only one reference liquid, which can be air. Sensor operation and design aspects are discussed in detail and an exemplary sensing setup is developed for experimental validation. A set of liquids is characterized within a three-decade bandwidth up to 42 GHz and fitted into a relaxation model along with a comparison against industry-standard broadband open-coax sensor captured data. The conducted study and error analysis certified the performance of the proposed setup.

A Compact Low-Profile Vertically Polarized Endfire Leaky-Wave Antenna Based on Double-Sided Parallel Strip Line

This article presents a vertically polarized (VP) endfire leaky-wave antenna (LWA) on a low-profile substrate by loading a series of shorting pins and slots along the double-sided parallel strip line (DSPSL). The periodically loaded shorting pins act as the VP radiator elements of the antenna, and also have the function to make the normalized phase constant of the original DSPSL equal to one so as to meet the endfire radiation condition. A series of slots etched on strip conductor around shorting pins are utilized to improve the radiation efficiency of the antenna in addition to its vertical polarization. In this way, the VP endfire LWA can be eventually realized with efficient radiation on a low-profile substrate. In our design, the mechanism of the proposed antenna is first analyzed based on the equivalent circuit model to investigate the effects of pins and slots on the antenna operation. Then, the attenuation properties of the antenna are detailly discussed under various structural dimensions to explore the relation between its physical sizes and radiation capability. Finally, a prototype is designed and fabricated to verify the predicted properties. The measured results match well with the simulated ones, thus demonstrating and confirming that the proposed endfire LWA can indeed realize efficient radiation with vertical polarization based on a single low-profile substrate.

Analysis and Design of Filtering Series-Feed Omni-Directional Antenna for V2X Application

In general, the vehicle-to-everything (V2X) series-feed antenna excites the spurious mode radiation in the adjacent bands and thus causes the strong mutual coupling between the vehicle antennas. To solve this problem, this article proposes a method to realize a filtering series-feed V2X antenna. This antenna consists of two radiators connected to a double-sided parallel strip line (DSPSL). The DSPSL operates as the series-feed structure and the first resonator. The radiators function as the second resonator. An equivalent filtering network is analyzed and derived. Then, based on the filter synthesis, the initial design parameters are obtained to realize a second-order bandpass response. However, the synthesis method only involves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> and efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula> ). The radiation performances are not concerned and satisfied. To solve this problem, the antenna currents are manipulated to generate the taper exciting. Thus, the upper sidelobe and the gain are improved. Moreover, to further enhance the out-of-band suppression level, three radiation zeros are generated by manipulating the current distribution on the DSPSL. The fabrication prototype demonstrates that the out-of-band suppression of the proposed antenna is better than 8.8 dB, which significantly reduces the mutual coupling.

Balanced-to-Unbalanced Quadrature Couplers With Wide-Band Common-Mode Suppression

In this paper, two types of balanced-to-unbalanced quadrature couplers with six hybrid ports and arbitrary power division ratio are proposed. For Type 1, the quadrature coupler can realize two power division functions, including balanced/unbalanced to balanced-unbalanced-hybrid, and for Type 2, the quadrature coupler contains balanced -to-unbalanced and unbalanced-to-balanced power division functions. To reduce the circuit size, double-sided parallel-strip line (DSPSL) swap structure is used to replace the half-wavelength transmission line, and compact circuit size can be easily achieved. To validate the performance of the quadrature couplers, two types of the balanced-to-unbalanced quadrature couplers centered at 1 GHz with power division ratios 1:1 and 3:1 are fabricated and measured, respectively. The common mode suppression higher than 10 dB (bandwidths over than 176%) can be realized, the isolation and in-band matching level can be also improved.

