Microstrip Transmission Line Research Articles

Fabrication Development for SPT-SLIM, a Superconducting Spectrometer for Line Intensity Mapping

Line Intensity Mapping (LIM) is a new observational technique that uses low-resolution observations of line emission to efficiently trace the large-scale structure of the Universe out to high redshift. Common mm/sub-mm emission lines are accessible from ground-based observatories, and the requirements on the detectors for LIM at mm-wavelengths are well matched to the capabilities of large-format arrays of superconducting sensors. We describe the development of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R$</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">$\lambda / \Delta \lambda = 300$</tex-math></inline-formula> on-chip superconducting filter-bank spectrometer covering the 120–180 GHz band for future mm-LIM experiments, focusing on SPT-SLIM, a pathfinder LIM instrument for the South Pole Telescope. Radiation is coupled from the telescope optical system to the spectrometer chip via an array of feedhorn-coupled orthomode transducers. Superconducting microstrip transmission lines then carry the signal to an array of channelizing half-wavelength resonators, and the output of each spectral channel is sensed by a lumped element kinetic inductance detector (leKID). Key areas of development include incorporating new low-loss dielectrics to improve both the achievable spectral resolution and optical efficiency and development of a robust fabrication process to create a galvanic connection between ultra-pure superconducting thin-films to realize multi-material (hybrid) leKIDs. We provide an overview of the spectrometer design, fabrication process, and prototype devices.

A 0.33–2.61-GHz Rectifier With Expanded Dynamic Input Power Range Using Microstrip Impedance Compression Circuit

In this letter, an ultra-broadband rectifier with expanded dynamic input power range (IPR) for both wireless power transfer (WPT) and radio frequency energy-harvesting (RFEH) is proposed and analyzed. Expanded dynamic IPR and broadband impedance matching are realized by utilizing a microstrip transmission line impedance compression circuit (MTLICC) with the topology of the paralleled voltage doubler. A proof-of-concept prototype shows a dynamic IPR of 8.5–23.5 dBm, a frequency range of 0.33–2.61 GHz (fractional bandwidth of 155%), PCE is greater than 50%, and a peak PEC of 79.7% (achieved at an input-power level of 19 dBm). The measurement results are in good agreement with the simulation. Covering most 3G/4G/5G/ISM frequency bands, this design is promising for RF power transmission and energy harvesting in the age of the Internet of Things systems.

Real-Time Discrete Fractional Fourier Transform Using Metamaterial Coupled Lines Network

Discrete fractional Fourier transforms (DFrFTs) are universal mathematical tools in signal processing, communications, and microwave sensing. Despite the excessive applications of DFrFT, the implementation of corresponding fractional orders in the baseband signal often leads to bulky, power-hungry, and high-latency systems. In this article, we present a passive metamaterial coupled lines network (MCLN) that performs the analog DFrFT in real-time at microwave frequencies. The proposed MCLN consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$</tex-math> </inline-formula> parallel microstrip transmission lines (TLs) in which adjacent TLs are loaded with interdigital capacitors to enhance the coupling level. We show that with the proper design of the coupling coefficients between adjacent channels, the MCLN can perform an M-point DFrFT of an arbitrary fractional order that can be designed through the length of the network. In the context of real-time signal processing for the realization of DFrFT, we design, model, simulate, and implement a 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 16 MCLN and experimentally demonstrate the performance of the proposed structure. The proposed innovative approach is versatile and is capable to be used in various applications where DFrFT is an essential tool. The proposed design scheme based on MCLN is scalable across the frequency spectrum and can be applied to the millimeter and submillimeter wave systems.

An Ultra-Wideband Integrated Filtering Antenna with Improved Band-Edge Selectivity Using Multimode Resonator

