JPH06294834A - Sensitivity measuring method for automotive antenna - Google Patents

Abstract

PURPOSE:To provide a method for measuring sensitivity of an automotive antenna which is not affected by a ground reflecting state of radio wave via a reference antenna at a different measuring place. CONSTITUTION:A method for obtaining relative sensitivity characteristics of an automotive antenna A has the steps of measuring a reception level of the antenna A to be measured, employing a dipole antenna as a reference antenna AS, measuring a reception level under the same measuring conditions, normalizing the level of the antenna A at the obtained level of the antenna AS, and comprises the steps of laying a radio wave absorber Q on a floor surface 3 of a measuring place 1 at the time of measuring at least the level of the antenna AS, and measuring the level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a method for measuring the sensitivity of an automobile antenna.

[0002]

2. Description of the Related Art In a conventional method for measuring the sensitivity of an automobile antenna, a radio wave transmitted from a transmitting antenna is received by a receiving antenna attached to a vehicle located at a predetermined distance,
Although the strength (reception level) of the received signal is measured, the measurement conditions are not always uniform due to the difference in measurement location, the height of the transmitting antenna, the positional relationship, etc. Therefore, these remain as uncertain factors.

On the other hand, changes in the measurement conditions, for example, changes in the antenna characteristics due to changes in the height of the transmitting antenna, the height of the receiving antenna, and the distance between the transmitting and receiving antennas are almost the same in both the dipole antenna and other vehicle antennas. It has been confirmed from the measured values that they have a common tendency.

For example, when the height of the transmitting antenna or the height of the receiving antenna is changed, the decreasing tendency of the receiving antenna sensitivity in a certain frequency band is almost the same for both the dipole antenna and the other vehicle antennas.

Focusing on such a property, in order to cancel and cancel the uncertainties, the conventional vehicle antenna sensitivity measurement method is under the same measurement condition as the reception level of the vehicle antenna to be measured. A method is used in which the ratio of the reception levels of a reference antenna (for example, a dipole antenna) is taken as the relative sensitivity characteristic. That is, the characteristic value normalized by the reference antenna is used.

[0006]

As described above, the sensitivity characteristic of the automobile antenna is displayed based on the contrast value with the reference antenna placed at the same measurement location. However, here, as the reference antenna, especially the dipole. Problems occur when using antennas. This will be described with reference to FIG. 4 which is a diagram showing a frequency dependence characteristic of a dipole antenna according to a conventional measuring method.

FIG. 4A shows a case where the radio wave reception level of the reference antenna AS is measured at the measurement location 100 where the ground reflected wave is present. The radio wave captured by the reference antenna AS by the dipole antenna is routed from the transmission antenna E to the route ld.
Although it is both the direct wave Wd that directly arrives and the ground reflected wave Wr (path lr) reflected on the ground, the dipole antenna is affected by the ground reflected wave Wr due to its directional characteristics in the vertical direction. It has the feature of being easy.

In particular, if the path difference (difference between lr and ld) between the direct wave Wd and the ground reflected wave Wr is large, the phase difference between the two waves at the receiving position greatly changes depending on the frequency. As a result of the strength of the composite wave of the waves also changing with the frequency, flat frequency characteristics cannot be realized even in the dipole antenna. This state is shown in FIG.

The graph of FIG. 4B shows the relative sensitivity of the dipole antenna when the reception level is 0 dB in a free space where no reflector is present in the surroundings, and the distance between the transmitting and receiving antennas is displayed as a parameter. According to the figure, according to the change of the distance between the transmitting and receiving antennas (9 to 10 meters),
The frequency characteristics of the dipole antenna are changing.

As is clear from the above, in the conventional method for measuring the sensitivity of the automobile antenna, the characteristic of the dipole antenna to be used as a reference changes due to the presence of the ground reflected wave Wr, so that the reception level for normalization becomes constant. As a result, there is a drawback that different characteristic values are obtained depending on the measurement location despite the same car antenna.