UHF RFID reader antenna with switchable far‐field and near‐field working state

An ultra-low profile and high-performance UHF RFID reader antenna is proposed in this letter, which can be switched between far-field (FF) and near-field (NF) operative modes. This antenna is composed of four dipoles and a reconfigurable feed network. The four dipoles form a square, and the feed network is located in the centre. The feed network is a four-way power divider, and the phase of the output signal can be controlled by switching diodes. As a balanced structure, double-sided parallel-strip lines (DSPSLs) are used to feed four dipoles. Compared to the balun structure, the application of DSPSLs can reduce the area of the feed network, thereby reducing the influence of the feed network on the central magnetic field. Experimental results show that the proposed antenna can provide a NF reading area of 180 × 180 mm2, and the identification rate can reach 100% within 30–60 mm height. The FF gain of the antenna is 4.7 dBic, and the overlapping range of 3 dB AR bandwidth and −10 dB impedance bandwidth is 800–960 MHz. The good FF and NF performance of this antenna is conducive to its application in RFID systems.

A High-Gain Endfire Periodic Leaky-Wave Antenna Using DSPSL-Based Rhombic Element

An endfire periodic leaky-wave antenna (LWA) with high gain is presented in this communication, which consists of a series of rhombic elements based on double-sided parallel stripline (DSPSL). The endfire mechanism of the proposed antenna is illustrated by the phase difference of the far field of each arm in the rhombic element. Meanwhile, a tradeoff between the tilted angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta _{0}$ </tex-math></inline-formula> and the width <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$w$ </tex-math></inline-formula> is found, which assures an optimum transverse aperture for achieving high-gain endfire radiation. Moreover, the improved Hansen–Woodyard (IHW) condition is applied to predict the optimum endfire phase constant. Finally, a prototype is fabricated and tested. The maximum endfire gain of 19.8 dBi is measured at 11.4 GHz, which is close to the simulated and predicted results. The proposed periodic rhombic antenna provides more choice for the modern communication system.

A Compact Dual-Band Differential Negative Group Delay Circuit With Wideband Common Mode Suppression

A compact dual-band differential negative group delay (DNGD) circuit with wideband common mode suppression is proposed. Two small 180° phase shift swap structures of double-sided parallel striplines (DSPS) are adopted to realize intrinsic wideband common-mode suppression. The dual-band DNGD characteristic is achieved by the DSPS coupled asymmetrically with two different-length open-circuited resonators. The DNGD times and center frequencies of the lower and upper bands can be tuned independently. To verify the proposed DNGD circuit topology, a prototype is designed, fabricated, and measured. From the measured results, DNGD times are −1.60 ns and −1.43 ns at the center frequencies of 1.227 GHz and 1.575 GHz, respectively. The differential insertion loss is lower than 3.55 dB, the differential return loss is larger than 13.3 dB and the common-mode suppression is over 30.8 dB in both DNGD bands.

Novel Wideband Bandpass Filters Using Double-Sided Quasi-SSPPs Transmission Line

In this brief, two wideband bandpass filters using a novel double-row staggered double-sided quasi-SSPPs transmission line are proposed. By loading U-shaped cells symmetrically, a transmission zero can be introduced into the original operating frequency band, which forms a high out-of-band suppression wideband bandpass filter. The structure can draw an analogy with double-sided parallel stripline, and the equivalent circuit model of microstrip line can be constructed to assist analysis and design. The passband selectivity can be further improved when the number of U-shaped cells is increased from 3 to 5. The measured result of 3-dB fractional bandwidth is 18.9 % (frequency 11.4 GHz), and the in-band return loss is greater than 10.2 dB. In addition, the out-of-band suppression is greater than 20 dB in the lower stopband (from 6.18 GHz to 10.12 GHz) and the upper stopband (from 12.78 GHz to 19 GHz).

An SIW-Fed Cross-Dipole Antenna With Broadband Circular Polarization for MMW Applications

In this communication, a broadband substrate integrated waveguide (SIW)-fed circularly polarized (CP) cross-dipole antenna is proposed for millimeter-wave (MMW) applications. Its radiation parts consist of a cross dipole and reflecting ground, which are etched on two substrates. The antenna is fed by an SIW through a double-sided parallel-strip line (DSPSL). In addition, zigzag edges and L-shaped etches are utilized to expand the impedance bandwidth (IBW) and axial-ratio bandwidth (ARBW), respectively. By these methodologies, the antenna prototype possesses a measured IBW of 34.6% from 22.5 to 31.9 GHz, an ARBW of 23.1% from 24 to 30.25 GHz, and a peak gain of 8.8 dBic at 29.5 GHz. In comparison to general coaxial-line-fed cross-dipole antennas with a nonplanar topology and high profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.25\lambda _{0}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength at the center frequency), the proposed antenna with PCB process maintains broadband and owns a low profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.16\lambda _{0}$ </tex-math></inline-formula> , which makes it more desirable for MMW integrated circuits.

