dB Return Loss Research Articles

Investigations on Input Impedance and Radiation Pattern of a UWB Antenna for Microwave Imaging

Investigations carried out on the Input Impedance and Radiation Pattern of an Ultra-wideband (UWB) antenna are presented in this study. The proposed antenna is fabricated on an FR4 printed circuit board with a rectangular aperture. Major applications of UWB technology are presented. The fundamental characteristics of the antenna, such as input impedance, return loss, radiation pattern, and realized gain, are obtained. Investigations on how to improve the directivity of the proposed antenna are also presented in this study. The antenna demonstrates good impedance bandwidth (S11≤ -10dB) from about 4GHz to 10.6GHz, except in the case when the width _W_ of the T-shaped stub was varied. A commercial simulation tool – CST Microwave Studio – is used for the optimization of the proposed antenna. The proposed antenna operates almost over the entire UWB band (3.1-10.6GHz), except at lower frequencies of 3.1-4GHz. The response of the designed UWB signal starts at 3.1-10.6GHz, giving a good performance between 4GHz to 10.6GHz with an operational bandwidth of 6.6GHz. The input impedance is well matched, as a return loss of 10dB is obtained between 4-10.6GHz. The return loss decreases even more at 4-5GHz and at 8-10GHz, which means that the proposed UWB antenna transmits a high percentage of its power while a very low power is reflected back.

Wideband 4×4 Nolen Matrix with 360° Continuously Tuned Differential Phase and Low In-Band Phase Deviation Error

In the paper, a wideband tunable 4×4 Nolen matrix is proposed. By using the presented topology of the Nolen matrix, tunable output port phase differences can be realized by inserting one type of tunable phase shifters (T-PS). Besides, the in-band phase deviation error is minimized by adding compensation phase shifters (C-PSs) to the output ports of the Nolen matrix. Analytical design methods based on signal flow graphs and complex exponential signal are given to obtain the rigorous relationships of the coupling and phase shifts in the Nolen matrix. Besides, a detailed method for output ports phase slope compensation is provided. For validation, a prototype centered at 5.8 GHz is designed and fabricated. Measurement results agree well with the simulated ones. By using only one voltage to control the phase shifts of the T-PS in a 90° range for each input excitation of the Nolen matrix, a full 360° range of the progressive phase difference is realized by switching four input ports. The measured fractional bandwidth under 10 dB return loss and isolation is larger than 24.5% with the in−band±1.5 dB amplitude imbalance and ±15° phase deviation error for ports 1-4 excitations. Besides, for a more strict criterion of ±1 dB amplitude imbalance and 10° phase deviation error, the measured bandwidths are larger than 15% for all port excitations.

Enhancing long-range radar (LRR) automotive applications: Utilizing metasurface structures to improve the performance of K-band Longitudinal Slot Array Antennas

In this paper, we introduce a groundbreaking modification to a K-band substrate integrated waveguide (SIW) Longitudinal Slot Array Antenna for Vehicle-to-Everything (V2X) applications, particularly long-range radar (LRR) in the automotive industry. Our approach harnesses an elliptic metasurface capable of distinguishing between TE and TM modes in relation to radiation direction. By utilizing metasurfaces, we effectively address the issue of mutual coupling between antenna elements, which often results in subpar antenna performance. This modification focuses on improving various antenna characteristics, including frequency bandwidth (expanded by approximately four times), sidelobe level (reduced by 4 dB), aperture efficiency (increased to about 44%), and cross-polarization (reduced by an average of 10 dB). In essence, the results demonstrate that the increased number of longitudinal elements can be effectively enhanced by utilizing the metasurface structure, while maintaining an acceptable level of efficiency. As an illustrative case, we design a 1 × 32-element Longitudinal Slot Array Antenna using the Elliott method operating at 24.3 GHz, with the antenna size measuring 12.5 × 154 mm2. Experimental measurements validate our design, showcasing a 10 dB return loss bandwidth of 24.05–24.45 GHz, a maximum gain of 14.45 dBi, a sidelobe level of 24.5 dB, cross-polarization exceeding 30 dB, and an impressive aperture efficiency of 65%.

