Stepped Impedance Transformer Research Articles

Compact Dual-Passband Doherty Power Amplifier Based on Stub-Loaded Stepped-Impedance Transformer

Compact Dual-Passband Doherty Power Amplifier Based on Stub-Loaded Stepped-Impedance Transformer

A low profile, dual‐polarised, high gain patch antenna

AbstractA low‐profile patch antenna with dual‐polarisation and high gain is proposed in this study. It contains a primary radiator, a secondary radiator, and a planar feed network. The primary and secondary radiators are square patches placed 5 mm from each other. Two planar feed networks are electrically connected with the primary radiator through the stepped impedance transformer, providing equal amplitude and 180° phase shift signals. These two feed networks are settled in different layers to weaken the coupling effect. The resonance generated by the primary radiator is merged with the one by the secondary radiator, covering the 3.3–3.6 GHz band. Benefiting from the differential feed method, antenna specifications such as port isolation and cross‐polarisation discrimination (XPD) are ideal. Moreover, as the primary radiator is fed by planar microstrip, the overall height can be reduced, and the gain can be enhanced. Finally, a 2 × 2 subarray is investigated. Desirable results show that the proposed antenna is suitable for application in Massive Multiple Input and Multiple Output (MIMO) systems.

600-GHz high-temperature superconducting sub-harmonic mixer coupled using a double-Y-type slot integrated lens antenna

In this paper, we present a quasi-optically coupled 600-GHz high-temperature superconducting (HTS) sub-harmonic mixer for communication and sensing applications. The mixer features an innovative double-Y-type slot integrated lens antenna, which can efficiently couple the radio frequency (RF) and local oscillator (LO) signals with a small frequency ratio by exciting the half-wave and full-wave resonant current modes on the slot, respectively. Considering the low impedance characteristics of HTS Josephson junctions, a coplanar-waveguide stepped impedance transformer is utilized for minimizing the mismatching loss. A cascaded filter network is designed to prevent the high-frequency signal leakage at both bands while coupling the intermediate-frequency (IF) signal output efficiently. Based on this antenna design and an established HTS step-edge junction technology, a 600-GHz mixer prototype was designed, fabricated and measured, which was compared with the simulation results. The achieved conversion gain and noise temperature are the best performance specs as reported to date for HTS harmonic mixers at comparable frequencies and operating temperatures.

A Wide-Angle Pattern Diversity Antenna System for mmWave 5G Mobile Terminals

A shared ground shared radiator with wide angular coverage for mmWave 5G smartphones is proposed in this paper. A four-element corporate-fed array with conventional impedance matched power divider is designed. Stepped impedance transformers are integrated with the corner most elements to achieve pattern diversity with wide angular coverage without significant compromise in gain. The proposed three-port shared radiator conformal commercial antenna could be easily integrated with commercial mmWave 5G smartphones. All the three ports’ excitations operate in the 28 GHz band. Radiation pattern bandwidth of the multi-port system is high. The gain variation is from 6 to 11 dBi amongst the ports and across the operating spectrum. The highest mutual coupling is 10 dB, in spite of the electrically connected structure. The proposed shared radiator element has a wide angular coverage of 100°, maintaining high front-to-back ratio when the respective port is excited. Simulation and measurement results for the proposed structure are illustrated in detail.

A K/Ka-Band Reconfigurable Substrate Integrated Coaxial Line to Waveguide Transition Technology

In this article, the designs of the K/Ka-Band reconfigurable Substrate Integrated Coaxial Line (SICL)-to-waveguide transitions are presented. Two types of reconfigurable SICL-to-waveguide transitions, with stepped impedance transformers waveguide transitions and ridge waveguide transitions, are designed for two operation frequency modes (K/Ka-band). Both simulated and experimental results are presented for the demonstration. Results indicate that the reconfigurable waveguide structure has the advantages of broad bandwidth and low return loss for both K/Ka-band compared with the conventional dual-band waveguide transitions. The presented waveguide transition designs with high function flexibility will be significant to satellite communication applications and massive MIMO beamforming networks with an active phased antenna array.

Design of a broadband diplexer based on substrate integrated plasmonic waveguide

In this article, a new wideband diplexer for microwave frequencies is proposed. This diplexer is designed based on the combination of spoof surface plasmon polariton structures with substrate integrated waveguide (SIW) structures. In the proposed diplexer, bandpass filters were designed within a frequency range of 6–9.2 GHz (bandwidth of 40%) and 11.7–16.2 Hz (bandwidth of 29%) by creating rectangular grooves on the top and bottom of the metallic layers of the SIW. These grooves generate surface plasmon waves in the SIW structure that limit the dispersion curve to an asymptotic frequency and cause a high cut-off frequency. The low cut-off frequency of the filters is determined by the SIW dimensions. Moreover, the two filters were fed using a microstrip T-junction with stepped impedance transformation. By optimizing the feed lines, the electromagnetic waves in each working band are directed to the filter of that band, and finally, the filters create a proper attenuation outside the band. A sample of the diplexer is fabricated and tested to verify the design. The simulation results are in good agreement with the experimental results. This diplexer can be a good candidate in microwave frequencies for telecommunication systems.

