Radar display options - clarify adv. v disadv.

[Paddy]

Hello Heatblur,

The Phantom F4 manual you have made is absolutely top notch by the way.  Hats off to you.

I have a question regarding the radar display options.  The manual states what B WIDE/B NAR/PPI WIDE/PPI NAR/VI are but it does not tell me what advantages/disadvantages or trade offs I get by using each option.

So is it that PPI WIDE for example, gives a greater angle of sweep but as a consequence updates slower and has shorter range than PPI NAR?  I have not yet found a mention of what one mode gives me over the other amongst these first 4 options?

Thank you,

Paddy

[Tiger-II]

RADAR is just a microwave transmitter. AFAIK this model has fixed power output, so with that in mind, think of it like this:

To detect an aircraft (for the signal to be strong enough to be detected), the target must reflect a certain amount of RF energy. How much energy is called the sensitivity of the RADAR set. If it requires a large percentage of the output power output to be reflected back, then it is not very sensitive; conversely, if it only requires a very small amount of that transmitted power to be reflected back, then it is considered sensitive.

How much energy reaches a target? The power output of the RADAR is spread over the area being scanned. There are two parts to consider: the output in the direction and cone angle the RADAR is looking, then the combined power in the area where the scan areas overlap.

The beam can be narrowed, which increases the power being transmitted to that area, meaning power reflected back from any objects is stronger, meaning they are more likely to be detected. This includes detecting the same object but at a further distance.

As you already stated, wider sweep angles mean you cover more sky, but that takes time, and reduces the overall power being beamed at a target. Targets therefore generally need to be a bit closer to you to be detected this way.

If you really focus the beam (no sweep, narrow beam width), then you pour much more energy into an area, as well as greatly increase the detection rate in that area, meaning targets you missed previously, could now be detected. This effect is so great, it can effectively double the detection range of the RADAR, but you are only looking at a very small cone in the sky.

Tracking a target is a different matter. Later aircraft with more sophisticated RADAR sets employ verious techniques to do this, but in the F-4, the way it is done is by nutating the RADAR head slightly to "search" for where the signal is strongest, then using additional logic, it detects the relative bearing of the strongest signal, and steers towards it. This is the essence of how it tracks a target.

The stronger the signal and the more frequently it updates, the easier for the RADAR to detect the target and follow it. This becomes more critical the closer the target is. Imagine a target close-in and maneuvering; its relative motion to the RADAR beam is very high. It can be so high, the target leaves the LOS of the RADAR before it can move to keep with it, thereby breaking lock (most extreme example is flying perpendicular to the RADAR beam at very high speed). There are other effects from this, but that is the basic premise of tracking.

Edited May 24, 2024 by Tiger-II

[Paddy]

Excellent explanation and clear.  Top stuff @Tiger-II