The present invention has been made in order to solve the above problems and drawbacks, and its purpose is to provide a vehicle antenna which is not affected by the ground reflection state of radio waves in the reference antenna even at different measurement locations. It is to provide a sensitivity measuring method.

[0012]

In order to solve the above-mentioned problems, a method for measuring the sensitivity of an automobile antenna according to the present invention is
The reception level of the automobile antenna to be measured is measured, while the dipole antenna is adopted as the reference antenna, the reception level is measured under the same measurement conditions, and the reception level of the obtained reference antenna of the automobile antenna is measured. In a method of obtaining a relative sensitivity characteristic of the automobile antenna by normalizing the reception level, at least when measuring the reception level of the reference antenna, a radio wave absorber is laid on the floor surface of the measurement location to measure the reception level. And

[0013]

[Operation] When the reception level of the dipole antenna, which is the reference antenna, is measured, the electromagnetic wave absorber laid on the floor of the measurement site absorbs the direct wave reaching the floor, so that the ground reflected wave is attenuated or the ground reflected wave is In the sensitivity measurement of the car antenna, which is performed by using the dipole antenna that does not occur and is therefore easily affected by the ground reflected wave as the reference antenna,
It is possible to obtain high accuracy.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a structural explanatory view of a method for measuring the sensitivity of an automobile antenna according to the present invention. FIG. 1A shows the configuration at the time of measuring the reception level of the reference antenna AS at the measurement location 1, in which the transmission antenna E and the reference antenna AS are arranged on the floor surface 3 at a distance D. The transmitting antenna is at height Ht, while the reference antenna AS is at height Hr. The reference antenna AS is arranged on the rotatable turntable 2 in order to obtain the data of the angle directivity.

A radio wave absorber Q is laid on the floor surface 3.
The laying range of the radio wave absorber Q is determined according to the situation of the measurement place 1, but generally, the transmission antenna E and the reference antenna AS are arranged at each of the two focus positions, and a substantially elliptical closed region. Also, it is effective to set the so-called Fresnel zone as the laying range.

The radio wave emitted from the transmitting antenna E is directly captured by the reference antenna AS as a direct wave Wd. Although a part of the radio wave reaches the floor surface 3, it is absorbed by the radio wave absorber Q laid on the floor surface 3 and the ground reflected wave is not generated or is significantly attenuated even if it is generated. It does not affect the measurement because it is not captured or it is weak if captured.

As a result, the reference antenna AS, which is a dipole antenna, can be measured under measurement conditions comparable to those in free space. In the present invention, this measurement condition is referred to as pseudo free space, and the characteristic obtained by measurement in the pseudo free space is referred to as pseudo free space characteristic. Since the pseudo free space characteristic of the dipole antenna is close to the straight line with the relative sensitivity of 0 dB in FIG. 4B, it can be used as a stable reference value for normalization.

Next, the measurement of the automobile antenna A to be measured will be described. Also in the measurement of the automobile antenna A, it is possible to replace the reference antenna AS with the automobile antenna A by using the configuration of FIG. 1 (a) as it is, but for example, a window glass antenna attached to an automobile window glass or the like. In the case of 1, the influence of the ground reflected wave Wr is smaller than that of the dipole antenna due to the directional characteristics in the vertical direction.

Therefore, in this case, the electromagnetic wave absorber Q is placed on the floor surface 3.
Often there is no need to lay. 1 (b) is shown in FIG.
It shows an example in which the reception level of the vehicle antenna A is measured with the radio wave absorber Q removed from the configuration of (a).

Next, the process of deriving the relative sensitivity of the automobile antenna A will be described with reference to FIG. FIG. 2A shows a reception level (sensitivity) measurement of the automobile antenna A at the measurement site A. The measurement place A where the ground reflected wave Wr exists is the transmission antenna height Ht1 and the vehicle antenna A height Hr.
1. The distance D1 between both antennas, and the sensitivity of the obtained automobile antenna A has a frequency characteristic A (instep A) having a peak near a frequency of 650 MHz.

