The rapid growth of the space industry and the increasing number of small spacecraft missions have underscored the critical need for robust, reliable antennas capable of surviving harsh space environments. For space applications, it is essential to use materials that can endure the extreme conditions of low Earth orbit (LEO), including temperature variations, atomic oxygen, and vacuum, while also possessing excellent electromagnetic properties. This work utilizes a spacegrade cyanate ester composite, known for its thermal stability, low outgassing, and mechanical robustness.This material's unique properties are essential for antennas intended to operate in space. Beam-scanning antennas are also particularly crucial for space applications, enabling adaptive coverage. This work presents an electromagnetic characterization of a cyanate ester composite, and its use to fabricate a novel C-band leaky-wave antenna, which integrates a grounded coplanar waveguide structure and unique feeding method. A silver ink is deposited for the conductive layers and the geometry is machined using a femtosecond laser. The relative permitivity was measured to be centered on 3.5 from 120 GHz. The antenna demonstrates a bandwidth of 3 GHz, and 94 degrees of frequency beam steering for a gain range of 6.4-9.1 dBi.

Over the last decade, spacecraft are increasingly integrating both microwave and optical communication systems, driving the need for electrically conductive and optically transparent materials. This study presents a comprehensive examination of advanced electromagnetic characterization techniques, focusing on Indium Tin Oxide (ITO) films on alkaline earth boro-aluminosilicate glass for transparent radio-frequency (RF) applications. Utilizing 4-point probes and coplanar waveguide (CPW) ground signal ground (GSG) probes, we investigated the electrical properties of ITO, including conductivity, permittivity, and loss tangent. The ITO films achieved an average permittivity of 7.16 in the range of 5-10 GHz, a DC conductivity of 6.86 MS/m, and a CPW loss tangent of 0.0054 at 10 GHz. These results underscore the suitability of ITO for hybrid optical and microwave hardware. Our findings offer critical insights for designing next-generation electronic and photonic devices, demonstrating the pivotal role of precise material characterization.

This paper presents a novel strategy for tailoring the phase shift in dual-layer metasurface (9mmx9mm) through the pixelated geometries on the conductive layers. We introduce designs featuring 72, 50, and 22 cells in dual-layered metasurface configurations, each maintaining the equivalent aggregate metal area to that of a standard patch metasurface. Both simulation and measurement in the X band have shown that this pixelation approach effectively maintains the transmission (greater than -1 dB) and reflection (less than -8 dB) properties of conventional patch metasurface, while also facilitating the customization of phase shifts ranging from -15 to -35 degrees. This innovative technique underscores the potential for precise and autonomous phase adjustment in metasurface designs, where leveraging the pixel placement as a means to explore optimal array element geometries via machine learning becomes possible. Such advancements promise to enhance the integration of metasurface into sophisticated array antenna design.

This study presents a novel design for a microlens coupler to transfer light from a straight waveguide to a single-mode fiber (SMF). Our design combines improved mode matching and enhanced alignment tolerance compared to edge coupling. An investigation of the alignment tolerance is done by assessing coupling efficiency under various degrees of manufacturing-induced misalignment. Singlet and diffractive lenses are incorporated into our design to focus the light into the fiber precisely. Comprehensive simulations demonstrate that the diffractive lens outperforms edge coupling and singlet lens in coupling efficiency. Fabrication methods such as additive manufacturing are discussed for future works. Our findings underscore the potential of innovative microlens coupler design in advancing free space optical communication (FSOC) systems.

The rapid growth of optical communications in space is driven by the need for higher data transmission rates to support the increasing demands of space missions. Our research focuses on a coherent free space optical communication (FSOC) setup, which serves as a framework for the development and experimental setup of optical communications hardware. By conducting an empirical examination of the propagation loss of coherent signals in FSOC systems, this study underscores the crucial influence of optical signal characteristics such as modulation schemes, polarization, and wavelength on system performance. With a 40GHz receiving bandwidth optical modulation analyzer (OMA), our experiments demonstrate a 3.5 dB loss of free space channel in lab for QPSK, 16QAM, 16APSK coherent optical signals at 1550 nm, regardless of polarization state (Linear and Circular). 1m space separation is set up between transmitter and receiver. This paper describes and characterizes a laboratory experiment setup and demonstrates how coherent signaling can leverage its inherent advantages to counteract the challenges of signal degradation in free-space optical links, thereby improving data rates and signal integrity over vast distances.

