JPS6225507A - Impedance matching apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an impedance matching device that is required to operate over a wide frequency band, and is particularly suited to impedance matching devices that are required to operate over a wide frequency band. The present invention relates to an impedance matching device particularly suitable for use in communication systems.

[Structure of the invention]

The impedance matching device according to the invention comprises: variable frequency means operating in a mode in which the frequency delivered to the frequency dependent impedance occurs repeatedly; impedance compensation means adapted to the variable frequency means and compensating for impedance variations of said frequency dependent impedance; In response to impedance mismatch at a certain frequency, means is included for controlling the characteristics of the impedance compensating means when the specific frequency occurs again so as to eliminate the mismatch.

The invention is particularly preferred for use with radio receivers and/or transmitters operating in frequency hopping mode over a wide frequency band. Frequency hopping requires a wireless receiver or transmitter to be tuned to a particular frequency for a very short period of time during which a portion of a message is transmitted or received. Changing frequencies, which are tuned many times per second, makes it difficult for third parties to eavesdrop without knowledge of the pattern of frequencies in use, and because each frequency is transmitted for such a short period of time, radio direction finding is difficult. It is also not easy to locate the transmitter using technology.
Sending messages is extremely secure.

A problem that arises when a frequency band is wide is that variations in impedance occur in certain parts of the system, primarily the antenna. It is important that the impedance of the antenna must match the impedance of the variable frequency transmitter or receiver, otherwise the power transferred to the antenna will not be maximized. When the transmitter or receiver of a communication system is mobile, the impedance at a particular frequency can vary widely depending largely on the characteristics of the local environment. Therefore, the effective impedance of the antenna is adaptively controlled so that the impedance presented to the transmitter or receiver remains substantially constant as the frequency changes and as the antenna is physically moved. It is highly desirable to do so. The impedance means is located between the variable frequency means of the transmitter or receiver and the antenna, and the discrimination position monitors the characteristics of the signal.
Preferably, the variable frequency means is configured to determine whether the voltage standing wave ratio (VSWR) of the signal is within a permissible range during a period in which the variable frequency means is tuned to a particular frequency. The next time the same frequency is used, the previously obtained data is used to control the impedance compensation means. Tuning is typically adjusted in a sequential manner, with the same frequency being used several times, until a sufficiently good impedance match is achieved. This type of data can be stored for many frequencies over long periods of time, and can be updated to change conditions, such that the magnitude of the impedance mismatch is immediately sufficiently reduced at any time. This allows the communication system to operate at maximum performance and any new errors to be corrected immediately.

The invention will be explained in more detail below by way of example with reference to the accompanying drawings, in which: FIG.

〔Example〕

Please refer to FIG. A wireless transceiver is shown in this figure. This radio transceiver has a frequency synthesizer l that tunes a radio transceiver circuit 2. These circuits are coupled to an antenna 5 via a signal discriminator 3 and an impedance compensation circuit 4. Such systems are capable of operating in a frequency hopping mode over "high frequencies" from 1.6 MHz to 30 MHz. Since the size of the antenna 5 is fixed, its impedance varies quite widely over this band, and the antenna 5 itself cannot exhibit a constant impedance of 50Ω. Circuit 2, however, is designed to operate into a 50Ω load. Therefore, if the load deviates significantly from the design value, the operation of the communication system will be seriously impaired. The discriminator 3 monitors the characteristics of the signal on the line and determines the phase of the load, the resistance of the load, the power on the line and the degree of signal reflection. These characteristics can be easily measured, and in response to these characteristics, the impedance compensation circuit 4 changes the corrected impedance value at a particular frequency so that an impedance closer to the corrected design value appears in the circuit 2. It can only be obtained after various adjustments have been made in succession.

The final value is obtained by an iterative method. That is, the effect of the previous adjustment is
The next time the same frequency is used, it will be referenced and this next adjustment will be made accordingly. The monitor and control circuit 6 determines the required new impedance value and introduces this value into a random access memory (RAM) 7. This value is now held until the frequency synthesizer 1 indicates that the same frequency will be used in the next frequency hop.