FIG. 2B shows the reception level (sensitivity) measurement of the reference antenna AS at the same measurement site A. A radio wave absorber Q is laid on the ground of the measurement site A, and the height of the transmitting antenna is Ht1, the height of the reference antenna AS is Hr1, and the distance between both antennas is D1. The sensitivity of the obtained reference antenna AS has a substantially straight pseudo-free space characteristic G (instep) with an inclination of a gentle angle θ1.

By using the data of the reception level obtained above, the data G (A) of the vehicle antenna A is normalized by the data A (A) of the reference antenna AS.
The relative sensitivity AJ (instep) of the automobile antenna A normalized by G (instep) shown in (c) is obtained.

As described above, the change in the antenna characteristics caused by the change in the measurement conditions shows a common tendency for the dipole antenna and the car antenna, and therefore, the relative sensitivity AJ of the car antenna A with the dipole antenna as a reference. In (A), the part that depends on the measurement conditions, which acts on both antennas in common, is canceled out.

Therefore, it can be considered that the AJ (instep) shows the characteristic tendency common to the dipole antenna and the vehicle antenna A even at different measurement locations. Based on this, as shown in the process of deriving the estimated relative sensitivity of the automobile antenna of FIG. 3, AJ (A) and the quasi-free space characteristic G (O) of the dipole antenna at the measurement location B where the electromagnetic wave absorber Q was laid.
Using, it becomes possible to estimate the normalized estimated relative sensitivity AJ (Otsu) of the automobile antenna A at the measurement place O without measuring.

In this way, if the dipole antenna pseudo free space characteristics are measured in advance at each measurement place including the place A, another different measurement place, for example, with respect to the reference antenna of the automobile antenna measured at B. It is possible to estimate the relative sensitivity characteristic of this car antenna with respect to the reference antenna at the measurement location A using the relative sensitivity characteristic and the above-mentioned characteristics of the dipole antenna pseudo free space in the former, without any actual measurement. .

Although the example of using the dipole antenna as the reference antenna has been described above, the sensitivity measuring method of the automobile antenna according to the present invention is not limited to the dipole antenna, and the directional characteristics in the vertical direction which are easily affected by the reflected wave on the ground. It can be applied to all cases where an antenna having is used as a reference antenna.

[0027]

As described above, the method of measuring the sensitivity of the automobile antenna according to the present invention attenuates the ground reflected wave by laying a radio wave absorber on the floor surface of the measurement location, and reduces the fluctuation of the dipole antenna measurement level. Since the influence of the ground reflected wave, which is the cause, can be reduced to a negligible range, it becomes easy to measure the quasi free space characteristics of the dipole antenna.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a method for measuring the sensitivity of an automobile antenna according to the present invention.

FIG. 2 is an explanatory diagram of a relative sensitivity derivation process of an automobile antenna.

FIG. 3 is an explanatory diagram of a process of deriving an estimated relative sensitivity of a car antenna.

FIG. 4 is an explanatory diagram showing frequency dependence characteristics of a dipole antenna according to a conventional measurement method.

[Explanation of symbols]

 1 Measurement place 2 Turntable 3 Floor surface A Car antenna AS Reference antenna (dipole antenna) D Distance E Transmit antenna Hr Receive antenna height Ht Transmit antenna height Q Radio wave absorber Wd Direct wave Wr Ground reflected wave

Claims (1)

[Claims] 1. A reception level of an automobile antenna to be measured is measured, while a dipole antenna is adopted as a reference antenna, and the reception level is measured under the same measurement conditions.
A method of normalizing the reception level of the automobile antenna with the obtained reception level of the reference antenna to obtain the relative sensitivity characteristic of the automobile antenna, wherein at least when the reception level of the reference antenna is measured, electromagnetic waves are absorbed on the floor surface of the measurement location. A method of measuring the sensitivity of an automobile antenna, which comprises laying a body and measuring a reception level.