CubeSats, with their standardized small form factor, are increasingly being used for space missions requiring cost-effective and compact communication systems. However, their limited size, power, and antenna capabilities present challenges for achieving high data rate transmissions necessary for advanced payloads. This paper details the design and implementation of a PC/104-compatible upconverter for CubeSat communication systems, operating within the 24 GHz ISM band. Utilizing commercial-off-the-shelf (COTS) components and a direct upcon-version architecture, the proposed system achieves a peak output of -13.47 dBm at 24.2 GHz. The upconverter integrates seamlessly with commercial SDRs, occupying only 0.3U of CubeSat space. The front end achieves up-conversion from an intermediate frequency (IF) of 4.2 GHz, to 24.2 GHz with an overall conversion loss of 8.47 dB. The 3 dB IF bandwidth of the system is 0.907 GHz, and the system achieves an output power of -13.47 dBm at 24.2 GHz.

As the space industry focuses more on low-cost small satellite platforms than large spacecraft, it is essential to develop antenna solutions compatible with small form factors such as the one-unit standards. Furthermore, additive manufacturing enables high-performance ad-hoc fabrication of space antennas with greater degrees of freedom in the geometry. A circularly polarized metasurface patch antenna is designed, manufactured, and tested for wideband X-Band applications. The co-planar waveguide (CPW)-back-fed metasurface patch antenna in this work is additively manufactured using digital light processing (DLP) and micro-dispending process for the Rogers Radix TM and Novacentrix HPS-FG57B conductive paste, respectively. The metasurface is comprised of truncated patches with engineered sizes and relative placement for wideband and polarization control purposes. The antenna shows a measured −10dB impedance bandwidth of 63% and a simulated 3dB axial ratio (AR) and peak gain of 12% and 7.7 dBi, respectively.

The laser-enhanced direct print additive manufacturing (LE-DPAM) process is used to fabricate and characterize low temperature co-fired ceramic (LTCC) paste for high temperature applications. Coplanar waveguides (CPW) were used to characterize the performance of the additive manufactured LTCC substrate and the permittivity is extracted using direct S-parameters measurements up to 40 GHz. The extracted permittivity is calculated to be an average of 21.3 over 1–40 GHz. A 4 dBi mm-wave antenna is designed and fabricated to demonstrate the capability to additive manufacture LTCC materials, with resonances in the 32–34 GHz range which endured at temperatures up to 980 °C. To the authors’ best knowledge, this is the first fully additive manufactured solution for LTCC technology, where both LTCC and conductive traces were printed using a microdispensing AM process.

As additive manufacturing technologies evolve and allow for easier conformal printing of 3D antennas, functional surfaces are used for both mechanical and electrical functions. E.g., a UAV wing can be used as both a flight surface and an antenna. These conformal antennas tend to have the radiation elements on the outer surfaces of the structures and the feed port on the inner surfaces. Using electric connections between the layers adds points for electric and mechanical failures, as these structures are subject to external forces and temperature cycles. This paper presents the concept of a wireless antenna feed, where a detachable electromagnetic coupling structure is used to feed the outer antenna element from the inner structure surface. Flat wireless feed prototypes with both, commercial microwave laminates and additive manufacturing are designed, manufactured, and tested for the 8–9 GHz band.

Ensuring the security of wireless networks entails ensuring the authenticity, confidentiality, integrity, and availability of the data exchanged through them. In this data-dependent era, global communications systems have been experiencing rapid increases in the amount of data shared daily, thanks to the evolution of technologies that enable low-cost and ubiquitous wireless connectivity. In the last two decades, there has been a continuous increase in wireless traffic due to wireless technology advancements and a wide range of applications, and the increase in wireless network users [1] , [2] . Although the total annual Internet traffic was a few exabytes of data fewer than 15 years ago, more than two hundred exabytes have been reached in the last two years. Moreover, by next year, the average Wi-Fi speed is predicted to be 92 Mb/s, up from 30 Mb/s in 2018 [3] , [4] . This evolution has been driven by user demand, which includes higher data rates and broader coverage and bandwidth capabilities in wireless networks. Promising updates for current communication tools are in the making, but the boom in the amount of the data shared by them is making global communication systems a larger and easier target for security attacks [5] , [6] .

