$re = '/\*\*QUESTION:\*\*\s*((?:.|\n)*?)\s*\*\*ANSWER:\*\*\s*((?:.|\n)*?)(?=\s*\*\*QUESTION:\*\*|\Z)/ms';
$str = '**QUESTION:**
What are the key design considerations for fabricating glide slope antennas in composite or metal aircraft, and how do these differ from those for other aviation antennas like VOR/LOC or DME antennas?
**ANSWER: Thought Process**
This question requires a detailed comparison between the design principles of glide slope antennas (used in composite/metal aircraft) and other aviation antennas like VOR/LOC or DME. I’ll structure the answer by first outlining the general design considerations for glide slope antennas, then contrasting them with the specific designs of VOR/LOC and DME antennas.
---
**Glide Slope Antennas in Composite/Metal Aircraft:**
1. **Ground Plane Requirements:**
- These antennas are typically shorter (scaled down from VOR/LOC) and mounted atop the windshield or canard.
- The ground plane must be flat and conductive (e.g., aluminum or copper foil strips) to ensure resonance.
- The antenna element is often folded back to avoid structural interference.
2. **Low-Noise Design:**
- Designed to avoid shadowing from the aircraft’s structure.
- The "gamma matching" network reduces coaxial feedline losses.
---
**Contrast with VOR/LOC Antennas:**
VOR/LOC antennas are longer (quarter-wavelength) and often hung from the vertical fin. Their ground plane is a flat metal sheet, and they’re resilient to shadowing from the aircraft’s structure. Feedline losses are minimal, allowing signal splitting to multiple receivers (e.g., dual VORs + GS).
---
**DME Antennas:**
- Quarter-wavelength vertical antennas with a flattened ground plane.
- Require heavy-duty mounting (e.g., brazed insulators, riveted flanges).
- Material choices differ: copper foil/Plexiglas for composite airplanes, aluminum for metal.
---
**Key Differences:**
- Glide slope antennas prioritize compactness and avoidance of structural shadowing, while VOR/LOC focus on long-range performance and vertical-fin mounting.
- DME antennas emphasize durability and material rigidity, especially in composite aircraft.
---
**Final Answer:**
Glide slope antennas for composite/metal aircraft demand flat ground planes, short lengths, and avoidance of structural interference. In contrast, VOR/LOC antennas prioritize quarter-wavelength design and vertical-fin mounting, while DME antennas require thick, rigid mounts (e.g., copper foil, Plexiglas) to handle composite aircraft stresses. The feedline characteristics also vary: glide slope antennas use a gamma match for low losses, while VOR/LOC and DME rely on tight, low-impedance coaxial runs.';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php