This paper presents the performance study of a 248 GHz voltage-controlled hetero-integrated signal source using indium phosphide (InP)-on-bipolar complementary metal-oxide-semiconductor (BiCMOS) technology. The source consists of a voltage controlled oscillator (VCO) in 0.25 µm BiCMOS technology and a frequency multiplier in 0.8 µm transferred-substrate InP-heterojunction bipolar transistor technology, which is integrated on top of the BiCMOS monolithic microwave integrated circuit in a wafer-level based benzocyclobutene bonding process. The vertical transitions from BiCMOS to InP in this process exhibit broadband properties with insertion losses below 0.5 dB up to 325 GHz. The VCO operates at 82.7 GHz with an output power of 6 dBm and the combined circuit delivers −9 dBm at 248 GHz with 1.22% tuning range. The phase noise of the combined circuit is −85 dBc/Hz at 1 MHz offset. The measured output return loss of the hetero-integrated source is >10 dB within a broad frequency range. This result shows the potential of the hetero integrated process for THz frequencies.

This paper presents a new artificial neural network (ANN)-based radar data processing approach for the detection of breast cancers located inside fibro-glandular tissues. The aim is not the breast imaging but detecting tumors through ANN processing of data extracted from the radar signals measured around the breast. The proposed approach has been assessed using several realistic two-dimensional breast geometries derived from the models provided by the numerical breast phantom repository of the University of Wisconsin Cross-Disciplinary Electromagnetic Laboratory (UWCEM). The pulsed radar system was assumed to operate in the mono-static configuration. The obtained results showed the abilities of the proposed approach to detect, for any single radar trace, tumors located inside the fibro-glandular tissues with a sensitivity of 93%, a specificity of 90%, and an overall accuracy of 92%.

In this paper, an antenna-to-antenna method to design high-efficiency polarization converters was proposed. Two in-linked split ring resonators (SRRs) were used as the fundamental unit cell, which can effectively make the original linear polarization angle deflected into a customized one (include but not limited to 90°). The same as the process of energy reception and transmitting of microstrip symmetric dipole antennas, the top SRR plays the role of a receiving antenna and the bottom one acts as a transmitting antenna. Under normal illumination, the strong coupling between electric resonance and magnetic resonance can result in high transmission and broad bandwidth. Since the two SRRs act as two independently polarization selective components, the polarization angle of transmitted waves can be easily controlled by rotating the transmitting SRRs around the center. The proposed concept and the design method are validated using numerical simulations, as well as experimental results of three examples for 45, 60 and 90° polarization angle rotation, the polarization conversion ratio of which is about 92.2, 88.9 and 91.9% from 7.5 to 10 GHz.

Normally, the reported gain of the microstrip patch antenna is within 8 dBi. Using properly located three shorting pins on three bisectors, the present work reports a method to convert the non-radiating TM11 mode of equilateral triangular patch antennas (ETPAs) to a deformed TM11 radiating mode. The boresight gain of ETPA operating in TM11 mode is enhanced from −10.75 to 12.1 dBi at 5.43 GHz. The boresight measured gain is further enhanced to 14.2 dBi at 5.52 GHz by using a triangular surface-mounted short horn (SMSH) of about ${{\lambda }}/5$ height. The aperture efficiency of the ETPA with the shorting pins is 84.2%. The aperture efficiency is further improved to 94.2% using the SMSH. The measured boresight cross-polarization and side-lobe level are −40 and −29 dB, respectively. The nature of the electricfield and surface current distribution is analyzed, using both the characteristic mode analysis method and high-frequency structure simulator, to understand the role of shorting pin and coaxial feed in converting the non-radiating TM11 mode to the radiating mode. A systematic design process also is presented for a fast design of shorting pin-loaded ETPA on the suitable substrate at a specified frequency.

Six four-element balun topologies are introduced that enable complex impedance matching in addition to common-mode rejection. Design equations for these topologies are presented. Three of these networks are universal, while the other three are capable of performing only specific impedance transformations. Examples of these networks were designed and fabricated along with a traditional lattice balun network for an operating frequency of 300 MHz. These networks were verified through extensive electromagnetic simulations and by measuring the fabricated networks. The fabricated novel network examples were able to achieve common-mode rejection ratios above 20 dB, power wave reflection coefficients below −20 dB, and insertion losses of approximately 0.1 dB; these results were similar to or better than the performance of the fabricated traditional lattice balun. The design example networks also provided power matching and low insertion loss over a greater bandwidth compared to the fabricated traditional network. These networks will allow for the footprints of lumped-element balun circuitry to be reduced, which is particularly useful in integrated circuit design. These topologies are also expected to further increase radio-frequency (RF) circuit design flexibility by offering more alternative realizations.

