On-board Antenna Research Articles

An algorithm for determining the geometric parameters of the aperture of an on-board deployable antenna system in an orbital flight

Earth remote sensing complexes placed on light-class spacecraft may have a radiating aperture size of the antenna system exceeding the specified dimensional limits, therefore such antenna system are placed on a multi-section frame. Their design feature is the ability to unfold in space after being put into orbit, which makes it possible to significantly increase the size of the aperture and, as a result, improve the quality of scientific and target remote sensing information. During deployment and in the conditions of orbital flight, under the influence of destabilizing factors of outer space, a distortion of the distribution of amplitudes and phases at the antenna aperture can be observed, which is caused, among other things, by a distortion of geometric parameters caused by a change in the position of the sections of the speaker relative to each other within the tolerances of the aperture installation. In this regard, it is an urgent task to determine the geometric parameters of the aperture of the speaker according to ground measurements, which can be compensated by adjusting the weight coefficients in a multi-channel speaker or by mechanically rotating the sections, depending on the available capabilities. Reducing the influence of destabilizing factors of the deployment of a multi-section radiating aperture on the directional pattern of the antenna system in orbital flight conditions. An algorithm is proposed for determining the geometric parameters of the deployment of the deployed antenna system in the conditions of orbital flight, which allows calculating the angles of the mutual position of the sections based on ground measurements. The main advantage of the developed algorithm is that it does not require measurements of directional patterns at the gain scale or measurement of complex readings of the directional pattern, which require high-precision certified stands. To successfully correct the parameters of the on-board antenna, it is enough to have the results of amplitude measurements. The application of the developed algorithm will make it possible to effectively use the energy potential of space-based on-board radio engineering complexes using large-sized deployable antenna arrays as antenna systems by determining and compensating for the influence of distortions in the geometric parameters of the aperture.

On UAV Terrestrial Connectivity Enhancement through Smart Selective Antennas

Nowadays, Unmanned Aerial Vehicles (UAVs) are widely used in heterogeneous contexts and, thanks to a continuous technological evolution, are going to be used for several applications such as, for example, Beyond Visual Line of Sight (BVLOS) operations. Since in BVLOS flights the UAV and the ground control center may not have a direct visibility with each other, a robust communication system is needed to provide reliable connectivity. Although a cellular (4G/5G) network is the current best candidate to enable BVLOS applications, there are still some limitations to overcome, as 4G (LTE) and 5G (NR) cellular networks are natively designed for terrestrial use. In this paper, we first investigate current cellular communication limitations for UAV-based applications, in particular taking into account both results available in the literature, as well as experimental performance campaigns. Then, a viable solution for mitigating these drawbacks exploiting selective on-board antennas is proposed, whose performance is experimentally investigated with a preliminary prototypical architecture.

A Full-Duplex 60 GHz Transceiver with Digital Self-Interference Cancellation

This paper presents the design and measurement of an IEEE 802.11ad standard compatible RF transceiver for 60 GHz wireless communication systems. In addition to the traditional half-duplex (HD) mode, this work supports full-duplex (FD) operations to deliver better channel utilization and faster response times for the system. The isolation between the transmitter and receiver from the architecture design to system integration for FD operations has been fully considered. A digital self-interference cancellation (DSIC) is implemented in MATLAB to verify the FD performance. The super-heterodyne architecture with an intermediate frequency (IF) of 12 GHz is designed to suppress the image frequencies without using extra filters. A flexible phase-locked loop (PLL) synthesizer provides a local oscillator (LO) frequency with a 2 kHz resolution. Other than the time division duplex (TDD) mode used in the conventional 60 GHz system, a wide-bandwidth baseband digital variable-gain amplifier (DVGA) with a 3 dB bandwidth of more than 4 GHz also supports frequency division duplex (FDD) operations. The transceiver chip is fabricated using the Tower Jazz 0.18 µm SiGe BiCMOS process. With an on-board antenna, the transceiver covers all four channels in the 802.11ad standard, with MCS-12 (7.04 Gbps under 1.76 GSym/s and 16-QAM) under 1.5 m. In the proposed system design, the RF frontend-based self-interference (SI) suppression from the local transmitter to receiver LNA is around 54 dB. To achieve a practical FD application, the SI is further suppressed with the help of a digital SI compensation. The measured power consumption for the transmitter and receiver configurations are 194 mW and 231 mW, respectively, in HD mode and 398 mW for the FDD or FD operation mode.