A Compact Bandpass Filter with Widely Tunable Frequency and Simple Bias Control

This research paper introduces an innovative design for a compact bandpass filter, notable for achieving a substantial tuning range of operational frequencies using just a single bias voltage. The design is based on a planar microstrip approach, distinguished by its straightforward and efficient structure. Additionally, this filter is characterized by its excellent performance in suppressing out-of-band frequencies. To validate the practicality and effectiveness of this novel design, a compact filter was designed, manufactured, and measured. The testing results were impressive, showing that the filter’s measured center frequency could be tuned across a wide spectrum, from 1.1 to 3.1 GHz, achieving a relative bandwidth of up to 95%. Herein, the relative bandwidth is derived from the calculation of 2(fhigh − flow)/(fhigh + flow). Remarkably, the filter consistently maintains a return loss exceeding 19 dB throughout its tuning range. Additionally, it sustains a 15 dB return loss bandwidth greater than 90 MHz, with the insertion loss varying between a minimum of 0.9 dB and a maximum of 2.1 dB. The compactness of the filter is one of its standout features, with circuit dimensions measuring a mere 0.06λg × 0.09λg (physical dimensions is 13.8 mm × 21.3 mm), where λg represents the wavelength at the filter’s lowest center frequency.

A compact high gain UWB planar monopole antenna using circular slots

In this manuscript, the design of a compact-size circular patch Ultra- Wideband (UWB) antenna with enhanced fractional bandwidth (BW), peak realized gain (PRG), and proper impedance matching is presented. The modified antenna has three circular slots etched from the circular path (top), fed by a 50? microstrip feed line. These circular slots play a significant role in improving the impedance bandwidth. Additionally, the partial ground plane with a slot integrated with a rectangular stub is used in order to achieve a bandwidth for an operating range of 3.25 GHz - 27 GHz. The proposed antenna is designed, fabricated, and tested in the laboratory in order to validate with simulation data. The designed antenna size is 25 mm ? 20 mm ? 0.508 mm. The experimental value of 10 dB return loss absolute/fractional BW of 23.75 GHz/157.08% at the center frequency, minimum/ maximum gain of 5.90/12.05 dBi, and maximum /minimum radiation efficiency of 85/97 % are achieved from the 3.25 GHz to 27 GHz frequency range. In addition, a comparison table is provided to prove the state-of-the-art of the antenna?s design. The proposed antenna is suitable for wireless services, radar, and satellite communication.

A 8–12 GHz power amplifier with high out-of-band rejection

This paper proposes an 8–12 GHz monolithic power amplifier (PA) with high out-of-band rejection. This PA adopts an impedance conversion technique to reduce the Q of the output impedance of the amplifiers for all stages, which is used to achieve broadband matching performance. In addition, the bandpass matching structures and a trap circuit are adopted to effectively suppress out-of-band signals. The proposed PA is fabricated by using a 0.5 μm GaAs pHEMT process. The measurement results show that the PA has an in-band small signal gain of 23 dB ± 0.7 dB, input and output return loss are both better than −14dB, the saturation output power is about 23dBm, the power-added efficiency (PAE) is better than 20 %, and rejection ratios are 65dBc and 51dBc at 3 GHz and 17 GHz respectively. The area is of 2.3mm × 1.1 mm.