In this paper, a novel design of ultra-wideband (UWB) filtering antenna integrated with the multimode resonator (MMR) bandpass filter is proposed, aiming to enhance band-edge selectivity. At the beginning, a MMR bandpass filter is modified and studied. Based on the classic MMR filter, the proposed filter folds the microstrip transmission line to reduce its size while retaining the original filtering performance. Moreover, an open stub and short stub are added to the proposed filter to obtain a transmission of zero. Then, the folded filter with stubs and a UWB bow-tie antenna are integrated together to form a filtering antenna. The open stub and short stub in the MMR structure enhance the antenna’s upper and lower band-edge selectivity, respectively. Series of parameters are studied to analyze their influences on the frequency selection range and band-edge characteristics. Compared with the original UWB dipole antenna, such an integrated approach brings many benefits. Firstly, the UWB filter not only broadens the bandwidth of the device, but also improves band-edge selectivity, which can eliminate the unwanted passband near the operating frequencies. Secondly, the integrated system reduces the size and cost of the devices, which is very important in the miniaturization of wireless systems. In this research, the reflection coefficient (S11) of integrated filtering antenna is lower than −10 dB between 2.92 and 11.51 GHz, and it has a fractional bandwidth of 119%. The measured shape factor is 1.027 (very close to 1), which proves that this design has a better band-edge selectivity. Simultaneously, good radiation characteristics are also attained, with a maximum realized gain of 6 dBi. Theoretical simulation results are similar to the experimental results. The measurement results of the manufactured device effectively validate that its performances have reached the simulation design requirements.

Tunable non-reciprocal waveguide using spoof plasmon polariton coupling to a gaseous magnetoplasmon.

We experimentally demonstrate non-reciprocal (one-way) waveguiding in a microstrip transmission line tailored to support the propagation of spoof plasmon polaritons. Time-reversal symmetry is broken by coupling the microstrip fields to a magnetized gaseous plasma discharge column thereby exciting non-reciprocal magnetoplasmons at the interface between the plasma and a surrounding quartz envelope. The magnetic bias introduces asymmetry in the dispersion of the surface plasmon polaritons at the gaseous plasma-dielectric interface, resulting in a breaking of the bidirectionality of the wave propagation in the microstrip. The isolation generated at conditions of modest magnetic bias is measured to be nearly 60 dB, and tunable by varying the plasma density through the voltage applied to the discharge. The advantage of using magnetized gaseous plasmas to produce this unidirectional waveguide structure is that it can be turned on or off at rates limited by the production and recombination of the plasma.

A wideband quasi-Yagi antenna using symmetrical slots on the ground plane

ABSTRACT A wideband quasi-Yagi antenna with symmetrical rectangular slots in the ground plane is studied. The feeding structure of the antenna is simplified, consisting of a microstrip transmission line and a short strip. The driver and director arms are designed as half on both sides of the substrate to improve pattern stability. The antenna’s bandwidth is improved by symmetrically adding rectangular slots to the ground. The antenna works between and GHz with a gain that varies between to dBi, a bandwidth of , and an efficiency of more than . The antenna has a very compact size of ( is the wavelength for the lowest operating frequency). The simulation and measurement results are in good agreement. The antenna has highly stable end-fire radiation within its operating frequency and can be used for wideband wireless communication systems.

A Microstrip Transmission Line Biosensor to Measure the Interaction between Microliter Aqueous Solutions and 1.0-17.0 GHz Radio Frequencies.

Radio frequency (RF) biosensors are an expanding field of interest because of the ability to design noninvasive, label-free, low-production-cost sensing devices. Previous works identified the need for smaller experimental devices, requiring nanoliter to milliliter sampling volumes and increased capability of repeatable and sensitive measurement capability. The following work aims to verify a millimeter-sized, microstrip transmission line biosensor design with a microliter well operating on a broadband radio frequency range of 1.0-17.0 GHz. Three successive experiments were performed to provide evidence for (1) repeatability of measurements after loading/unloading the well, (2) sensitivity of measurement sets, and (3) methodology verification. Materials under test (MUTs) loaded into the well included deionized water, Tris-EDTA buffer, and lambda DNA. S-parameters were measured to determine interaction levels between the radio frequencies and MUTs during the broadband sweep. MUTs increasing in concentration were repeatably detected and demonstrated high measurement sensitivity, with the highest error value observed being 0.36%. Comparing Tris-EDTA buffer versus lambda DNA suspended in Tris-EDTA buffer suggests that introducing lambda DNA into the Tris-EDTA buffer repeatably alters S-parameters. The innovative aspect of this biosensor is that it can measure interactions of electromagnetic energy and MUTs in microliter quantities with high repeatability and sensitivity.

Wideband Single-Fed Circularly Polarized Stacked Patch Antenna With L-Shaped Stub

A wideband single-fed circularly polarized (CP) stacked patch antenna with an L-shaped stub is presented. The CP antenna is made up of the bottom gradient microstrip transmission line, middle driven patch and top square radiation patch. The driven patch with an L-shaped stub and opening slot can achieve a wideband CP radiation which is different from a conventional patch. The presented CP stacked patch antenna maintains good directional radiation, while featuring wideband CP radiation. The final tested results indicate that the presented CP antenna has significant performance with a −10 -dB impedance bandwidth of 42.1% (4.26-6.53 GHz), a 3-dB AR bandwidth of 26.0% (4.36-5.66 GHz) and broadside peak gain of 8.6 dBic. Moreover, the fifth-generation (5G) N79 band (4.4-5.0 GHz) and 5G wireless local area network (WLAN) band (5.15-5.35 GHz) can be covered by the operating bandwidth of the presented CPantenna.

