Inverted Microstrip Research Articles

Ferrite-Loaded Inverted Microstrip Line-Based Artificial Magnetic Conductor for the Magnetic Shielding Applications of a Wireless Power Transfer System

In this paper, we propose a ferrite-loaded inverted microstrip line (IML)-based artificial magnetic conductor (AMC) with a novel design that can provide complete magnetic shielding at the backside of the transmitting (Tx) coil while slightly improving the power transfer efficiency (PTE) of a wireless power transfer system (WPTS). The target frequency of the WPTS application is approximately 6.78 MHz. In the proposed design, the AMC is placed behind the Tx coil, and its magnetic shielding capability and PTE performance were verified through simulations and measurements. The size of the proposed AMC is 528 × 528 × 6.6 mm3. The measurement results verified that, compared with the Tx coil without an AMC surface, the proposed ferrite-loaded IML-based AMC can provide complete magnetic shielding while improving the PTE of the WPTS by approximately 8.05%.

Rethinking Liquid Crystal Tunable Phase Shifter Design with Inverted Microstrip Lines at 1–67 GHz by Dissipative Loss Analysis

Growing 5G/6G phased-array beam-steering applications, for which liquid crystal (LC) is one of the enabling technology candidates, have sparked interest in the modulation of the phase (and amplitude) of microwave and millimeter-wave signals. In this communication, fresh insights into the systematic design analysis of a 1–67 GHz passive inverted microstrip line (IMSL) phase shifter filled with highly anisotropic LC as tunable dielectric media are obtained. Based on waveguide disturbance tests to characterize the dielectric properties of the non-tunable PCB and tunable LC used in the IMSL phase shift device filled with a GT3-24002 LC layer (125 µm thick) partially enclosing a 220 µm wide, 17 µm thick, 1.35 cm long copper core line, a 0–π differential phase shift in the 1–67 GHz range with less than 2 dB insertion loss is reported. Dissipative loss analysis shows that the dielectric absorption of the LC is 21.28% of the input signal power at 60 GHz. Further investigation is performed to quantify the impacts of dielectric substrate thicknesses (PCB and LC) on the wave-occupied volume ratio (and hence the phase tuning range), as well as on dissipative losses (including conductor loss and dielectric loss). Specifically, conductor loss is observed to follow a linear relationship with the reciprocal of the LC thickness.

Compact dual‐band inverted‐microstrip ridge gap waveguide diplexer

A compact dual-band inverted microstrip ridge gap waveguide (IMRGW) diplexer composed of four dual-mode IMRGW resonators and an IMRGW T-junction matching network is proposed in this letter. The dual-band diplexer is based on a dual-mode IMRGW resonator which can produce both the inverted microstrip resonant mode and the cavity resonant mode. Two resonant modes of the IMRGW resonator are highly independent, so the passbands of dual-band IMRGW diplexer can be easily tuned to the desired frequencies. A second-order dual-band IMRGW diplexer is designed and simulated. The simulated passbands of the second-order dual-band IMRGW diplexer are 13.13-13.38, 14.85-15.26, 18.57-19.42, and 20.85-21.35 GHz with fractional bandwidth of 2%, 2.7%, 4.8%, and 2.4%. A prototype is fabricated and measured to verify the feasibility of the proposed IMRGW diplexer. The measured passbands of the second-order dual-band IMRGW diplexer are 13.07-13.35, 14.88-15.35, 18.45-19.37, and 20.82-21.28 GHz with fractional bandwidth of 2.1%, 3.1%, 4.9%, and 2.2%. The measured isolation is better than 23 dB over 12-22 GHz. The measured results agree well with the simulations.

