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A high isolation antenna is presented which offers dual-polarization monopulse beam patterns, making the design suitable for polarization diverse or full-duplex (FD) systems. The single-layer structure is defined by a network of 2-D sub-arrays oriented in a cross-shape configuration using series-fed slots in substrate integrated waveguide (SIW) technology. Also, the proposed design exploits dual-differential feeding to achieve a −10 dB impedance matching bandwidth (BW) from 23.2 GHz to 25.4 GHz, and measured isolation values are more than 70 dB (peaking to about 90 dB) over this same operating range. Realized gain values are 13 dBi (and above) while cross-polarization values are less than 35 dB below the beam maximum. The novelty in the design can be defined by the inclusion of a simple SIW isolation element at the center of the antenna structure. This provides enhanced isolation and enables co-location for the vertical and horizontal SIW sub-array branches, and this simple and low-profile arrangement supports efficient dual-linear polarized radiation. To the best knowledge of the authors, no similar 2-D planar antenna design has been previously reported offering high isolation in the K-band and which can offer sum and difference beam patterns in the far-field (FF). Some applications include monopulse tracking setups for communications as well as in-band FD systems which require dual-polarization at microwave and millimeter-wave frequencies.

A circuit-based calibration system is presented for active phased arrays. In particular, to achieve the desired (and corrected) consecutive phase differences and relative magnitudes between RF channels, a computer controlled circuit system was developed for dynamic adjustment. The proof-of-concept demonstrator uses a phase sensor, phase shifters (PSs), and variable gain amplifiers, along with other active hardware, to realize a self-calibrating circuit system which achieves the required magnitude and phase for each array element. In addition, measured magnitude and phase imbalances are less than 0.10 dB and 3$^\circ$, respectively. The computer-controlled feed network is then used to demonstrate that the system can automatically calibrate an active antenna array for various beam steering examples. Also, the S-band feed system can self-calibrate due to any monitored magnitude and phase drifts due to temperature changes and practical component ageing, or, other general channel offsets. This can be considered advantageous and simpler when compared to more established approaches which characterize the coupling between elements or the response of the entire array in the near- or far-field for example.

Planar metasurface lens structures based on microstrip technology, optimized to control the propagation of surface waves (SWs), are presented. Two different lenses are studied, i.e., a converging or plane-wave-like lens and a diverging lens. Near-field simulations and measurements are reported to demonstrate the guiding features of the designed lenses, which have also been proposed as a feeding system for planar leaky-wave antennas (LWAs). Far-field results show improvements in terms of reduced cross polarization and sidelobe level as well as increased realized gain when compared without these SW lenses. The proposed structures are also simple to manufacture and are employed herein to control SW fields generated by a TM0 surface-wave launcher (SWL) integrated in the ground plane of the developed prototype demonstrators. Some applications include high-gain radar and remote sensing satellite antennas as well as microwave and millimeter-wave communication systems.

The modelling and design of a full wireless microwave communication system is examined, where the signal propagates within an overmoded circular metallic pipeline. Applications include the oil and gas industry. A specific link budget equation was also developed for the S-band transmission system and measured successfully using a 36-meter carbon steel pipeline, which can be easily extended to more than 150 meters. Also, based on the measured system data, the receiver sensitivity was determined to be −77 dBm and 15 dB in terms of the signal-to-noise ratio (SNR). Additionally, some digitized images, sensory information such as temperature and pressure, and live stream videos were successfully transmitted and monitored in real-time, using N210 universal software radio peripheral (USRP) modems by National Instruments and coded in Matlab/Simulink and LabVIEW. To the best knowledge of the authors, no similar microwave communication system has been developed with supporting theory, full wave simulations, and measurements for propagation within for oil and gas industry wells.

Flexible and lightweight textile-based coaxial transmission lines for wearable applications are presented. In particular, textile yarns defined by copper (Cu), polyester (PES), and polytetrafluoroehtylene (PTFE) materials were used to design transmission line prototypes offering a 50-$\Omega$ characteristic impedance. These structures, which have the weight and texture of a cylindrical shoe lace, were also simulated and measured using a commercial simulator and results are in agreement. In addition, the textile cables were also studied in various straight, bent and wet conditions to ensure flexibility and durability whilst observing low reflection and insertion losses in these scenarios. In addition, the mass and DC losses of the fabricated cables were measured and are competitive when compared to a commercially available cable. To the best knowledge of the authors, this is the first implementation of simple RF/microwave coaxial cables whilst achieving a 50-$\Omega$ characteristic impedance, made possible by using purely wearable yarns and materials, whilst adopting a textile braiding process during manufacturing. Findings suggest that the reported textile-based cables are suitable for data connectivity between wearable devices in the UHF and the 2.4 GHz ISM frequency bands, for example, and can provide an alternative to more established strategies for wireless connectivity between body worn IoT devices and other related technologies.