Sensing High 17β-Estradiol Concentrations Using a Planar Microwave Sensor Integrated with a Microfluidic Channel.

The global issue of pollution caused by endocrine-disrupting chemicals (EDCs) has been gaining increasing attention. Among the EDCs of environmental concern, 17β-estradiol (E2) can produce the strongest estrogenic effects when it enters the organism exogenously through various routes and has the potential to cause harm, including malfunctions of the endocrine system and development of growth and reproductive disorders in humans and animals. Additionally, in humans, supraphysiological levels of E2 have been associated with a range of E2-dependent disorders and cancers. To ensure environmental safety and prevent potential risks of E2 to human and animal health, it is crucial to develop rapid, sensitive, low cost and simple approaches for detecting E2 contamination in the environment. A planar microwave sensor for E2 sensing is presented based on the integration of a microstrip transmission line (TL) loaded with a Peano fractal geometry with a narrow slot complementary split-ring resonator (PF-NSCSRR) and a microfluidic channel. The proposed technique offers a wide linear range for detecting E2, ranging from 0.001 to 10 mM, and can achieve high sensitivity with small sample volumes and simple operation methods. The proposed microwave sensor was validated through simulations and empirical measurements within a frequency range of 0.5-3.5 GHz. The E2 solution was delivered to the sensitive area of the sensor device via a microfluidic polydimethylsiloxane (PDMS) channel with an area of 2.7 mm2 and sample value of 1.37 µL and measured by a proposed sensor. The injection of E2 into the channel resulted in changes in the transmission coefficient (S21) and resonance frequency (Fr), which can be used as an indicator of E2 levels in solution. The maximum quality factor of 114.89 and the maximum sensitivity based on S21 and Fr at a concentration of 0.01 mM were 1746.98 dB/mM and 40 GHz/mM, respectively. Upon comparing the proposed sensor with the original Peano fractal geometry with complementary split-ring (PF-CSRR) sensors without a narrow slot, several parameters were evaluated, including sensitivity, quality factor, operating frequency, active area, and sample volume. The results showed that the proposed sensor exhibited an increased sensitivity of 6.08% and had a 40.72% higher quality factor, while the operating frequency, active area, and sample volume showed decreases of 1.71%, 25%, and 28.27%, respectively. The materials under tests (MUTs) were analyzed and categorized into groups using principal component analysis (PCA) with a K-mean clustering algorithm. The proposed E2 sensor has a compact size and simple structure that can be easily fabricated with low-cost materials. With the small sample volume requirement, fast measurement with a wide dynamic range, and a simple protocol, this proposed sensor can also be applied to measure high E2 levels in environmental, human, and animal samples.

Fully Aerosol Jet-Printed Passive Components for 140–220-GHz Operation

This letter focuses on the unique capabilities that aerosol jet printing (AJP) provides for manufacturing electronics at near-THz frequencies. For the first time, we demonstrate fully aerosol jet-printed passive components above the <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> -band. Dielectric substrates and conductors are printed on metal carriers via AJP. These components include microstrip (MS) transmission lines (TLs) and radial stubs, and utilize vialess grounded coplanar waveguide (GCPW)-to-MS TL launches. Two separate sets of components and calibration structures are realized, for two different dielectric thicknesses. For the TLs, measured from 140 to 220 GHz, the average loss varies from 0.86 to 2.6 dB/mm. The radial stub return loss, measured from 200 to 220 GHz, is closely aligned with simulations.

