JPH0137001B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The microwave circuit according to the present invention is used in microwave communication equipment, SHF receivers, etc., and is particularly suitable for harmonics of local oscillators and harmonic components of local oscillator frequencies generated in mixer circuits. This is used to remove the signal.

Configuration of conventional example and its problems The local oscillator includes harmonic (frequency nf _L , n=2, 3, . . . ) components in addition to the fundamental wave (frequency f _L ). Also, in the mixer circuit, harmonic components of the local frequency are generated in the mixer diode,
Along with the local frequency component, signals of its harmonic components are also radiated to the outside from the input terminal of the mixer circuit as unnecessary leakage power. Among these harmonic components of the local frequency, the one with the highest signal level is the second harmonic component. To remove this second harmonic, it is necessary to provide a filter on the output line of the local oscillator that exhibits a pass characteristic at the local oscillator frequency and a filter that exhibits a blocking characteristic at the frequency of the second harmonic. In the mixer circuit, it is necessary to provide a filter on the signal input terminal side that exhibits a blocking characteristic for the second harmonic of the local oscillation frequency that exhibits a passing characteristic at the input signal frequency.

In a microwave circuit using a strip line or a microstrip line, a band rejection filter as shown in FIG. 1 has conventionally been used as a filter for blocking the second harmonic. In FIG. 1, 1 is a main line, and 2 is a half-wavelength strip line resonator coupled in parallel with the main line 1. This band-stop filter had the disadvantage that the stop band width was narrow and it was difficult to obtain large attenuation characteristics.

OBJECTS OF THE INVENTION An object of the present invention is to provide a microwave circuit which is a spacing rejection filter having a wide rejection band width and large attenuation characteristics, which has a simple configuration and does not have the drawbacks of the conventional example described above.

Structure of the Invention In the microwave circuit of the present invention, two or three stubs or a plurality of sets of two or three stubs are provided in the main line, and the length of the stub is determined by the attenuation pole frequency of the stub. Predetermined frequency band (f ₁ ~
f ₂ ), and set the spacing between the stubs and the characteristic impedance of the main line and stub so that the input/output impedance of the circuit in or around the frequency band (f ₁ /2 to f ₂ /2) is determined. This is determined to match the characteristic impedance of the main line.

Description of examples Examples of the present invention will be described below.

FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, stubs 4 and 5 (characteristic impedance Z ₁ ) with a length l ₁ (electrical angle θ ₁ ) are provided at an interval l ₀ (electrical angle θ ₀ ) on the main line 3 (characteristic impedance Z ₀ ). . The transfer matrix T ₂ of this circuit is However, Y=jZ ₀ /Z ₁ tanθ ₁ ...(2) From the relationship between the transfer matrix T ₂ and the scattering matrix S, the transmission coefficient S ₂₁ of this circuit is calculated as follows: S ₂₁ = 1/T ₂₂ = 4/( 2+Y) ² e ^j 〓0−Y ² e ^-j 〓0…(3
) The condition for complete transmission of the signal through this circuit is |S ₂₁ | ² = 1 ...(4) From equations (3) and (4), the condition for complete transmission is tanθ ₁・tanθ ₀ =2Z ₁ /Z ₀ ...( 5) is given by. At the second harmonic, stub 4,
5 gives an attenuation pole, so at the local frequency,
Since tanθ ₁ =1, the condition given by equation (5) can be further simplified as follows.

tanθ ₀ = 2Z ₁ /Z ₀ …(6) Therefore, the length of stubs 4 and 5 is set to 1/1 of the local frequency.
If 8 wavelengths are selected, and the spacing and characteristic impedance of stubs 4 and 5 are selected to satisfy the condition of equation (6) at the local oscillation frequency, input/output matching will be good at the local oscillation frequency, and at the second harmonic frequency. A second harmonic rejection filter serving as a rejection band is obtained.

When used in a mixer circuit, the lengths of stubs 4 and 5 are selected to be 1/8 wavelength of the local frequency, but the length of stubs 4 and 5 is selected so that the condition of equation (6) is satisfied at the input signal frequency. It is necessary to select the spacing of 4 or 5 and the characteristic impedance.

