8.1 Wi-Fi 6E in your home
Your router has 2 to 6 patch antennas inside, often hidden in flat plastic enclosures. Some are vertical-polarized, some horizontal-polarized, providing diversity. The router runs MU-MIMO: it shapes beams toward each connected device using DSP weights across the antennas, sending different streams to each device on the same frequency. At 6 GHz, cm, so the antennas are tiny and the spacing fits in a normal-sized box.
Walls, floors, furniture, and people all cause multipath. The OFDM modulation in Wi-Fi sends the data on hundreds of narrowband subcarriers, each of which sees its own complex channel response. The receiver equalizes per subcarrier, undoing the multipath in the digital domain.
8.2 Satellite TV reception
A geostationary satellite at 36,000 km transmits at 12 GHz with about 50 dBW EIRP. Your 0.5 m offset-fed dish gives about 35 dBi at 12 GHz. The LNB (Low-Noise Block) at the focal point converts 12 GHz down to 1–2 GHz before sending it down the coax to your set-top box. The LNB has a noise figure of about 0.3 dB and a gain of about 60 dB, dominating the system noise temperature.
The link budget closes by milliwatts per square meter at the dish, decoded as QPSK or 8-PSK using Reed-Solomon and convolutional coding. Heavy rain can fade the link by 5 dB and the signal flickers; that is the rain margin running out.
8.3 NASA Deep Space Network
The DSN is three sites (Goldstone California, Madrid Spain, Canberra Australia) on three continents, 120° apart, providing 24-hour coverage of any deep-space probe. Each site has multiple 70 m and 34 m parabolic dishes. Cassegrain feeds, cryogenic LNAs at about 30 K system temperature, and elaborate coherent integration over many seconds let DSN pull signals out of thermal noise from billions of km away.
The combination of Friis-equation reach, antenna directivity, low-noise receiving, error-correction coding (Reed-Solomon plus convolutional or modern turbo codes), and patient integration is what makes Voyager 1 (now in interstellar space) still a viable scientific platform after 47 years.
8.4 Cellular base stations
A 4G LTE base station has typically 6 to 9 panel antennas covering 3 sectors, each 120°. Each panel is a vertically-oriented array of patches, electrically downtilted by a few degrees so the main beam covers a defined cell radius without splashing into the next cell. The antenna gain is around 16 to 18 dBi per panel.
5G base stations replace this with massive MIMO: a 64-element or 256-element planar array per sector, with full digital beamforming. The beam tracks individual users instead of being fixed. At mm-wave frequencies (28, 39 GHz), the array is so small that hundreds of elements fit in a panel the size of a laptop screen.
8.5 Smartphones with PIFA and multiple antennas
A modern phone has 5 to 10 antennas:
- LTE main and diversity (PIFAs along the bezel).
- 5G mid-band PIFAs.
- 5G mm-wave patch arrays (in iPhones with 5G UWB, four small phased arrays around the edges).
- Wi-Fi 2.4 / 5 / 6 GHz (often shared with BT).
- GPS (small patch under glass, RHCP).
- NFC (loop antenna).
- UWB (ultra-wideband, for spatial ranging like AirTag).
Phone designers spend enormous effort packaging these without crosstalk. The metal frame is often electrically part of the antennas (Apple did this to elegant effect, and chaotic effect with the iPhone 4 "death grip" issue). Diversity and MIMO use multiple antennas to combat fading.
8.6 Automotive 77 GHz radar
Modern cars have multiple radars at 77 GHz (the band 76–81 GHz is allocated for automotive). Long-range radar (front bumper) sees out to 250 m for adaptive cruise control. Short-range radars (corners, rear) see ~30 m for blind-spot, parking, cross-traffic.
The radars are tiny phased arrays (the wavelength is 4 mm) integrated into MMICs. They scan electronically in azimuth, transmitting frequency-modulated continuous-wave (FMCW) chirps and processing the return. The patches and feeds are printed directly into the SiGe or CMOS package.
8.7 Starlink and other LEO constellations
A SpaceX Starlink user terminal is a 50 cm phased-array of patch antennas, electronically steered to track a low-orbit satellite passing overhead in 4–5 minutes. As one satellite sets, the array re-steers to the next. The satellite has its own phased array on board.
The combination of high antenna gain, low orbit (550 km versus 36,000 km for GEO), and steerable beams makes Starlink-class systems competitive with terrestrial broadband, at a cost of much more complex hardware than a fixed dish.