Multi Frequency Controllable In-Band Suppressions in a Broad Bandwidth Microstrip Filter Design for 5G Wi-Fi and Satellite Communication Systems Utilizing a Quad-Mode Stub-Loaded Resonator

The key elements used for receiving and processing signals in communication systems are the bandpass filters. Initially, a common operating mechanism was applied for the design of broadband filters, i.e., by cascading low-pass filters or high-pass filters using multiple line resonators with length quarter-half- or full-wavelength with central frequency, but using these approaches, the design topology becomes expensive and complex. The above mechanisms can be possibly overcome using a planar microstrip transmission line structure due to its simple design fabrication procedure and low cost. So, pointing out the above problems in bandpass filters such as low-cost, low insertion loss, and good out-of-band performance, this article presents a broadband filter with multifrequency suppression capability at 4.9 GHz, 8.3 GHz, and 11.5 GHz using a T-shaped shorted stub-loaded resonator with a central square ring coupled to the basic broadband filter. Initially, the C-shaped resonator is utilized for the formation of a stopband at 8.3 GHz for a satellite communication system, and then a shorted square ring resonator is added to the existing C-shaped structure for the realization of two more stopbands at 4.9 GHz and 11.5 GHz for 5G (WLAN 802.11j) communication, respectively. The overall circuit area covered with the proposed filter is 0.52 λg × 0.32 λg (λg is the wavelength of the feed lines at frequency 4.9 GHz). All the loaded stubs are folded in order to save the circuit area, which is an important requirement of next-generation wireless communication systems. The proposed filter has been analyzed using a well-known transmission line theory, even–odd-mode, and simulated with the 3D software HFSS. After the parametric analysis, some attractive features were obtained, i.e., compact structure, simple planar topology, low insertion losses of 0.4 dB over the entire band, good return loss greater than 10 dB, and independently controlled mutli stopbands, which make the proposed design unique and can be used in various wireless communication system applications. Finally, a Rogers RO-4350 substrate is selected for the fabrication of the prototype using an LPKF S63 ProtoLaser machine and then measured using a ZNB20 vector network analyzer for matching the simulated and measured results. After testing the prototype, a good agreement was found between the results.

Analysis of SMT component land pad discontinuity effect on the overall transmission line impedance in high-speed applications

Abstract High-speed and high-frequency PCB interconnect solutions with the slightest discontinuities in the physical geometry along the microstrip transmission line can significantly degrade the integrity of the signal being transferred. This paper presents an analysis of SMT component pads and their impact on the successive transmission line impedance. During 0805, 1206 and 2512 package size SMT component pad discontinuity evaluations it was spotted, that the increasing deviation from target impedance affects the microstrip impedance segment following the discontinuity. A 25 Ω impedance offset at the SMT pad reduces the line impedance afterwards by up to 7 Ω. A 37 Ω impedance offset results in a microstrip impedance reduction by up to 15 Ω, whereas a 45 Ω impedance change leads to a reduction of successive segment impedance by up to 30 Ω. This effect is also present in multiple evenly-spaced discontinuities. But a single reference plane cut-out, which is twice as wide as the SMT component discontinuity, substantially improves the overall impedance of the transmission line, including the successive line segment impedance drop.

Performance Evaluation of Broadband Characterization of Coupled Transmission Lines Even- and Odd-Mode Propagation Constants Using Differential and Common Mode S-Parameters

This work encompasses some relevant issues that arise when using a broadband method to characterize the even and odd mode propagation constants of symmetric microstrip coupled lines using four-port pure-mode differential and common mode S-Parameters. Correct excitations of differential and common modes play a significant role in experimental results. From these 4-port measurements, parameters corresponding to the even and odd modes can be extracted from the multi-mode generalized S-parameters obtained by the vector network analyzer. Differential and common mode sub-matrices are considered as two independent equivalent 2-port transmission lines. The method will be applied to extract the propagation constants of even and odd modes of coupled microstrip transmission lines. A discussion is included on ensuring the correct excitation of the modes in the structure and avoiding possible unwanted effects such as radiation, that negatively affects the final estimation, both in phase and attenuation. Two figures of merit are defined to evaluate how transitions affect the performance of the method. These figures of merit allow a reasonable estimation of how the final experiment is affected by selected excitation of modes. To assess the theory presented, two sets of seven lines of different lengths are manufactured. The experimental results show an excellent agreement, both with electromagnetic simulations and with the analytical model used, for the phase constant in the improved case of 30° bends, and an improvement in the useful bandwidth of the attenuation constant. This fact verifies the correct functioning of the method. In addition, the measurements are presented in the range of 0.01–67 GHz, which represents a significant advance in bandwidth for this type of structure.