In recent years, advances in material science for high-frequency electronics have generated novel materials that offer superior performance. Additive manufacturing (AM) has expanded the frontiers of microwave material manufacturing going beyond flat geometries and unique properties such as graded permittivity materials. Accurate electromagnetic (EM) material characterization for AM materials remains challenging given the printing volume constraints for manufacturing processes, as traditional EM property extraction techniques often require electrically large samples. Furthermore, loss extraction techniques typically cannot differentiate dielectric and conductor losses in waveguides. This paper presents a novel conformal mapping-based characterization technique using coplanar waveguides (CPW) with air pockets that allows for dielectric permittivity and dielectric loss extraction. The underlying principle of the techniques is to use a set of CPWs with different air slot depths to extract the loss behavior as a function of the slot depth. A new loss-slot rate metric is introduced to decouple the dielectric and conductor losses in the structure. The theoretical foundation of the technique is used to develop a physical-mathematical model for dielectric property extraction that is verified with simulations and experiments for materials with permittivity in the range 2.33–29, and loss tangents of 0.02–0.055. The average error for the equivalent capacitance of the CPW with air pockets (CPW-AP) between the presented model and simulated or measured data is 2.4% for all the studied cases. The experimental confirmation is performed with traditionally manufactured FR-4 and additively manufactured yttria-stabilized zirconia (YSZ) dielectrics up to 10 GHz.

Reflectarray antennas (RA) have been proven as a transformational technology for a variety of applications, including space missions, where flat antenna reflectors are engineered with a great degree of freedom on operational bands and beam shapes. RA also offer the ability of using deployable flat geometries which are highly desirable for CubeSat missions. On the other hand, additive manufacturing processes have evolved over the last decade to achieve overall antenna performance and feature sizes that enable their operation for mm-wave frequencies. In this paper, dual-band RA elements are designed for the 18-32 GHz frequency band. The multilayer elements are fabricated using direct digital manufacturing, combining fused deposition modeling of polycarbonate (PC) and micro-dispensing of Ag ink, with an intermediate step of milling to enhance the surface roughness. The phase response of the elements is measured using WR-34 waveguides, and the geometry is inspected using X-Ray CT scanning.

Inter small satellite/CubeSat communication (C2C) plays a key role in configuring mega low earth orbit satellite constellation. Highly directional laser links for C2C allows high-data-rate communication to enable massive data transmission with low delay and power consumption. However, the pointing loss from imperfect acquisition and tracking between satellites with different relative velocities prevent the optical links from achieving desired ultra-reliable link capacity. In this paper, we propose an agile beaconless laser beam alignment (ABLBA) method that requires less scanning time for pre-alignment between CubeSats. Mm-wave beamforming with uniform phased array (UPA) antennas is used to find the optimal half power beam width (HPBW) to guide the laser beam to achieve mutual alignment. Various HPBW with different transmitter configu-rations are considered for more power efficient and low delay C2C optical communication. The trade off between UPA antenna design and acquisition time is discussed. Based on studies of various parameter settings and corresponding laser beam width values, we conclude that ABLBA is capable of reducing the delay of laser beam pre-acquisition time in the presence of the CubeSat rigid body perturbation. Accuracy of mutual alignment is measured based on rating intersection surface in a geometric coverage model, which provides a direct mapping from the platform distance uncertainty to the performance of free space optical beam alignment.

Additive manufacturing (AM) enables the development of rapid, low-cost prototypes for ad-hoc and on-demand manufacturing to repair and keep up the continuous operation of systems, especially in time-sensitive scenarios where the system recovery cannot wait for the shipment of new components. Therefore, the industry, military, and academia continue to invest in these technologies to potentially achieve novel 3D geometries based on high-temperature dielectric and conductors to endure harsh environments, such as commonly found in the oil and gas, defense, and aerospace sectors. This paper reports the electromagnetic properties of 3D-printed Yttria-Stabilized Zirconia (YSZ) for 2–6 GHz and the DC and RF effective conductivity of sintered platinum ink, where the dissipative losses of the additively manufactured coplanar waveguides (CPWs) are less than 0.05 dB/mm when the frequency is below 4 GHz. In addition, the AM CPWs are exposed to thermal cycling up to 600 °C to study the material’s thermal fatigue and potential degradation. However, the samples do not exhibit appreciable degradation after thermal cycling. Also, a two-layer back-fed antenna based on 3D-printed YSZ and platinum ink is designed, manufactured, and tested. Results show a measured gain of 2.5 dBi and a front-back ratio of 9.6 dB at 4.1 GHz.

