JPS6342444B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna duplexer using a band-elimination filter for high frequencies.

As shown in FIG. 1, a multistage band-elimination filter used in a high frequency band often has a configuration in which a plurality of series resonant circuits 13 are connected by a transmission line 14. In the figure, 11 and 12 indicate input and output terminals, respectively. The series resonant circuit 13 may be a lumped constant resonator, but in order to improve the characteristics of the circuit, the unloaded Q
It is common practice to use a distributed constant type resonator with a high . By the way, the transmission line 14 is made small by using a coaxial cable at frequencies below 1000 MHz, and the line length l is selected to be approximately 1/4 wavelength at the center frequency to form a wave transmitter.

In this case, the frequency characteristic of insertion loss has symmetrical characteristics above and below the center frequency, as shown in the graph of FIG. However, although such conventional examples have good symmetrical characteristics, they cannot be said to be sufficient in terms of sharpness of frequency characteristics.

However, depending on the application, reduction in insertion loss may be required even if symmetry is ignored, as will be described in detail later.

In the antenna duplexer according to the present invention, the length of the conventionally used λg/4 coaxial cable is set to be approximately 5 to 20% shorter or longer than λg/4, so that the frequency characteristics of insertion loss are centered around the center frequency. It uses a band-elimination waveformer that is vertically asymmetric and further reduces insertion loss.

The basic configuration of the band-elimination filter will be explained below.

If the coaxial cable length is longer than λg/4, the second
As shown in the figure, the characteristics can be steep at frequencies higher than the center frequency and gentle at frequencies lower than the center frequency. On the other hand, by making the cable length shorter than λg/4, it is possible to obtain characteristics opposite to 2, as shown in FIG.

By the way, when designing the cable length to be shorter or longer than λg/4 (90 degrees in electrical length), there are certain restrictions on the length. FIG. 3 shows an example of the passband characteristics of a three-stage band-elimination filter. The center frequency is o, and the detuning frequency from the center frequency is Δ
Δ/o is plotted on the horizontal axis and insertion loss is plotted on the vertical axis. This is an example where the cable is located above o in the passband and the electrical length of the cable is 90° or more.
In the figure, the electrical length is 90°, 94.5° (+5%), 99° (+10
%), 108° (+20%), and 117° (+30%), and it can be seen that ripples occur in the passband characteristics as the line length increases. In normal applications, it is desirable that the pass band ripple of the filter be within 1 dB, so the line length can only be increased by about 20% at most. On the other hand, it can be seen that if the line length is increased by less than 5%, the effect is small because the change in characteristics itself is small.

As a specific example, consider designing a filter with a stopband center frequency of 450MHz and a passband of 454±0.1MHz (Δ=4.0MHz±100KHz). The insertion loss in the passband can be found from FIG. 3, and the relationship between this insertion loss and the line length increase is illustrated in FIG. 4.
In order to keep insertion loss within 1dB, it can be said that an increase in line length of about 5 to 20% is appropriate.
It can also be seen that the lowest loss is 10-15%.

In the above example, the case where the line length is longer than λg/4 is explained, but the same applies when the line length is shorter, and a reduction in line length of 5 to 20% is a practical range.

As mentioned above, even if the cable length is designed to be shorter or longer by 5% or less, the symmetry of the characteristics does not deteriorate much, and if the cable length is changed by 20% or more, the insertion loss in the passband and VSWR characteristics deteriorate. It is appropriate that the cable length change is within about 5 to 20% of λg/4. Further, in this state, the amount of attenuation at the center frequency is almost the same as when l=λg/4.

By providing such asymmetric characteristics,
Insertion loss in the passband can be reduced without sacrificing stopband characteristics. That is, in a normal circuit, when the blocking frequency is o, the passband is often greater than or equal to o+Δ or less than or equal to o−Δ.

For example, when receiving TV, on a UHF channel,
A problem that often occurs is that, as shown in FIG. 5, there are cases in which interference waves with a level much higher than the signal level of the desired wave are present in channels adjacent to the desired wave. When such radio waves are received, cross-modulation interference occurs and the quality of the receiving line is significantly degraded. As a countermeasure to this problem, CATV receivers are designed to sufficiently attenuate the interfering waves with a band-stop filter, while allowing the desired signals to pass through. The reason for this is that the gap between the band edges of the desired wave and the interfering wave is as narrow as 6MHz, so the pass band loss in a band pass waveformer becomes large.

The above-mentioned frequency characteristics are also required in the case of transmitting or receiving filters related to mobile radio having a narrow transmitting/receiving frequency interval, which will be described later.

In other words, let the stopband center frequency be o,
When the passband is more than o+Δ, as shown in Figure 2, the insertion loss in the passband is (l>λg/4),
Since it increases in the order of (l=λg/4) and (l<λg/4), it can be seen that in this case, using (l<λg/4) is more effective in terms of insertion loss. Conversely, if the passband is o−Δ, (l>
It can be seen that it is more effective to use λg/4).

As mentioned above, when the passband exists either above or below the center frequency o of the stopband, and the frequency interval between the passband and the stopband is narrow, the bandstop filter reduces insertion loss in the stopband. It turns out that it is extremely effective.

