# Reading — IADS Radar Taxonomy

By the end of this lesson you should be able to:

1. Name the **radar classes** in a layered integrated air-defense system (IADS).
2. Match each class to its **band**, **PRF regime**, and **beam type**.
3. Map each class to the **kill-chain link** it advances.
4. Predict how low-observable (LO) design changes the IADS's effective coverage at each layer.

## An IADS is not one radar

It is tempting to picture "the threat radar" as a single dish. A modern IADS is nothing of the sort. It is a **cascade of specialized radars**, each doing one job and handing the result to the next. A long-range set finds you; a 3D set builds a track; a fire-control set holds you tightly enough to shoot; a missile seeker takes over for the last few kilometers. Knowing which radar is which — from its band, PRF, and beam — is half of electronic warfare, because each class is attacked differently and sits at a different link of the kill chain.

The classes trade **range for precision**. The early ones see far but coarsely; the late ones see close but exactly. Information is *handed off* down the chain, and breaking a handoff degrades everything downstream.

:::{admonition} Key Concept
:class: key-concept

The IADS isn't one radar — it's seven cooperating ones. Each trades range for precision, and each passes its track to the next. Break one handoff and the links downstream starve.
:::

## The cast of characters

### Detection layer — Early Warning (EW) radar

The long-range eyes of the system. EW radars use **UHF or L band** for low atmospheric loss and good propagation, with large antennas and **low PRF** (big unambiguous range, poor velocity). The beam is a wide fan on a slow rotation, giving a 2D track only (range and azimuth, no height). Job: detect inbound activity at hundreds of kilometers and alert higher echelons. This is where stealth pays its biggest dividend in absolute kilometers.

### Tracking layer — Acquisition (ACQ), Height-Finder (HF), GCI

**ACQ** radars produce the 3D tracks that engagements need, typically in **S band** at long-but-shorter-than-EW range, with low-to-medium PRF. A 2D ACQ can be paired with a **height-finder (HF)** pencil beam to add elevation, or a modern 3D ACQ does both at once. **GCI** (ground-controlled intercept) sits at the command-and-control layer, vectoring interceptor aircraft using the 3D picture.

### Engagement layer — TTR and TIR

The **target-tracking radar (TTR)** is the SAM site's fire-control sensor: **X band**, a narrow slewable pencil beam, medium-to-high PRF (often pulse-Doppler), at tens to a low hundred kilometers. The **target-illuminating radar (TIR)** floods the target with continuous energy so a semi-active missile's seeker can home on the reflection. Break the TTR-to-missile lock and the engagement is over.

### Terminal layer — AI, seekers, fuses

**AI** (airborne interceptor) radar is a fighter's X-band AESA fire control, running search, track, and scan-while-track. The missile's own **active seeker** uses **Ka or mmW** for a compact aperture and very high PRF over the final 5–20 km. The **proximity fuse** is a very-short-range CW or high-PRF sensor that triggers the warhead at burst radius.

| Class | Band | Range | PRF | Beam | Job |
| --- | --- | --- | --- | --- | --- |
| EW | UHF / L | ~700 km | Low | Wide fan | Detect, alert |
| ACQ / HF | S | ~400–470 km | Low–med | Fan + pencil | 3D track for handoff |
| GCI | S / C | ~350 km | Med | Medium | Vector interceptors |
| TTR | X | ~150 km | Med–high | Pencil | Fire-control track |
| AI | X | ~80 km | High | Pencil | Airborne intercept |
| Seeker | Ka | < 20 km | Very high | Narrow | Terminal homing |
| Fuse | mmW | Burst radius | CW / high | Near | Trigger warhead |

## Mapping to the kill chain

Each class advances one link of the chain from L1:

| Kill-chain link | Radar class | Band |
| --- | --- | --- |
| Detect | EW | UHF / L |
| Track | ACQ + HF, GCI | S |
| Identify | ACQ multi-mode, ESM | S |
| Engage (cue) | TTR, AI | X |
| Engage (illuminate) | TIR | X |
| Engage (terminal) | Active seeker | Ka |
| Kill | Proximity fuse | mmW |

Break one row and you break the chain. EW investments tend to attack the **early rows** — they are cheaper to defeat and the payoff is higher, because everything downstream depends on them.

## What LO does to the coverage

Recall the fourth-power law: $R_{\max}$ scales as $\sigma^{1/4}$. A B-21-class target at roughly $-30$ dBsm has about $10^{-3}$ the RCS of a $0\ \text{dBsm}$ legacy fighter, which collapses detection range to about **17.8%** of the legacy value at every layer. Apply that to the notional ranges above:

| Layer | $R_{\max}$ vs 1 m² | $R_{\max}$ vs B-21 ($-30$ dBsm) | Absolute shrink |
| --- | --- | --- | --- |
| EW | ~700 km | ~125 km | ~575 km |
| ACQ | ~470 km | ~84 km | ~386 km |
| TTR | ~150 km | ~27 km | ~123 km |
| AI | ~80 km | ~14 km | ~66 km |

The *percentage* reduction is the same everywhere — that is what $\sigma^{1/4}$ guarantees. But the **absolute** kilometers bought are largest where the rings start largest: at the **EW and ACQ layers**. LO does not make the bomber invisible; it shrinks every ring proportionally, and the biggest raw payoff is at the long-range surveillance layers. The engagement layers still close in — which is why LO buys *time and standoff*, not invulnerability, and why the later blocks add active EW on top.

::::{admonition} Quick Exercise
:class: quick-exercise

You intercept these signals. Identify the most likely radar class.

1. $f = 1$ GHz, PRF $= 200$ Hz, large antenna, $360^\circ$ scan in seconds.
2. $f = 10$ GHz, PRF $= 10$ kHz, narrow pencil beam, locked on you.
3. $f = 35$ GHz, very high PRF, range collapsing, under 10 km away.

:::{admonition} Solution
:class: dropdown

1. **EW radar** — UHF, very low PRF, large rotating antenna: long-range surveillance.
2. **TTR or AI** — X band, pencil beam, locked: a fire-control track. Disambiguating the two needs more context (geometry from ES, an ELINT library).
3. **Active missile seeker** — Ka band, terminal, range collapsing: the missile is homing.
:::

::::

## Wrap-Up

An IADS is a cascade of radar classes, each doing one job and handing off to the next. Band, PRF, and beam type together tell you the class and the kill-chain link it serves. LO buys the most absolute kilometers at the EW and ACQ layers, while the engagement layers still close in — so stealth is standoff and time, not invisibility. Next, **L8** supplies the missing piece behind every "$R_{\max}$": how detection actually happens, in terms of SNR, $P_d$, and $P_{fa}$.