Abstract The development of a dual‐band folded shorted patch (FSP) antenna array is presented which offers dual‐circularly polarized radiation. Applications include small satellites like CubeSats and picosatellites. The proposed 2 × 2 FSP array design operates at 1.1 and 2.4 GHz and offers good radiation performance in terms of minimal reflection coefficient losses, broad beamwidths (which is generally required for low gain antenna structures ensuring link connectivity), as well as low cross‐polarization levels. The antenna array consists of a meandered layer defining the top of the FSPs. The shorting and folding technique as well as the noted meandering allows further size reduction of the quarter‐wavelength patch. In particular, the proposed antenna array is compact with a total size of 50 mm by 50 mm (or 0.18λ by 0.18λ at the lower operational frequency). An eight‐port coaxial and microstrip feed system is integrated onto the backside of the antenna ground plane, two ports for each element, and with external phase feeding of 90°, dual‐circularly polarized is made possible for the compact antenna unit. To the best knowledge of the authors, no similar antenna structure has been designed, manufactured and tested being useful for picosatellites and other small satellites.

Abstract A self‐calibrating circuit system for use within active phased array antennas is presented. The system addresses the issue of unwanted channel phase imbalances and random phase errors which can deteriorate array performance. Basically, unwanted insertion phase offsets that can originate within each RF channel, due to the supporting and active circuit components and possible temperature variations, can be eliminated by our designed, simulated, and experimentally verified self‐calibrating circuit. With existing technologies and calibration approaches, it is practically difficult and time consuming to check the phase feeding accuracy, as typically a large number of data sets are required to achieve similar channel corrections. As an alternative, our proposed circuit system allows for the consecutive phase shift between RF channels to be inspected and self‐corrected within a feedback loop managed by a MATLAB‐Arduino program. The active S‐band feed system can self‐calibrate in about 25 s (or less), using commercially available phase sensors and voltage controlled phase shifters. To the best knowledge of the authors, no similar computer controlled feed‐back circuit to support the self‐correction of active phased arrays has been previously reported.

Automotive radars are designed to enhance road user safety and reduce the number of accidents on public roads and there is a constant demand to improve the performance for these radars. In this paper, a novel proof-of-concept multiple-input multiple-output (MIMO) radar architecture is presented by frequency modulated continuous waveform (FMCW) transmission. For enhanced angular resolution, the radar uses a two-tier antenna setup leading to a sparse array arrangement, mainly in an effort to mitigate grating lobes and to offer different illuminations of the same scenario. Also, the experimentally verified sparse radar antenna designed for target detection at the receiver, achieves modest sidelobe levels and grating lobes well below 12 dB from the main beam maximum, whilst still maintaining competitive half-power beamwidths when compared to more conventionally spaced arrays. Moreover, the high impedance bandwidth of this receiver array and the supporting radar electronics (more than 6%) allows for the detection of targets at only a 10 cm spatial separation. The complete system is also capable of seeing a wide field-of-view (FOV) since it utilizes a network of radar modules to cover the forward −90$^\circ$ to +90$^\circ$ angular range by sectorization. In the best case, the measured radar system can resolve targets that are a distance of just $\pm 2^\circ$ apart in angular separation.

A miniaturized planar Yagi-Uda antenna for integration with PicoSats or other SmallSat missions is proposed. Miniaturization techniques, such as meandering and 1-D artificial dielectric concepts to reduce the guided wavelength, are employed to overcome space constraints imposed by the SmallSat footprint while still maintaining good performance for the FR-4 antenna. Simulations and measurements have been carried out on the Unicorn-2 PicoSat chassis from Alba Orbital and are in good agreement. Also, antenna dimensions have been reduced between 15% and 66% when compared to a more conventional planar Yagi-Uda antenna working at the same frequency. This compactness allows for simple integration with the deployable solar panel array of the Unicorn-2 PicoSat spacecraft. Full end-fire radiation is achieved and peak gain values are about 5 dBi for the antenna when fully integrated on the satellite chassis, offering an attractive solution for downlink connectivity. This compact antenna design can also be used within an array for beam steering or integrated within the solar cell modules of other PicoSats, CubeSats and SmallSats. Applications include Earth observation, remote sensing, as well as SmallSat to ground station communications. The planar Yagi-Uda antenna may also be useful wherever end-fire radiation is required from a compact antenna structure.

