JPS6033410Y2 - High frequency impedance measurement device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an impedance measuring device that calculates the impedance of an antenna system or a circuit element, that is, the root mean square value of VSWR, and the maximum and minimum values of VSWR by performing analog calculation processing.

FIG. 1 shows an example of a conventional VSWR measuring device.

To explain the measurement method, the sweep signal generator 1 is F.

F where is the center frequency and Δf is the sweep width. AM with a ±Δf sweep signal generator and a constant modulation depth at a frequency of F□
(amplitude modulation) is applied.

The reflected power detector 2 receives a constant output signal from the sweep signal generator 1, and all or part of the signal is reflected from the object to be measured connected to the ρ8 terminal in proportion to the voltage reflection coefficient, resulting in a high The signal is sent to the square law detector 3 of the dynamic range.

In this case, the reflected power detector 2 uses a magic T to prevent the high frequency signal from the sweep signal generator 1 from directly leaking to the square law detector 3.
Or use a directional coupler etc.

The reflected signal from the object to be measured is detected by a square law detector 3 and becomes an F□ component, that is, a modulated wave level.

The reactance attenuator 4 is graduated with a value obtained by converting the voltage reflection coefficient into VSWR.

Amplifier 5 amplifies only the F1 signal, and passes through detector 6 to obtain an envelope signal proportional to the voltage reflection coefficient.

The envelope signal from the detector 6 that is input to the Y axis of the cathode ray tube indicator 7 is a sweep signal that is applied to the X axis, for example, 50
It is synchronized with a Hz signal and displayed as a static image on the cathode ray tube surface.

With this circuit configuration, first connect a standard gummy wire with a known VSWR to the ρ8 terminal of the reflected power detector 2 and calibrate the measurement system (this calibration is performed by using the VSWR value of the sweep signal generator 1 to scale or activate the (This can also be done without using a standard dummy using a drawer attenuator).

Next, connect the object to be measured to the ρ8 terminal, adjust the reactance attenuator 4 so that the deflection on the cathode ray tube is the same, and obtain the VSWR value of the object from the VSWR scale attached to the attenuator dial. It's a method.

However, in the above circuit configuration, the reactance attenuator is expensive, and in order to obtain the root mean square value within the measurement band,
N pieces of data are collected using the point-by-point method and calculated using five formulas, but the accuracy is not good and it takes time to complete the test.

In order to eliminate these drawbacks, the present invention uses an analog calculation circuit to measure the best and worst values of VSWR within a predetermined band, and also measures the root mean square value. Explain in detail.

FIG. 2 is a block diagram showing an embodiment of the present invention, in which blocks common to those in FIG. 1 are given the same reference numbers.

8 other than the above is a range attenuator, 9 is a linear detector, 1
0 is an integration circuit, and 11 is a route conversion circuit.

The range attenuator 8 described above is a level variable device using a variable volume switch or a volume switch for a group of fixed attenuators for enlarging and observing or measuring a part of the image on the cathode ray tube surface.

The reflected signal from the object to be measured obtained in the same manner as in the embodiment of FIG. 1 is detected by the square law detector 3 and becomes FtJi,
The wave is amplified by the amplifier 5 via the range attenuator 8, detected by the high dynamic range linear detector 9, and the envelope is taken out.An amount corresponding to 2 ('r is the sweep period) is output by the integrating circuit 10. be done.

After processing this in the route conversion circuit 11, it is added to the Y-axis of the CRT indicator 7 and synchronized by a sweep signal applied to the X-axis, and the VS is displayed as a static image on the CRT surface.
The root mean square value within the sweep band of WR is displayed linearly.

The linear detector 9 described above is an ideal diode circuit in which negative feedback is applied to an operational amplifier by a diode, so a wide range of linearity can be obtained, and the route conversion circuit 11 is a lo# conversion circuit using an operational amplifier. 1/between reverse 1o exchange circuits
This can be achieved by inserting a two-resistance voltage divider circuit.

Next, if the integrating circuit 10 is removed from this measurement system by tilting the switch downward, the frequency characteristics of the VSWR sweep band can be directly read from the VSWR scale attached to the surface of the cathode ray tube.

In order to know the absolute value of this VSWR, it is sufficient to calibrate this measurement system by connecting a standard dummy whose VSWR is known to the ρ8 terminal of the reflected power detector 2, as in the conventional method.

Also, this measuring device has a VSWR of 1.
Suitable for measuring objects under test with good impedance characteristics close to 0 with high accuracy.

In other words, this measuring device does not directly measure VSWR (ρ), but measures the voltage reflection coefficient (r) and calculates ρ=1+1.
The -r scale of the VSWR value converted by ρ=1
．． If 0 full scale is taken as ρ=1.1, then ρ between them can be obtained on an equal division scale, and the reading accuracy is very good.

The maximum error at that time is Q, which is a mismatch attenuation amount, and is only 3 dB.

As explained above, unlike a reactance attenuator, the present invention does not require precision in machining and does not have any movable parts, so a highly reliable and inexpensive measurement system can be constructed.

In particular, for a device under test with a good VSWR value, the VSWR
It has the advantage that the root mean square value and the maximum and minimum VSWR values can be observed at the same time, and the measurement operation is easy.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional VSWR measurement system, Figure 2 is a block diagram showing a conventional VSWR measurement system.
The figure is a block diagram showing a VSWR measurement system according to the present invention. 1...Sweep signal generator, 2...Reflected power detector, 3...Square detector, 5...
Amplifier, 7... CRT indicator, 7...
・Range attenuator, 9... Linear detector, 10
...Integrator circuit, 11...Route conversion circuit.

Claims (1)

[Scope of utility model registration request] A high frequency output that is swept at a low frequency and amplitude modulated at a constant frequency is sent to the object to be measured, and the reflected wave is detected and the obtained modulated wave level is compared with the modulated wave level of the known VSWR value. An impedance measuring device for obtaining the VSWR value of an object, which includes means for adjusting the modulated wave level to an appropriate size, a linear detector having sufficient linearity with respect to the fluctuation width of the modulated wave level, and a detection voltage of the detected voltage. A high-frequency impedance measuring device comprising an integrating circuit that performs integration within a sweep band as required, and a root conversion circuit that further performs square root calculation.