Physical layer security is increasingly being exploited as a technique to enhance the security of wireless communications. Well-known hardware security techniques leverage unintended manufacturing process variations or fixed unique hardware structures in the semiconductors for identification of different copies of an RF system. The fundamentally different concept of engineering a unique fingerprint for each antenna produced, by leveraging additive manufacturing, is presented in this work. To the best of the author’s knowledge, this is the first application of the concept of radio frequency (RF) fingerprint engineering using additively manufactured (AM) antennas for hardware-based security mechanisms. AM engineered fingerprints (AMEF) are based on intentional features added to antenna’s geometries using 3D printing, enabling more accurate signal source identification and classification. Such unique features per unit produced would be prohibitively costly by using traditional photolithographic processes. The AMEF concept is validated using AM right hand circularly polarized (RHCP) truncated corner probe fed (TCPF) patch antennas and a testbed setup with software-defined radios and MATLAB implementations to create, transmit, receive, and prepare a convolutional neural network (CNN) to classify the transmitted raw I/Q data of Wi-Fi signals (IEEE 802.11). The AMEF technique greatly improves the physical layer security performance limitations in large-scale applications where the features of the devices can overlap, at a low-cost and low production time impact, and it allows the use of the antenna features for both individual and type classification and identification of RF sources.

Recent radio-frequency resonance-based hightemperature sensors have enable the next generation of passive wireless sensing for harsh environments, such as inside of jet engines. A novel manufacturing technique for an evanescentmode-resonator-based and antenna-integrated wireless passive pressure sensor is proposed therein. This technique employs a planar PCB manufacturing tool to laser etch a 3-D structure on an alumina substrate. A laser machining study is conducted to find etch consistency and fine-tune laser etching parameters. The wireless passive pressure sensor is tested through various mechanical and thermal loads to measure its performance. The sensor is proven to work in the range of $25^{\circ}\mathrm{C} -1700^{\circ}\mathrm{C}$, sensing pressures of 0 psi to 163 psi with resonances within the frequency range of 6.33 GHz--6.7 GHz.

The involvement of different entities in the life cycle of wireless electronics has increased the risk of adversary attacks, in particular, hardware Trojans (HTs). Wireless network hardware need to be compliant with a set of minimum security requirements to protect the data that these systems exchange and ensure the system reliability, however, HTs make them vulnerable. Hardware-based malicious attacks and defense mechanisms are continuously being analyzed to provide prevention and detection capabilities against them. Considering the unpredictability of HTs, there is a need for blind countermeasures that can detect and identify HTs without any previous knowledge of their characteristics: fingerprint-based methods. This paper presents a technique for the detection of unanticipated HTs based on antenna input reflection coefficient measurements (S11) over a wide range of frequencies expanding far beyond the antenna operation frequency. This work includes the design, manufacturing and testing of printed circuit boards with a WiFi system-on-chip (ESP8285), a meandered inverted-F antenna, and a HT that shorts the antenna to disrupt the communication link. The effects of the insertion of the HT in both operational and non-operational modes are successfully used to detect its presence without anticipation of its characteristics using data similarity and distance measures (Pearson’s coefficient, Euclidean and Manhattan distances) that can be extrapolated to machine learning algorithms for large scale analyses.

Due to the exponential growth of small satellite technology, novel shapes for antennas have been explored to make them low-cost, lightweight, compact, and easy to deploy. The use of frequency beam-scan antennas reduces the complexity of the small satellite front-end by avoiding the need to use phase shifters, especially when a reliable inter-satellite link (ISL) is required to keep up the communication and the formation accurately in a CubeSat swarm mission. This paper reports the design and a manufacturing process focused on in-space manufacturing (ISM) of a fully 3D-printed leaky-wave antenna, using ULTEM 9085 for aerospace applications. The antenna shows frequency beam steering capabilities from 4.4 GHz to 7.4 GHz, and a gain reconfigurable by angular rotation of the ground planes. The resulting antenna shows a measured peak gain of 10.07 dBi at 6.5 GHz, with a gain reconfigurability, as function of the elevation angle of the ground planes, in the range of 0 to 40°, providing an additional gain from 0 to 2 dBi, respectively.

Additive manufacturing (AM) techniques for high-frequency electronics have evolved in the past decade to not only offer similar performance as traditional manufacturing, but to offer unprecedented design freedom. One of the main challenges of AM of radio-frequency devices is the losses associated with the printed conductive layers. Recent studies have shown that pulsed laser can enhance the conductivity of the conductive inks. In this work, the photonic curing process, or PulseForgeOR, is applied to AM coplanar waveguides (CPW) to measure its effect on the high-frequency electric conductivity. Dissipative losses are reduced by 2.58 dB, from -4.74dB to -2.16dB, at 40 GHz over a 10 mm long line, after photonic curing, when compared to thermally cured samples.