JP3398243B2 - Antenna duplexer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna duplexer, and more particularly to an antenna duplexer used for mobile communication devices such as mobile phones.

[0002]

2. Description of the Related Art Conventionally, a technology of an antenna duplexer using a coaxial resonator has been proposed (for example, actual Kaihei 6-920).
No. 6), an antenna duplexer is used as a filter that separates a transmission signal and a reception signal of, for example, a mobile phone.

The antenna duplexer will be described below with reference to FIG.

The antenna duplexer has three terminals, Tx (transmitting circuit connecting terminal), Rx (receiving circuit connecting terminal), and Ant (antenna connecting terminal). Tx (transmitting circuit connection terminal)
Between the antenna and Ant (antenna connection terminal) is a transmission filter that passes the transmission frequency.
And Rx (reception circuit connection terminal), a reception filter is configured to pass the reception frequency. The transmission filter is a BEF (band elimination filter) for realizing low loss, and the reception filter is a BPF (band pass filter) for removing interference waves of various frequencies.

First, the transmission filter will be described. R
Reference numerals 1 and R2 are coaxial resonators, which usually resonate at a quarter wavelength while short-circuited and open-ended type are used. C4, C5
Is a capacitor, which is connected in series to each of the coaxial resonators R1 and R2. Since the coaxial resonators R1 and R2 exhibit L property at a frequency lower than the resonance frequency, the capacitor C
4 and C5 are connected in series to form a coaxial resonator R1,
Series resonance will occur at a frequency lower than the resonance frequency of R2. This series resonance frequency forms an attenuation pole in the transmission characteristic of the BEF (band elimination filter), and this attenuation pole is set in the reception frequency band. The π-type circuit composed of the inductor L1, the capacitors C1 and C2 is
It is a phase shift circuit. It functions as a gyrator in the transmission band, matching each series resonance circuit, and operates as an LPF (low-pass filter) at frequencies higher than the transmission frequency, and also has a spurious suppression effect. Normally, the series resonance frequency of each series resonance circuit is adjusted to a different value in order to secure the amount of attenuation in the entire reception band.
The series resonance frequency which is the attenuation pole frequency can be freely controlled by adjusting the resonance frequencies of the coaxial resonators R1 and R2 and the values of the capacitors C4 and C5. The inductor L2 and the capacitor C3 (which may include C2) are matching circuits that ideally make the impedance in the reception band of the transmission filter viewed from the antenna infinite.

On the other hand, the receiving filters are coaxial resonators R3 and R.
4 is connected by a capacitor C7, and capacitors C6 and C8 are connected.
Therefore, the antenna and the receiving circuit are matched.
Also in this case, the resonance frequencies of the coaxial resonators R3 and R4 are adjusted to be higher than the reception frequency. This is because the resonators are connected to each other by a gyrator in order to realize the bandpass filter only with a series or parallel resonant circuit, and the coaxial resonator absorbs the negative capacitance that is the gyrator component. is there. This state is shown in FIG.
Shown in. Here, the symbols of inductor and capacitor are considered as inductance and capacitance as they are. The π-type circuit composed of the capacitors C, -C, -C is a gyrator, and connects the parallel resonator composed of the inductor L0 and the capacitor C0. The resonance frequency (= 1 / {2π√ (L0 × C0)}) of this parallel resonator is equal to the center frequency of the filter. -C cannot be realized, so-
Positive capacitance C0 ′ (= C0−C which can be realized by combining C with the capacitance C0 of the parallel resonator
> 0). The coaxial resonator is replaced so that the resonance frequency is equivalent to that of the parallel resonator formed of L0 and C0 '. This resonance frequency is 1 / {2π√ (L0 × (C0
-C))}, which is higher than the resonance frequency before absorbing -C. That is, it becomes higher than the center frequency of the filter. As described above, the conventional antenna duplexer has been constructed.

[0007]

However, in the prior art, coaxial resonators are used for both the transmitting and receiving circuits, and there is a demand for miniaturization of the antenna duplexer accompanying the miniaturization of mobile phones and the like. In order to respond, the size of the coaxial resonator, which occupies most of the volume, had to be reduced. The miniaturization also has a drawback that the insertion loss of the filter becomes large due to the reduction of the Q value due to the miniaturization of the coaxial resonator shape, and the miniaturization is naturally limited.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an antenna duplexer that solves these problems of the prior art.

In order to solve the above-mentioned problems, the present invention has an antenna duplexer having transmission and reception paths and using a coaxial resonator, and at least one coaxial resonator is provided on both the transmission and reception paths. The antenna duplexer was configured to be shared.

[0010]

According to the above-described structure of the present invention, since the coaxial resonator can be shared, the miniaturization of the antenna duplexer can be achieved with almost no increase in insertion loss.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The same parts are designated by the same numbers.

FIG. 1 is a block diagram of an antenna duplexer according to an embodiment of the present invention, and FIG. 2 is a diagram showing transmission characteristics of the antenna duplexer. Here, it is assumed that the reception band has a lower frequency than the transmission band. R1 and R2 are coaxial resonators, capacitors C3 and C4 are connected in series, and the series resonance frequency is adjusted to the reception band. These series resonance circuits are connected by a π-type phase shift circuit composed of an inductor L and capacitors C1 and C2. During transmission, diodes D1 and D
BEF (band elimination filter) is configured by setting the diodes D2, D3 in the conductive state and the diodes D4, D5, D6 in the non-conductive state.