An implantable ISM band antenna for biomedical application

Abstract This article presents a compact implantable antenna for biomedical use in the ISM band (2.4–2.48 GHz). The antenna is designed with Roger RT/duroid 6010.2LM high permittivity substrate of thickness 0.25 mm, and feed with a 50 Ω co-axial feed. A hybrid-loop resonator slot structure and C & I-shaped slots in the radiating patch has enabled the antenna to work in the ISM band. Via less ground makes this design simple, easier to fabricate, and a suitable candidate for implantable application. The proposed antenna occupies a small volume of 0.0984 λ 0 × 0.082 λ 0 × 0.00468 λ 0 and retained 152 MHz bandwidth (2.4077–2.5599 GHz with FBW 7.64 %) with a maximum gain of −22 dBi where λ 0 is guided wavelength. The projected antenna has good performance in the multi-layer tissue model, male human head voxel model, frequency-dependent skin model, and in muscle phantom by maintaining a minimum −20 dB return-loss in the ISM band. The proposed antenna’s Device Integration using a frequency-dependent skin phantom was performed and the results are well-suited for biomedical applications in the ISM band. The bare antenna was used to study the Specific Absorption Rate (SAR) in the human scalp. Where for 1 g and 10 g tissues the investigated results are 626.05 W/kg and 84.4 W/kg for an input power of 1 W, however the input power is limited to maximum 2.55 mW (for 1 g tissue) and 23.56 mW (for 10 g tissue) to comply with IEEE SAR guidelines. The qualities of the manufactured antenna are verified in a skin-imitating gel and animal tissue that exhibits good agreement with the simulation outcomes.

Research of the WIFI/WIMAX patch type antenna on varying embedded material’s dimensions

The microstrip patch antenna with the feeder gap is improved with nematic liquid crystal of type E7 embedded material, which has replaced the part of dielectric substrate. The investigation is focused on the impact of the geometrical parameters of the fragment of embedded material to the S parameters of the microstrip patch antenna. Authors presents initial simulation results to investigate how embedded material influences and changes typical antenna electrical characteristics. The computer-based modeling is performed with Ansys HFSS®. The embedded material has allowed to control the resonance frequencies and directivity and also to improve the gain of the antenna. The best case is obtained with –21.76 dB return loss at 2.4 GHz frequency when the length and width of the fragment of embedded material were equal to 1 mm and 20 mm respectfully. The designed antenna is characterized by good directivity when all energy is concentrated in main lobe.

A Compact Microwave Quadrature Hybrid Coupler Using Capacitive Composite Lines and Meandered Stubs

In this paper, a new structure of the quadrature hybrid coupler (QHC) with compact size is proposed using capacitive composite lines and meandered open stubs. The proposed coupler works at 1.6 GHz with a 0.4 GHz bandwidth, which shows 25% fractional bandwidth (FBW). The proposed QHC occupies only 15 mm × 15 mm (0.12 λ × 0.12 λ), while the typical QHC size is 32 mm × 32 mm (0.25 λ × 25 λ) at the same working frequency. In the designed structure, two symmetric meandered stubs and two symmetric π-shaped composite networks including capacitors and microstrip lines are applied together. The designed QHC has a small size and occupies only 22% of the area of the conventional QHC, resulting in a 78% size reduction. The designed prototype has been analyzed, fabricated and tested, and the experimental results verify the simulated and analysis results. The results show a better than 27 dB return loss, more than 28 dB isolation between the output ports and less than 0.4 dB insertion loss at the working frequency of 1600 MHz. With the achieved desirable specifications, the fabricated QHC is a suitable choice for wireless microwave applications.

Linear programming solve-predict for tunable couplers with coupling and phase differences

