Antenna Switch Module

This application is a U.S. National Phase Application of PCT International Application PCT/JP2005/013031.

The present invention relates to an antenna switch module including an antenna switch which switches antennas, and a filter which passes fundamental frequencies and has an attenuation pole.

FIG. 12 shows a block diagram of a conventional communication device including conventional antenna switch module 80 . Conventional antenna switch module 80 will be described with FIG. 12 . In FIG. 12 , the communication device includes antenna switch module 80 , transmission part 41 , reception part 42 , filter 83 , antennas 44 and 45 , and capacitors C 81 to C 84 .

Conventional antenna switch module 80 includes antenna switch circuit 87 and filter 86 . Signals from transmission part 41 are inputted to filter 86 through capacitor 81 . Filter 86 passes fundamental frequencies and removes unnecessary signals. Signals outputted from filter 86 are emitted from antenna 44 or 45 selected by antenna switch circuit 87 , after passing through capacitor C 83 or C 84 .

On the other hand, signals which are received by antenna 44 or 45 selected by antenna switch circuit 87 and then are passed through capacitor C 83 or C 84 are inputted to filter 83 through capacitor C 82 . Filter 83 removes unnecessary signals from the received signals and outputs them to reception part 42 . Reception part 42 demodulates the signals from filter 83 .

Filter 86 included in antenna switch module 80 will be described with reference to FIGS. 13 to 16 . FIG. 13 shows the structure of the filter for the conventional antenna switch module. In FIG. 13 , capacitors C 94 connected to the ground are open circuit to low frequency components and are short circuit to high frequency components. Inductor L 94 connected in series with capacitors C 94 are short circuit to low frequency components and are open circuit to high frequency components. Thus, the filter shown in FIG. 13 is a low pass filter, which passes low frequency components only.

The low pass filter shown in FIG. 13 has a large circuit size because rapid attenuation can be achieved only by a large number of stages. Alternatively, rapid attenuation can be achieved by a few number of stages when the constant of each element of this filter is determined in such a manner as to make the filter a Chebychev low pass filter. However, it is difficult for this filter to achieve wideband filtering at low loss because the filter has ripples in the passband. Another possible structure is achieved by the use of distributed constant lines. In this case, however, when a certain frequency is reached, inductive distributed constant lines are changed to capacitive distributed constant lines, whereas capacitive distributed constant lines are changed to inductive distributed constant lines. The input impedance greatly changes depending on the frequency, thereby sometimes causing the filter to lose its function as a filter.

In view of this situation, a polarized low pass filter shown in FIG. 14 has been contrived. FIG. 14 shows the structure of this filter for the conventional antenna switch module. FIG. 15 shows frequency characteristics of this filter for the conventional antenna switch module. The principle of operation of the filter will be briefly described with FIGS. 14 and 15 .

Polarized low pass filter 90 includes LC series circuits 96 , 98 and 99 . As shown in FIG. 15 , the attenuation band in the frequency characteristics of filter 90 has three poles: a first pole of 13.2 KHz; a second pole of 15.4 KHz and a third pole of 25.3 KHz. Here, for example, decreasing the resonant frequency of LC series circuit 98 , that is, the second pole frequency can reduce the interval between the first pole and the second pole. Reducing the interval between these poles results in an increase in the amount of attenuation between the poles.

As a filter for the conventional antenna switch module, one example of the aforementioned polarized low pass filter is disclosed in Japanese Patent Unexamined Publication No. 61-77408.

Another known filter for an antenna switch module is a notch filter with little filtering loss. A notch low pass filter can be formed of a combination of a plurality of ¼ wavelength open stubs and ½ wavelength terminated stubs. FIG. 16 shows frequency characteristics when antenna 44 or 45 is seen from transmission part 41 in a case where filter 86 of the conventional antenna switch module is a notch filter. Fundamental frequencies are from F 1 =4.9 GHz to F 2 =5.85 GHz. Second harmonic frequencies are from F 3 =9.8 GHz to F 4 =11.7 GHz. Third harmonic frequencies are from F 5 =14.7 GHz to F 6 =17.55 GHz. The frequencies of the attenuation poles are set so as to attenuate the second and third harmonics.