This paper details the design and development of a planar switched beam network using 4 × 4 Butler matrix (BM) over a thin and flexible type biocompatible substrate. Four mils thick liquid crystal polymer (LCP) is used as a substrate here (ϵr = 2.92, tanδ = 0.002). The proposed design is centered at 28 GHz, targeting commercial millimeter-wave applications. Floral-shaped antenna with defective ground structures has been implemented as basic radiating elements. The whole structure is based on microstrip line configuration. The architecture occupies an area of 23.85 × 19.20 mm2 over the LCP substrate. Individual components of the BM are detailed here, followed by a system analysis of the whole integrated structure. The present work also covers the electrical equivalent circuit modeling of the whole beam-forming network. The fabricated prototype offers better than 18 dB return losses at each input port for the desired frequency band with 6 dBi (max.) peak gain and 500 MHz bandwidth around the center frequency. Port-to-port isolation of better than 15 dB is achieved with this topology. Experimental and simulated results are in good agreement in all aspects. A comparative study is also chalked out to highlight the significance of the current research work with respect to alike earlier reported structures.

In this paper, a new method based on a genetic algorithm and Minkowski Island fractal is proposed for multiband antennas. Three-antenna configurations are chosen to validate the proposed optimization procedure. The first configuration is a wide-band antenna, operating in the WLAN (wireless local area network) UNII-2C band. The second configuration is a dual-band antenna, operating in the WLAN UNII-2 and UNII-2C bands. In contrast, the third is a tri-band antenna operating in the UNII-2, UNII-2C, and UNII-3 bands. The optimization process is accelerated by using the Computer Simulation Technology (CST) Application Programming Interface which allows all genetic operators to be performed in MATLAB while the numerical calculations are running in the internal CST Finite-Difference Time-Domain -solver using parallel computing with GPU acceleration. All three designed configurations are manufactured using a $\textstyle0.8\;\text{mm}$ thick FR4 epoxy substrate with a relative dielectric constant of $4.8$. The return loss and the radiation pattern’s measurements agree well with the simulation results. Further, the methodology presented can be very effective in terms of size reduction; the designed antennas are $24 \times 24 \times 0.8\;{\textrm{m}}{{\textrm{m}}^3}$ ($460\;{\textrm{m}}{{\textrm{m}}^3}$).

A novel reconfigurable circular microstrip G-slotted antenna having a circularly defected ground structure (DGS) capable of switching its resonance frequency for several microwave applications is presented in this paper. Reconfigurability of the proposed G-slot antenna is obtained by incorporating three PIN diodes. One diode is embedded in the patch and two diodes are integrated into the DGS structure at appropriate places in the slot to achieve four different wireless applications such as aeronautical radio navigation (4.3 GHz with gain 3.6 dB), satellite communication (3.78 GHz with gain 3.7 dB), mobile communication (4.55 GHz with gain 4.0 dB), and WiMAX (3.35 GHz with gain 3.3 dB). These four bands are achieved depending on the different biasing conditions of the three PIN switches used. Antenna performance has been analyzed in ANSYS Electronics Desktop 2018.2 software. The equivalent circuit component of the switching element (PIN diode) has been considered and designed during the simulation. The creative structure lies in the way that it exhibits higher gain with compact size than the previously reported similar antenna. A prototype of the proposed patch antenna has been fabricated on a Roger substrate and its testing and measurement have been performed to demonstrate its desirable characteristics and features.

This work presents a study where a sinusoidal corrugated antipodal Vivaldi antenna (SC-AVA) operating in the ultra-wideband (UWB) region is employed as a transducer for microwave imaging (MWI) of a cancerous breast. The functionality of the antenna within the UWB range is confirmed based on performance parameters like return loss, gain, radiation pattern, fidelity factor, and group delay. E-field distribution, H-field distribution, and near field directivity simulations in the presence of the breast phantom have also been carried out and reported. The practical application of the developed antenna for biomedical imaging is evaluated by measuring the specific absorption rate (SAR) readings at multiple frequencies within its operating range. The SAR readings are obtained from an electromagnetic simulator by modelling a realistic heterogeneous breast phantom with multiple embedded tumors, and placing them in close proximity to the transducer. The modelled SC-AVA is further utilized for imaging multiple tumors hidden inside the gland layer of the heterogeneous breast phantom developed in-house. The fabricated breast phantom is scanned using the in-house developed multistatic MWI setup. Based on the data obtained from the scanning setup the images are reconstructed using both the delay multiply and sum (DMAS) and iterative DMAS imaging algorithms. Furthermore, a comparison of the reconstructed images is done to check in which case the obtained images are closer to the fabricated breast phantom.

