RU2589467C1 - Octave filter - Google Patents

Abstract

FIELD: radio engineering and communications.

SUBSTANCE: invention relates to radio electronics and can be used in broadband radio transmitters. Invention consists in fact that in octave filter additionally included phase shifting circuit, wherein input of phase-shifting circuit is connected in parallel with high-pass filter of octave filter and output of broadband power amplifier, and its output is connected to input of low-pass filter of octave filter.

EFFECT: reduced time of transient process in output power amplifier of broadband radio transmitter, containing octave filter.

1 cl, 2 dwg

Description

The invention relates to electronics and can be used in broadband radio transmitters.

Broadband shortwave power amplifiers include switchable octave filters for suppressing carrier harmonics. They are duplexers - a low-pass filter (LPF) connected in parallel at the input, the load of which is a high-frequency feeder with an antenna, and a high-pass filter (HPF), loaded on ballast resistance.

Known filters for suppressing harmonics of the carrier frequency, for example, US Patent No. 371569, RF Patent No. 5880 of 03/06/2006.

The closest in technical essence is the octave filter RF Patent No. 130166 of 07/10/2013.

The disadvantage of both analogues and the prototype is that the duration of the transition process (EI Manaev. Fundamentals of radio electronics. - M .: Radio and communications, 1985. P. 18.) during the transition from one operating frequency to another may exceed the permissible tuning frequency of the transmitter during its operation in a radio link with frequency adaptation.

The aim of the invention is to reduce the transient time in the output circuit of a power amplifier of a broadband radio transmitter containing an octave filter.

This goal is achieved by the fact that the octave filter contains low-pass and high-pass filters, a broadband matching device, a half-wave rectifier with a capacitor, a choke, and a limiting diode; a phase-shifting circuit is additionally included, and the phase-shifting circuit input is connected in parallel with the high-pass filter of the octave filter and the output broadband power amplifier, and its output is connected to the input of the low-pass filter of the octave filter.

The block diagram of the device is shown in FIG. 1. In accordance with it, the device consists of the following functional units and elements:

1 - phase-shifting circuit;

2 - low pass filter;

3 - high-pass filter;

4 - broadband matching device;

5 - a half-wave rectifier;

Z _A is the complex resistance of the antenna;

C is the storage capacity;

Dr. - throttle;

D is a limiting diode.

The operation of the circuit is as follows.

The signal at the frequencies of higher harmonics from the output of the power amplifier passes through the HPF “3”, transparent for these frequencies and opaque for the frequency of the first harmonic, and then to the elements in the circuit for suppressing higher harmonics.

The first harmonic from the output of the power amplifier passes to the input of the phase-shifting circuit “1” and then through the low-pass filter “2”, transparent for this frequency and opaque for higher harmonics, and arrives at the load Z _A. The presence of reactive elements in this chain leads to the appearance of a transition process. Moreover, the time constant of the circuit τ, characterizing the transient, is proportional to the capacitance C and inductance L in the circuit: τ = RC; τ = L / R. The transition process time is most often determined by the value t = 3τ, at which the voltage (current) in the circuit reaches 95% of the final (steady-state) value.

нагруженной длинной линии с распределенными параметрами рассчитывается по формуле (А.Ф. Белецкий Основы теории линейных электрических цепей. - М.: Связь, 1967. стр. 373):The value of τ is determined by the values of the active component R and the reactive component C or L at the input of the low-pass filter of the octave filter. The output circuit of a typical broadband transmitter allows it to be represented as an equivalent long line. Input impedance

loaded long line with distributed parameters is calculated by the formula (AF Beletsky Fundamentals of the theory of linear electrical circuits. - M .: Communication, 1967. p. 373):

where: Z _B - wave impedance of a long line connected to an amplifying element; p is the modulus of the reflection coefficient from the load; α is the specific attenuation; β = 2π / λ is the linear phase shift; l is the physical length of a long line.

определяется выражением:Given the complex nature of the reflection coefficient, it can be represented by the modulus and phase pe ^-iϕ . The phase shift ϕ can be taken into account in the βl phase. The linear attenuation α of modern V.Ch. feeders are negligible and with relatively short feeders can be taken equal to zero. Active component

defined by the expression:

определяется выражением:Reactive component

defined by the expression:

The magnitude of the reactive component of the input resistance determines the capacitance C and inductance L, since X _BX = 2πfL or X _BX = 1 / 2πfC, where f is the operating frequency.

Taking into account expressions (2) and (3), the analytical expressions for the time constant with capacitive and inductive load characteristics τ _C and τ _L have the following form:

As can be seen from expressions (4) and (5), the values of τ _C and τ _L will be maximum at minimum values of the operating frequency.

For short-wave transmitters, the minimum frequency is assumed to be 1.5 MHz. In the calculations of the maximum values of transients, the values sin (2βl) = 1 were taken into account when calculating τ _L. In the calculation of τ _C with 2βl tending to zero, sin (2βl) tends to infinity.

In FIG. Figure 2 shows graphs of the dependence of the values of transients (in microseconds) on the traveling wave coefficient (KBW), taking into account the conversion of the reflection coefficient values into the values of the KBV, KBV = (1-p) / (1 + p).

The designations adopted in FIG. 2, the following: τl1 - corresponds to 3τ _L at a frequency of 1.5 MHz; τl2 - corresponds to 3τ _L at a frequency of 30.0 MHz; τcl - corresponds to 3τc at a frequency of 1.5 MHz; τc2 - corresponds to 3τc at a frequency of 30.0 MHz; K - KBV.

As can be seen from the analysis of the graphs shown in FIG. 2, the worst case corresponding to the maximum values of the duration of the transient process is the case when the load of the amplifying element will have a capacitive character. In this case, the duration of the transient process can exceed 1000 microseconds in the interval of KBM values from 0.9 to 1 in cases where the value 2βl tends to zero. By changing l, due to the inclusion of the first harmonic in series with the low-pass filter, the segment of V.Ch. feeder, change the value of sin (2βl) so that it will be equal to or close to unity. To realize this, a preliminary calibration of the transmitter at the frequencies of a specific octave filter with a measurement of the duration of the transition process is necessary. Under the condition that the duration of the transition process exceeds the permissible value, a phase-shifting circuit is additionally switched on sequentially with the low-pass filter (for example, a segment of a V.Ch. feeder). When an additional feeder segment is turned on, its length is determined from the condition sin (2βl) = 1. From this condition, we obtain 2πl / λ = (2k-1) 0.25π and l = (2k-1) 0.125λ.

Claims (1)

An octave filter comprising low-pass and high-pass filters, a broadband matching device, a half-wave rectifier with a capacitor, a choke, and a limiting diode, characterized in that the phase-shifting circuit is additionally switched on, and the phase-shifting circuit input is connected in parallel with the high-pass filter of the octave filter and the output of the broadband power amplifier , and its output is connected to the input of the low-pass filter of the octave filter.

Images