The demands for high flexibility in signal phase modulation, operating frequency, and amplitude modulation in contemporary wireless communication systems present challenges for reconfigurable devices. To address this issue, two tunable couplers have been designed, which consist of two parallel microstrips couplers with one-eighth wavelength and phase-shift networks composed of two varactors and coupling lines. Adjusting the even-odd mode impedances of one-eighth wavelength parallel coupled microstrip lines has been established as a means to control the coupling. The alteration of the capacitance of the varactors allows for manipulation of the phase differences in the couplers. Considering the disparities among simulation, manufacturing, and theoretical models, to get the capacitance combinations corresponding to the specific phase differences more quickly and accurately, the linear programming solve-predict method is introduced to this design. Finally, the errors between the predicted values and the theoretical values for the actual values are compared. The relative errors of the theoretical values are not less than 31.76 %, and the maximum errors of the predicted values are not more than 12.5 %, which shows the effectiveness of the method. For demonstration, two couplers operating at 2.4 GHz with different tuning ranges were designed and fabricated, work-1 with a tuning range of 45–135° and work-2 with a tuning range of 0–180° degrees. Based on the standard of 10 dB return loss and 1 dB unbalanced coupling, the relative bandwidths of work-1 and work-2 are not less than 42 % and 25 %. The relative bandwidths of phase differences effective modulation (±5°) are 20.1–42 % and 6–25%, respectively.

A Wideband Low-Profile Dual-Polarized Antenna Based on a Metasurface

A wideband, low-profile, dual-polarized antenna using a metasurface (MS) is proposed in this paper. This design consists of a pair of crossed dipoles, an MS, a metal cavity and two baluns. The proposed MS acts as an artificial magnetic conductor (AMC), which is designed for the ±90° reflection-phase bandwidth of 1.4–2.9 GHz. Compared with the 0.25λ0 profile of the traditional crossed dipoles, the profile is reduced to 0.15λ0 by using the in-phase reflection characteristics of the MS, which realizes the utilization of space. The measured results show that the antenna has a 10 dB return loss of 68.2% with isolation of more than 30 dB (1.45–2.95 GHz). The realized gain is 9 dBi with ±1 dBi variation, especially exceeding 10 dBi from 2.1 to 2.8 GHz.

Fused deposition modeling for 1 × 2 array of double ridge horn antenna

AbstractIn this letter, fused deposition modeling (FDM) was used to create a 1 × 2 array of the double ridge horn antenna (DRHA). The material used for FDM was acrylonitrile butadiene styrene. The DRHA was designed using an electromagnetic simulator and printed using FDM as well as the inner surface of the DRHA was painted with silver conducting paint. Two printed DRHA were connected together as a 1 × 2 array via a power divider. The main operating frequency of the array antenna was focussed on the range from 3 to 7 GHz. The 1 × 2 array DRHA is capable of better than −10 dB return loss, greater than 10 dBi gain, and a minimum half‐power bandwidth of 27.5°.

High gain compact wearable antenna for IoT applications

In this paper, the design of a Defected Ground Structure (DGS)-based microstrip patch antenna tailored for sub-6 GHz 5G applications is reported. The proposed patch antenna is crafted using Jeans textile material. By integrating DGS into the traditional patch antenna design, we achieve a significant reduction in size while simultaneously enhancing the antenna’s performance. The antenna features a rectangular patch shape and is powered through a 50-ohm microstrip feed line. Boasting a compact size of 35.6 × 42.6 × 1.6 mm³, the antenna’s performance is further improved by incorporating DGS and etching slots on the patch. The expertly designed antenna yields a 34.87 dB return loss and a gain of 10.9 dB at a frequency of 3.5 GHz. The fabricated antenna demonstrates a robust impedance bandwidth within the range of 3.41–3.606 GHz. Consequently, the proposed antenna is well-suited for applications in WiMAX and IoT technologies.

An S-band MMIC LNA in GaAs 0.15-μm pHEMT

The study adopts a monolithic microwave integrated circuit (MMIC) low-noise amplifier (LNA) applied in S-band was designed using ADS simulation software, GaAs 0.15-um pseudomorphic high electron mobility transistor (pHEMT) process. The LNA small signal gain is greater than 30.8 dB, gain flatness is ±0.45 dB, noise coefficient is less than 1.5 dB, input and output return loss is greater than 10 dB, and the chip area is 1.2*2.4 mm2. The low noise amplifier is composed of a two-stage cascade structure. Gain flatness, gain control, and bandwidth broadening are improved by RLC negative feedback network. The minimum noise coefficient circle and maximum gain circle are narrowed by adding negative feedback to achieve better noise coefficient and gain.