A novel wideband reflectarray antenna (RA) is designed for 5G millimeter (mm) wave communications in the frequency range of 26.5–36 GHz. The proposed unit cell is constructed using a grid periodicity of 0.52${{\lambda }_0}{ }$ that offers 636° phase change through phase delay lines (PDLs) (${{\theta }_{\text{s}}}$). These PDLs are attached to the outer end of the unit cell comprising semi-circular rings. Bandwidth enhancement is achieved by incorporating a corrugated slot technique and a suitable air gap beneath the substrate. The proposed center-fed reflectarray is composed of 513 elements distributed in a circular aperture (13.46${{\lambda }_0}$). Using mirror-symmetrical distribution of the unit cells, a cross-polarization reduction as low as −50 dB is realized. At 30 GHz, RA has a measured peak gain of 28.2 dBi, a sidelobe level of −14.3 dB, and an aperture efficiency of 31.4%. The prototype antenna is fabricated, and the simulation results are experimentally validated. The measured 1-dB and 3-dB gain bandwidths of the proposed reflectarray antenna are 31.3% and 41.6%, respectively. The proposed broadband reflectarray can be a potential choice for inter-satellite services like inter-satellite networking/satellite positioning and control; fixed satellite services such as GPS satellite synchronization and data direct to home TV; and satellite position fixing.

By combining the technique of energy selective surface and frequency selective rasorber, an energy selective rasorber is proposed, which performs selective energy protection in the low communication frequency band (0.8–2 GHz) and wave-absorbing property in the high-frequency band (6–18 GHz). The design consists of two layers, of which the bottom one contains a lumped diode structure for energy selection function in the transmission band, while together with the top layer, they perform a wideband wave absorbing function. The simulated and measured results agree well with each other, and both show good absorption in 6–18 GHz and energy-selective property around 1.86 GHz. That is, when the incident power changes from −30 to 14 dBm, the reflection coefficient changes from below −22 dB to above −2 dB, while the transmission coefficient changes from above −3 dB to below −17 dB.

This research article proposes a dual-sense dual-port wideband circularly polarized (CP) multi-input multi-output (MIMO) antenna designed for Wi-Fi 6E applications. The main novelty lies in achieving CP for both ports using a truncated rectangular-shaped aperture. By incorporating design and spatial diversity and defective ground structure between the two radiators, the design improves isolation and enables the antenna to generate Left-Hand Circular Polarization (LHCP)depending on the selected feed port. The proposed MIMO rectangular dielectric resonator antenna demonstrates an impressive impedance-matching bandwidth (IBW)from 5.5 to 8.0 GHz (37.10%) as well as an axial ratio bandwidth (ARBW) covering from 6.0 to 6.55 GHz (12.20%). Additionally, the dual-port wideband CP MIMO antenna exhibits satisfactory diversity performance parameters. To validate the simulated results, a physical prototype is fabricated and subjected to experimental testing. The measured outcomes of the fabricated model align closely with the simulated results, confirming the accuracy of the design. With both MIMO and CP capabilities and improved isolation, this proposed model proves beneficial in reducing latency and minimizing the impact of multipath fading. Therefore, it stands as an excellent choice for future devices utilizing the Wi-Fi 6E band due to its broad IBW and overlappingAR.

This paper proposes a lightweight frequency selective surface polarization-insensitive wideband metamaterial absorber in C band and X band that employs only a few resistive elements. The proposed absorber is embodied with four quadrature slotted inner circular patch, which is horizontally and vertically bisected, and outer concentric copper rings of 0.035 mm thickness are attached with four lumped resistors placed at 90° apart. A slotted inner circular patch provides significant inductive and capacitive loading. The absorption bandwidth of 8.02 GHz with more than 90% absorption is observed from 5.69 to 13.71 GHz under normal incidence and maintains almost same absorptivity range under oblique incidence up to 45° in both transverse electric mode and transverse magnetic mode. The designed metamaterial absorber is fabricated and measured using free space measurement technique. The actual experiments and the simulated ones are in good agreement.

Frequency-modulated continuous-wave radar systems profit from increasing the absolute bandwidths of the generated frequency chirps to improve range resolution. As the relative bandwidth of SiGe-voltage-controlled oscillators (VCOs) is limited to about 80%, increasing the center frequency fundamentally or via frequency multiplication is the most direct way to increase that absolute bandwidth. However, as some applications require penetration depth, which dramatically decreases with frequency, other solutions are necessary. Therefore, state-of-the-art concepts rely on the down-conversion of generated frequency chirps via two separately stabilized frequency sources. This article implements a novel architecture, offering relative bandwidths of >100% within a single phase-locked loop (PLL). Therefore, two VCOs at different center frequencies are fed into a down-conversion mixer, whose output is directly stabilized via that PLL with one loop filter generating both tuning voltages. Those circuit blocks can be summarized as one equivalent VCO, offering a higher relative bandwidth and a significantly more linear tuning curve. Thereby, a solution to limited relative bandwidths with high VCO gain variation of single VCO synthesizers is offered while substantially reducing the hardware and implementation effort compared to the state-of-the-art.