Resonant Radar Reflector On VHF / UHF Band Based on BPSK Modulation at LEO Orbit by MRC-100 Satellite

This paper presents a novel method for identify ing and tracking PocketQube satellites: the MRC-100 satellite is a model, and this method is based on a resonant radar reflec tor. The resonant reflector’s basic concept is that the resonant reflector uses a VHF/UHF communication subsystem antenna; there is no radiated RF signal, which means the power con sumption is only some Milliampere (mA). The continuous wave (CW) illuminator RF source is on the ground, and the onboard antenna receives the CW RF signal from the Earth. The micro controller (uC) periodically switches PIN diode forming BPSK modulated signal reflection so that another Earth station can receive the backscattered Binary Phase Shift Keying (BPSK) modulated signal. Also, it can detect the satellite if the ground station receiver can use a matched filter like a correlation re ceiver. If the ground station receiver knows the BPSK code of the satellite, it can detect it. If not, there is no way to detect the satellite. This method is similar to Radio Frequency Identifica tion (RFID) applications, but the reader is the ground station, and the tag is the satellite.

Precise orbit determination of Haiyang-2D using onboard BDS-3 B1C/B2a observations with ambiguity resolution

The Haiyang-2D altimetry mission of China is one of the first Low Earth Orbit (LEO) satellites that can receive new B1C/B2a signals from the BeiDou-3 Navigation Satellite System (BDS-3) for Precise Orbit Determination (POD). In this work, the achievable accuracy of the single-receiver ambiguity resolution for onboard LEO satellites is studied based on the real measurements of new BDS-3 frequencies. Under normal conditions, six BDS-3 satellites on average are visible. However, the multipath of the B1C/B2a code observations presents some patchy patterns that cause near-field variations with an amplitude of approximately 40 cm and deteriorate the ambiguity-fixed rate. By modeling those errors, for the B2a code, a remarkable reduction of 53% in the Root Mean Square (RMS) is achieved at high elevations, along with an increase of 8% in the ambiguity-fixed rates. Additionally, an analysis of the onboard antenna's phase center offsets reveals that when compared to the solutions with float ambiguities, the estimated values in the antenna’s Z direction in the solutions with fixed ambiguities are notably smaller. The independent validation of the resulting POD using satellite laser ranging at 16 selected high-performance stations shows that the residuals are reduced by a minimum of 15.4% for ambiguity-fixed solutions with an RMS consistency of approximately 2.2 cm. Furthermore, when compared to the DORIS-derived orbits, a 4.3 cm 3D RMS consistency is achieved for the BDS-3-derived orbits, and the along-track bias is reduced from 2.9 to 0.4 cm using ambiguity fixing.

The results of navigation spacecraft observations with asymmetry of the amplitude patterns of onboard antenna feed systems

The results of navigation spacecraft observations with asymmetry of the amplitude patterns of onboard antenna feed systems

The propagation of Alfvén wave in magnetized plasma sheath of hypersonic vehicles in near space

Hypersonic plasma sheath could shield communication signals, which results in the so-called “blackout.” Blackout is a major risk to the safety of re-entry vehicles and cruise hypersonic vehicles in near space. In this study, a propagation model of Alfvén waves in plasma sheaths is developed. The impacts of the external magnetic field, the wave frequency, and the boundary conductivity on the Alfvén attenuation were investigated. According to the simulation results, once the conductivity is close to the Alfvénic conductivity near the onboard antenna, the attenuation of Alfvén waves in the plasma sheath could reach its minimum. The total attenuation of the Alfvén wave in the plasma sheath decreases with the carrier frequency. Also, the attenuation decreases with increasing magnetic field strength.

