FI88749C - Calibration of calibration Foer rum utan radioeko och kalibreringsanordning Foer utfoerande av foerfarandet - Google Patents

Description

1 88749

Calibration method and calibration equipment for a radio-free room to perform the method

The invention relates to a method for calibrating a radio-sounding room or a corresponding radio measuring point, in which method .

In addition to the task 15 primarily intended for them, almost all electronic devices cause various disturbances in their environment, e.g. radio frequency interference radiation. When the electronic device is turned on and in normal use, electromagnetic radiation from the device can be measured around the device.

These interference radiation measurements can be performed 20 both at open measuring points and at the so-called

in rooms without radio. The aim is to construct rooms without radio echoes in such a way that there is as little reflection of radio frequency signals from the wall surfaces as possible, ie radio echoes. In practice, however, it is not possible to build a completely radio-free room, so the measurement rooms have to be calibrated regularly.

One known way to calibrate an anechoic room is to measure the radiation spectrum emitted by a special calibration equipment with equipment normally used in an anechoic room. Once the actual emission spectrum of the calibration equipment is known, the necessary calibration factors can be calculated from the difference between the known radiation spectrum and the radiation spectrum measured in the anechoic chamber.

'1' 35 A signal generator with a wiper 2 88 7 '- y and a transmitter antenna, the characteristics of which are known, are generally used as calibration equipment. In order to obtain a sufficiently accurate and reliable measurement result, the sweep must be performed rather slowly. When the frequency range to be measured is typically 5 to 30 MHz, the calibration procedure is very time consuming.

In another known calibration apparatus, the signal generator simultaneously generates a certain fundamental frequency as well as their harmonics which occur in the frequency band to be measured at certain frequency intervals. This paddle method avoids inertia slowness, but since calibration is performed at only relatively few discrete frequencies, no resonant frequencies in the anechoic room between these frequencies are detected, resulting in the room not being properly calibrated.

It is an object of the invention to provide a method of calibrating an anechoic room or the like which avoids the problems of known methods.

This is achieved by a method of the type described in the introductory paragraph, which according to the invention is characterized in that the calibration apparatus generates a noise signal containing substantially all the frequencies of the desired frequency band.

The basic idea of the invention is to transmit a previously known noise spectrum in the calibrated frequency range. In this case, the calibration goes through all the frequencies in the frequency range to be calibrated at the same time, which makes the measurement fast and any resonances in the anechoic room that may be in the frequency band will be taken into account. The actual noise spectrum of the calibration equipment, to which the measurement result of the anechoic chamber is compared, is obtained at a separate calibrated measuring point, the measurement results of which are sufficiently accurate.

The invention also relates to a calibration apparatus 35 for carrying out the method according to the invention, characterized in that the calibration apparatus comprises noise generating means for generating white noise in at least said desired frequency band, radio frequency amplifier means for amplifying at least said desired frequency band and

The antenna is most preferably a monopoly because it does not cause balancing problems over a wide measurement band like a dipole.

The noise generating means preferably comprises

A semiconductor interface that generates Schottky noise, in which case it can be implemented, for example, with a transistor.

The invention will now be described in more detail by means of exemplary embodiments with reference to the accompanying drawings, in which Fig. 1 is a schematic view of a soundless room calibration measuring arrangement, Fig. and an associated amplifier wiring diagram.

In the calibration method according to the invention, a calibration apparatus 2 generating and transmitting its spectrum and a receiver antenna 3 are placed in the anechoic-free room 1 and at a certain distance therefrom a receiver antenna 3 is usually connected by an antenna cable 6 to a measuring apparatus 4 located outside the anechoic room 1. space used. The anechoic room 1 is usually coated on the inside with a material 5 which reduces reflections from the walls.

Electromagnetic radiation spectrum means; 35 electromagnetic field strength as a function of frequency.

4 8 8 7-: 9

The radiation spectrum generated around the calibration apparatus 2 in an ideally anechoic environment is known with sufficient accuracy and information about it is stored in the measuring apparatus 4. When the calibration apparatus 2 is placed in a room 1 which is not completely anechoic or contains other non-idealities, the receiver antenna 3 receives the radiation emitted by the calibration apparatus 2 distorted by. The radiation spectrum measured by the measuring apparatus 4 is compared with the known radiation spectrum of the apparatus 10 2 and, based on their difference, the calibration coefficients are calculated for the entire frequency range used in the measurements. Later, the radiation spectra t obtained in the actual radiation measurements of the electronic devices under study are corrected by these calibration factors to remove the distortions caused by the anechoic 15 room 1 from the measurement results.

In the calibration method according to the invention, the calibration apparatus generates a noise signal containing substantially all the frequencies of the frequency band to be calibrated. To this end, the device according to the invention comprises a noise generator, a radio frequency amplifier whose gain band covers at least the frequency range to be calibrated, and an antenna connected to the output of the amplifier, to which the amplified noise signal is input.