Next, an antenna duplexer according to an embodiment of the present invention will be described. FIG. 6 is a conceptual diagram showing an antenna duplexer according to an embodiment of the present invention, which is used in mobile radio equipment, etc., and uses the above-mentioned band-elimination device. In FIG. 6, 31 is an antenna duplexer, and terminals 32, 33, and 34 are a receiving terminal Rx, a transmitting terminal Tx, and an antenna terminal Ant, respectively.

The function of the antenna duplexer is that the received signal of frequency r that enters from the antenna does not propagate to the transmitting terminal Tx33 and all enters Rx32, and the transmitting signal of frequency _T that enters from the transmitting terminal Tx33 does not propagate to the receiving terminal Rx32 and all goes to Ant34. It has the property of propagation. Currently, the signal band is several hundred MHz with a transmission/reception interval of 10MHz or less.
When constructing a duplexer for frequencies below 5MHz, a method using two band-elimination filters is often used.

As an example, if the center frequency of the received signal band is
Ro, the center frequency of the transmission signal band is To,
Consider the case of Ro>To. FIG. 7 shows the circuit configuration of the duplexer in the case that both of the two band-elimination devices used in the duplexer can be realized in a three-stage configuration. Terminals 41, 42, and 43 are transmission terminals, respectively.
Tx, reception terminal Rx antenna terminal Ant is shown. 4
4 and 45 are series resonators, 46 and 47 are coaxial cables used for wave generators, and 48 and 49 are cables for signal synthesis. The band-elimination waveform device connected to the transmission terminal Tx41 consists of a series resonant circuit 44 and a coaxial cable 46, and the series resonator 44 is tuned at a center frequency Ro. Also, the coaxial cable length 46 is
Design to be 5 to 20% shorter than λg/4 at Ro. Further, by selecting the coupling cable 48 to be λg/4, the impedance seen from the antenna terminal Ant43 to the transmission terminal Tx41 side becomes infinite at the frequency Ro, so that the received signal does not propagate to the transmission terminal Tx41 side. In addition, since the transmitting signal uses the wave transmitter of the present invention, the transmission signal is transmitted from the transmitting terminal Tx41 to the antenna terminal Ant.
43 with low loss.

Also, the receiving terminal Rx42 side is also connected to the series resonator 4.
5 is tuned at To, and the length of cable 47 is
5 to 20% from the quarter wavelength λg/4 at To
The cable 49 for signal synthesis is designed to be long, and the cable 49 for signal synthesis is λg/
Design equal to 4. By doing this, the received signal is transferred from the antenna terminal Ant43 to the receiving terminal Rx42.
It can be designed so that the transmission signal propagates to the receiving terminal Rx42 side with low loss, and the wraparound of the transmitted signal to the receiving terminal Rx42 side is extremely small.

FIG. 8 shows an example of characteristics that can be achieved by this method.

The curve in the figure shows the propagation characteristics between the receiving terminal Rx and the transmitting terminal Tx, and a sufficient amount of attenuation can be ensured in the signal band. In addition, , respectively, are between the transmitting terminal Tx and the antenna terminal Ant, and between the antenna terminal Ant and the receiving terminal.
Although it shows the propagation characteristics between Rx, it is a method that reduces insertion loss in the passband, so it is an extremely effective characteristic.

As described above, the present invention utilizes a band-elimination device having a configuration in which a plurality of series resonant circuits are connected via a coaxial cable, and the band-elimination waveform device is configured to make the coaxial cable length longer or shorter than a quarter wavelength. This provides an antenna duplexer using two wave elements, and the frequency characteristics of the wave elements are made asymmetric above and below the center frequency, thereby reducing insertion loss.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing the configuration of a multi-stage band-elimination filter, Fig. 2 is a characteristic diagram showing the frequency characteristics of insertion loss of the present invention and conventionally used band-elimination filters, and Fig. 3 is a diagram showing the frequency characteristics of the insertion loss of the band-elimination filter used in the present invention and conventionally used band-elimination filters. A characteristic diagram showing an example of the pass band characteristics of a band-stop waver. Figure 4 is a relationship diagram showing the relationship between insertion loss and line length increase. Figure 5 is a diagram showing the relationship between interference waves and desired waves during VHF reception. 6 is a conceptual diagram of the antenna duplexer, FIG. 7 is a wiring diagram showing the configuration of the antenna duplexer in an embodiment of the present invention, and FIG. 8 is the antenna duplexer shown in FIG. 7. FIG. 11...Input terminal, 12...Output terminal, 13...Series resonant circuit, 14...Transmission line (coaxial cable).

Claims (1)

[Claims] 1 A band-stop waveform device consisting of multiple series resonant circuits connected via coaxial cables is provided on the transmitting and receiving sides, and the transmitting and receiving frequencies are different from each other, such as a transmitting frequency _T and a receiving frequency _R.
In _{the antenna duplexer} that _processes In addition, when the length of the coaxial cable used for the band-elimination filter on the receiving side is longer than a quarter wavelength, and on the other hand, when the transmission frequency _T and the reception frequency _R have a relationship such that _R > _T , the above-mentioned An antenna duplexer in which the length of a coaxial cable used for a band-elimination waveform on a transmitting side is longer than a quarter wavelength, and the length of a coaxial cable used for a band-elimination waveform on a receiving side is shorter than a quarter wavelength.