Whether military aircraft or civil aircraft, there will be several sets of communication equipment. Some are connected with satellites and some are connected with the ground. No matter what kind of connection, you need an antenna. Even a small four rotor UAV needs to be located through GPS antenna.
Similarly, there are more and more array antennas on smart cars, such as various cellular bands, Wi Fi, even 5g and its MIMO requirements, V2V (vehicle to vehicle), radar (77GHz, etc.). Its own mobility increases the difficulty of design. In terms of RF requirements and constraints, the antenna design and layout of autonomous vehicles will become more like aircraft design.
High frequency (HF)
High frequency (HF) communication system provides long-distance sound communication. It provides communication between aircraft or between ground stations and aircraft.
HF system operates between 2mhz-29.999mhz. The system uses the earth’s surface and ionosphere to reflect communication signals back and forth. The distance of reflection varies with time, RF and aircraft altitude.
The control panel sends information and control signals of the selected frequency to the transceiver. The audio control board sends these signals to the reu:
– HF radio selection signal
– receive volume control
– push to talk (PTT)
During transmission, microphone audio and PTT signals enter HF transceiver through reu. The transceiver uses microphone audio to modulate the RF carrier signal generated by the transceiver. The transceiver sends the modulated RF signal to the antenna through the antenna coupler and transmits it to other aircraft or ground stations.
Also during transmission, the flight data acquisition component receives PTT signals from the transceiver. Use the DFU as the keying event to record the signal.
During reception, the antenna receives the modulated RF signal and sends it to the transceiver through the antenna coupler. The transceiver demodulates or separates audio from the RF carrier. The received audio is sent from HF transceiver to in-flight interphone speaker and earphone through reu.
Select the call decoder to receive audio from the HF transceiver. The SELCAL decoder monitors the SELCAL call audio from the ground station.
HF transceiver receives air / ground discrete signals. The HF transceiver uses this discrete signal to calculate the flight segment for the internal fault memory.
The HF antenna is at the leading edge of the vertical stabilizer.
The antenna coupler is inside the vertical stabilizer.
Warning: when launching the HF system, ensure that personnel are at least six feet (2 meters) away from the vertical stabilizer. Transmitting RF energy from HF antenna is harmful to people.
VHF communication system
VHF communication system provides visual distance communication of sound and data for the crew. VHF communication system can be used for communication between aircraft and between aircraft and ground station.
The tuning frequency range of VHF communication radio is 118.00 to 136.975mhz. VHF radio is used for the transmitter to receive voice communication.
The working frequency of VHF communication system is 118.00mhz to 136.975mhz, and the interval of 8.33khz is only applicable in these frequency bands:
- 118.000-121.400
- 121.600-123.050
- 123.150-136.475
Instrument landing system (ILS)
Course antenna
The localizer antenna has two elements. One element provides RF input to ILS receiver 1 and the other element provides RF input to ILS receiver 2. The localizer antenna receives frequencies from 108.1mhz to 111.95 MHz, spaced at odd bits of one tenth of the bandwidth.
Glide path antenna
The glide path antenna also has two elements. One element provides RF signal input to MMR 1 and the other element provides RF signal input to MMR 2. The glide slope antenna receives frequencies from 328.6 MHz to 335.4 MHz.
The glide path and heading path antennas are in the front radome. The glide slope antenna is above the weather radar antenna. The course antenna is below the weather radar antenna.
Radio altimeter system
The radio altimeter (RA) system measures the vertical distance from the aircraft to the ground. The radio altitude is displayed on the display unit (DU) in the cockpit. The radio altitude is calculated by comparing the transmitted signal with the received signal using the receiver transmitter assembly. The R / T module transmits a radio signal and then receives the reflected RF signal returned from the ground to determine the altitude of the aircraft. The R / T outputs the calculated altitude data to two ARINC 429 data buses and sends it to the use system on the aircraft.
The flight crew and other aircraft systems use this altitude data during low altitude flight, approach and landing. The range of the system is – 20 to 2500 feet.
The adjustable radio minimum altitude warning is operated by the radio altitude system and can be independently selected from 0-999 feet by the captain and co pilot EFIS control panel. This radio minimum altitude option is compared and processed in the display electronic unit (DEU) with the existing radio altitude value output from the radio altitude receiver / transmitter. When the aircraft descends to the selected radio minimum altitude, a flashing radio minimum warning appears on the available Du.
The RA antenna is at the bottom of the body.



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