Realizing packaged state-of-the-art performance of monolithic microwave integrated circuits (MMICs) operating at millimeter wavelengths presents significant challenges in terms of electrical interface circuitry and physical construction. For instance, even with the aid of modern electromagnetic simulation tools, modeling the interaction between the MMIC and its package embedding circuit can lack the necessary precision to achieve optimum device performance. Physical implementation also introduces inaccuracies and requires iterative interface component substitution that can produce variable results, is invasive and risks damaging the MMIC. This paper describes a novel method for in situ optimization of packaged millimeter-wave devices using a pulsed ultraviolet laser to remove pre-selected areas of interface circuit metallization. The method was successfully demonstrated through the optimization of a 183 GHz low noise amplifier destined for use on the MetOp-SG meteorological satellite series. An improvement in amplifier output return loss from an average of 12.9 dB to 22.7 dB was achieved across an operational frequency range of 175–191 GHz and the improved circuit reproduced. We believe that our in situ tuning technique can be applied more widely to planar millimeter-wave interface circuits that are critical in achieving optimum device performance.

Despite the great progress in data transmission systems using dielectric waveguides (DWGs) in the millimeter-wave (mm-wave) frequency band (30–300 GHz), the signal distortions caused by DWGs have not yet been fully understood. However, such investigations would help to optimize DWGs as a transmission channel in order to further increase data rate and transmission distance of such systems without the need for more complex transceivers. Therefore, this paper presents a detailed study of the expected signal distortions caused by frequency-dependent attenuation and frequency-dependent group delay of circular DWGs at mm-wave frequencies. Based on a low-complexity digital transmission system, the effects of DWGs on the signal-to-noise ratio and the intersymbol interference at the receiver are evaluated. The figures and equations given in this paper allow the reader to easily calculate the channel properties and signal distortions for a wide range of circular DWGs without the need of finite element method solver or other time-consuming numerical simulations. Finally, design recommendations are given to minimize signal distortions for transmitting signals along DWGs.

Sensors based on metamaterial absorbers are very promising when it comes to high sensitivity and quality factor, cost, and ease of fabrication. The absorbers could be used to sense physical parameters such as temperature, pressure, density as well as they could be used for determining electromagnetic properties of materials and their characterization. In this work, an attempt has been made to explore the various possible applications of these sensors. Metamaterial-based sensors are very popular for its diverse applications in areas such as biomedical, chemical industry, food quality testing, agriculture. Split-ring resonators with various shapes and topologies are the most frequently used structures where the sensing principle is based on electromagnetic interaction of the material under test with the resonator. Overcoming the design challenges using metamaterial sensors involving several constraints such as cost, compactness, reusability, ease in fabrication, and robustness is also addressed.

In this paper, an eight-shaped polarization-dependent electromagnetic bandgap (ES-PDEBG) structure is proposed. The unit cell of ES-PDEBG structure consists of an outer eight-shaped EBG patch with two inner square patches and three vias. Surface wave bandgap and reflection phase characteristics have been studied for the proposed structure. From the measurement results, two surface wave bandgaps with center frequencies 3.42 and 5.88 GHz are observed along the X-direction, and one surface wave bandgap with center frequency 3.69 GHz is observed along the Y-direction. The refection phase bandgap of the proposed structure is centered at 5.61 and 3.31 GHz for x- and y-polarized incident plane waves, respectively. Furthermore, the application of the proposed structure as polarization reflector is presented. The study demonstrates that the structure can act as dual-band in-polarization reflector for circularly polarized waves. In addition, incident linearly polarized waves are reflected as circularly polarized waves in four operating bands.

In this paper, an unconditionally stable time-domain method is proposed to investigate the external electromagnetic (EM) field illumination on the nonlinearly loaded transmission lines. In the proposed algorithm, the field to line coupling equations and linear/nonlinear boundary conditions are incorporated and expressed in a matrix form. The derived differential matrix equations are then discretized and solved using the proposed finite difference time domain (FDTD) method approach. The discretized nonlinear matrix equations are also solved by applying a globally convergent iterative method to ensure the stability of the method. Moreover, the experimental investigations are conducted using a transverse EM (TEM) cell for a single microstrip line and a power detector circuit as a nonlinearly loaded transmission line to confirm the accuracy and stability of the proposed method. With the merit of satisfactory accuracy and unconditional stability for the entire range of time steps, the presented approach would be applicable for analyzing the microwave linear/nonlinear circuits subjected to the external incident EM wave.