The results of navigation spacecrafts observations with asymmetry of the onboard antenna amplitude radiation pattern

The received in the Earth surface layer satellite radio signal power depends on the space navigation vehicle onboard antenna parameters, primarily it depends on the amplitude radiation pattern shape. The spacecraft onboard antenna radiation pattern has a complex shape in order to compensate for radio navigation signal power changes as a result of the removal (or approach) of the navigation satellite from the signal consumer. For this reason, the shape of the radiation pattern must have axial symmetry, i.e. it has to be close to the rotation fi gure. As a result of the global navigation satellite system GLONASS radio navigation signals energy characteristics monitoring, VNIIFTRI evaluated amplitude radiation patterns of the onboard antenna-feeder devices of satellites from the orbital constellation, the amplitude radiation patterns asymmetry of some of them was discovered. The asymmetry of the radiation pattern leads to the radio navigation signal (received by the consumer) power dependence on the device angle of the, i.e. on the position of the onboard radiating antenna system of the relative to the signals consumer. The probable reason for the asymmetry is the gradual aging of the active devices in the antenna system. The article purpose is to pay attention of competent specialists to the existing problem.

Effect of electron number densities on the radio signal propagation in an inductively coupled plasma facility

Spacecraft entering a planetary atmosphere are surrounded by a plasma layer containing high levels of ionization, due to the extreme temperatures in the shock layer. The high electron number densities cause attenuation of the electromagnetic waves emitted by the on-board antennas, leading to communication blackout for several minutes. This work presents experimental measurements of signal propagation through an ionized plasma flow. The measurements are conducted at the VKI plasma wind tunnel (Plasmatron) using conical horn antennas transmitting in the Ka-band, between 33 and 40 GHz. Testing conditions at 15, 50 and 100 mbar, and powers between 100 and 600 kW cover a broad range of the testing envelope of the Plasmatron as well as a broad range of atmospheric entry conditions. The transmitting antenna is characterized at the UPC anechoic chamber, obtaining the radiation patterns, beamwidth, and gain at the boresight direction; and an optical ray tracing technique is used to describe the electromagnetic waves propagation in the plasma flowfield inside of the Plasmatron chamber. The signal propagation measurements show clear attenuation when the signal is propagating through the plasma, varying between 2 and 15 dB depending on the testing conditions. This attenuation increases with electron number densities, which are driven by the Plasmatron power and pressure settings. Preliminary evidence of Faraday rotation effects caused by the plasma is also observed.

On control of spacecraft orientation to the ground data acquisition station

The article dwells on the spacecraft attitude control to point the onboard antenna to the ground data acquisition station during the communication session. Antenna is fixed relative to the spacecraft body. Pur-pose of the antenna is to receive the flight task aboard the spacecraft and to downlink the telemetry infor-mation. When orbiting, the spacecraft position relative to the ground data acquisition station changes contin-uously. It is due to the diurnal rotation of the Earth, spacecraft orbital motion and angular motion of the spacecraft relative to the center of mass under the impact of the disturbing and control moments. To tilt the spacecraft uses reaction wheels, installed in axes of coordinate system coupled with spacecraft center of mass. Electromagnets are used to unload the reaction wheels. The reaction wheels control law is suggested, which tilts the spacecraft to point the antenna to the ground data acquisition station. Mathematical model of the spacecraft dynamics relative to center of mass is given, using the suggested reaction wheels control law. The following external disturbing moments, acting on the spacecraft in flight, are taken into consideration: gravitational, magnetic, aerodynamic moments and solar radiation moment of forces. Dipole model of the magnetic field of the Earth is used to calculate the magnetic moments. Software was developed and space-craft dynamics was simulated on the personal computer with the specified initial data. Simulation initial con-ditions correspond to the attitude control mode of the spacecraft relative to the orbital coordinate system with the specified accuracy. Simulation results verify the applicability of the suggested reaction wheel control law. Key words: electrical axis of the antenna, mathematical model, coordinate system, transformation matrix, vector.

