Microwave Landing System Research Articles

Ground Test of Radio Frequency Compatibility for Cn-Band Satellite Navigation and Microwave Landing System

Ground Test of Radio Frequency Compatibility for Cn-Band Satellite Navigation and Microwave Landing System

A Compatibility Analysis between GNSS and Radio Astronomy/Microwave Landing System in C band

Due to the spectrum congestion of current navigation signals in L band, C band has been taken into consideration as a candidate frequency band for Global Navigation Satellite System (GNSS). However, the compatibility between navigation signals in C band and the existing signals in adjacent frequency bands must be carefully analyzed before any new band for satellite navigation is put into use. The radio astronomy (RA) band and microwave landing system (MLS) band are adjacent to C band, in order to evaluate the compatibility and interference between these signals, interference analysis between the C band which would be used for satellite navigation service and RA/MLS are proposed. The compatibility assessment rule by comparing the maximum of the power flux density (PFD) of the navigation signals in C band with the PFD threshold of RA and MLS is utilized. Simulation results show that this new type of signal modulation named as MSKBCS2 is more suitable considering the interference out of band of C band to RA/MLS. In addition, the restriction of the leak out of C band from the RA is more stringent. Consequently the navigation service in C band is more compatible with MLS compared with RA.

John Paul Wild AC CBE FAA FTSE. 17 May 1923 — 10 May 2008

Paul Wild stands tall among the founding fathers of modern radio astronomy. His early work became the foundation for all future research on solar radio bursts. He established the theory and identified the different types of radio bursts. He developed new types of instrument, including the dynamic spectrograph and a radioheliograph to make two-dimensional movie images. His early interest in the radio spectrum of hydrogen led to an analysis of the hyperfine structure of hydrogen emission and a publication that became a classic paper in the field. Recognition that the 21 cm hydrogen line could be used to measure the Zeeman effect, and through that magnetic fields in astronomical sources, was another key contribution to modern astronomy. He became Chief of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Division of Radiophysics and developed and demonstrated an outstanding microwave landing system for aviation. As Chairman of CSIRO he led the organization through a major restructuring and adapted CSIRO to bring it closer to industry while maintaining a high standard of excellence and originality. Throughout his career, Paul Wild provided great leadership at all levels of science in Australia.

John Paul Wild 1923 - 2008

Paul Wild stands tall among the founding fathers of modern radio astronomy. His early work became the foundation for all future research on solar radio bursts. He established the theory and identified the different types of radio bursts. He developed new types of instrument including the dynamic spectrograph and a radioheliograph to make two-dimensional movie images. His early interest in the radio spectrum of hydrogen led to analysis of the hyperfine structure of hydrogen emission and a publication that became a classic paper in the field. Recognition that the 21 cm hydrogen line could be used to measure the Zeeman effect and through that magnetic fields in astronomical sources was another key contribution to modern astronomy. He became Chief of the CSIRO Division of Radiophysics and developed and demonstrated an outstanding microwave landing system for aviation. As Chairman of CSIRO he led the organization through a major restructuring and adapted CSIRO to bring it closer to industry while maintaining a high standard of excellence and originality. Throughout his career, Paul Wild provided great leadership at all levels of science in Australia.

Investigation of Low Altitude Air-to-Ground Channel over a Tropical Sea Surface at C Band