Design of a 3.7 GHz TE10 – TE30 mode converter using stepped impedance transformer for CW applications

This paper presents the design and simulation of a novel TE10 to TE30 mode converter operating at 3.7 GHz and is subjected to high RF power of 500 kW in Continuous Wave (CW) regime. The design incorporates a stepped impedance transformer as opposed to the conventional capacitive button to improve the return loss and power handling capacity of the converter. A rigorous RF, breakdown and multiphysics analysis including thermal, fluid dynamics and stress physics is performed on the mode converter to ascertain its viability and usefulness as a power dividing network in the Passive Active Multijunction launcher for Lower Hybrid Current Drive systems of tokamaks. The proposed mode converter exhibits a return loss of ∼50 dB, mode conversion efficiency of ∼97% and a peak E-field of 685 kV/m is obtained as compared to that of 4.2 MV/m obtained in the conventional mode converter. Thus, the power handling capacity of the proposed mode converter design is found to be 97.3% higher than the conventional mode converter.

A low‐loss Ka‐band waveguide to substrate integrated waveguide transition based on ridged stepped‐impedance transformer

A low-loss Ka-band transition from waveguide to substrate integrated waveguide (SIW) is presented based on ridge waveguide stepped-impedance transformer. This novel transition can operate across a full Ka-band (26.5 to 40 GHz) with an insertion loss lower than 0.59 dB and return loss over 14.2 dB. Furthermore, compared to existing transitions the introduction of ridges reduces the metal usage, resulting in weight reduction and offering an encouraging application for weight-sensitive satellite communications (SatComs).

Two-port dual-band circularly polarized dielectric resonator-based MIMO antenna with polarization diversity

ABSTRACT In this communication, dielectric resonator based two-port Multi Input Multi Output (MIMO) antenna is structured and examined. L-shaped microstrip line with a serial step impedance transformer is used to excite moon-shaped aperture, which in turn stimulates ring-shaped dielectric resonator antenna. Some of the important features of the proposed MIMO radiator are: (i) alteration of cylindrical to ring-shaped dielectric resonator is supportive to give wide-impedance bandwidth; (ii) aperture excites dual orthogonal hybrid ( and ) mode inside the ring dielectric resonator antenna, which aids to get dual-band circular polarization waves; and (iii) use of polarization diversity concept is helpful to give lesser mutual coupling (less than −20 dB) between the ports. After doing experimental confirmation, the proposed radiator is working over the frequency range 2.4–3.88 GHz. It also supports 3-dB axial ratio in dual-frequency range, i.e., 2.44–2.64 GHz and 3.4–3.65 GHz, respectively. Right-handed circular polarization and good value of diversity parameters make the proposed antenna employable for WLAN (2.5 GHz) and WiMAX (3.3 GHz) applications.

An in-line coaxial-to-circular waveguide transition at X band

Abstract A wideband transition from the coaxial TEM mode to the TM01 mode of the circular waveguide with in-line input-output architecture is proposed in this paper. The transition employs multi-stage stepped impedance transformer to achieve wideband responses. Both mode transition and impedance matching characteristics are discussed in the paper. A demonstrator is developed and validated experimentally. As compared with some recently published reports, a better performance is observed. Moreover, the developed transition could facilitate the mechanical fabrication more easily. It can be found wide applications such as the circular waveguide based slot array antenna, the nondestructive detection, cracks inside the conductive pipes, and so on.

A Full-Band Digital Television Transmitting Antenna Array With Dual-Layer Bowtie Dipole Unit

A full-band digital television (DTV) transmitting antenna array with dual-layer bowtie dipole unit is proposed in this paper. The dual-layer bowtie dipole is utilized as the antenna unit to broaden the frequency bandwidth, and its key parameters are discussed. Besides, a wideband impedance matching network with stepped complex impedance transformers is designed to achieve the full-band low voltage standing wave ratio (VSWR). For verification, a prototype is designed, fabricated, and measured. The experimental results agree well with the simulations. The measurement shows a relative bandwidth of 62.4% (455 MHz - 868 MHz) under the criterion of VSWR <; 1.15. Particularly, the VSWR is less than 1.13 within the range of 470 MHz - 862 MHz, (i.e. the full band of the DTV transmitting system). And the proposed antenna maintains a stable gain larger than 11.6 dBi over the operating frequency band with the half-power beam width of $70^{\circ } \pm ~3^{\circ }$ in the horizontal plane, which meets the requirements of the full-band signal transmission in the DTV broadcasting system.

