Capt Pankaj Pahil
www.ghostaviator.com
Capt Pankaj Pahil
www.ghostaviator.com
Capt Pankaj Pahil
DGCA CPL / ATPL Study Notes • Radio Navigation • Ch 12
✈ Chapter 12: Ground Radar
ATC Radar Systems
© Capt Pankaj Pahil | www.ghostaviator.com
1. Introduction
ATC uses ground radars extensively to serve a large number of requirements. Both primary and secondary radar techniques are used. Primary radar detects all aircraft (including those without transponders) and may incorporate Moving Target Indication (MTI).
📡 ATC Ground Radar Systems
- Area Surveillance Radar (ASR) — long range en-route
- Terminal Area Surveillance Radar (TAR) — medium range TMA
- Aerodrome Surveillance Approach Radar — short range approach
- Precision Approach Radar (PAR) — talk-down
- Airport Surface Movement Radar (ASMR/ASMI) — surface movement
2. Area Surveillance Radar (ASR)
Fig 12.1 & 12.2: Coverage of London ACC and Scottish ACC radars
📡 ASR Characteristics
Longer pulse length ensures good target illumination at long range. Low PRF ensures echo returns from max range before next pulse.
| Parameter | Value |
|---|---|
| Range | 200–300 NM |
| Wavelength | 10–50 cm |
| Pulse length | 2–4 µs |
| PRF | 300–400 pps |
| Scan rate | 5–6 rpm |
| Purpose | Airway surveillance — range and bearing of aircraft |
3. Terminal Surveillance Area Radar (TAR)
📡 TAR Characteristics
| Parameter | Value |
|---|---|
| Range | Up to 75 NM |
| Wavelength | 10, 23 or 50 cm |
| Pulse width | 1–3 µs |
| Purpose | Traffic control in TMAs |
| UK radar separation | 3 NM within 40 NM (or 60 NM approved) of radar head, below FL245 |
4. Aerodrome Surveillance Approach Radar
📡 Aerodrome Radar Characteristics
| Parameter | Value |
|---|---|
| Range | Up to 25 NM |
| Wavelength | 3 cm or 10 cm |
| Pulse width | 0.5–1 µs |
| Services provided | Radar vectoring to ILS; Surveillance Radar Approach (SRA); positional information/control in vicinity |
5. Airport Surface Movement Radar (ASMI)
Fig 12.4: ASMI display — with and without fixed features processed out
⚠ ASMI Key Design Parameters
| Parameter | Value |
|---|---|
| Frequency | 15–17 GHz (SHF) |
| Wavelength | 1.76–2 cm |
| Beamwidth | 0.2°–1° (very narrow) |
| Scan rate | 60 rpm |
| PRF | 4,000–20,000 pps |
| Pulse width | 0.03 µs |
| Range | 2.5–6 NM in light precipitation |
| Purpose | Detailed display of aircraft/vehicles on runways and taxiways in all weather |
⚡ ASMI Limitations
- High frequency (SHF) → increasingly attenuated by precipitation → range reduces in heavy rain
- EHF band NOT suitable for ASMI — too much attenuation in most precipitation types
- Processing can remove selected fixed features (buildings, taxiways) leaving only moving targets visible
6. Radar Characteristics Summary
Fig 12.3: UK airways structure — served by ground radars
| System | Range | Wavelength | PW | PRF | Scan Rate |
|---|---|---|---|---|---|
| ASR | 200–300 NM | 10–50 cm | 2–4 µs | 300–400 pps | 5–6 rpm |
| TAR | Up to 75 NM | 10, 23, 50 cm | 1–3 µs | Medium | Medium |
| Aerodrome | Up to 25 NM | 3 or 10 cm | 0.5–1 µs | Higher | Higher |
| ASMI | 2.5–6 NM | 1.76–2 cm | 0.03 µs | 4,000–20,000 pps | 60 rpm |
7. Practice Questions
Q1. A primary radar has a PRF of 275 pps. Time interval between leading edges of successive pulses:
(a) 3.64 milliseconds
(b) 36.4 milliseconds
(c) 3.64 microseconds
(d) 36.4 microseconds
Answer: (a)
PRI = 1/275 s = 1,000,000/275 µs = 3636 µs = 3.64 milliseconds.
PRI = 1/275 s = 1,000,000/275 µs = 3636 µs = 3.64 milliseconds.
Q2. Primary radar PRF = 450 pps. Maximum range (ignoring PW and flyback):
(a) 333 NM
(b) 180 NM
(c) 666 NM
(d) 360 NM
Answer: (b)
Max range = 81,000/450 = 180 NM.
Max range = 81,000/450 = 180 NM.
Q3. Frequency band and scan rate of Airfield Surface Movement radars:
(a) SHF; 60 rpm
(b) SHF; 200 rpm
(c) EHF; 100 rpm
(d) EHF; 10 rpm
Answer: (a)
ASMI operates in the SHF band (15–17 GHz) at a scan rate of 60 rpm.
ASMI operates in the SHF band (15–17 GHz) at a scan rate of 60 rpm.
Q4. Radar with scanner rotation 60 rpm, beamwidth ~0.5°, PRF 10,000 pps. This is:
(a) ASMI with theoretical range 8 NM
(b) Precision Approach Radar
(c) ASMI with theoretical range 16 NM
(d) High resolution Surveillance Approach Radar
Answer: (a)
All characteristics (60 rpm, narrow beam, high PRF, short PW) match an ASMI. Max range = 81,000/10,000 = 8.1 NM ≈ 8 NM.
All characteristics (60 rpm, narrow beam, high PRF, short PW) match an ASMI. Max range = 81,000/10,000 = 8.1 NM ≈ 8 NM.
DGCA CPL/ATPL Radio Navigation Study Notes
Chapter 12 — Ground Radar
Capt Pankaj Pahil | www.ghostaviator.com
For personal study use only.
Chapter 12 — Ground Radar
Capt Pankaj Pahil | www.ghostaviator.com
For personal study use only.