This paper investigate a low altitude air-to-ground channel over a sea surface in the tropical region at C band. It is found that, compared to a high altitude air-to-ground channel where a free space propagation condition can be assumed, the sea surface re∞ection and other multipath propagation phenomena for lower altitude air-to-ground channel can readily be observed. Therefore, for low altitude ∞ight paths, spatial diversity at the ground station can be used to overcome signal degradation. Due to the rapid increase in aircraft density, the current air tra-c control (ATC) system that operates at VHF band is fast becoming saturated. Therefore, an alternative frequency band is introduced for tra-c control communication systems in order to satisfy this increasing demand. At present, C band is assigned for Microwave Landing System (MLS) in aviation navigation. In order to optimize the MLS performance at C band, thorough air-to-ground channel measurement in order to perform characterization is important. Matolak etal. (1) started an interesting piece of research work on wireless channel characteri- zation for the 5GHz MLS system in 2007. They covered the characterization of both small and large size airports, mainly using wideband characterization. In addition to this work, Tu etal. (2) conducted a comparative study of the conventional VHF system and the MLS C band system. The focus of both studies (1,2) concentrates on the propagation over land environments. However, little research work is done on the study of the air-to-ground link over a sea surface at C band. The evap- oration duct is a well recognized form of propagation mechanism that can result in a substantial increase in signal strength when signals of frequencies above 3GHz propagate over-water paths (3). Therefore, there is interest in the investigation of the air-to-ground link near to a tropical ocean. These results are important to modern military and commercial applications for a seashore country such as Singapore. As a continued work of our previous studies (4,5); C band channel characterization at a small airport (4), and air-to-ground channel investigation over a sea surface at high airborne altitude (20kft to 40kft) (5), in this study, a series of air-to-ground channel measurements at low airborne altitudes (1.2kft to 6kft) are conducted over the sea surface in the tropical region. The main objective of this paper is to report on the preliminary study of the spatial diversity at the ground station for the improvement of signal quality of the communication links. This is helpful for future research work in this area.

Channel Measurement/Modeling for Airport Surface Communications: Mobile and Fixed Platform Results

We provide examples of measurement and modeling results for wireless channel characteristics around airport surface areas. This is done for three settings: two mobile settings and one non-mobile setting, in the 5 GHz Microwave Landing System extension band. New findings, useful for communication system design in this environment, are reported.

Performance and Capacity of Direct-Sequence Spread Spectrum Overlay in the Microwave Landing System Band

We examine the performance of a direct-sequence spread spectrum (DS-SS) code-division multiple-access (CDMA) system used in a spectral overlay mode in the Microwave Landing System (MLS) band, from 5091–5150 MHz. The purpose of the overlay system is to enable increased spectral efficiency (higher data throughput), for future potential aeronautical datalink communications, particularly for short-range systems such as for airport surface, and terminal areas. We estimate the performance degradation incurred by both systems for a range of relative transmit powers, several DS-SS bandwidths and data rates, and example MLS and DS-SS system parameters, including the number of DS-SS users. We also briefly examine the use of multicarrier (MC) DS-SS signaling techniques. Our study uses both analysis and computer simulations, and complements prior work done for the use of DS-SS in the Instrument Landing System Glideslope band, where the ILS signal is an analog signal, in contrast to the (analog and) digital MLS signal. We provide examples that explore both MLS and DS-SS system parameter values appropriate for the successful application of overlay.

Harry Clive Minnett 1917 - 2003

In April 1940, Harry Minnett joined the Council for Scientific and Industrial Research (CSIR, renamed CSIRO in May 1949), soon after the establishment of the Radiophysics Laboratory for research into advanced radar systems. He remained with the organization until his retirement in 1981. Harry's ability as a meticulous engineer with a thorough understanding of the related underlying scientific principles was recognized by his being appointed to leading roles in a number of significant projects. These were to have a long-term impact on Australian science and technology. Among the most important was his role in guiding the design of the Parkes 64-m radio telescope to successful completion, and the establishment of a world-recognized research group on antenna design to support radio telescope design and upgrades. He also had considerable impact on the construction of the 3.9-m Anglo-Australian optical telescope at Siding Spring Mountain, New South Wales, and the 'Interscan' aircraft Microwave Landing System being developed by the Division of Radiophysics in collaboration with industry. He was Chief of the Division from 1978 to 1981. Harry died on 20 December 2003 after a short period of illness.

VLSI data demodulator for a microwave landing system

A VLSI circuit for demodulating the microwave landing system data format is presented. The approach is based on a second- order all-digital phase locked loop. The primary goal of the work is to find a cost effective way of embedding the demodulator within an integrated navigation receiver built around a customised application specific processor (ASP). While the fully digital nature of the design increases the demodulator's immunity to analogue-related problems, the dedicated hardware approach relieves the ASP from computationally complex tasks, such as carrier acquisition and clock synchronisation.

