Microwave Camera for Detecting Hidden Objects

Camera systems are in widespread use as sensors that provide information about the surrounding environment. But this can struggle with image interpretation in complex scenarios. In contrast, mmWave radar technology offers a more straightforward view of the geometry and motion of objects, making it valuable for applications like autonomous vehicles, where radar aids in mapping surroundings and detecting obstacles. Radar’s ability to provide direct 3D location data and motion detection through Doppler effects is advantageous, though traditionally expensive and bulky. Advances in SiGe device integration are producing more compact and cost-effective radar solutions. Plextek aims to develop mm-wave radar prototypes that balance cost, size, weight, power, and real-time data processing for diverse applications, including autonomous vehicles, human-computer interfaces, transport systems, and building security.

This paper presents a range of novel low-cost millimeter-wave radio-frequency sensors that have been developed using the latest advances in commercially available electronic chip-sets. The recent emergence of low-cost, single chip silicon germanium transceiver modules combined with license exempt usage bands is creating a new area in which sensors can be developed. Three example systems using this technology are discussed, including: gas spectroscopy at stand off distances, non-invasive dielectric material characterization and high performance micro radar.

This technical paper by Dr. Rabbani and his team presents research on metamaterial-based, high-gain, flat-panel antennas for Ku-band satellite communications. The study focuses on leveraging the unique electromagnetic properties of metamaterials to enhance the performance of flat-panel antenna designs, aiming for compact structures with high gain and efficiency. The research outlines the design methodology involving multi-layer metasurfaces and leaky-wave antennas to achieve a compact antenna system with a realised gain greater than +20 dBi and an operational bandwidth of 200 MHz. Simulations results confirm the antenna's high efficiency and performance within the specified Ku-band frequency range. Significant findings include the antenna's potential for application in low-cost satellite communication systems and its capabilities for THz spectrum operations through design modifications. The paper provides a detailed technical roadmap of the design process, supported by diagrams, simulation results, and references to prior work in the field. This paper contributes to the advancement of antenna technology and metamaterial applications in satellite communications, offering valuable insights for researchers and professionals in telecommunications.

A comprehensive analysis of the historical Kootwijk VLF (Very Low Frequency, which covers 3-30 kHz) antenna, including the development of a numerical model to gain insight into its operation. The Kootwijk VLF antenna played a significant role in long-range communication during the early 20th century. The paper addresses the challenge of accurately modelling this electrically small antenna due to limited historical technical information and its complex design. The main goal is to understand if the antenna’s radiation efficiency might explain why “results were disappointing” for the Kootwijk to Malabar (Indonesia) communications link. Through simulations and comparisons with historical records, the numerical model reveals that the Kootwijk VLF antenna had a low radiation efficiency – about 8.9% – for such a long-distance link. This work discusses additional loss mechanisms in the antenna system that might not have been considered previously, including increased transmission-line losses as a result of impedance mismatch, wires having a lower effective conductivity than copper and inductor quality factors being lower than expected. The study provides insights into key antenna parameters, such as the radiation pattern, the antenna’s quality factor, half-power bandwidth and effective height, as well as the radiated power level and the power lost through dissipation. This research presents the first documented numerical analysis of the Kootwijk VLF antenna and contributes to a better understanding of its historical performance. While the focus has been at VLF, this work can aid future modelling efforts for electrically small antennas at other frequency bands.

This technical paper highlights the ambiguity in the antenna technical literature regarding the radiation resistance of folded antennas, such as the half-wave folded dipole (or quarter-wave folded monopole), electrically small self-resonant folded antennas and multiple-tuned antennas. The feed-point impedance of a folded antenna is increased over that of a single-element antenna but does this increase equate to an increase in the antenna’s radiation resistance or does the radiation resistance remain effectively the same and the increase in feed-point impedance is due to transformer action? Through theoretical analysis and numerical simulations, this study shows that the radiation resistance of a folded antenna is effectively the same as its single-element counterpart. This technical paper serves as an important point of clarification in the field of folded antennas. It also showcases Plextek's expertise in antenna theory and technologies. Practitioners in the antenna design field will find valuable information in this paper, contributing to a deeper understanding of folded antennas.