Design of Planar Microstrip Ultrawideband Circularly Polarized Antenna Loaded by Annular-Ring Slot

A miniaturized planar microstrip circularly polarized ultrawideband (UWB) antenna loaded by annular-ring slot is proposed and implemented in the paper. With the annular-ring slot loaded in the radiating patch of the antenna, the side of the radiating patch is connected by the asymmetric inverted L-shaped microstrip. At the same time, a quarter of a circle is cut off from the radiating patch. The above designed structure shows improvements on the operating frequency band and realization of the circular polarization radiation. A tapered microstrip is placed between the feed line and the radiating patch to achieve the slow-changing impedance transformation. The results of simulation and measurement demonstrate that the 3 dB axial ratio (AR) fractional bandwidth of the antenna structure achieves 21.25%. The peak gain within the 3 dB axial ratio bandwidth fluctuates between 3.74 and 4.59 dBi. The antenna shows good impedance matching in the ultrawideband range. With the compact structure of the UWB antenna, it has potential application in various wireless communication devices.

Millimeter-Wave Ultrawideband Circularly Polarized Planar Array Antenna Using Bold-C Spiral Elements With Concept of Tightly Coupled Array

An ultrawideband circularly polarized (CP) planar array antenna built by new radiation elements, the bold-C spiral elements, in millimeter-wave band is presented in this article. Using the tightly coupled array (TCA) technique, the embedded CP bold-C spiral element in the infinite array has achieved both impedance bandwidth and 3 dB axial ratio (AR) bandwidth of 50.7% covering 18.1-30.4 GHz for the fixed broadside beam. Then, a feeding network is designed by using the dielectric-based inverted microstrip gap waveguide (DIMGW) technology in order to have a compact layout. An 8×8 CP planar array based on the proposed radiating element and the feeding network is designed and prototyped. The measured results show that the impedance bandwidth of the whole array for the reflection coefficient below -10 dB is 49% from 18.2 to 30 GHz, and 3 dB AR bandwidth is 44.9% covering 19-30 GHz.

Compact Dual-Band Inverted-Microstrip Ridge Gap Waveguide Bandpass Filter

A compact dual-mode inverted microstrip ridge gap waveguide (IMRGW) resonator and a series of dual-band IMRGW bandpass filters (BPFs) with easily controllable passbands are proposed for the first time in this article. The resonator is embedded into the ridge of the IMRGW without disturbing the placement of the mushroom-type bed of nails. A metalized via-hole is introduced to the center of the IMRGW resonator to ground a central patch, resulting in an inverted microstrip resonance mode and a cavity resonance mode simultaneously. The cavity resonant mode is relatively insensitive to the dimensions of the central patch, while the inverted microstrip resonance is insensitive to the dimensions of the cavity enclosed by electromagnetic band-gaps (EBGs) and two rows of metalized via-holes. Therefore, the resonant frequency of the two modes can be tuned independently. The resonators can be cascaded easily with a short IMRGW transmission line. A series of IMRGW based dual-band BPF with different orders are designed, fabricated, and measured. The third-order BPF’s simulated passbands are 13.07–13.41 and 18.46–18.91 GHz with a fractional bandwidth of 2.5% and 2.3%. Low insertion losses better than 1.7 and 2.1 dB are obtained on the two passbands. The measured passbands are 13.52–13.86 and 18.9–19.34 GHz with a fractional bandwidth of 2.3% and 2.2% while the insertion losses are better than 2.5 and 2.3 dB for the third-order BPF.

Ultra‐wideband linearly polarised planar bowtie array antenna with feeding network using dielectric‐based inverted microstrip gap waveguide

A tightly coupled bowtie array antenna at a millimetre-wave band is presented in the study. The antenna has a simple structure and exhibits a high performance over an ultra-wide bandwidth. The feeding network is designed by using the dielectric-based inverted microstrip gap waveguide technology in order to have a compact layout. An 8 × 8 planar array is designed and prototyped. The measured results show that the proposed array has achieved an overall bandwidth of 55.7% from 18.7 to 33.15 GHz. The maximum measured gain is 21.8 dBi at 32.5 GHz, and the total antenna efficiency is above 40% through the whole bandwidth.