A dual‐band filtering structure for highly selective reconfigurable bandpass filter and filtering balun

This article proposes a filtering structure consisting of two half-wavelength resonators and two open-stub loaded resonators, which generates two third-order passbands. Multiple transmission zeros are introduced by the newly developed coupling scheme, resulting in extremely sharp roll-off desirable for highly selective filters. The proposed structure is applied to design a PIN-diodes switch-controlled reconfigurable dual-band bandpass filter (BPF) with four-state filtering responses: both passbands ON, both passbands OFF, high-frequency passband ON, and low-frequency passband ON. Stepped-impedance open stubs and one-end-grounded coupled lines are studied and employed in the design to suppress unwanted responses. In addition, two filtering structures are placed symmetrically to design a dual-band balun BPF. Double-sided parallel-strip lines are added in the input port of the filter, and their inherent out-of-phase feature enables the balun filter to convert unbalanced signal to balanced signal at desired frequencies. The measured results of both fabricated devices agree well with the simulated results. The switchable BPF and balun BPF have two passbands (2.8 and 4.8 GHz) with high selectivity with the minimum roll-offs from −3 to −15 dB are 1.70 × 103 and 2.71 × 103 dB/decade, respectively. The insertion loss of the switchable BPF is 2.3/2.0 dB and the minimum signal suppressions level OFF state is measured as −18.2 dB. The insertion loss of the balun BPF is 1.8/1.4 dB, and the phase and magnitude imbalances are less than 0.3 dB and 5°, respectively. The excellent performances of the implemented filter and filtering balun successfully demonstrate the advantages and design efficacy of the proposed filtering structure for different applications.

Quasi-Reflectionless Double-Sided Parallel-Strip Line Bandpass Filter With Enhanced Selectivity

A novel quasi-reflectionless bandpass filter (BPF) using double-sided parallel-strip line (DSPSL) is proposed in this brief. It is composed of a BPF and two symmetric absorptive bandstop filters (ABSFs) terminated by a pair of resistors that can dissipate the input untransmitted signal energy. Through detailed analysis, the high characteristic impedance is required for the open-circuited stubs of the ABSFs to enhance the selectivity. This cannot be realized in traditional microstrip designs, but it can be obtained easily by offsetting the DSPSL. Meanwhile, the BPF with T-shaped structure consists of a half-wavelength ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> ) DSPSL with a centrally-loaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> stub, which answers for generating two transmission zeros (TZs) to achieve better out-of-band suppression. For demonstration, a prototype is designed, fabricated and measured, and the simulated and measured results with good agreement are presented.

Design of an Ultrawideband Planar Guanella Balun

This article presents the design and implementation of an ultrawideband multioctave planar Guanella balun (balanced-to-unbalanced) using double-sided parallel strip lines (DSPSLs). The operating frequency of the balun is found to be 0.5–2.6 GHz. The DSPSL is a type of balanced transmission line where two metal strips are present on the opposite sides of a flat dielectric substrate. Wideband transition between these balanced lines to a microstrip line has also been implemented. The measured amplitude and phase imbalance between the output signals at the balanced ports are less than 0.75 dB and 7°, respectively. The impact of these amplitude and phase imbalances on the combining loss of the balun has been presented. In order to understand the behavior of the balun with respect to differential and common mode signals, the mixed-mode <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters have been calculated. The physical size of the fabricated balun is 27.25 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times\,\,49$ </tex-math></inline-formula> mm. The design has been validated with the help of its measurement results.

