The radio laboratory in the APNet section serves multiple purposes related to radio propagation and radio equipment.
Main areas are: Radio Channel sounding, optical links and measurement Antennas
Radio Channel Sounding
One of the core activities of the APNet radio laboratory has traditionally been radio channel sounding, ie. measurement of the radio channel. Depending on the desired properties of the measurements different sounding techniques and equipment may be used, as described below.
The sounding system has been developed in the APNet laboratory over many years and is continually being adapted to the needs of projects. Two main principles are used:
Ultra wideband (UWB) sounding
- Measuring the complex impulse response
- Sounding bandwidth 1 GHz
- Frequency range 0.5 – 6 GHz
- Sliding correlation
- Up to 2x2 MIMO
Wideband MIMO sounder
- Measuring the complex impulse response.
- Frequency range 0.3 – 6 GHz
- Sounding bandwidth of 100 MHz
- 8 fully parallel Rx channels, can be extended with switching up to 64 channels
- 16 Tx branches
- Possibility of splitting Tx unit into several (phase locked) locations
- Rx and Tx units can be at separate locations
- Rx to Tx distances up to 10 km
- High speed measurement up to 100 km/h
- Can be fitted with optical links
- Simultaneously measurement of different frequencies for groups of Tx/Rx branches
- Interface to positioners/pedestals for antennas (sledges, phi/theta)
In addition to the locally developed sounding systems described above, the APNet laboratory also has available:
- Network Analyzer up to 67 GHz
- Spectrum up to 26 GHZ
which may be used for channel sounding in special applications.
The purpose of using an optical link (radio on the fibre) is to replace the typical coaxial cable carrying the radio signal from an antenna to measurement equipment. Such a cable may in some cases interfere with the signals to be measured, e.g. due to the cable effectively becoming part of the antenna or due to reflections on the cable. In many cases these effects will invalidate the measurements.
To avoid these problems, different optical units have been developed over the years to meet different demands for the measurements, LNA, filtering, switching, etc.
Typically, optical fibers lengths of some 10 m are used, but hundreds of meters have also been used for µs delay lines.
Version #1, year 2000: Handset with 2 parallel channels and an antenna switch. More information may be found in APM-paper and EuCAP-paper.
Depending on the desired link direction, different optical link solutions may be used.
For downlink, or receive-mode, the laser must be at the DUT and the radio signal is received by the antenna and transmitted to the receiver via the optical link. This requires a lot to power in order to supply the laser, and often a LNA is necessary. Therefore, the required battery may become an issue.
In the uplink direction, or tx-mode, an optical detector diode is placed at the DUT. Very little supply power is needed in this case, allowing long operation time. The drawback is low RF output power.
Various other sets available:
- Laser (Tx)
- Miteq laser, up to 6 GHz
- Locally developed laser, up to 3 GHz
- Detectors (Rx)
- Discovery up to 18 GHz
- Locally developed, up to 6 GHz
The locally developed units are fitted with battery supply, RF amplifiers, filters and switches in various combinations.
A large amount of antennas are available in the laboratory, ranging from standard gain horns to test antennas developed locally for specific applications. The frequency bands are normally in the range 400 Mhz to 6 GHz, but equipment from 1 MHz up to 67 GHz can be used. Some of the available measurement antennas are listed below.
Horn antenna, AAU design
For radio channel sounding and over-the-air (OTA) channel generation an open boundary quad-ridged horn antenna has been designed. The antenna is dual-polarized, with a frequency range from 700 MMz to 6 GHz. Further information is available in TAP-paper.
Spherical Horn Array
For channel sounding 16 horns have been assembled to a spherical array.
Probe Array for Over-the-Air (OTA) Testing
The same horn has been used for MIMO OTA:
Array of with 16 monopoles, similar to “Laptop”
Disk cone antennas, various types ranging from 400 MHz to 6 GHz
Ultra wide band antennas 2 – 6 GHz
Rectangular arrays of monopoles 5 – 6 GHz
- 4x8 elements
- 4x4 elements