Instrumental Landing System

[Paco Martinez]

Hello everyone,

I’m doing a report about the Instrumental Landing System, and I have a question.

The Instrumental Landing System is a worldwide used system to assist airplanes to land. It’s operation principle it’s explained here:

https://landingsystem.com/

My questions are, could someone tell me if is there any difference if the localizer signal is sent in log-periodic type or dipole antennas?

And, In the localizer, a signal can be sent to confirm whether or not the information is properly received. Does somebody know how is this clearance signal sent?

Thanks a lot!

 

[alec_t]

is there any difference if the localizer signal is sent in log-periodic type or dipole antennas?

Not sure what distinction you're making there, since a log-periodic antenna consists of an array of dipole antennas.
A log-periodic antenna is designed to operate over a wide range of frequencies. I don't see any advantage in using one in an ILS system, for which both the localizer and the glide-slope signals are narrow band.

 

[Paco Martinez]

Sorry if you don't explain me well.
The point is, if I'm not mistaken, that historically Localisers used dipole antennas, and currently they use log-periodic antennas. The question is whether you would know what advantage this change offers.
Thanks in advance.

 

[alec_t]

As I said, I can't see any advantage.

 

[JimB]

could someone tell me if is there any difference if the localizer signal is sent in log-periodic type or dipole antennas?

I know next to nothing about ILS/Localiser systems, but I do know quite a lot about radio.

A simple dipole antenna will radiate an equal strength signal in many directions, for a localiser it is best if all the radio signal is transmitted in one direction, along the line of the runway.
By using a directional antenna, all the RF energy is transmitted in the direction where it is most useful to a distant aircraft.

A log-periodic antenna is one form of directional antenna, it will also work across a wide range of frequencies.

So, coming back to your question, there will be no difference in the form of the signal, but by using a directional antenna, more effective use will be made of the RF energy from the transmitter.

JimB

 

[alec_t]

It's my understanding that the usual localiser antenna system is a horizontal co-linear array of dipoles to give narrow-beam directionality in the horizontal plane at ~110MHz. Is that what you mean by "dipole antennas", or do you have some other configuration in mind?

 

[unclejed613]

and currently they use log-periodic antennas.

those are yagi antennas... much different from a log-periodic. the purpose of the yagi is to make a tight directional beam. a log periodic is designed to work over a wide spread of frequencies, the yagi used for ILS is narrow-band. in the picture at the top of the page you linked, each antenna is actually two yagis staggered vertically, this creates an upper lobe at one frequency, and a lower lobe at another frequency. where the two beams are equal signal strength is the glide slope, and the pilot keeps these signals equal strength on his display as he descends towards the runway. the localizer keeps the plane on track horizontally, while the glide slope aligns the descent vertically. you can find more detailed information here: https://en.wikipedia.org/wiki/Instrument_landing_system

ILS is a modernized adaptation of various landing aids used during WWII, such as the Lorenz Blind Approach system used to guide planes to the runway during bad weather, and one adaptation of it during the war was to have two long range lorenz beams to guide bombers to a target on night raids, the first beam was followed across the english channel, and a second beam crossed the path of the first beam over the target. when the planes were in the center of both beams, they dropped their bombs.

 

[Boxnut]

Usually, localizer beacons are twin dipole to radiate the signal upward, centered down the runways, that point where the signals from each dipole are 180 degrees out of phase and cancel each other. the marker beacons are not much different, just lacking that phasing.
The localizer works much like the VOR stations but in horizontal plane. the glide slope the same but in the vertical plane.
Instead of 360 degree phased array, these are narrow, centered in line with the runways.
The log periodic is not used given the narrow frequency of about 110 Mhz. Cophased dipoles are more than effective. Yagy's are sometimes used