Enhanced vision for adverse weather aircraft landing

Landing in poor weather is a crucial problem for the air transportation system of the future. To aid the pilots for these conditions several solutions have been suggested and/or implemented including instrument landing system(ILS) and microwave landing system(MLS) that put the responsibility of the landing to a large extent in the hands of the airport facilities. These systems even though useful are not available due to their high costs except in few major metropolitan airports. This shortcoming has generated interest in providing all weather capabilities not on the landing facility but on the vehicle itself. The Synthetic Vision System Technology Demonstration sponsored by the United States Federal Aviation Administration(FAA) and the US Air Force represents an effort to respond to the above needs[1,2]. In this paper we present a summary of a typical synthetic vision system. This system consists of a scanning 35GHz radar a scanning antenna, a signal/image processor and a head up display(HUD). The pilot is presented a final perspective image of the scene sensed by the radar with associated flight guidance symbology. This systems is implemented in real time hardware and has been under going tower and flight testing under a variety of weather conditions since early 1992.

An automated approach for implementing GTD to model 2-D terrain effects at microwave frequencies

The impetus for the work described arose out of the need to model absolute signal strength for a microwave landing system (MLS) operating in the presence of irregular terrain. A complete, automated approach for predicting absolute signal strength at microwave frequencies for sites involving irregular, 2-D terrain profiles is presented. The approach involves two computer models: one to convert raw terrain elevation data into a linear profile; the other to estimate path loss using the geometrical theory of diffraction. The linearization of a terrain profile is accomplished by mapping raw terrain data into a phase domain and then identifying significant terrain features from the stationary phase points as defined by Fermat's principle. Since the entire modeling process is automated, little expertise on the part of the user is required. Validation of the approach is given by comparisons of measured and modeled signal strength data for representative sites. While the model described is limited to 2-D terrain, the approach is applicable to 3-D terrain as well.

A Review of the Interference Resistance of SPS GPS Receivers for Aviation

Demonstrations of GPS-based approach and landing systems have caused many potential users of the Microwave Landing System (MLS) to question whether it is appropriate to install such a costly system. An investigation of the resistance to electromagnetic interference of Standard Positioning Service (SPS) C/A-code GPS receivers in aviation environments demonstrated their susceptibility to inband noise; for example, 1 W of radiated power jammed an airborne receiver at ranges in excess of 30 km. Although resistance to out-of-band interference is significantly greater, transmissions from communications systems in frequencies adjacent to the GPS bands present considerable problems for GPS reception. Consequently, the use of C/A-code receivers for applications requiring high reliability and integrity, such as approach and landing, must be questioned.

MLS guidance errors due to runway approach-light structures

A data analysis program utilizing the boundary discrete points (BDP) technique is developed to predict the effect of runway approach-light systems (ALSs) on the microwave landing system (MLS) signal in space in terms of angle guidance error, path following error (PFE) and control motion noise (CMN). Various ALS configurations are modelled and field-tested. In this study, the MLS peak guidance errors caused by the presence of the ALS are found to be small, but such that they could cause out-of-tolerance conditions. Initial field-test results are in agreement with those predicted by the developed model.

Going strong after 50 years: antenna R&D at the CSIRO division of radiophysics

A brief history is given of antenna research and development at the Commonwealth Scientific and Industrial Research Organization (CSIRO) Division of Radiophysics. It covers wartime radar (1939-45), radio astronomy (1945-76), reflector-feed R&D (1963 to present), a microwave landing system (1971-83), the Australia telescope (1982-90), and satellite communications (1977 to present). Antenna measurement facilities and current projects are briefly described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Phase centre analysis of planar array antennas: Application to a microwave landing system

A mathematical model is developed to determine the antenna phase centre and its uniqueness. The model is then used to investigate the phase centre location for the azimuth antenna of a microwave landing system (MLS) and to determine its movement due to beam scanning and various design or operational errors. It is shown that, for an ideal antenna, i.e. the error-free case, the phase centre coincides with the antenna's geometrical centre. However, any deviation from ideal conditions, due to design, fabrication or operational errors, phase shifter quantization and the scan angle algorithm, causes its nonuniqueness and movement from the antenna's geometrical centre. The method is also used to treat environmental effects, such as ground reflection an thermal expansion or contraction, on the location of the antenna phase centre.