Design of Novel Ultra-wideband Slow-wave Microstrip Transmission Line

Microwave passive devices with high efficiency, small size, and light weight are one of the fundamental requirements for mobile communication coverage in the 5G frequency band. In this paper, the design of a novel ultra-wideband slow-wave microstrip transmission line is proposed and studied. The electromagnetic field simulation software HFSS is used to simulate the slow-wave microstrip transmission line, and the simulation results show that the ultra-wideband slow-wave structure has the advantage of wider bandwidth, smaller size, and lower cost, which meets the needs of 5G communication systems. Finally, the proposed slow-wave microstrip line is used in the U-shaped phase shifter, and the experimental results show that the novel slow-wave microstrip transmission line has a large application potential in the base station antenna system.

A horn-coupled millimetre-wave on-chip spectrometer based on lumped-element kinetic inductance detectors

Context. Millimetre-wave astronomy is an important tool for both general astrophysics studies and cosmology. A large number of unidentified sources are being detected by the large field-of-view continuum instruments operating on large telescopes. Aims. New smart focal planes are needed to bridge the gap between the large bandwidth continuum instruments operating on single-dish telescopes and high spectral and angular resolution interferometers (e.g. ALMA in Chile and NOEMA in France). The aim is to perform low to medium spectral resolution observations and select a lower number of potentially interesting sources (i.e. high-redshift galaxies) for further follow-up. Methods. We have designed, fabricated, and tested an innovative on-chip spectrometer sensitive in the 85–110 GHz range. It contains 16 channels, each of which covers a frequency band of about 0.2 GHz. A conical horn antenna coupled to a slot in the ground plane collects the radiation and guides it to a millimetre-wave microstrip transmission line placed on the other side of the mono-crystalline substrate. The millimetre-wave line is coupled to a filter-bank spectrometer. Each filter is capacitively coupled to a lumped-element kinetic inductance detector (LEKID). The microstrip configuration provides the benefit of low loss, due to the mono-crystalline substrate, and protects the LEKIDs from illumination by stray un-filtered light. Results. The prototype spectrometer exhibits a spectral resolution R = λ/Δλ ≈ 300. The optical noise equivalent power is in the low 10−16 W Hz−1/2 range for an incoming power of about 0.2 pW per channel. The device is polarisation-sensitive, with a cross-polarisation lower than 1% for the best channels.

Aerosol Jet Printed Interconnects for Millimeter-Wave Components

As millimeter wave RF device applications expand above traditional microwave frequency bands in the global communications, automotive and Mil-Aero markets, the need to limit interconnect signal losses related to parasitic elements has never been more important. As the frequency increases, device designers are facing numerous challenges, complications, and costs when fabricating interconnects with techniques such as copper pillar bumps, wire, ribbon or wedge bonding in 3DIC packaging. Printing conformal interconnects with Aerosol Jet® direct-write technology can offer package designers and RF engineers a new approach for optimizing interconnect transitions to active die, tailoring the loss characteristics to specific application requirements and eliminating the need to compensate for high signal transmission losses. Printed interconnects can be digitally designed into the package with a variety of metallic and dielectric materials. As these interconnects are conformally printed on the 3D surface of the package, the trace length can be minimized with zero loop height, reducing parasitic inductance to active die circuitry specifically for die on board, die in trench, or die on die with pads-up packaging configurations. In this work, Aerosol Jet® printed interconnects with silver nanoparticle inks are compared with the gold microstrip transmission lines as well as traditional gold bond wires, for performance up to 110 GHz. We will share examples showcasing that the printed interconnects can have similar RF transmission performance to microstrip, with significantly lower loss than bondwires especially at high frequencies. We will also discuss design effects for Aerosol Jet® printed RF interconnects up to 110 GHz based on a set of results for different line heights with a given line width printed with a silver ink.

A Wideband Transition from Microstrip Line to Microstrip Spoof Surface Plasmon Polariton Line for Microwave/Millimeter-Wave Applications

In this article, a wideband transition from a microstrip transmission line to a microstrip spoof surface plasmon polariton (SSPP) transmission line is reported. The proposed transition is realized to achieve better performance starting from low frequencies up to 40 GHz. The proposed shape of the unit cell is taken in such a manner that the momentum, impedance, and polarization of the microstrip line can be matched with that of the SSPP transmission line. The wide operating band of the transition can be achieved by perturbing only the shape of the unit cell. Extra care is taken in choosing the shape of the unit cell so that the fabrication of the circuit becomes easier, especially at millimeter-wave frequencies. The proposed transition has a good transition-occupation ratio and transmission efficiency. The achieved transition-occupation ratio and transition efficiency for all three designed cases are excellent, and it is 34.18%, 44%, and 39% for p = 1 mm, 2 mm, and 3 mm, respectively. It is a potential candidate for realizing millimeter-wave antennas and devices due to its attractive properties, such as compact layout, low fabrication cost, ease of fabrication even at millimeter-wave frequencies, and good operational characteristics.