Position optimization for mobile relay communications with constrained energy over a whole horizontal plane

This paper concerns the position optimization problem of a mobile relay over a whole horizontal plane. This problem is important because the position of a mobile relay directly affects the end-to-end performance, e.g., reliability, connectivity, and data rate. In this paper, we propose a new position optimization scheme of a mobile relay over a whole horizontal plane based on the one-bit feedback information from the destination node, which improves the performance over the prior scheme whose position of the mobile relay is optimized over a fixed orbit. In the proposed scheme, the mobile relay is equipped with merely one single onboard antenna. Moreover, no prior information about the positions of both the source node and the destination node is required. Thus, the proposed scheme can work at low network resources scenario, which is particularly suitable for mobile relay communication with constrained energy, e.g., the communications in a disaster area where the infrastructure is heavily damaged, volcano monitoring, and wireless powered communication networking. According to the characteristics of the proposed scheme, we further design two heuristic implementations to calculate the optimal position of a mobile relay over a whole horizontal plane. The first implementation has better steady performance whereas the second implementation has better convergence speed. We implement the proposed scheme and conduct an extensive performance comparison between the proposed scheme and prior schemes to verify the advantages of the proposed scheme.

Design and Evaluation on Onboard Antenna Pointing Control System for a Wireless Relay System Using Fixed-Wing UAV

Among several usages of unmanned aerial vehicles (UAV), wireless relay systems for high altitudes using fixed-wing UAVs, or high-altitude platform stations (HAPS), are some of the most promising applications. To realize the systems by making the most of advantages of the long flight duration and endurance of fixed-wing airplanes, this paper proposes an antenna pointing control system using mechanical gimbals onboard a fixed-wing UAV continuously turning midair and describes results of the blocking analysis of the antenna driving angles of the gimbal directed to a ground station, the design of the antenna pointing control system, and the evaluation of its performance. It is confirmed by the evaluation that, though the antenna pointing control accuracy is greatly influenced by the noisy antenna pointing direction command, its accuracy is greatly improved by using the highly accurate RF sensor to detect antenna pointing direction.

3D ray tracing solver for communication blackout analysis in atmospheric entry missions

During the atmospheric entry phase at hypersonic speed, the radio communication from/to a space vehicle can be disrupted due to the formation of a plasma sheath within the surrounding flow field. In order to characterize such communication blackout phases, this work presents a numerical methodology combining Computational Fluid Dynamic (CFD) simulations of ionized chemically reacting entry flows by means of Computational Object-Oriented Libraries for Fluid Dynamics (COOLFluiD) and a ray tracing analysis by means of the newly developed BlackOut RAy Tracer (BORAT). The latter is based on the numerical solution of the 3D Eikonal system of equations, offering a fast, efficient and accurate method to analyse the interaction between electromagnetic signals and weakly ionised plasmas. The proposed methodology, and BORAT in particular, is first verified on popular benchmark cases and then used to analyse the European Space Agency (ESA) 2016 ExoMars Schiaparelli entry flight into Martian environment. The corresponding results demonstrate the validity of the proposed ray tracing approach for predicting communication blackout, where signals emitted from the on-board antenna undergo reflection and refraction from the plasma surrounding the entry vehicle, and the advantage of a 3D approach for analysing real flight configuration.

Влияние неоднородной теплозащиты на характеристики излучения антенны космического аппарата

Introduction: Knowledge of the electrical characteristics of the onboard antenna on the trajectory of the descent of the spacecraft makes it possible to assess the presence or absence of radio communication. Under conditions of aerodynamic heating, the thermal protection of the onboard antenna heats up unevenly in thickness and becomes electrically inhomogeneous. Purpose of the work: Determination of the radio technical characteristics of the onboard antennas of the returning spacecraft with the effect of high-temperature heating on the thermal protection of the antenna based on calculations using the developed mathematical model of the antenna with thermal protection. Methods: Expressions for the structure of the radiation field of a rectangular waveguide under the above conditions were derived by the WKB method. Of the well-known analytical methods of solution, it is possible to use the method of integral transformations and the method of eigenfunctions. Both of these methods were used in this work. Results: The obtained theoretical results are new, they allow predicting the radio technical characteristics of the onboard antenna, taking into account uneven heating across the thickness of the thermal protection at low temperature gradients. A mathematical model of the spacecraft's onboard antenna on the descent trajectory has been developed, taking into account the inhomogeneity of thermal protection under conditions of aerodynamic heating. Practical significance: The development of a mathematical model of the main radio technical characteristics of onboard antennas, taking into account the impact of high-temperature aerodynamic heating, as well as the results of numerical calculations, can be applied in the development of recommendations for choosing thermal protection and recommendations for reducing the effect of temperature changes in the electrical parameters of thermal protection on the characteristics of onboard antennas and reducing time loss of radio communication or loss recovery.

