Radio detection and ranging, spined into 35 articles and seven three.js microsims: how a transmitted waveform becomes a target's range, radial velocity, angle and image once its echo comes back. Article face: [[Radar]]. Radar sits downstream of its sibling spine [[PORTAL_Signal_Processing]] — the sampling, filtering, matched-filtering and detection machinery that portal treats in the abstract, this one aims end to end at a single problem: find the target, resolve what it is doing, and know how sure to be about it. The physics is closed-form throughout, nothing baked, computed fresh on every control change from the pack's own `wt-radio.js` library (`ant`, `line`, `radar`, `rx`, `spectrum` namespaces). ## Microsims — three.js (built, gate-verified — awaiting deploy) Seven root sims for the portal pack (`specs/portals/PORTAL_Radar.pack.json`, `BRIEFS_radar.md`: 7 roots). All seven are built and gate-verified (SHIP) in the working tree; none are live yet on the production Netlify site, so — the same honesty rule as Signal Processing's own build-target row — this table carries the real explanatory text a live embed would otherwise carry, not an iframe. Intended path once deployed: `https://wikitube-3d-microsims.netlify.app/radar/<slug>.html`. | # | Station | Concept | Explanatory text | Try | |---|---------|---------|-------------------|-----| | 1 | [[Pulse-repetition_frequency]] | Range/velocity ambiguity | Two stacked fold panels show that one PRF sets both the unambiguous range (c/2PRF) and the blind speeds (k·PRF·λ/2) at once — a target beyond either limit folds back to a false reading, and a second PRF resolves which fold is real. At PRF = 1000 Hz and f0 = 10 GHz, unambiguous range works out to 149.9 km and the first blind speed to 14.99 m/s. | Turn on dual PRF and find where both fold curves agree. | | 2 | [[Continuous-wave_radar]] | CW vs. FMCW ranging | Two stacked frames plot transmit and receive frequency against time. Unmodulated CW gives Doppler only, no range; switching to FMCW's sawtooth sweep buys range back as a beat frequency, at the price of the target's own Doppler biasing that beat. At R = 1500 m, v = 40 m/s, B = 20 MHz and T = 2 ms, that coupling produces a range error of exactly 40.0 m — 2.67% of R. | Switch to fmcw and shrink the sweep period. | | 3 | [[Moving_target_indication]] | Clutter cancellation & blind speeds | A canceller-response curve plots response against velocity, with blind-speed ticks and an optional staggered-PRF overlay. A delay-line canceller cancels stationary clutter, but also cancels any target whose Doppler lands on a PRF multiple; staggering a second PRF re-opens that hole. A 15 m/s target reads response 0.0043 (nearly cancelled) on one PRF, and 0.589 once staggered. | Turn on stagger at a blind-speed velocity. | | 4 | [[Constant_false_alarm_rate]] | Adaptive detection threshold | A range-cell power profile carries clutter and two injected targets, with an adaptive CFAR threshold riding the local average against a dashed fixed-threshold reference. CFAR holds the false-alarm rate constant across a clutter edge that would swamp a fixed threshold: at a 16-cell reference window and Pfa = 1e-6, alpha = 17.28 (a 12.37 dB margin), and the fixed threshold at that same margin misfires on most of the clutter cells while the adaptive one stays clean. | Raise snr until the in-clutter target crosses the adaptive threshold. | | 5 | [[Monopulse_radar]] | Single-pulse angle error | Two stacked frames show a squinted beam pair and the sum/difference error curve it produces. Sum and difference beams built from one pulse trace an S-shaped error curve that reads angle-off-boresight directly, with no scanning needed. The boresight slope, 21.18 per radian, matches the closed form 4·ln2·squint/beamwidth² to six figures. | Widen the beamwidth and watch the error curve's linear region shrink. | | 6 | [[Radar_display]] | Sweep & phosphor persistence | A 3D top-down circular scope rotates a sweep line over target blips that fade with phosphor-persistence afterglow, with optional clutter. A display shows an afterglow of past returns, not returns as they arrive — reading it means knowing sweep rate and persistence together. At age = 2 s and tau = 2 s, persistence works out to 1/e, or 0.368. | Shorten persistence and