FIG. 3 shows another embodiment of the present invention, in which the main line 6
(characteristic impedance Z ₀ ) and length l ₁ (electrical angle θ ₁ )
The stubs 7, 8, 9 (characteristic impedance Z ₁ ) are provided at intervals l ₀ (electrical angle θ ₀ ). The transfer matrix T ₃ of this circuit is From the relationship between the transfer matrix and the scattering matrix S, the reflection coefficient S ₁₁ of this circuit is S ₁₁ = T ₁₂ /T ₂₂ (8) Considering that the condition for a signal to completely pass through this circuit is a lossless circuit. , S ₁₁ =0, that is, T ₁₂ ]-1/8 {Y(2-Y) ² e ^-2j 〓0+2Y(2
−Y ² )+Y(2+Y) ² e ^2j 〓0}=0…(9) From equation (9), the perfect transmission condition is 1+2cosθ ₀ /sinθ ₀ =Z ₀ /Z ₁ tanθ ₁ …(10) or −1+2cosθ ₀ /sinθ ₀ =Z ₀ /Z ₁ tanθ ₁ …(11) θ ₀ that satisfies the condition of equation (10) or equation (11) is 0<θ ₀
There are four types within the range <2π. Letting them be θ ₀₁ , θ ₀₂ , θ ₀₃ , θ ₀₄ in order from the smallest value,
0<θ ₀₁ <π/3, θ ₀₁ <θ ₀₂ <2π/3, π<θ ₀₃ <4
π/3, θ ₀₃ < θ ₀₄ <5π/3, θ ₀₂ and θ ₀₃ satisfy the condition of equation (10), and θ ₀₁ and θ ₀₄ satisfy equation (11).

Therefore, the lengths of the stubs 7, 8, and 9 are selected to be 1/8 wavelength of the local frequency, and the spacing and characteristic impedance of the stubs 7, 8, and 9 are determined by formula (10) or formula at the local frequency or input signal frequency. If the condition (11) is selected so that the condition is satisfied, the second harmonic rejection filter becomes a passband for the local oscillation frequency and the input signal frequency, and a stopband for the second harmonic of the local oscillation frequency. can get.

FIG. 4 shows a typical example of the frequency characteristic of the insertion loss of the second harmonic blocking filter in the embodiment shown in FIG. Local frequency f _L0 = 10.74 GHz, input signal frequency f _R = 11.7 to 12.5 GHz (center frequency
12.1GH ₂ ), the input VSWR (Voltage
Standing Wave Ratio) is 1.12 or less, and the second harmonic insertion loss is 48dB or more within the range of 2f _L0 ±1GHz. θ ₀ = θ ₀₂ (θ ₀₁ < θ ₀₂ <
2π/3), the characteristics shown by the broken line in FIG. 5 are obtained, and the input VSWR of the second harmonic rejection filter is 1.33 or less at the input signal frequency.

θ ₀ = θ ₀₃ (π<θ ₀₃ <4/3π) and θ ₀ =θ ₀₄ (
Even in the case of θ ₀₃ < θ ₀₄ <2π), the circuit of the embodiment shown in FIG. When shortened, that is, as shown by the solid line in Figure 5, θ ₀ =
The characteristics are the best when θ ₀₁ .

FIG. 6 is a diagram showing an example of application of the filter according to the present invention to a mixer circuit. Reference numeral 10 denotes a second harmonic rejection filter, which is arranged between the frequency mixer 11 and the signal input terminal 12. 13 is a local oscillator, 1
4 is an intermediate frequency signal output terminal. As a characteristic of the second harmonic rejection filter 10, the input signal frequency
If f _R is selected so that the pass characteristic is excellent, and frequency 2f _L0 , which is twice the local oscillation frequency f _L0 , is a stop band, the second harmonic of the local frequency generated by the frequency mixer 11 is It is blocked by the harmonic blocking filter 10 and does not leak to the signal input terminal 12 side. If the characteristics of the second harmonic rejection filter 10 are selected so that it has excellent pass characteristics at the input signal frequency f _R and has a rejection band at the sum frequency f _R +f _L0 , then the sum frequency signal generated by the frequency mixer 11 ( The frequency (f _R +f _L0 ) is reflected by the second harmonic rejection filter 10 and returned to the frequency mixer 11, where it is again converted into an intermediate frequency signal and taken out from the intermediate frequency signal output terminal 14 side. It will be done. Therefore, the conversion loss characteristics of the mixer circuit are improved.

Moreover, as a characteristic of the second harmonic rejection filter 10, as shown in FIGS. 4 and 5, the rejection band is wide band, so it can be used not only as a second harmonic rejection filter for the local frequency, but also for sum frequency signals. It is also possible to operate it as a blocking filter.