Three-Dimensional Printed mm-Wave Circularly Polarized Filtering Antenna With Flexible Design and Spurious Suppression

In this communication, a 3-D printed circularly polarized (CP) filtering antenna with spurious suppression for 5G mm-wave applications is presented. First, a composite resonator, serving as both the last-stage resonator of a waveguide filter and an aperture antenna, is utilized to realize a filtering linearly polarized (LP) antenna. The 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order electric cross-coupling topology is employed to generate two radiation nulls at both sides of the passband, enhancing the selectivity. Then, a polarizer is presented and placed in front of the LP antenna to obtain the CP radiation. The operating principles of the polarizer are analyzed in detail, which features flexible size and insensitivity to the original filtering response. To demonstrate the concept, three filtering CP antennas with different polarizer dimensions are designed, exhibiting similar responses. After that, to suppress spurious modes and extend the spurious-free region, the defected ground structures (DGSs) are introduced. Finally, all three CP antennas are fabricated using 3-D printing and tested. Measured results show that 10 dB return loss and 3 dB AR bandwidths for all antennas are about 7% and 9%, respectively.

Sickle-shaped high gain and low profile based four port MIMO antenna for 5G and aeronautical mobile communication

The construction of the four-port MIMO antenna in the form of a sickle is provided in the article. Initially, the single port element is designed and optimized. Next, a structure with two ports is created, and lastly, a design with four ports is completed. This process is repeated until the design is optimized. Three types of parametric analysis are considered, including variations in length, widths of sickle-shaped patches, and varying sizes of DGS. The frequency range of 2–8 GHz is used for structural investigation. The − 18.77 dB of return loss was observed at 3.825 GHz for a single-element structure. The optimized one-port structure provides a return loss of − 19.79 dB at 3.825 GHz. The port design offers a bandwidth of 0.71 GHz (3.515–4.225). The four-port design represents two bands that are observed at 3 GHz and 5.43 GHz. Both bands provide the return loss at respectively − 19.79 dB and − 20.53 dB with bandwidths of 1.375 GHz (2.14–3.515) and 0.25 GHz (5.335–5.585). The healthy isolation among both transmittance and reflectance response is achieved. The low-profile material was used to create the design that was presented. The article includes a comparison of the findings that were measured and those that were simulated. The four-port design that has been shown offers a total gain of 15.93 dB, a peak co-polar value of 5.46 dB, a minimum return loss of − 20.53 dB, a peak field distribution of 46.43 A/m and a maximum bandwidth of 1.375 GHz. The values for all diversity parameters like ECC are near zero, the Negative value of TARC, Near to zero MEG, DG is almost 10 dB, and a zero value of CCL is achieved. All diversity parameter performance is within the allowable range. The design is well suited for 5G and aeronautical mobile communication applications.

Broadband Dual-Polarized Magnetoelectric Dipole Antenna for In-Band Full-Duplex Application

A broadband dual-polarized magneto-electric (ME) dipole antenna is proposed for in-band full-duplex (IBFD) application. The exploited antenna comprises a cross ME dipole, two П-shaped and Г-shaped feedlines, and a ground with a box-shaped baffle. A wideband 180° power divider is connected to the П-shaped feedline and a coaxial line directly to the Г-shaped feedline to excite the cross ME dipole with dual-polarization. Meanwhile, the introduced baffle will stable the radiation pattern and improve the realized gains over a wideband frequency range. As a result, a broadband hybrid decoupling technique is adopted in this design, and the measured antenna prototype realizes an impedance bandwidth of 1.7 - 2.7 GHz (45.4%) for the 10 dB return loss, high isolation of better than 50 dB and the realized gains of more than 7 dBi. These characteristics make the proposed antenna a promising candidate for IBFD base station systems.

