We report a self-biased, low-profile circulator operating in the Ka-band fabricated by an entirely low-temperature (70 °C) screen-printing approach on printed circuit board (PCB). The magnetic material for the circulator is a barium hexaferrite BaFe12O19 (BaM)/polydimethylsiloxane (PDMS) nanocomposite that exhibits a zero-bias ferromagnetic resonance frequency (fFMR) at 46.6 GHz. Using this material, a microstrip-based circulator operating at 35 GHz is designed, fabricated, and characterized. A combination of mechanical milling, screen printing, photolithography, and electroplating is used for fabricating the circulator, in which the circulator disk (diameter of 2 mm and thickness of 250 μm) is completely embedded in the PCB, realizing a packaging compatible low-profile architecture with the total device area of 33 mm². The measured isolation (IS) and insertion loss (IL) of the fabricated circulator at 35 GHz is 3.9 and 8.7 dB, respectively. When the additional magnetic bias is applied to the circulator using external permanent magnets, the IS and IL performance is improved to be 7.4 and 8.4 dB, respectively. The impact of the loss factors associated with dielectric loss and surface roughness on the device performance is analyzed using High Frequency Structural Simulator (HFSS).

High radiation-efficient $4\times 4 $ array antennas consisting of multiple nanolayered nonmagnetic copper (Cu) and ferromagnetic cobalt (Co), termed as Cu/Co metaconductor, are reported for 5G and millimeter-wave applications. The performance of a ten paired Cu/Co metaconductor-based array antenna, where the thickness of each metal layer is 150 and 25 nm, respectively, is compared with that of two reference antennas. The first reference antenna has the same total thickness but is made of sputtered solid copper and the second one made of five times thicker electroplated solid copper. Because of eddy current cancellation and skin effect reduction in metaconductor, the Cu/Co-based antenna shows lower RF resistance in both feeding lines and antenna patches than reference antennas in $K_{a}$ -band. Nearly 6 dB enhancement in the received signal power and the bandwidth (BW) improvement of 0.18 GHz is obtained for the Cu/Co-based antenna compared to the reference ones. Also shown is the possibility of more than 80% conductor weight reduction without losing antenna performance. Analysis for the enhancement in the antenna gain and BW is provided. Simulations performed in a high-frequency structural simulator are compared with the measured results. The total area of a fabricated $4 \times 4$ array antenna is 5.6 cm ² .

This work introduces a material and method for high-volume, low-temperature, screen printing of self-biased magnetic films made from a composite of M-type strontium ferrite SrFe ₁₂ O ₁₉ (SrM) particles and polydimethylsiloxane (PDMS). The magnetic particles are aligned under a dc magnetic field, while the PDMS is cured at 75 °C, making this fabrication process compatible with semiconductor and printed-circuit-board substrates. Aligned composites with estimated SrM particle volume percentages of 14 vol.%, 20 vol.%, and 27 vol.% are fabricated, as well as an unaligned 14 vol.% composite for comparison. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to examine the structure and composition of the composites. Furthermore, vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are performed to determine their dc and ac magnetic properties. Results show that the aligned composites have magnetic textures between 1.47 and 1.95, crystalline anisotropies between 1860 and 1960 kA/m, FMR frequencies of 45.5–45.9 GHz, and FMR linewidths between 3400 and 3500 Oe, indicating the potential for these materials in self-biased, non-reciprocal device applications. The analysis identifies that increased particle loading and better particle alignment may further improve these films by decreasing the linewidth.

Human beings are naturally mobile and crave freedom. But, for many years, we were leashed to our office desks/homes to make a long-distance phone call. Finally, in 1973, the first-ever cellular phone call was made by Motorola engineer Dr. Martin Cooper using a handmade prototype device that weighed almost 2.5 lb. As Greek philosopher Heraclitus said, “Change is the only constant,” and over the past 50 years, cellular phone technology has undergone a drastic makeover where we drifted from a 2.5-lb cellular phone to a 0.4-lb smartphone (an iPhone 13), from typewriters to digital systems like desktops and laptops, and from paper maps to GPS for navigation. Similarly, as shown in Figure 1, our journey in wireless mobile communications started with 1G with analog data transmission and a data rate at ∼2.4 Kb/s to a full-fledged and operating 4G at a maximum data rate of 1 Gb/s.

In this paper we report the demonstration of a multilayer 4X4 array antenna using Through Fused Silica Via (TFV) glass technology targeting 28 GHz as the operational frequency for 5G applications. Due to its low loss tangent, smooth surface and excellent Coefficient of Thermal Expansion (CTE) match with silicon, glass possesses several advantages compared to other substrate materials. 4X4 antenna array patches are fabricated on the top substrate and feed lines on the bottom substrate where both the substrates are separated with a ground plane in the middle. All the metal layers are deposited using an electroplating process after the seed layer deposition by sputtering. Two resonance frequency measurements are performed. In the first method, direct Cu to Cu bonding is implemented. In the second one, fully cross linked SU-8 polymer is used as bonding material between the glass substrates. Designs are simulated using High Frequency Structural Simulator (HFSS, ANSYS Inc.) and compared with the measured ones. The total area occupied by 4X4 patches on the top substrate and feed lines on the bottom substrate is 4.29 cm ² and 3.67 cm ² , respectively.

In this paper, we demonstrate a quintuple band λ/4 stub using a Bridged Composite Right Left Handed (B-CRLH) transmission line approach. The five bands are achieved using two B-CRLH unit cells. Design is carried out using the B-CRLH transmission line theory and two numerical simulation tools of Advanced Design Systems (ADS, Keysight Technologies, Inc.) and High Frequency Structural Simulator (HFSS, ANSYS Inc.). A prototype device is fabricated on a PCB substrate using milling machine. The demonstrated five stub frequencies are 0.6 GHz, 1.2 GHz, 2.4 GHz, 3.2 GHz and 6.19 GHz. The dimensions of fabricated unit cell-1 and unit cell-2 are 2.52 cm^2 and 0.25 cm^2, respectively.