An Electrically Steerable Parasitic Array Radiator in Package Based on Liquid Crystal

An electrically steerable parasitic array radiator in package based on liquid crystal (LC) is presented. It consists of one main and two parasitic inverted microstrip patch elements on an embedded LC layer with direct current bias. The antenna is designed to operate under the voltage mode at Ka-band. By varying the induced voltages on parasitic elements, the main beam can be steered to the desired direction. Measured results show that the pattern can be steered from –27° to +29° continuously in the H-plane at 28 GHz. The peak realized gain is 6.03 dBi with 1 dB variation within the steering range. The array achieves an 8.3% impedance bandwidth and avoids both large direct current power consumption and complicated bias scheme, making it a good antenna candidate for millimeter-wave 5G access point applications.

Frequency Tunable Differentially Fed Inverted Microstrip Patch Antenna with Low Cross-Polarized Radiation

In this article tunable characteristic of differentially fed inverted microstrip patch antenna is presented for C-band operation. Differential feeding is applied through a unilayer integrated coupler feed. Near the operating frequency of the designed antenna the fabricated coupler shows that the amplitude imbalance is 0.3 dB and phase imbalance corresponds to 3.2°. Tuning is achieved by changing the air gap height in the antenna structure from 1 to 4 mm. Proposed concept of tunablity is verified for two different patch geometries (circular and rectangular) and three different patch dimensions through analysis and experiments. Closed form expressions are proposed to predict the tuning frequency. This design offers low cross-polarized radiation in the H-plane and symmetric co-polarized radiation in both principal planes. Fabricated prototype is measured and compared with simulated and theoretical values. The comparison among the simulated values, theoretically computed values and the measured values for different air gap heights of 2, 3, and 4 mm, shows an error less than 1%.

A general design method for tunable microstrip devices at microwave frequency based on liquid crystal technology

ABSTRACTThis paper proposes a general design method for microstrip devices using liquid crystal (LC) at microwave frequencies. The method employs lumped element modelling to first optimise the filter at the working frequency. Then EM simulation is used for the second optimisation and the full-wave simulation. LC is used as the tunable material since the anisotropy can be changed with low voltages. The approach of modelling LC as a homogeneous anisotropy demonstrated with Computer Simulation Technology (CST) Microwave Studio is an acceptable approximation, which accurately predicts the tuning range. A new tunable inverted microstrip filter using nematic LCs at millimetre-wave frequencies is designed to verify the method. The proposed design utilises interdigital capacitors in parallel with two inductive loops to form a bandpass filter. It is fabricated and measured, and shows that the centre frequency varies from 5.01 to 5.51 GHz (10% tunability) and achieves a 3-dB bandwidth of 450 MHz, which is in good agreement with simulation results. A finite element simulation is used to investigate the behaviour of LC directors in the fully switched state; the effective permittivity is extracted from finite-element simulation and used in CST to achieve an even more accurate agreement with experimental results.

Tunable microwave bandpass filter integrated power divider based on the high anisotropy electro-optic nematic liquid crystal.

A novel, compact microwave tunable bandpass filter integrated power divider, based on the high anisotropy electro-optic nematic liquid crystal, is proposed in this letter. Liquid crystal, as the electro-optic material, is placed between top inverted microstrip line and the metal plate. The proposed structure can realize continuous tunable bandpass response and miniaturization. The proposed design concept is validated by the good performance of simulation results and experimental results. The electro-optic material has shown great potential for microwave application.