Wideband RCS Reduction of Slot Array Antenna Utilizing 3-D Absorptive Frequency-Selective Structure

A low radar cross-section (RCS) slot array antenna based on absorptive frequency-selective structure (AFSS) is presented in this letter. The AFSS unit cell is constructed by two lossy layers and four double-sided parallel strip lines (DSPSLs). The radiation performance of the antenna can be preserved due to the transmission window of the lossy layers. Wide absorption bands of the AFSS are achieved due to periodic impedance of the DSPSL and the combination of the lossy layers. The operating principle of the design is demonstrated, and a prototype is fabricated and measured to validate the design. The proposed design features both wide RCS reduction band of the antenna and wide transmission band of the AFSS.

Millimeter-Wave Wideband Circularly Polarized Endfire Planar Magneto-Electric Dipole Antenna Based on Substrate Integrated Waveguide

A wideband circularly polarized (CP) endfire planar magneto-electric dipole antenna based on substrate integrated waveguide (SIW) is proposed for millimeter-wave (mm-wave) applications. The antenna mainly consists of an open-ended rectangular SIW radiating like a magnetic dipole, a parallel electric dipole, and a double-sided parallel-strip line which connects the two dipoles and provides 90° phase difference between them to generate CP radiation. To increase the axial ratio (AR) bandwidth, a pair of triangular slots are etched at the end of the upper and lower broad walls of the SIW, and moreover, a specific bowtie-shaped electric dipole is used instead of the traditional linear one. It has been shown that both the slots and the bowtie-shaped electric dipole can regulate or tune the magnitude of the radiation field of the electric dipole, making it tend to balance with radiation field generated by the magnetic dipole, and hence, leading to a good CP performance. The antenna has a single-layer planar structure, and it shows a −10 dB impedance bandwidth of over 50%, a 3 dB AR bandwidth of 36.6%, and a peak gain of 9.3 dBic.

Wideband Balanced Filters With Intrinsic Common-Mode Suppression Using Coplanar Strip Double-Sided Shunt-Stub Structures

In this article, two coplanar-strip (CPS) wideband balanced bandpass filters with intrinsic common-mode (CM) suppression are proposed based on shunt-stub structures. As previously reported with higher integration and greater flexibility, the double-sided shunt-stub structures could make sufficient use of various transmission lines (TLs), such as double-sided parallel-strip line (DSPSL), microstrip line (MSL), and slot line (SL). Compared with its conventional dual circuit, the proposed structure herein is capable of realizing ideal CPS-based resonant characteristics without degraded performance. As such, a DSPSL-loaded CPS triple-mode resonator and a microstrip-to-CPS (MS-to-CPS) transition are developed as two distinctive double-sided shunt-stub element units. Meanwhile, their equivalent circuit models are generalized for analysis of these proposed shunt-stub units and the corresponding synthesis design is further theoretically derived. For experimental verification, one fifth-order and one seventh-order balanced filters are designed, fabricated, and measured. It has been well demonstrated that both the wideband differential-mode (DM) filtering property and intrinsic CM suppression are satisfactorily achieved at the same time, with a certain range of available bandwidths.

Miniaturized Ultrawideband Reconfigurable Power Divider Based on Slotline and Double-Sided Parallel-Strip Line

A novel miniaturized ultrawideband reconfigurable power divider based on slotline and double-sided parallel-strip line (DSPSL) is presented in this article. The switch from the two-way out-of-phase power divider to the four-way in-phase power divider can be realized by using only two PIN diodes in the presented power divider, which will simplify greatly the circuit design and reduce the cost. Two working states in different transmission modes can be switched under the different bias conditions of the two PIN diodes. The equivalent-circuit model is developed to analyze the presented power divider. An ultrawideband reconfigurable power divider is designed and fabricated. At the four-way in-phase power-dividing mode, the measured insertion loss is less than 2.15 dB, the output isolation is greater than 15 dB, and the relative bandwidth is about 59.3%. At the two-way out-of-phase power-dividing mode, the measured insertion loss is less than 1.8 dB, and the relative bandwidth is about 57.1%.