Multiplexer design is a challenging task due to the high number of variables involved, raising the difficulty as the numbers of filters increase. Numerical computing tools provide a suitable environment to evaluate topologies and technologies before starting the long journey to the device. A direct scattering matrix solution for a star-junction multiplexer, based on the circuit theory, is presented in this work. The resulting star-junction matrix is introduced in a matrix system with the scattering matrix of each filter to evaluate the overall multiplexer response. This approach allows the acquisition of main multiplexer parameters like transmission, reflection, and cross-isolation response in a compact way, achieving a good starting point for the further full-wave optimization procedure. Furthermore, an approach for the design of a star-junction multiplexer is tackled based on the reflection coefficient phase. A triplexer under this interpretation is presented and evaluated using lumped elements.

Main aim behind this study is to utilize 3D printing technique for designing and fabrication of a flexible wideband Vivaldi antenna for the upcoming 5 G systems. Frequency bands starting from 24 up to 65 GHz are receiving particular attention as they have potential for both high data rate communications and high-resolution radar applications. A Vivaldi antenna is used for its very wideband properties and planar design. The radiating structure covers a bandwidth of 25–65 GHz for a match better than −10 dB and demonstrates reasonably high gain and efficiency performance. The simulated radiation efficiency of the antenna remains above 90% for the entire bandwidth. Hence, the main advantage of this approach is that wideband or switched transceivers for future 5 G communications can be integrated using this concept without the need of complex matching networks.

This paper presents design of quintuple-mode wideband bandpass filters, implemented with off-centered perturbed metallic cylinders in a rectangular waveguide cavity. Three perturbation cylinders are placed at the bottom of the rectangular waveguide cavity, along with a pair of perpendicularly fed coaxial lines; excite five quasi-transverse magnetic modes to realize the desired passband. The height of the waveguide cavity and the shape of the perturbation cylinders are exploited to shift the resonant modes far away from the passband and achieve a good out-of-band rejection and sharp skirt selectivity. The filter operates at the center frequency of 2.68 GHz with a wide fractional bandwidth of 43%. The proposed filter is fabricated with aluminum. The measured and simulated results are in good agreement with each other.

A novel dual-band planar antenna with a low profile for mobile communication system is proposed in this paper. The antenna is composed of one shorted patch with two radiating notches for low frequency resonance and one square patch for high frequency resonance. The low profile is achieved via the shorting patch, which introduces the parallel electrical field between the reflector and antenna. A step-impedance microstrip line is used to feed the antenna. The coupling between the square patch and microstrip line cancels out the inductance of shorting probe, which increases the working bandwidth of proposed antenna. A prototype with a low profile of 0.0286λ is fabricated and measured. The antenna achieves dual impedance bandwidths of 1.6% for the low frequency band and 60% for the high frequency band, covering the frequency range 851–865 MHz and 1.97–3.65 GHz, respectively. The measured results show good agreements with the simulated ones.

This paper presents a miniaturized tri- and quad-band power divider (PD)based on substrate integrated waveguide (SIW). By adopting different types of modified circular complementary split-ring resonators on the top surface of SIW, multiple passbands are generated propagating below the SIW cut-off frequency. The working principle is based on evanescent mode propagation that decreases the operating frequency of the PD and helps in the miniaturization of the proposed structure. The operating frequency of the proposed PD can be individually controlled by changing the dimensions of the resonator. To verify the proposed concept, a tri-band and a quad-band PD exhibiting 3 dB equal power division at 2.41/3.46/4.65 GHz and 2.42/3.78/4.74/5.8 GHz are designed using the full-wave simulator, validated through circuit model, fabricated and experimentally verified. The measured results agree well with the simulations. The proposed PDs have good performance in terms of reasonable insertion loss, isolation, minimum amplitude and phase imbalance, smaller footprint, easy fabrication and integration. The size of the fabricated prototype is 18.3 mm × 8.4 mm, which corresponds to 0.205λg × 0.094λg, λg being the guided wavelength at the first operating frequency.

In this paper, an algorithm for extracting and localizing a radar pulse in a noisy environment is described. The algorithm combines two powerful tools: wavelet denoising and the short-time Fourier transform (STFT) analysis with statistical-based threshold. We aim to detect radar pulses transmitted by any radar in blind mode regardless of the intra-pulse modulation and parametric features. The use of the proposed technique makes the detection and localization of radar pulses possible under very low signal-to-noise ratio conditions (−18 dB), which leads to a reduction of the required signal power or alternatively extends the detection range of radar systems. Radar classes pattern-based analysis is used in blind mode to decrease the probability of false alarm.