A novel tunable inverted microstrip filter based on liquid crystal

In this work, a microwave tunable filter of inverted microstrip with dual-mode resonator using liquid crystal (LC) technology has been designed, manufactured, and characterized. It comprises a thin LC layer between a ground plane and a directly coupled and inverted microstrip line. Central frequency tunability was realised by applying low ac voltages, thus involving low power consumption. The transmission characters of the filter were specifically designed for working at C-band microwave frequency range, which are allocated for many communication applications such as satellite, cordless telephone or weather radar systems. Additionally, its compact structure allows the device to be integrated on circuit board to adapt with other MW components for expanded applications. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1626–1628, 2016

A V-Band Inverted Microstrip Gap Waveguide End-Coupled Bandpass Filter

This letter presents an end-coupled bandpass filter (BPF) based on the recently introduced inverted microstrip gap waveguide technology. The inverted microstrip gap waveguide is advantageous for millimeter wave applications because of its low-loss, self-packaging characteristics, and cost-effectiveness. A fourth order Chebyshev-type end-coupled BPF is designed to provide a 2 GHz bandwidth at 60 GHz center frequency. The fabricated prototype embedded within a 10 cm inverted microstrip gap waveguide, containing two back-to-back transitions to rectangular waveguide, exhibits an insertion loss of 3 dB in the passband. However, the insertion loss of the filter itself is better than 1.6 dB.

An Effective Modeling Framework for the Analysis of Interconnects Subject to Line-Edge Roughness

This letter proposes a complete and efficient simulation framework to assess the effects of line-edge roughness appearing in on-chip lines. The modeling approach consists of three steps. First, a stochastic macromodel is created for the per-unit-length RLGC parameters of the line. Secondly, random conductor edge profiles are generated using randomized splines. These are combined with the stochastic macromodel to readily provide place-dependent RLGC parameters. Finally, the resulting nonuniform transmission line is analyzed by means of a fast and accurate perturbation technique. To validate the proposed approach, a statistical analysis of the response of a coupled inverted embedded microstrip line is carried out for different roughness parameters.

Analysis of an open-ended inverted L-shaped slot-loaded microstrip patch antenna for size reduction and multifrequency operation

This paper proposes a detail analysis of a single layer, single-feed microstrip patch antenna for size reduction and multifrequency operation. An open-ended inverted L-shaped slot is introduced at the left-hand side radiating edge of the patch to reduce the size of the antenna by reducing the resonant frequency. Multiple resonant frequencies are also obtained by introducing the open-ended inverted L-shaped slot. The measured result shows that the size of the proposed antenna has been reduced by 74.3% when compared with conventional rectangular microstrip antenna with same patch area. The proposed antenna also provides increased frequency ratio (the ratio of second or higher resonant frequency to the first resonant frequency). The conventional and proposed antennas are designed and simulated by method of moment-based IE3D software. An extensive analysis of the antenna parameters (reflection coefficient, radiation pattern, gain, etc.) including surface current distribution is given in this paper.

Rectangular Microstrip Antenna with Slot Embedded Geometry

In this paper, a novel design that improves the performance of conventional rectangular microstrip antenna is discussed. Design adopts basic techniques such as probe feeding technique with rectangular inverted patch structure as superstrate, air filled dielectric medium as substrate and slot embedded patch. Prototype of the proposed antenna has been fabricated and various antenna performance parameters such as impedance bandwidth, return loss, radiation pattern and antenna gain are considered for Electromagnetic-study. The antennas are designed for the wireless application operating in the frequency range of 3.3 GHz to 3.6 GHz, and UK based fixed satellite service application (3 GHz to 4 GHz), and are named as single inverted patch conventional rectangular microstrip antenna (SIP-CRMSA) and slots embedded inverted patch rectangular microstrip antenna (SEIP-RMSA), respectively. Measurement outcomes for SEIP-RMSA1 and SEIP-RMSA2 showed the satisfactory performance with an achievable impedance bandwidth of 260 MHz (7 %) and 250 MHz (6.72 %), with return loss (RL) of −11.06 dB and −17.98 dB, achieved gain of 8.17 dB and 5.17 dB with 10% and 8% size reduction in comparison with the conventional patch antenna.