Microstrip patch antenna as a paper moisture sensor

This paper reports the use of non destructive, microstrip patch antenna as paper moisture sensor. Microstrip patch antenna is designed to resonate at 2.4GHz. This design is simulated and fabricated on copper clad type FR4 (εr= 4.4) having thickness of 1.6mm. Patch dimension are 27mm × 30mm and substrate dimension is 63mm × 60mm. The microstrip transmission line is used to provide excitation for the antenna. This design for microstrip patch antenna after fabrication showed a resonance at 2.38 GHz on vector network analyzer at S11=-19.38dB with impedance =49Ω. The variations in frequency in relation with water content in the paper is measured using Vector Network Analyzer by placing wet paper on the patch antenna. Moisture content in the paper was found out by taking wet weight and dry weight of the paper. The model of the wet paper is recommended primarily on the basis of water-dry paper reactions, along with the thickness and surface roughness explaining tendencies of the sensitivity graphs. Paper samples of 13 different types, with different GSM values and thicknesses, havingdimensions same as that of the substrate were tested. From the results it is observed that as the moisture content in the paper increases the frequency decreases. The change in frequency with respect to the moisture content is seen to have quadratic relation with moisture. The variations in the frequency are fitted in the form of equations. The calculated %Mwet indicates an error around ±0-4% in the calculated value as compared to the actual value. The response of sensor is almost linear with respect to the references but the coefficients depend non-linearly with the paper dimension.

Full-wave and plasma simulations of microstrip excited, high-frequency, atmospheric pressure argon microdischarges

Two-dimensional fully coupled electromagnetic (EM) wave-plasma simulations are used to study the formation, early transient and quasi-steady state of the argon plasma excited by a two-dimensional discontinuous microstrip line. The EM waves that normally propagate in the microstrip transmission line, radiate and scatter at the position of the gap and the electric field is enhanced primarily at the corner of the gap. The microdischarge is preferentially formed at this position of the EM field hotspot and in low frequencies propagates on the dielectric surface, much like a microwave surface streamer. In longer times, diffusion dominates and the whole gap is filled with plasma of maximum density in the order of 1020 while it occupies a volume larger than the gap. Cycle-averaged mean electron temperatures range from 2.8 to 3.9 eV, while the plasma reaches a quasi-static regime in approximately 2 µs having reconfigured the transmission and radiation patterns of the slitted microstrip line. The tunability of the microstrip due to plasma formation provides means for sustaining the discharge in a stable regime. For the same input EM power, the electron temperature increases with increasing excitation frequency while electron densities found to decrease. For the same wave frequency, a decrease of the electron densities with increasing gap is also found in addition to a restriction of the discharge expansion. Finally, thicker dielectrics result to higher electron densities and electron temperatures as well as absorbed power from the plasma. These findings are attributed to the dependence of absorbed EM power and skin depth on the EM wave angular frequency, the critical for shielding electron density as well as the restructuring of the S-parameters due to the changes in operational parameters.

Periodic Asymmetric Trapezoidal Perturbation Microstrip Antenna for Millimeter-Wave Automotive Radar Sensors

This article presents a new design and experimental verification of a broadband wide-beam microstrip array antenna for short-range automotive radar sensors. The antenna is designed based on a pure microstrip transmission line, by inserting short inverted trapezoidal stubs alternately on both sides of the microstrip line periodically to generate a trapezoid-cascaded electric field, which enables the proposed antenna to radiate effectively. Therefore, the proposed antenna has the advantage of a simple structure. The antenna has a larger effective radiation aperture, which leads to a smaller quality factor, so the antenna has a broad bandwidth of 13% (74.02–85.08 GHz), completely covering 76–81 GHz automotive radar frequency band. The peak gain is up to 10.4 dBi. Based on the proposed antenna, a three transmitting antennas and four receiving antennas (3T4R) multiple-input-multiple-output (MIMO) radar antenna array is designed. To reduce the influence of strong surface waves on the radiation pattern, a design conception of a dummy array with an absorbing load is introduced. The array antenna of each transmitting (TX)/receiving (RX) channel can achieve a wide half-power beamwidth (HPBW) of 120° in the azimuth plane. Besides, the MIMO array exhibits good consistency, with the absolute amplitude error of TX-RX channels less than 3 dB and the phase error less than 20° in the azimuth plane.