Microwave landing system modeling with application to air traffic control automation

Compared to the current instrument landing system, the microwave landing system (MLS), which is in the advanced stage of implementation, can potentially provide significant fuel and time savings as well as more flexibility in approach and landing functions. However, the expanded coverage and increased accuracy requirements of the MLS make it more susceptible to the features of the site in which it is located. An analytical approach is presented for evaluating the multipath effects of scatterers that are commonly found in airport environments. The approach combines a multiplane model with a ray-tracing technique and a formulation for estimating the electromagnetic fields caused by the antenna array in the presence of scatterers. The model is applied to several airport scenarios. The reduced computational burden enables the scattering effects on MLS position information to be evaluated in near real time. Evaluation in near real time would permit the incorporation of the modeling scheme into air traffic control automation; it would adaptively delineate zones of reduced accuracy within the MLS coverage volume, and help establish safe approach and takeoff trajectories in the presence of uneven terrain and other scatterers.

MLS system error model identification and synthesis

Signal-in-space modeling of approach and landing guidance systems such as the microwave landing system (MLS), which is necessary for aircraft certification, is addressed. A technique which can, in principle, identify the error sources in navigation systems and can also perform the inverse operation of synthesizing an error generator whose output is statistically equivalent to the original error data is described. The technique can also be used to validate equipment error budget assumptions. The identification and synthesis technique applies not only to MLS but to all navigation systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and Flight Test of a Differential GPS/Inertial Navigation System for Approach/Landing Guidance

A flight test project evaluating an integrated differential GPS (DGPS)/inertial navigation system as an approach/landing aid has recently been completed. The test objectives were to acquire a system performance database, and to demonstrate automatic landings using the integrated DGPS/inertial system augmented with barometric and radar altimeters. The airborne and ground components of the DGPS/inertial system are built around standard transport aircraft avionics: a global positioning/inertial reference unit and two GPS sensor units. Flight tests were conducted using a specially modified Boeing 737-100. Performance of the DGPS/inertial system was evaluated in real time by comparison against Microwave Landing System (MLS) position. DGPS/inertial, MLS, and laser tracking system position data were recorded during the tests for postflight analysis. Over 120 landings were flown during the project, 36 of which were fully automatic DGPS/inertial landings. The paper describes the objectives of the project, the system implementation, and the flight tests conducted. Laboratory test results and preliminary flight test results are also presented.

Terrain modeling for microwave landing system

A powerful analytical approach for evaluating the terrain effects on a microwave landing system (MLS) is presented. The approach combines a multiplate model with a powerful and exhaustive ray tracing technique and an accurate formulation for estimating the electromagnetic fields due to the antenna array in the presence of terrain. Both uniform theory of diffraction (UTD) and impedance UTD techniques have been employed to evaluate these fields. Innovative techniques are introduced at each stage to make the model versatile to handle most general terrain contours and also to reduce the computational requirement to a minimum. The model is applied to several terrain geometries, and the results are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The impact of the Microwave landing system (MLS) on runway capacity at British regional airports

The Microwave Landing System (MLS) has the ability to support curved and steep angle approaches and provides improved precision approach guidance when compared with the current Instrument Landing System (ILS). These MLS characteristics produce reduced inter‐arrival spacing when compared with ILS procedures and therefore increase runway capacity if the runway occupancy time is not the limiting factor. This paper considers the effect of MLS on runway capacity at British regional airports. Single runway and intersecting runways operations are examined.