On the other hand, when receiving, on the contrary, the diode D
1, D2, D3 are non-conductive, diodes D4, D5, D6
Is made conductive, and a BPF (band pass filter) is configured. In the figure, the diode bias circuit is omitted. The resonance frequencies of the coaxial resonators R1 and R2 are higher than the reception band, as shown in the description of the related art. The coaxial resonators R1 and R2 are selected so that their resonance frequencies match the transmission band, and capacitors C3 and C4 are used.
The series resonance frequency of the series resonance circuit added with is selected so as to be in the reception band. Further, the capacitor C6 is adjusted so that the center frequency of the reception filter matches the reception band even during reception. At this time, if the pass band width of the reception filter becomes too wide (decays in the amount of attenuation) or becomes too narrow (deteriorates the insertion loss) relative to the reception band, making adjustments difficult The characteristic impedance may be changed to change the adjustable range of the capacitor C6. In this way, by selecting the resonance frequency of the coaxial resonator, the coaxial resonator can be used for both transmission and reception.

FIG. 3 is a block diagram of an antenna duplexer according to another embodiment of the present invention, and FIG. 4 is a diagram showing transmission characteristics of the antenna duplexer. Here, it is assumed that the reception band has a higher frequency than the transmission band. The embodiment of FIG. 3 has almost the same configuration as that of FIG.
Inductors L2 and L3 are connected in series to 1 and R2, and a diode D4 and a capacitor C6 and a diode D5 and a capacitor C7 are connected in parallel to the coaxial resonators R1 and R2 and the ground. Since the coaxial resonators R1 and R2 exhibit C-characteristics at a frequency equal to or higher than the resonance frequency, the series resonance circuit causes series resonance at a higher frequency side than the resonance frequency. That is, the attenuation pole as a filter occurs on the higher frequency side than the pass band. The resonance frequencies of the coaxial resonators R1 and R2 are adjusted to be higher than the reception band in order to match the pass band of the filter with the reception band during reception. As it is, it is impossible to set the pass band of the filter at the time of transmission to a lower frequency side than the reception band. Therefore, at the time of transmission, the diodes D4 and D5 are made conductive to connect the capacitors C6 and C7 to the coaxial resonators R1 and R2. Is connected in parallel to the ground to lower the resonance frequency of the resonance circuit including the coaxial resonators R1 and R2 and the capacitors C6 and C7. Therefore, in the diode, D1, D2, D3, D4, and D5 are conducted during transmission, and D6, D7, and D8 are conducted during reception. In this way, the coaxial resonator can be used for both transmission and reception.

In this example, the C-coupling type is considered as the receiving filter, but even in the L-coupling type, the parallel reactance added to the coaxial resonator by selecting the resonance frequency of the coaxial resonator and turning the diodes on and off is appropriate. By selecting and adjusting, the coaxial resonator can be shared for both transmission and reception. Although the coaxial resonator is considered to have two stages of transmission and two stages of reception in the above embodiment, the present invention is not limited to the number of stages, and if one coaxial resonator is shared, the size of the antenna duplexer can be reduced. Is possible, and the greater the number of shared devices, the greater the merit of downsizing. In addition, the transmission filter is BEF and the reception filter is BPF.
It may be the same type of filter, F or BEF.

[0016]

As described above, according to the structure and method of the present invention, the number of the coaxial resonators having the largest shape among the components forming the antenna duplexer can be reduced to about half, and therefore the antenna duplexer can be used. Can be miniaturized most effectively.

Further, since it is not necessary to reduce the size of the coaxial resonator, there is a remarkable effect that the insertion loss hardly increases.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an antenna duplexer according to an embodiment of the present invention.

FIG. 2 is a diagram showing transmission characteristics of an antenna duplexer according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of an antenna duplexer according to another embodiment of the present invention.

FIG. 4 is a diagram showing transmission characteristics of an antenna duplexer according to another embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of an antenna duplexer according to a conventional example.

FIG. 6 is a diagram for explaining coupling by a gyrator.

[Explanation of symbols]

C0 to C8 capacitors L0 to L3 inductor R1 to R4 coaxial resonator D1 to D8 diode Rx receiver circuit connection terminal Tx transmitter connection terminal Ant antenna connection terminal

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Claims (4)

(57) [Claims] 1. An antenna duplexer comprising at least one coaxial resonator, wherein the coaxial resonator is shared by both a transmission path and a reception path, and a capacitor is provided in a series resonance circuit including the coaxial resonator. Alternatively, a transmission circuit for selectively connecting the inductor via the first switching means for switching between transmission and reception may be configured to transmit the antenna during transmission.
Is switched to the transmission path and connected, and when receiving, the reception
A second switching means for switching and connecting to the signal path, and transmitting
The first switching means and the second switching means depending on time and reception.
The key is switched via the first switching means during transmission.
Used as the transmission filter the transmission circuit is connected to Yapashita or inductor, walk the capacitor during reception
Is an antenna duplexer characterized in that the transmission circuit is used as a reception filter without connecting an inductor . 2. The antenna duplexer according to claim 1, wherein the first switching means and the second switching means are diode switches. 3. The transmission filter has a band stop characteristic (BE).
The antenna duplexer according to claim 1, wherein the antenna duplexer is F). 4. The bandpass characteristic (BP) of the reception filter
The antenna duplexer according to claim 1, wherein the antenna duplexer is F).