watch blips vanish before the sweep returns. | | 7 | [[Synthetic-aperture_radar]] | Synthetic antenna aperture | An oblique 3D scene lays out the ground plane, flight path, footprint wedge and aperture segment, with a top-down view toggle. A moving antenna's flight path becomes a long synthetic antenna, and azimuth resolution collapses to a strikingly simple D/2 — independent of range and wavelength. A 2 m real antenna gives 1.00 m resolution unchanged whether range is 10 km or 30 km, even though the aperture triples in length. | Shrink the real antenna D and watch the resolution readout improve, not worsen. | ## Child articles All 35 are written and gate-verified at wt-article density, grouped below by the spine's own four parts. ### Part A — Principles and the range equation <!-- SECTIONSIMS:BEGIN g34 2026-09-19 - microsims the articles linked here play; generated by _tools/generate/g34_portal_section_sims.py; do not hand-edit inside --> *Microsims from the articles this section links:* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/flight/Radar.html" data-title="Radar"></div> <!-- SECTIONSIMS:END --> - [[Radar]] — object-detection system using radio waves; the hub article - [[Radar_cross_section]] — strength of an object's radar echo - [[Radar_horizon]] — the distance at which earth curvature hides ground targets - [[Pulse-repetition_frequency]] — number of pulses of a repeating signal *(sim above)* - [[Continuous-wave_radar]] — radar that transmits a known, stable continuous wave *(sim above)* - [[Doppler_radar]] — radar equipment that reads radial velocity from the return's frequency shift - [[Radar_signal_characteristics]] — the time- and frequency-domain parameters every radar waveform is described by ### Part B — Waveforms and signal processing - [[Pulse_compression]] — signal-processing technique - [[Chirp]] — frequency-swept signal - [[Moving_target_indication]] — radar signal-processing technique *(sim above)* - [[Constant_false_alarm_rate]] — adaptive detection algorithm *(sim above)* - [[Clutter_(radar)]] — unwanted echoes in electronic systems - [[Radar_tracker]] — radar component that maintains target tracks - [[Track_while_scan]] — radar operation mode - [[Pulse-Doppler_radar]] — radar system combining pulsed transmission with Doppler processing ### Part C — Antennas, beams and displays - [[Phased_array]] — array of antennas creating a steerable beam - [[Active_electronically_scanned_array]] — type of phased-array radar - [[Monopulse_radar]] — single-pulse radar system *(sim above)* - [[Beamforming]] — signal-processing technique for sensor arrays - [[Radar_display]] — electronic device that shows the processed returns *(sim above)* - [[Plan_position_indicator]] — radar sweep display ### Part D — Systems, imaging and countermeasures - [[Synthetic-aperture_radar]] — radar used to create images of landscapes *(sim above)* - [[Inverse_synthetic-aperture_radar]] — radar 2D mapping technique - [[Weather_radar]] — radar used to locate and monitor meteorological conditions - [[Secondary_surveillance_radar]] — radar system used in air traffic control - [[Over-the-horizon_radar]] — long-distance radar technology - [[Bistatic_radar]] — radar system defined by the separation of its transmitter and receiver - [[Passive_radar]] — radar system that does not transmit - [[Ground-penetrating_radar]] — geophysical method that images the subsurface with radar pulses - [[Radar_altimeter]] — measures an aircraft's height above the terrain - [[Radar_jamming_and_deception]] — form of electronic countermeasures - [[Stealth_technology]] — military technology to make personnel and material less visible - [[Radar_astronomy]] — observing nearby astronomical objects by analyzing reflected microwaves - [[Cavity_magnetron]] — device for generating microwaves - [[Chain_Home]] — radar defense system in Britain during World War II --- *Spine portal, curated (WIKI_RULES §7). Assets: 35 child articles (gate-verified) + 7-sim three.js slate (SHIP, awaiting Netlify deploy). Pack: `specs/portals/PORTAL_Radar.pack.json`. Sibling spine: [[PORTAL_Signal_Processing]].* --- *Repopulated 2026-09-19 · append-only · source: _tools/generate/g34_portal_section_sims.py@00a28cb2 (players of the linked articles, each URL 200-checked) · 8 added · 0 deletions*