This impedance matching device is then read from memory 7 and sent to impedance compensation circuit 4, where it is used to adjust the values of the inductances and capacitances that make up the circuit. In fact, this circuit 4 consists of a large bank containing inductances and capacitors having different values over a wide range and which can be switched into use when required.

Generally, a different combination is in use for each different frequency used in a frequency hopping system.

To enable very fast frequency hopping, the frequency synthesizer 1 sends to the monitor and control circuit 6 the value of the frequency to be used in the next frequency hop. The memory and control circuit 6 varies the frequency value to the address of the random access memory 7. The impedance conditioning devices needed in this memory are collected for use at the moment they are needed.

In order to maintain the impedance match value when the device is not in use, or for long periods of time when antennas of different impedance characteristics are used, this impedance match value is stored in electrically erasable programmable read only memory (EEPROM) 8. will be introduced synchronously.

When radio waves are generated after a period of inactivity, the data held in the memory 8 is transferred within the memory 7 and used when needed. Rarely are large changes required in the stored impedance values, and each identified frequency only needs to occur several times to ensure that the correct impedance is obtained.

FIG. 2 shows a timing diagram illustrating the tuning operation of the present invention. In this figure, line 21 is the hop period;
That is, it indicates a period in which the tuned frequency is constant.

After this, the frequency value changes rapidly to the next value. Line 22 shows the interval at the start of the hop period, during which the capacitance and inductance of circuit 4 are physically switched to the stored values for the selected frequency. A short signal is then transmitted at the selected frequency, as shown on line 23, while the discriminator determines whether further modification is required the next time the same frequency is selected. If required, a correction amount is calculated and a new impedance matching value is determined during the period indicated by line 24 and introduced into the memory 7 together with the associated frequency value. The next frequency value is communicated to be selected between periods 22 and 25. During period 25,
This frequency is made into a memory address, allowing the next set of impedance matching values to be assembled for use at the start of the next hop period.

Line 26 shows the period during which the r, f signal output is generated in the case of the transmitter.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an impedance matching device used in a communication system, and FIG. 2 is a timing diagram illustrating the adjustment operation of the present invention. DESCRIPTION OF SYMBOLS 1... Frequency synthesizer, 2 Transmission/reception circuit, 3 Discriminator, 4 Impedance compensation circuit, 5 Antenna, 6 Monitor and control circuit 7 Random access memory, 8 Programmable read-only memory.

Claims (7)

[Claims] (1) variable frequency means operating in a mode in which a certain frequency is repeatedly transmitted to a frequency-dependent impedance; impedance compensation means adapted to the variable frequency means and compensating for impedance changes of said frequency-dependent impedance; and a certain frequency an impedance matching device comprising: means for controlling characteristics of said impedance compensating means when said particular frequency occurs again in response to an impedance mismatch in said impedance matching device to eliminate said mismatch; (2) The impedance matching device according to claim (1), wherein the frequency-dependent impedance is formed by an antenna. (3) The impedance matching device according to claim (2), wherein the impedance matching device constitutes a part of a frequency hopping radio passing system. (4) the impedance compensation means is located between the variable frequency means of the transmitter or receiver and the antenna, and a discrimination device monitors the characteristics of the signal so that the variable frequency means The impedance matching according to claim (3), wherein the impedance matching is configured to determine whether the voltage standing wave ratio (VSWR) of the signal is within a permissible range during a frequency-tuned period. Device. (5) An impedance matching device as claimed in claim (4), wherein the results of said monitoring are introduced into storage means for later use when the same frequency is next required. (6) the stored result is read out of the storage means during a frequency hopping before a hop in which the frequency concerned occurs again, and the result is made available for adjusting the impedance compensation means; Claim No. 4
) The impedance matching device described in item 2. (7) The impedance matching device according to claim (5) or (6), further comprising a backup memory for storing the result or data obtained from the result for a long period of time.