Flexible Wideband Microstrip-Slotline-Microstrip Power Divider and its Application to Antenna Array

In the satellite microwave power transmission (MPT) system, antenna arrays are usually adopted for a higher gain. For the passive wideband antenna array, wideband power dividers are essential when the feed network is constructed. Because the microstrip-slotline coupled power divider could achieve wide bandwidth and compact size at the same time, it becomes a potential candidate for the feed network. However, impedance matching is always needed in the slotline, e.g., the fixed slotline length or the stepped impedance transformation. So, the power divider is not flexible. In this paper, a flexible Microstrip-Slotline-Microstrip (MSM) power divider is presented. When the ratio of the coupling coefficients $n_{1}$ of the microstrip-to-slotline transition (MST) and $n_{2}$ of the slotline-to-microstrip transitions (SMT) is 2, the MST and SMTs could be self-matched respectively. Then no impedance matching is needed anymore in the slotline. Thus, the slotline length can be arbitrarily chosen, and no stepped impedance transformations are needed. This power divider eliminates the drawback limiting the free wire routing for the microstrip-slotline coupled feed network. It could serve as a new kind of feed network, especially be considered when the simple T-junction feed network cannot achieve enough bandwidth. Besides, a wideband Vivaldi array with this feed network is presented.

A Broadband Millimeter-Wave Waveguide Power Divider with High Isolation

In this paper, an <i>E</i>-plane stepped-impedance transformer and Y-junction bifurcation are used to form a waveguide power divider with ceramic substrate loaded with thin film resistors. This structure is realized high isolation in </i>V</i>-band by inserting a ceramic substrate at the <i>H</i>-plane center of the Y-junction waveguide bifurcation, both sides of which loaded with thin film resistors. The waveguide power divider was fabricated with aluminium-50% silicon, and has characteristics of light weight, lower coefficient of thermal expansion, good thermal conductivity, and its properties are more compatible with those of ceramic substrate. The principle and design procedure are described in detail. A </i>V</i>-band E-plane waveguide power divider is designed, fabricated, and measured. The measured results show that insertion loss is less than 0.4dB in the frequency range of 50~60GHz, with typical isolation levels of 25dB between the two output ports and amplitude imbalance less than 0.19dB, phase imbalance less than 1.4°. The measured and simulated results show good amplitude, phase, and isolation characteristics validating the proposed power divider.

TE 20 mode substrate integrated waveguide based high gain eight‐beam leaky‐wave antenna for multi‐directional radiation coverage

In this article, a TE20 mode substrate integrated waveguide (SIW) is utilized to design a leaky-wave antenna (LWA) which is capable to scan all the four directions (eight quadrants) simultaneously. With the eight radiated main beams, frequency beam scanning range of the proposed antenna is 56° in all the eight quadrants. By exploiting co-axial probe feeding and step impedance transformer, four ways microstrip power divider is designed which is further exploited to feed all the four TE20 mode SIW sections containing microstrip-coupled slotline-SIW transitions. For radiation, ±45° rectangular slots are systematically placed on the top as well as bottom plane of the structure. The proposed antenna is working within the frequency range of 10-11.7 GHz having the maximum peak gain of 14 dBi. The proposed design is verified by experimental results which are in good agreement with the simulation. Along with the utilization of higher order mode of SIW to achieve compactness and design simplicity, the four directional frequency beam scanning capability makes it a promising candidate in various microwave circuits and several beam-scanning applications including navigational and surveillance purpose.

High-Gain Normal-Mode Omnidirectional Circularly Polarized Antenna

This letter presents a high-gain normal-mode omnidirectional circularly polarized (CP) antenna with a simple feed structure for the WLAN application. The proposed omnidirectional CP antenna is based on a coaxial line. Helix-shaped slot etched on an outer conductor is used to excite the CP wave. Besides, the rectangular slots cut on an outer conductor are introduced to improve the axial ratio (AR). By adjusting the dimensions of the rectangular slots, the required circular polarization is obtained over the operating band. Additionally, the stepped impedance transformer structure and a core-shaped inner conductor are employed to achieve a good impedance matching. Finally, the measured impedance bandwidth with VSWR < 2 covers the required frequency band. In the azimuth plane at 2.4 GHz band, the average measured left-handed CP gain and the AR of an antenna are 10.4 and 2.5 dBic, respectively. Thus, the proposed antenna acquires a good CP omnidirectional performance without a complex feeding network, while keeping the stable radiation patterns for the WLAN application.