Wide Band Measurement of Dielectric Properties of Electronic Assembly Materials Inside an LTCC Fluidic Structure

Assembly materials such as underfillers or glob top epoxies are typically not specified regarding their dielectric properties for frequencies higher than 1 MHz. However, their behavior should be known for a wider frequency range in order to implement the appropriate parameters for RF and microwave simulations and designs. Typical methods to measure permittivity and loss tangent are based on parallel plate capacitor measurement with an impedance or network analyzer (up to about 1 GHz), S-parameter measurement of filled waveguides, coaxial transmission lines, or resonance methods (e.g., split post resonator, slit cavity resonator, ring resonator, open resonator). Most of these methods require specific sophisticated sample preparation. The paper describes a novel method based on suspended or inverted microstrip evaluation in a 3D LTCC structure. Suspended and inverted microstrip lines have lower insertion losses than standard microstrip lines due to the air gap between the line and the ground plane (reduced dielectric losses). Low loss structures are necessary to be able to measure low loss dielectrics. Such suspended or inverted microstrip lines can be easily achieved in LTCC by implementing a cavity structure. Inlets and outlets allow for the cavity to be filled with fluids after an initial S-parameter measurement of line properties (i.e., impedance, insertion loss, phase velocity). Measuring is repeated once the assembly material is cured. The change in impedance, phase velocity, and insertion contains the information about the material under test. Its properties are derived by curve fitting methods with a 3D electromagnetic field simulator. It is also possible to implement line resonators instead of through lines. In the latter case, the resonant frequency shift and the quality factor contains the material information. The procedure is demonstrated on a multilayer LTCC substrate based on low loss DP 9k7 and a commercial underfill material.

Wide Band Measurement of Dielectric Properties of Electronic Assembly Materials Inside a LTCC Fluidic Structure

Assembly materials like underfillers or glob top epoxies are typically not specified regarding their dielectric properties for frequencies higher than 1 MHz. However, their behavior should be known for a wider frequency range in order to implement the right parameters for RF and microwave simulations and designs. Typical methods to measure permittivity and loss tangent are based on parallel plate capacitor measurement with an impedance or network analyzer (up to about 1 GHz), S-parameter measurement of filled wave guides or coaxial transmission lines or resonance methods (e.g. split post resonator, slit cavity resonator, ring resonator, open resonator). Most of these methods require specific sophisticated sample preparation. The paper describes a novel method based on suspended or inverted microstrip evaluation in a 3D LTCC structure. Suspended and inverted microstrip lines have lower insertion losses than standard microstrip lines due to the air gap between the line and the ground plane (reduced dielectric losses). Low loss structures are necessary to be able to measure low loss dielectrics. Such suspended or inverted microstrip lines can be easily achieved in LTCC by implementing a cavity structure. In- and outlets allow filling the cavity with fluids after an initial S-parameter measurement of line properties (impedance, insertion loss, phase velocity). Measuring is repeated once the assembly material is cured. The change in impedance, phase velocity and insertion contains the information about the material under test. Its properties are derived by curve fitting methods with a 3D electromagnetic field simulator. It is also possible to implement line resonators instead of through lines. In the latter case, the resonant frequency shift and the quality factor contains the material information. The procedure is demonstrated on a multilayer LTCC substrate based on low loss DP 9k7 and a commercial underfill material.

Finite Element Approach of Shielded Suspended and Inverted Microstrip Lines

Finite Element Approach of Shielded Suspended and Inverted Microstrip Lines

A 325 GHz InP HBT Differential-Mode Amplifier

An MMIC amplifier operating at the highest reported frequency up to date for indium-phosphide double-heterojunction bipolar (DHBT) transistor technology is presented. The amplifier chain consists of seven unit-cell stages that contain differential-pair common-base HBTs and compact inverted microstrip matching networks. Amplifier operation in differential mode generates a virtual RF ground at a convenient location inside the unit cell. The measurements at 325 GHz show a small signal gain of 25 dB and a maximum output power of -1.5 dBm. An amplifier gain of greater than 20 dB is observed over 60 GHz bandwidth extending from 285 to 345 GHz.