Mathematical Model of the On-Board Antenna of Reentry Spacecraft Taking into Account Surface Waves

Introduction. The onboard antennas of the returned hypersonic aircraft are weakly directional, which is achieved by radiation from the open end of the waveguide. When passing through dense layers of the atmosphere, they are exposed to aerodynamic heating, for protection from which a heat-resistant radio-transparent thermal protection is used. The case of uniform thermal protection of the antenna can be interpreted as the absence of heating or heating uniform in the thickness of the thermal protection.Aim. The problem of obtaining an analytical description of the radiation characteristics of a circular waveguide closed by a flat homogeneous dielectric plate is solved. Since in such a formulation it is necessary to consider the resonant domain, a strict solution of Maxwell's equations is required.Materials and methods. Of the known analytical methods of solution, it is possible to use the method of integral transformations and the method of eigen functions. Both of these methods are used in the work. In this case, the assumption is used that the electrical parameters of the dielectric plate (thermal protection) and the geometric dimensions do not depend on time.Results. The relations describing the directional pattern of a circular waveguide with dielectric thermal protection and taking into account the electrical parameters of thermal protection and its thickness are obtained. Expressions are also obtained for the fields of lateral, surface and outflow waves, from which it is possible to calculate the power output by these fields. Relations for the separation of singular points of integrand expressions into poles corresponding to surface, outflow and lateral waves are obtained. Surface, outflow and lateral waves can have a certain effect on the radiation pattern. To determine this conclusion, analytical relations are obtained for determining the poles of integrand expressions that fully describe surface, outflow and side waves. All the analytical results obtained correspond to Numerical calculations were carried out on some of the obtained ratios.Conclusion. The results showed that the power of the side waves is zero. It also follows from the calculations carried out that there is no radiation field of surface and outgoing waves, i.e. there is no contribution of them to the radiation pattern.

Matching Traffic Demand in GEO Multibeam Satellites: The Joint Use of Dynamic Beamforming and Precoding Under Practical Constraints

To adjust for the non-uniform spatiotemporal nature of traffic patterns, next-generation high throughput satellite (HTS) systems can benefit from recent technological advancements in the space-segment in order to dynamically design traffic-adaptive beam layout plans (ABLPs). In this work, we propose a framework for dynamic beamforming (DBF) optimization and adaptation in dynamic environments. Given realistic traffic patterns and a limited power budget, we propose a feasible DBF operation for a geostationary multibeam HTS network. The goal is to minimize the mismatch between the traffic demand and the offered capacity under practical constraints. These constraints are dictated by the traffic-aware design requirements, the on-board antenna system limitations, and the signaling considerations in the K-band. Noting that the ABLP is agnostic about the inherent inter-beam interference (IBI), we construct an interference simulation environment using irregularly shaped beams for a large-scale multibeam HTS system. To cope with IBI, the combination of on-board DBF and on-ground precoding is considered. For precoded and non-precoded HTS configurations, the proposed design shows better traffic-matching capabilities in comparison to a regular beam layout plan. Lastly, we provide trade-off analyses between system-level key performance indicators for different realistic non-uniform traffic patterns.

Two-Leg Deep-Space Relay Architectures: Performance, Challenges, and Perspectives

In this article, architectures for interplanetary communications that feature the use of a data relay are investigated. In the considered “two-leg” architecture, a spacecraft orbiting the Earth, or in orbit at a Lagrange point, receives data from a deep-space probe (leg-1) and relays them toward ground (leg-2). Different wireless technologies for the interplanetary link, namely, radio frequencies above the Ka band and optical frequencies, are considered. Moreover, the cases of transparent and regenerative relaying as well as different different orbital configurations are addressed, offering a thorough analysis of such systems from different viewpoints. Results show that, under certain constraints in terms of pointing accuracy and onboard antenna size, the adoption of a two-leg architecture can achieve the data rates supported by direct space-to-Earth link configurations with remarkably smaller ground station antennas.