Compact Inkjet-Printed Flexible MIMO Antenna for UWB Applications

In this paper, a miniaturized fully inkjet-printed flexible multiple-input-multiple-output (MIMO) antenna for ultrawideband (UWB) application is proposed, occupying a compact size of $22\times 31\times 0.125$ mm3. In the proposed antenna, two half-planar radiators are introduced to minimize the antenna size. Moreover, a modified T-shaped stub is employed on the ground plane to improve the impedance performance. In addition, a slot is etched on this modified T-shaped ground stub to further enhance the isolation. By doing so, the proposed antenna can operate from 2.9 to more than 12 GHz with the mutual coupling less than −15 dB. Furthermore, to address the out-of-band characteristic drawback that existed in most of the previous UWB antenna, a parallel coupled band-pass filter with stepped impedance transformation and defected ground structure is incorporated in the feedline of the antenna to achieve sharp rejection at the edges of the UWB band. The measurements indicate that the proposed filter-antenna can cover from 3.43 to 10.1 GHz, with the envelope correlation coefficient below 0.3 and the channel capacity loss below 0.4 bit/s/Hz, which ensures its good MIMO performance.

Wideband Full-Corporate-Feed Waveguide Continuous Transverse Stub Antenna Array

A Ka-band waveguide continuous transverse stub antenna array with full-corporate-feed network is presented in this paper. Multiple-section stepped-impedance transformers are used for wideband impedance matching of the radiation slots. The required high-quality quasi-TEM wave excitation is generated by a wideband plane-wave generator (WPWG). Compared with the conventional pillbox structure, the WPWG produces a quasi-TEM wave with more uniform amplitude distribution. By using the combination of these design features, significant increases both in bandwidth and antenna aperture efficiency are achieved. For demonstration, a prototype is designed, fabricated, and measured. Excellent agreement is achieved between simulations and measurements. The antenna is matched over the entire Ka-band of 26–40 GHz. A high antenna aperture efficiency of over 75% and a low cross-polarization of less than −46 dB are achieved over the entire bandwidth. The demonstrated features of wideband, high aperture efficiency, and low cross-polarization have great potentials for millimeter-wave applications.

Tunable In-Phase Power Divider for 5G Cellular Networks

A tunable power divider that operates in the 28-GHz band for future 5G mobile systems is presented. The proposed power divider can be used in the feeding network of the antenna array of a cellular network for a beamforming purpose. The proposed design is a modification of the traditional Wilkinson power divider and has the ability to change the output power division ratio continuously. To realize that, two varactor-loaded L-shaped open-ended stubs are connected to the two branch lines of the device to ensure the flatness of the power division. Moreover, two asymmetrical coupled lines are adopted in the output ports and a stepped-impedance transformer is added at the input port to enhance their matching across different power divisions and wide frequency range. A prototype is developed and tested. A tuning power ratio range from 1:1 to 1:2.3 across the band (27–29 GHz) is achieved. The return losses are more than 13 dB, while the isolation is more than 10 dB across that band. In addition, the simulated and measured amplitude and phase imbalances are less than 0.2 and 0.5 dB, and 5° and 12°, respectively, from the ideal values.

A Cryogenic Waveguide Mount for Microstrip Circuit and Material Characterization

A waveguide split-block fixture used in the characterization of thin-film superconducting planar circuitry at millimeter wavelengths is described in detail. The test fixture is realized from a pair of mode converters, which transition from rectangular-waveguide to on-chip microstrip-line signal propagation via a stepped ridge-guide impedance transformer. The observed performance of the W-band package at 4.2K has a maximum in-band transmission ripple of 2dB between 1.53 and 1.89 times the waveguide cutoff frequency. This metrology approach enables the characterization of superconducting microstrip test structures as a function temperature and frequency. The limitations of the method are discussed and representative data for superconducting Nb and NbTiN thin film microstrip resonators on single-crystal Si dielectric substrates are presented.

Wideband turnstile junction coaxial waveguide orthomode transducer

A wideband turnstile junction coaxial waveguide orthomode transducer (OMT) is presented in this paper, featuring coaxial waveguide input and orthogonal rectangular waveguide outputs. It primarily comprises of a turnstile junction, bending stepped impedance transformers and power combiners. The symmetrical geometry helps achieve wide operating bandwidth and balanced output phases. The OMT covers the whole Ku band from 12 to 18 GHz, which aims at wideband dual-polarized signal combination and separation within coaxial-type multi-band antenna systems. An experimental prototype is manufactured and the measured results confirm that the reflection coefficient is lower than −15 dB within the whole band, and the port isolation is better than 35 dB. Turnstile junction coaxial waveguide OMTs can be adopted widely in circular/coaxial waveguide hybrid feeding networks for multi-band satellite communication/remote sensing antenna systems.