FIG. 7 shows another example of application of the filter according to the present invention to a mixer circuit, and the same parts as in FIG. 6 are given the same numbers. In the figure, 15 is a second harmonic rejection filter for the local frequency, and 16 is a sum frequency signal rejection filter. Both filters 15 and 16 have excellent pass characteristics at the input signal frequency, and the frequency mixer 11 and signal input terminal 12
placed in between. 13 is a local oscillator, and 14 is an intermediate frequency signal output terminal. Frequency mixer 11
The local oscillation frequency generated by the signal is blocked by the second harmonic filter 15 and does not leak to the signal input terminal 12 side. The sum frequency signal generated by the frequency mixer 11 is reflected by the filter 16 and returned to the frequency mixer 11, and is again converted into an intermediate frequency signal by the frequency mixer 11, and then output from the intermediate frequency signal output terminal 14 side. taken out. Therefore, the conversion loss characteristics of the mixer circuit are improved.

In the above embodiments, the number of stubs is 2 or 3.
Although we have explained the case of 2 stubs, when the number of stubs is 4, two sets of circuits with 2 stubs are provided, and when the number of stubs is 6, a circuit with 2 stubs is provided. This can be realized by providing two sets of circuits each having three sets of. It goes without saying that by sequentially connecting a plurality of sets of the circuit shown in FIG. 2 or the circuit shown in FIG. 3 in this way, the attenuation characteristics of the second harmonic can be further improved.

Effects of the Invention As explained above, the microwave circuit of the present invention can be configured with a simple circuit in which stubs are provided at two or three locations on the main line, and for example, the second harmonic of the local frequency can be blocked. However, the insertion loss is very low for the local oscillation frequency itself or the input signal frequency. Moreover,
As for the blocking characteristic for the second harmonic, a large attenuation characteristic and a wide blocking band width are obtained. Therefore, the microwave circuit according to the present invention is not only very effective as a second harmonic rejection filter for the local oscillator frequency and an unnecessary second harmonic elimination filter for local oscillators, mixer circuits, etc. In circuits, it is effective in improving conversion loss by using it as a blocking filter for sum frequency signals.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional band rejection filter, FIG. 2 is a diagram showing one embodiment of a microwave circuit according to the present invention, and FIG. 3 is a diagram showing another embodiment of a microwave circuit according to the present invention. , FIG. 4 is a frequency characteristic diagram of the microwave circuit of the embodiment shown in FIG. 2, FIG. 5 is a frequency characteristic diagram of the microwave circuit of the embodiment shown in FIG. 3, and FIGS. 6 and 7. 1 is a diagram showing an embodiment in which the microwave circuit according to the present invention is applied to a mixer circuit. 3, 6... Main line, 4, 5, 7, 8, 9... Stub.

Claims (1)

[Claims] 1. Even if the main line (characteristic impedance Z ₀ ) is equally spaced l ₀ (electrical angle θ ₀ ), the length is l ₁
(electrical angle θ ₁ ) stub (characteristic impedance Z ₁ )
are connected in parallel, and the length of the stub is selected to be _1/4 wavelength of the stop frequency so that the attenuation pole frequency is at the stop frequency _f1 , and the length of the stub is set to 1/4 wavelength of the stop frequency. _{θ 0 ( or l 0 )} , _θ ¹ _{( or}
A microwave circuit characterized in that l ₁ ), Z ₀ , and Z ₁ are selected. 2 Even if the main line (characteristic impedance Z ₀ ) is equally spaced l ₀ (electrical angle θ ₀ ), the length is l ₁
(electrical angle θ ₁ ) stub (characteristic impedance Z ₁ )
are configured by connecting three in parallel, and the length of the stub is selected to be 1/4 wavelength of the stop frequency so that the attenuation pole frequency is at _the stop frequency _f1 , and the passband frequency is f ₁ /2 or its vicinity, and in the passband (±1+2cosθ ₀ )/sinθ ₀ =
A microwave circuit characterized in that _{θ 0} (or l ₀ ), θ ₁ (or l ₁ ), Z ₀ , and Z ₁ are selected so as to satisfy the conditional expression Z 0 tan θ ₁ /Z ₁ . 3 Between the stub spacing l ₀ (or θ ₀ ), the length l ₁ (or θ ₁ ), the characteristic impedance Z ₀ of the main line, and the characteristic impedance Z ₁ of the stub (-1 +
2cosθ ₀ )/sinθ ₀ = Z ₀ tanθ ₁ /Z ₁ condition is satisfied,
and 0<θ ₀ <π/3 or 0<l ₀ <(1/6 wavelength of the frequency of the passband). wave circuit.