Evaluation of BER for the EHF Communication System Serving Sharp-Coned Reentry Vehicles

“Communication blackout” could lead to severe risks to reentry vehicles. Previous studies have shown that EHF (extremely high frequency) communication is a potential solution to the “communications blackout” and was mostly used for blunt-coned vehicles. EHF communication with sharp-coned vehicles was rarely concerned before. In the present study, the propagation characteristics of the modulated EHF signals in a time-varying plasma sheath covering sharp-coned vehicles were studied numerically. The plasma sheath was obtained by solving a hypersonic fluid dynamics model. The signals propagation model is developed based on geometric optical theories. The carrier frequencies concerned in the present study are the “atmospheric window” frequencies, which are 94, 140, and 225 GHz, respectively. Based on the signal propagation characteristics, the EHF communication system was modeled. The modulation modes concerned in the present study are the 2ASK, 2PSK, and 2FSK, respectively. The results show that 1) the transmission coefficient of EHF signals in the side channel of the plasma sheath of the sharp-coned reentry vehicle increases with carrier frequency, 2) the gap between different channels at specific carrier frequency decreases with time, 3) the phase shift tends to be stable as the carrier frequency increases, and 4) the bit error rate (BER) varies with time and is affected by the location of the onboard antenna, carrier frequency, and modulation mode. The study shows that, in order to achieve good BER performance for the EHF communication system, 2PSK modulation of the signal at 140 GHz is recommended, and the onboard antenna is suggested to be installed on the wall and close to the bottom of the sharp-coned vehicle.

Radiation and Scattering of EM Waves in Large Plasmas Around Objects in Hypersonic Flight

The hypersonic flight regime is conventionally defined for Mach > 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but, in typical situations of interest, it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ the equivalence theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free-space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life reentry vehicle with full 3-D plasma computed via computational fluid dynamic (CFD) simulations. We address both scattering [radar cross section (RCS)] from the entire vehicle and radiation from the onboard antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses to an extent that matches well the usually perceived blackout in crossing layers in the cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope.

ЦИФРОВАЯ ОБРАБОТКА СИГНАЛОВ В ПАССИВНОЙ МНОГОПОЗИЦИОННОЙ РЛС, СОЗДАННОЙ НА БАЗЕ ГРУППИРОВКИ БЛА

The expediency of creating a passive multi-position radar based on a grouping of unmannedaerial vehicles is substantiated. The variant of building of such radar is proposed, the main technicalproblems of the sonar developing are evaluated and possible ways to overcome them areconsidered. It is shown that for detecting aerial targets and determining their coordinates fromthe radio emission of on-board equipment, the difference-rangefinder method is the most promisingas it does not depend on signal modulation and is potentially resistant to interference. Forsmall-sized UAV for transmitting information over open radio channels, the typical frequencyranges are 2.4 and 5.0 GHz. A block diagram of a passive multi-position radar has been developed,including digital shapers of the quadrature components of the received signal, blocks fordetecting and determining the coordinates of the target. The main parameters are calculated andanalytical expressions of digital signal processing algorithms for detecting and determining thecoordinates of the target are given. A stroboscopic effect is used in the digital quadrature componentshaper, which allows for bandpass signals to select the sampling frequency not by the upperboundary frequency of the spectrum, but by its width, which significantly reduces the requirementsfor the performance of the ADC and the DSP devices following it. The complex envelopes of thedetected signals are generated by the method of digital generation in the time domain using digitallow-frequency filters. The detection of signals is performed by an energy detector, the advantagesof which are simplicity of implementation and operability in the absence of a priori informationabout the received signal. To determine the coordinates of the radio source, signal delays arecalculated between pairs of signals received by three UAV from a multi-position radar, which aredetermined by the maximum modulo values of the mutual correlation functions of the signals inthese pairs. It is shown that the proposed algorithms are well adapted to the processing of possiblesources of radio emission on board small-sized UAV. It is established that the required performanceof the radar computer for real-time operation does not exceed 84.62 GFLOPS. The designof an on-board antenna module of a passive multi-position radar in the form of a microstrip reconfigurableantenna, tunable in frequency and polarization, is proposed.