ILS

Technology Overview

The instrument landing system (ILS) is a ground-based aeronautical radio navigation system. ILS assists aircraft pilots during the landing approach. ILS enables safe landing, especially when visibility is reduced due to bad weather conditions and at night, but also for cross-wind approaches. The ILS uses two different signals to deliver information about the aircraft’s position in relation to the ideal landing course:

• The localizer signal for lateral guidance
• The glide slope signal for vertical guidance

By demodulating the received signals and calculating the difference in DDM between the two tones, the ILS provides the pilot with course profile data. The difference in the depth of modulation (DDM) is the relative difference between the two 90 Hz and 150 Hz AM carriers for both the localizer and the glide slope.

Instrument landing system – localizer (ILS-LOC or ILS-LLZ) consists of two carriers. One carrier is modulated at 90 Hz, the other at 150 Hz, each with a depth of 20 %. Both modulated signals are transmitted as a narrow beam, one slightly to the left, the other slightly to the right of the runway. The aircraft’s ILS receivers demodulate the signals and calculate the DDM to deliver the horizontal deviation to the centerline of the runway.

Instrument landing system – glide slope (ILS-GS) also consists of two carriers. A 90 Hz modulated carrier is transmitted above the ideal landing course and a 150 Hz modulated signal is transmitted below it. Both tones are modulated with a depth of 40 % each. Again, the resulting DDM is evaluated by the aircraft’s ILS receivers. In this case, it is displayed to the pilot as vertical deviation.

Applications

ILS is applied as a navigation aid in international civil and military air traffic. It provides aircraft pilots with landing approach data relative to the ideal landing course. Marker beacons (MB) or DME indicate the aircraft’s distance to the runway. In combination with MB or DME, an ILS provides aircraft pilots with adequate guidance during landing approaches and landing.

Rohde & Schwarz Test Solutions

Air navigation systems such as ILS systems are subject to the highest safety requirements. Rohde & Schwarz offers unique and highly reliable test solutions for both ILS transmitter and receiver testing – from R&D to production as well as during calibration, installation and maintenance.

Excellent accuracy and highest spectral purity make the R&S®SMA100A signal generator ideal for ILS receiver testing. The generator simulates ILS-GS, ILS-LOC and COM/ID (for LOC) signals in line with ICAO standards.

ILS signal generators can be fully calibrated with the R&S®FSMR measuring receiver, a one-box solution that provides highest linearity. In combination with the R&S®NRP-Z37 power sensor module, minimum power measurement uncertainty down to lowest signal levels is possible.

The R&S®FSU spectrum analyzer and the R&S®FSQ signal analyzer deliver the optimal solution for testing ILS ground infrastructure in R&D, production and maintenance. The instruments precisely demodulate and analyze ILS signals. They provide the highest performance and flexibility and are easy to operate.

The R&S®EVS300 ILS/VOR analyzer offers the performance required in test applications for ground and flight inspection of ILS installations in the field. It offers very high accuracy and an extremely fast measurement speed of 100 measurements per second. The portable analyzer also features FFT, frequency scan and oscilloscope options in a single box for maximum flexibility in the field. In combination with the R&S®NRP-Z81, accurate measurement of envelope and timing in DME systems is possible.

The R&S®TS6300 ILS test system is a mobile automatic test solution for ILS ground measurements. The R&S^®ILSChecker software was developed in cooperation with skyguide, swiss civil and military air navigation services ltd. It offers significant cost savings through simplified operation and reduces the number of test flights required for antenna alignment.

Key Parameters

Standardization

To ensure the accurate operation of radio navigation systems, the International Civil Aviation Organization (ICAO) has specified the critical parameters for ILS systems, which are regularly controlled, calibrated and certified by flight inspection organizations.