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In this study, the Df (dissipation factor or loss tangent) and Dk (dielectric constant or permittivity) of the low-loss dielectric material from three different vendors are measured by the Fabry–Perot open resonator (FPOR) technique. Emphasis is placed on the sample preparation, data collection, and the comparison with the data sheet values provided from vendors. A coplanar waveguide with ground (CPWG) test vehicle with one of these raw dielectric materials (vendor 1) is designed (through Polar and simulation) and fabricated. The impedance of the test vehicle is measured by TDR (time-domain reflectometer), and the effective Dk of the test vehicle is calculated by the real cross-section of the metal line width, spacing, and thickness of the test vehicle and a closed-form equation. In parallel, the insertion loss and return loss are measured with the VNA (vector network analyzer) of the test vehicle. Finally, the measurement and simulation results are correlated. Some recommendations on the low-loss dielectric materials of the Dk and Df are also provided.

This paper briefly overviews and discusses the existing techniques using antennas for passive sensing, starting from the antenna operating principle and antenna structural design to different antenna-based sensing mechanisms. The effects of different electrical properties of the material used to design an antenna, such as conductivity, loss tangent, and resistivity, are discussed to illustrate the fundamental sensing mechanisms. Furthermore, the key parameters, such as operating frequency and antenna impedance, along with the factors affecting the sensing performance, are discussed. Overall, passive sensing using an antenna is mainly achieved by altering the reflected wave characteristics in terms of center frequency, return loss, phase, and received/reflected signal strength. The advantages and drawbacks of each technique are also discussed briefly. Given the increasing relevance, millimeter-wave antenna sensors and resonator sensors are also discussed with their applications and recent advancements. This paper primarily focuses on microstrip-based radiating structures and insights for further sensing performance improvement using passive antennas, which are outlined in this study. In addition, suggestions are made for the current scientific and technical challenges, and future directions are discussed.

The demand for broad-band antennas has been increased in the recent years. They find to be extensively used in high frequency and high speed data communication. The factors affecting the bandwidth of the microstrip antenna is discussed in this paper. There are two main parameter responsible for the broadening of the antenna. One is the height of the dielectric substrate and another one is the width of the patch.  In this paper, we study the performance characteristics of rectangular patch antenna with variable thickness of the substrate and width of the patch. One of the parameter is varied keeping the other fixed and the characteristic effects on resonant frequency, band width and gain are studied.

Switched filter banks find widespread application in frequency-hopping radar systems and communication networks with multiple operating frequencies, especially in situations demanding elevated filter element isolation. In this paper, the design and implementation of a highly isolated switchable narrow-bandpass filter bank architecture using hairpin microstrip topology is presented. The filter bank has four discrete bandpass filters with passbands of 2.0–2.2 GHz, 2.3–2.5 GHz, 3.1–3.3 GHz, and 3.9–4.1 GHz. These filters span the radar S-frequency band (2.0–4.0 GHz). In order to switch between channels with a switching speed of nanoseconds, low-loss and highly isolated SP4T switches are implemented. Advanced design system (ADS) software is used to design the various filter functionalities, and the entire system is tested on a vector network analyzer (VNA). The proposed architecture makes it much easier to put the filter bank into practice and switch it to the desired frequency, which is useful for radar receiver applications.

In this paper, two novel dual-band bandpass filters (BPFs) and a compact quad-channel diplexer working at 1.7/3.3 GHz and 1.9/3.6 GHz are proposed. In the proposed diplexer design, triangular loop resonators and rectangular loop resonators are used together to reduce the circuit size and improve diplexer performances. Insertion loss (IL) and return loss (RL) of the proposed diplexer are better than 0.8 dB and 21 dB, respectively, at these four operating frequencies. Output ports isolation parameter is better than 30 dB. With the achieved specifications, the proposed diplexer can be used in L and S band applications.

This paper aims to investigate and design a Yagi disc antenna with a variable number of director elements for Band 3 in fourth-generation long term evolution (4G LTE) mobile applications. The array technique was introduced by increasing the number of director elements to achieve superior results and better performance, such as higher gain and lower return loss. Initially, the simulated results of return loss and gain with one director element were -19.02 dB and 8.51 dBi, respectively. Then, by increasing the number of directors to three and five elements, the antenna’s performance improved significantly from -32.44 to -42.68 dB for return loss and from 8.51 to 11.17 dBi for gain, respectively. The simulated circular Yagi disc antenna provided a response in the range of 1.78 to 1.82 GHz. Therefore, a model was fabricated and tested to validate the antenna design. The measured results matched well with the simulated ones. By increasing the number of director elements, the measurement results of gain and return loss at a frequency of 1.8 GHz also showed improvement from 7.70 to 11.09 dBi and from -27.31 to -32.91 dB, respectively. Meanwhile, the measured antenna provided a wider bandwidth in the range of 1.72-1.82 GHz.