In this paper, a compact 4-port band-notched multi-input-multi-output (MIMO) antenna with asymmetric coplanar strip (ACS) feed is presented for ultra-wide band (UWB) applications. The MIMO antenna is comprised of four semi-elliptical radiators with ACS feed for UWB applications and it is printed on inexpensive FR4 substrate of size 48 × 52 mm2 with ɛr = 4.4 and 1.6 mm height. The impedance characteristics of the suggested MIMO antenna ranges from 2.7 to 11 GHz with a band-notched behavior from 3 to 4 GHz to reduce the interception with WiMAX applications, and the isolation level over the achieved band is more than 20 dB between any two adjacent elements. Moreover, the radiation pattern of the proposed UWB antenna is almost omnidirectional with an average realized gain of 3.5 dBi over the entire achieved frequency band. The proposed ACS-fed antenna is confirmed by fabricating and measuring it's impedance and radiation characteristics. Finally, good consistency between simulation and measured outcomes is obtained confirming the validity of the MIMO antenna for real-life UWB wireless systems.

A compact circularly polarized (CP) patch antenna is presented for modern communication systems. The prospective antenna consists of a microstrip-line inset-fed rectangular patch and a defected ground plane. A rotated rectangular slot and a modified electric-inductive-capacitive (m-ELC) resonator are introduced in the patch and the ground plane to achieve multiband behaviour. A corner of the radiating patch is truncated and an arrow-shaped stub is introduced for generating circular polarization. The physical area of the substrate is 0.26λ0 × 0.22λ0, and the radiator size is 0.16λ0 × 0.14λ0, where λ0 is the free-space wavelength estimated at the lowest frequency. The measured (S11≤-10 dB) bandwidths of the antenna are 80 MHz (3.58%) at 2.23 GHz, 75 MHz (2.64%) at 2.84 GHz, 80 MHz (2.50%) at 3.19 GHz, and 70 MHz (1.82%) at 3.83 GHz. The measured 3-dB axial ratio bandwidths are 40 MHz (1.41%), 100 MHz (3.12%), and 60 MHz (1.57%) at 2.84, 3.20 and 3.82 GHz, respectively. The proposed planar antenna design does not need dual-feed or multi-layered patches for achieving multiple CP bands. It offers easy integration with the printed circuits of the communication systems.

This paper presents a 60 GHz connected slots linear-phased array feeding a high-gain semi-symmetric lens antenna. This design provides high gain, broadband, and beam-steering capabilities for gigabit rate access and backhaul communications. The connected slots antenna array (CSAA) is excited at 16× equidistant points which not only yields spatial power combining but also allows the progressive phase changes to steer the beam in ±45° in azimuth plane. To characterize the CSAA-fed lens antenna, four different power splitters are fabricated which steer the main beam in 0, 15, 30, and 45°. The lens is designed in a way to overcome the scan loss and get comparatively higher gain when beam is steered away from the broadside. The measured results show 25.4 dBi maximum gain with 3 dB gain bandwidth covering the full band 57–66 GHz whereas 3 dB beam-steering range is ±45° for all frequencies. Besides, the half power beamwidth is 6 and 10° in elevation (E-plane) and azimuth plane (H-plane), respectively.

In this paper, a semi-flexible 2 × 1 array antenna is proposed with epoxy glass fiber and graphene as patch and ground, respectively. Microstrip patch antenna with a center parasitic patch of half-wavelength and slot in the radiating patch have been incorporated for the bandwidth enhancement in order of 79.56% (2.21–5.13 GHz). The antenna has an overall size of 0.30λ × 0.24λ at a lower frequency of operation (2.45 GHz). The incorporation of slotted Graphene in radiating element leads to a wideband regime with satisfactory gain values of 2.73 and 3.744 dBi at 2.40 and 4.0 GHz, respectively. Antenna radiation efficiency in the range of 78% with linear polarization makes the antenna appropriate for WLAN band and smart wireless devices application.

In this article, we present two efficient closed-form models to examine thoroughly the dependence of resonant frequency, quality factor, probe reactance, input impedance, bandwidth, and gain on parameters such as patch radius, probe location, substrate electrical parameters, and air gap of a coax probe-fed circular patch antenna. The implementation of these models is very easy and the computation cost is very low. The proposed models show excellent agreements with experimental and simulation results. We have also investigated experimentally the gain patterns of a suspended substrate circular patch antenna.

Designing miniaturized multiband antennas to cover both the 5G new radio frequencies (FR1 and FR2) simultaneously is a challenge for wireless communication researchers. This paper presents two antenna designs : a dual-band printed antenna of size 18 × 16 × 0.285 mm3 operating at FR1–5.8 GHz and FR2–28 GHz and a triple-band printed antenna with dimensions 30 × 25 × 0.543 mm3 operating at FR1–3.5 GHz and 5.8 GHz (sub-6 GHz microwave frequency bands) and FR2–28 GHz (mm-wave frequency band). The final projected triple-band antenna has a compact size with an impedance bandwidth of 12.71%, 11.32%, and 18.3% at 3.5 GHz, 5.8 GHz, and 28 GHz, respectively with the corresponding gain of 1.86 dB, 2.55 dB, and 4.41 dB. The measured radiation characteristics of the fabricated prototypes show that the proposed designs are suitable for trendy 5G-RFID and mobile Internet of things (IoT) applications.