In a preferred embodiment of the invention, the noise signal is broadband amplified noise, Schottky noise generated at the semiconductor interface, also referred to as grain noise or shot noise. In this case, the p-n junction of the transistor biased close to the zener voltage close to the blocking direction-30, for example, can act as a noise generator. Figure 4 illustrates one such noise generator generator circuit in which transistor TRI generates Schottky noise which is amplified by transistors TR2 and TR3. The radio frequency output OUT is connected to the antenna. The Kyt-35 field is housed in a protective housing 25.

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Figures 2 and 3 illustrate a calibration apparatus 2 according to a preferred embodiment of the invention, which mainly consists of a monopoly antenna. The monopoly antenna is not the only antenna type that can be used, 5 but it is clearly the simplest to implement in the required wide frequency band without the balancing problems that occur with a dipole, for example. In Figs. Attached to the upper end of the antenna stick 23 is an electrically conductive disc 24 which expands the frequency band of the antenna-15 in the direction of lower frequencies.

The antenna rod 23 may be removable and replaceable to allow the use of antenna rods of different lengths to improve sensitivity at different frequencies. By shortening the antenna stick 23, the sensitivity is improved at the upper end of the measuring range and vice versa.

The noise generator and the amplifier form a radiation-tightly encapsulated unit 25 located below the plate 21 substantially at the antenna stick 23 and the sleeve 22. The unit 25 is connected to the plate 21. 25 through the hole and the connector in the sleeve 22 to the antenna stick 23.

The calibration apparatus according to the preferred embodiment of the invention can be used for C.I.S.P.R. 22 for the calibration of rooms intended for the measurement of radiated disturbances in accordance with measurement standard 22. In this case, the measuring range is 30 MHz to 1000 MHz and the receiving antenna 3 moves vertically during the measurement in the range 1-4 m from the ground plane (e.g. floor) of the anechoic room 1.

For the experiments, a calibration apparatus 35 2 was constructed in which the size of the brass plate 1 was 60x60 cm and in which two lengths of copper antenna rod 23 of 20 cm and 40 cm were used alternately with a rod diameter of 1.5 cm. At the end of the antenna stick 23 was a removable aluminum disc 24 with a diameter of 25 cm and a thickness of 1 mm.

5 The radiation spectrum of the built calibration equipment was first measured at a known officially accurate position with sufficient accuracy to obtain the known radiation spectrum used for calibration in open terrain.

Claims (11)

1. Calibration method for rooms without radio echo or corresponding radio measurement point, in which method 5 in the radio echo-free room (1) to be calibrated, a beam spectrum measurement is carried out at the desired frequency band, using a calibration device (2) to generate the beam spectrum to be measured. ) with known beam spectrum, and calibration information regarding the radio-echo space 10 is obtained on the basis of the difference between the beam spectrum measured by the calibration device and its known beam spectrum, characterized in that the calibration device (2) generates a noise signal which contains substantially all of the frequencies for the desired frequency band. 15 2. A method according to claim 1, characterized in that on the basis of the difference between the known spectrum of the calibration device (2) and the beam spectrum measured in the echo-free space to be calibrated, calibration coefficients for radiation measurements to be performed in the the ecofree room (1). Method according to claim 1, characterized in that, when measuring the beam spectrum of the calibration device (2), the receiving antenna (3) of the measuring device (4) is displaced in the vertical direction, preferably in an elevation range of 1-4 meters measured from the bottom of the measuring station. 4. A method according to claim 1, 2 or 3, characterized in that the noise signal is a broadband amplified Schottky noise which arises in a semiconductor interface. 30 Method according to any of the preceding claims, characterized in that the known beam spectrum of the calibration device (2) is determined by a measurement carried out at a separate, calibrated measuring point. 6. Calibration device (2) for a radio echo without radio echo or corresponding radio measuring point with known radiation ί 8 / ·; y spectrum to generate a beam spectrum to be measured at the beam spectrum measurement performed in the radio-echo-free space (1) to be calibrated, at the desired frequency band, characterized in that the calibration device (2) comprises a noise generator means (TRI) for generating a vaulted noise containing substantially all frequencies of the desired frequency band 1, a radio frequency amplifier (TR2, TR3) for amplifying the noise of the signal tone, the desired frequency band in question 10, and for feeding 21 to the antenna , 23,24). 7. Device according to claim 6, characterized in that the antenna (21,22,23,24) is monopole. 8. Device according to claim 7, characterized in that the monopole comprises a first disc (21) made of a material conducting the electricity, which disc acts as a ground surface for the monopole, and an antenna canister (23), which is directed upwardly from said disk and which has at its lower end encountered said disk (21) in a manner which isolates electricity. Device according to claim 8, characterized in that the antenna cap (23) has at its upper end a second disc (24) which conducts electricity. 10. Device according to claim 8 or 9, characterized in that the noise generator means (TRI) and the radio frequency amplifier means (TR2, TR3) are located below the first disk (21). Device according to any one of claims 6-10, characterized in that the noise generator means 30 comprise a semiconductor interface which generates Schottky noise.