Synthesis of Wideband All-Frequency Absorptive Filtering Power Divider with High Selectivity and Flat Output Port Distributions

In this paper, a wideband absorptive filtering power divider (AFPD) which features the characteristics of high selectivity and flat output distributions is proposed. It is composed of one unequal width three-coupled line (TCL), two coupled lines (CLs), two stepped open-circuited stubs, two kinds of isolation resistors, and two types of absorptive branches. The design equations of the proposed AFPD are derived using an even-odd decomposition method, and parametric investigations are also performed. It is found that the passband bandwidth can be adjusted by the stepped open-circuited stub which generates two transmission zeros (TZs). By combining the TCL with the CLs, the passband bandwidth is effectively enlarged. In addition, two isolated resistors are utilized for achieving good isolation and output-port matching performance. Without affecting the passband responses, the input port absorptive feature within the whole frequency band can be obtained by loading the absorptive branches both on the input and output ports. For validation, an example operating at the center frequency of 2 GHz was modeled and tested. Results exhibit that the passband FBW reaches 72% under 1 dB criterion, which illustrates flat output port distributions. In addition, for 10 dB return loss, the input and output impedance matching bandwidths are 250% and 78%, respectively. The features of good filtering responses are demonstrated by realizing the rectangle coefficient of 1.24 and the out-of-band suppression of more than 20 dB.

Design of a compact wideband bi-directional pattern antenna for 5G applications

In this research, a wideband bi-directional pattern antenna implemented by a circular monopole encircled with an enforced-radiation circular ring incorporated with inversed L-shaped stub is designed to operate over the mid-band of 5G applications ranging from 2 to 6 GHz. It is contrived of a copper overlaid on FR4 substrate with relative permittivity of 4.3 and height of 1.6 mm. This proposed antenna is fed by a 50-ohm coplanar waveguide, which is printed on the same side of the radiated circular monopole. To further enrich the impedance matching, a pair of etched slots is added-on the ground plane near the fed line to reduce the return loss. In the study, the initial parameters are theoretically worked out, and then simulation is then performed by using an electromagnetic solutions tool to numerically discover the set of solution parameters. From the simulation results, this proposed antenna offers the |S11|&lt;–10 dB covered the operating frequency running from 1.79 to over 8 GHz with fractional bandwidth 126.90 % and 1.74 to 7.07 GHz with fractional bandwidth 101.04 % for the simulation excluded and included SMA, respectively. It provides a linear polarization with total efficiency better than 81.5 %. After that, an antenna prototype with compact dimensions of 45×45×0.6 mm3 was fabricated and testified to validate the simulation results. The measurement results provide a stability bi-directional pattern with peak gain of 5.54 dBi covering a 10 dB return loss bandwidth of 118.5 % (1.93–7.54 GHz). Simulated |S11|, 2D radiation pattern and gain are reasonably in good agreement with experimental results. Furthermore, this proposed antenna is compared with the current compact, wideband and 5G antenna to indicate its prospective for the interested bands

A Bandpass Filter Realized by Using Pixel Structure and Genetic Algorithm Optimization.

This paper presents a flexible method for designing a bandpass filter (BPF) using pixel structure and genetic algorithm (GA) optimization. The pixel structure is made up of a grid of metallic microstrip stubs, and the GA is utilized to determine the connections between these stubs. The pixel structure enables the construction of step impedance and shunt branches, which are used to design a traditional BPF. To enhance the design freedom, one side of the discrete grids is connected to the ground via metallic holes. For verification, a BPF was designed, simulated, and measured. The experimental results showed that the 10 dB return loss bandwidth ranges from 1.1 to 1.9 GHz and the insertion loss is approximately 2.5 dB. There is good agreement between the calculation, EM simulation, and measurement results. The proposed GA-based design method offers significant advantages in terms of one-time EM simulation, feasibility, and labor time savings, making it more convenient than the traditional design method.