This paper presents a comparison of Chilton ionosonde critical frequency measurements against vertical-incidence HF propagation predictions using ASAPS (Advanced Stand Alone Prediction System) and VOACAP (Voice of America Coverage Analysis Program). This analysis covers the time period from 1996 to 2010 (thereby covering solar cycle 23) and was carried out in the context of UK-centric near-vertical incidence skywave (NVIS) frequency predictions. Measured and predicted monthly median frequencies are compared, as are the upper and lower decile frequencies (10% and 90% respectively). The ASAPS basic MUF predictions generally agree with fxI (in lieu of fxF2) measurements, whereas those for VOACAP appear to be conservative for the Chilton ionosonde, particularly around solar maximum. Below ~4 MHz during winter nights around solar minimum, both ASAPS and VOACAP MUF predictions tend towards foF2, which is contrary to their underlying theory and requires further investigation. While VOACAP has greater errors at solar maximum, those for ASAPS increase at low or negative T-index values. Finally, VOACAP errors might be large when T-SSN exceeds ~15.

This paper presents the antenna G/T degradation incurred when communications systems use very inefficient receive antennas. This work is relevant when considering propagation predictions at HF (2-30 MHz), where it is commonly assumed that antennas are efficient/lossless and external noise dominates over internally generated noise at the receiver. Knowledge of the antenna G/T degradation enables correction of potentially optimistic HF predictions. Simple rules of-thumb are provided to identify scenarios when receive signal-to-noise ratios might be degraded.

This paper describes the design and characterization of a frequency-scanning meanderline antenna for operation at 60 GHz. The design incorporates SIW techniques and slot radiating elements. The amplitude profile across the antenna aperture has been weighted to reduce sidelobe levels, which makes the design attractive for radar applications. Measured performance agrees with simulations, and the achieved beam profile and sidelobe levels are better than previously documented frequency-scanning designs at V and W bands.

Signal power measurements for a UK-based network of three beacon transmitters and five receiving stations operating on 5.290 MHz were taken over a 23 month period between May 2009 and March 2011, when solar flux levels were low. The median signal levels have been compared with monthly median signal level predictions generated using VOACAP (Voice of America Coverage Analysis Program) and ASAPS (Advanced Stand Alone Prediction System) HF prediction software with the emphasis on the near-vertical incidence sky wave (NVIS) links. Low RMS differences between measurements and predictions for September, October, November, and also March were observed. However, during the spring and summer months (April to August), greater RMS differences were observed that were not well predicted by VOACAP and ASAPS and are attributed to sporadic E and, possibly, deviative absorption influences. Similarly,the measurements showed greater attenuation than was predicted for December, January, and February, consistent with the anomalously high absorption associated with the “winter anomaly.” The summer RMS differences were generally lower for VOACAP than for ASAPS. Conversely, those for ASAPS were lower during the winter for the NVIS links considered in this analysis at the recent low point of the solar cycle. It remains to be seen whether or not these trends in predicted and measured signal levels on 5.290 MHz continue to be observed through the complete solar cycle.

This paper shows that the Q-factor and VSWR of a monopole are significantly lowered when made resonant by reactive loading (as is used in practice). Comparison with a self-resonant Koch fractal monopole of equal height gives similar values of VSWR and Q-factor. Thus, the various electrically small monopoles (self-resonant and reactively loaded) offer comparable performance when ideal and lossless. However, in selecting the optimum design, conductor losses and mechanical construction at the frequency of interest must be considered. In essence, a trade-off is necessary to obtain an efficient, electrically small antenna suitable for the application in hand.

The design of a 16-element waveguide array employing radiating T-junctions that operates in the Ku band is described. Amplitude weighting results in low elevation sidelobe levels, while impedance matching provides a satisfactory VSWR, that are both achieved over a wide bandwidth (15.7-17.2 GHz). Simulation and measurement results, that agree very well, are presented. The design forms part of a 16 x 40 element waveguide array that achieves high gain and narrow beamwidths for use in an electronic-scanning radar system.

A lightweight, wideband tapered-slot antenna that uses an antipodal Vivaldi design and provides useable gain from ~5 GHz to in excess of 50 GHz is described. Simulations and measurements are presented that show excellent agreement. This antenna design is currently deployed in handheld test equipment.