We present the design of a novel K-band radar architecture for short-range target detection. Applications include direction finding systems and automotive radar. The developed system is compact and low cost and employs substrate-integrated-waveguide (SIW) antenna arrays and a $4\times 4$ Butler matrix (BM) beamformer. In particular, the proposed radar transmits a frequency modulated continuous-wave (FMCW) signal at 24 GHz, scanning the horizontal plane by switching the four input ports of the BM in time. Also, in conjunction with a new processing method for the received radar signals, the architecture is able to provide enhanced resolution at reduced computational burden and when compared to more standard single-input multiple-output (SIMO) and multiple-input multiple-output (MIMO) systems. The radar performance has also been measured in an anechoic chamber and results have been analyzed by illuminating and identifying test targets which are 2° apart, while also making comparisons to SIMO and MIMO FMCW radars. Moreover, the proposed radar architecture, by appropriate design, can also be scaled to operate at other microwave and millimeter-wave frequencies, while also providing a computationally efficient multi-channel radar signal processing platform.

A new dual-polarized antenna and array are presented for In-Band Full-Duplex (IBFD) applications, offering high inter-port isolation. The single-element antenna system consists of four H-shape slots, stacked patches for wide bandwidth, and two external hybrid couplers. The multilayer antenna is well matched from about 2.1 to 2.4 GHz and provides high isolation in this frequency range in excess of 60 dB. Two different prototypes are simulated and measured to highlight the design process. In addition, a new and compact hybrid coupler with excellent phase and magnitude stability is also presented for improved antenna radiation and IBFD performances. When compared to other similar types of hybrid coupler and antenna systems, the proposed configurations are simple to manufacture, provide a higher isolation bandwidth (10%), and higher gain of 7.3 dBi with cross-polarization levels of 30 dB or lower. The single-element design was also extended to a $2\times 2$ array and studied for different beam steering and feeding scenarios. The operating bandwidths and isolation values offered by these S-band antenna and array systems can support new data link possibilities for beam steering and future low-cost IBFD wireless networks by simple antenna fabrication.

A flexible folded-shorted patch (FSP) antenna with dual-band functionality for wearable applications is presented. The proposed antenna is operational at 400 MHz and 2.4 GHz and can be considered compact for the lower operational frequency band (0.13λo × 0.13λo × 0.02λo). Flexible polydimethylsiloxane (PDMS) is used as the substrate due to its relatively low-cost as well as its robustness for wearable applications. A comparison of the fields radiated by the FSP, in terms of the TM010 and TM001 modes are also presented considering the cavity model which is actually related to the two noted operating bands. Equations needed to calculate the beam pattern and directivity for these modes are also derived and their results are compared to commercial full-wave simulations and measurements of a wearable PDMS prototype. An analysis was also performed to characterize the relevant dimensions that are important for independently controlling or tuning the resonant frequencies for these two radiating modes. The proposed antenna can be suitable for robust wearable applications such as military search and rescue operations, emergency response team units, and medical services.

The development of a dual‐band folded shorted patch (FSP) antenna array is presented which offers dual‐circularly polarized radiation. Applications include small satellites like CubeSats and picosatellites. The proposed 2 × 2 FSP array design operates at 1.1 and 2.4 GHz and offers good radiation performance in terms of minimal reflection coefficient losses, broad beamwidths (which is generally required for low gain antenna structures ensuring link connectivity), as well as low cross‐polarization levels. The antenna array consists of a meandered layer defining the top of the FSPs. The shorting and folding technique as well as the noted meandering allows further size reduction of the quarter‐wavelength patch. In particular, the proposed antenna array is compact with a total size of 50 mm by 50 mm (or 0.18λ by 0.18λ at the lower operational frequency). An eight‐port coaxial and microstrip feed system is integrated onto the backside of the antenna ground plane, two ports for each element, and with external phase feeding of 90°, dual‐circularly polarized is made possible for the compact antenna unit. To the best knowledge of the authors, no similar antenna structure has been designed, manufactured and tested being useful for picosatellites and other small satellites. [ABSTRACT FROM AUTHOR]