This paper presents a compact broadband 4 × 4 Butler matrix (BM) with high input return loss and without crossover components. The design employs four broadband 90‐degree hybrids, each achieving 49% fractional bandwidth at a center frequency of 3.5 GHz with input return loss greater than 30 dB. The complete BM has a 20 dB return loss bandwidth of about 37% from 3 to 4.4 GHz and an insertion loss of less than 0.5 dB at the center frequency. Such high input return loss and low insertion loss are highly desirable in base station applications. A prototype of this structure is fabricated, and the measurement results are compared with the simulations. The measurement results show that this BM can cover 5G bands of N77 (3.3–4.2 GHz) and N78 (3.3–3.8 GHz) as well as the LTE bands 42 (3.4–3.6 GHz) and LTE band 43 (3.6–3.8 GHz) with 0.5 dB insertion loss, ±9° phase variations, and stable beamforming across 3.0–4.4 GHz. These features make the design highly suitable for 5G base station applications. The final design of the proposed Butler matrix without crossover. (a) Butler schematic with the port numbers and (b) fabricated prototype of the proposed compact Butler matrix.

This study suggests a bail-shaped microstrip patch antenna designed for 5G applications. This antenna model operates in the 3.45 GHz wireless communication frequency range, which is a component of the so-called C-band (3.3 to 4.2 GHz), which is widely utilized for mid-band 5G deployments across the globe. Antenna size optimization is achieved at 31×28 mm2. On the patch, a slot is added to enhance the return loss features. The light gradient boosting machine (LightGBM) model for prediction acts as an objective function of the considered piranha foraging optimization algorithm (PFOA) to adjust the antenna's slot dimension, which will be used to optimize the slot width. In order to get a superior return loss value of around -39.90<-10 dB, the optimization approach that is provided seeks to achieve the ideal slot length. The proposed device exhibits remarkable radiation efficiency by partially grounding, with a peak gain of around 2.535 dBi at 3.45 GHz. A novel hybrid approach combines the LightGBM prediction model with the PFOA to fine-tune slot dimensions, achieving a superior return loss of -39.90 dB. The exclusivity of this effort is the incorporation of machine learning algorithms to attain significantly improved parameters.

The proposed antenna contains a rectangular patch with semicircular slots on four corners to it for achieving a broader bandwidth. The bending analysis is done for the proposed antenna to show the antenna performance irrespective of any bending angle. A broad bandwidth can be achieved by introducing semicircular slots for each of its four sides. The prescribed antenna is designed on polyimide substrate, which had a permittivity of 3.5 and loss tangent of 0.0027. The copper material thickness contains 0.035 mm. The proposed antenna contains an overall size of 15 x 13 x 0.2 mm3. The simulated results confirm that the proposed antenna possesses peak resonant frequency at 8.2 GHz and operates from 5.6 to 9.6 GHz with a bandwidth of 4 GHz. In addition to having a bandwidth of 4 GHz, the suggested design also had an S11 value of – 27 dB and a VSWR value of 1.09 at the resonance frequency. Up to a bending angle of 30 degrees, the proposed antenna is achieving same response with a minor difference. Additionally, the proposed antenna consists of a gain of 7.6 dBi, and it has a radiation efficiency of 96 %. Analysis of the field and current distributions is presented in this article to show the effectiveness of the proposed antenna.

This paper presents a novel broadband monopole antenna that was equipped with a bottom semicircle ground structure, a parasitic patch, a T-shaped slot, s transmission line, a parasitic strip, heart-shaped slices and a coplanar waveguide (CPW). The simulation results revealed that the proposed design had a relatively high return loss, a wide bandwidth and high efficiency. A prototype of the proposed antenna with an overall size of 0.94 λ0 × 0.94 λ0 × 0.02 λ0 (λ0 is the free-space wavelength) was fabricated and measured. The measurement results showed that the prototype had a bandwidth of 4.02 GHz (4.69–8.71 GHz) and a relative bandwidth of 60%. Besides, the maximum gain was 3.31 dBi and the maximum efficiency was 91.1% in the range of 5 to 8.5 GHz. Furthermore, it was found that the prototype almost achieved omnidirectional radiation. Its operating frequency band covered those of industrial scientific medical (ISM) (5.725–5.850 GHz), the radio frequency identification (RFID) (5.8 GHz) and the wireless local area network (WLAN) (5.15–5.25 GHz and 5.725–5.825 GHz).