In such a conventional structure, the second harmonic frequencies have small attenuation at other than the two attenuation poles F 3 and F 4 , and the third harmonic frequencies have small attenuation at other than the two attenuation poles F 5 and F 6 . In other words, the impedance when the output side of filter 86 is seen from the input side, and the impedance when the input side is seen from the output side both approach 50 ohms. On the other hand, impedance Z 813 when terminal T 83 connected with capacitor C 83 is seen from terminal T 81 of antenna switch circuit 87 , which is connected with filter 86 is about 50 ohms at the fundamental frequencies. Impedance Z 842 when terminal T 82 connected with capacitor C 82 is seen from terminal T 84 connected with capacitor C 84 is also about 50 ohms at the fundamental frequencies. On the other hand, impedance Z 814 when terminal T 84 is seen from terminal T 81 and impedance Z 832 when terminal T 82 is seen from terminal T 83 are open circuit. However, as the frequency gets higher, the capacity component and induction component of the package and terminals of the PIN diode become influential. This causes impedances Z 813 , Z 842 , Z 814 and Z 832 to change their values. More specifically, impedances Z 813 and Z 842 have values close to open circuit at the harmonic frequencies ranging from 4.9 GHz to 5.85 GHz, and impedances Z 814 and Z 832 have values close to 50 ohms. As a result, at the harmonic frequencies, the impedance Z 813 when filter 86 is seen from terminal T 81 , and impedance Z 814 when antenna switch circuit 87 is seen from terminal T 81 can be complex conjugates of each other. This may deteriorate the amount of attenuation at the attenuation poles or cause a rebound phenomenon between the attenuation poles, thereby making it impossible to have enough attenuation.

The present invention provides an antenna switch module including a filter which can reduce filtering loss so as to achieve high attenuation in a wide band at harmonic frequencies.

The antenna switch module of the present invention includes the filter, an antenna switch circuit and an adjustment line. The filter passes fundamental frequencies and has an attenuation pole. The antenna switch circuit switches antennas matching the fundamental frequencies. The adjustment line is connected between the filter and the antenna switch circuit, and adjusts properties of the fundamental frequencies at the harmonic frequencies. When the filter and the antenna switch circuit are directly connected with each other at a connection point, the adjustment line prevents the impedance when the filter is seen from the connection point and the impedance when the antenna switch circuit is seen from the connection point from becoming complex conjugates of each other at the harmonic frequencies.

This antenna switch module can easily reduce rebound components between the attenuation poles of the filter at the harmonic frequencies without degrading the amount of attenuation at the attenuation poles, thereby fully attenuating the harmonic components without increasing the number of stages of the filter. For example, fundamental frequency signals amplified by a power amplifier in the front end module of a wireless LAN (Local Area Network) are passed at low loss, and the harmonic components generated by the power amplifier can be removed in a wide band at high attenuation.

FIG. 1 is a block diagram showing the structure of a communication device including an antenna switch module of an embodiment of the present invention.

FIG. 2 shows a first layer of the antenna switch module of the embodiment.

FIG. 3 shows a second layer of the antenna switch module of the embodiment.

FIG. 4 shows a third layer of the antenna switch module of the embodiment.

FIG. 5 shows a fourth layer of the antenna switch module of the embodiment.

FIG. 6 shows a fifth layer of the antenna switch module of the embodiment.

FIG. 7 shows a sixth layer of the antenna switch module of the embodiment.

FIG. 8 shows the structure of an antenna switch circuit of the antenna switch module of the embodiment.

FIG. 9 is an equivalent circuit diagram when a PIN diode as a component of the antenna switch circuit of the embodiment is “ON”.

FIG. 10 is an equivalent circuit diagram when the PIN diode of the embodiment is “OFF”.

FIG. 11 shows frequency characteristics of the antenna switch module of the embodiment.

FIG. 12 is a block diagram showing the structure of a communication device including a conventional antenna switch module.

FIG. 13 is a circuit diagram of a filter for the conventional antenna switch module.

FIG. 14 is a circuit diagram of another filter for the conventional antenna switch module.

FIG. 15 shows frequency characteristics of the filter for the conventional antenna switch module.

FIG. 16 shows frequency characteristics of the conventional antenna switch module.

3 , 7 , 8 round conductor

4 , 5 A, 5 B ground part

6 A, 6 B, 6 C, 6 D, 6 E electrode

11 A, 11 B, 11 C, 11 D, 13 A, 13 B, 13 C stripline

13 D adjustment line

15 coupling line

30 antenna switch module

31 , 43 filter

33 antenna switch circuit

35 directional coupler

41 transmission part

42 reception part

44 , 45 antenna

51 passing signal

52 reflected signal

An embodiment of the present invention will be described as follows with drawings.

FIG. 1 is a block diagram showing the structure of a communication device including an antenna switch module of the embodiment of the present invention. In FIG. 1 , a communication device includes antenna switch module 30 , transmission part 41 , reception part 42 , filter 43 , antennas 44 and 45 , and capacitors C 11 to C 14 . Antenna switch module 30 includes antenna switch 33 , filter 31 and adjustment line 13 D. Adjustment line 13 D, together with other components described later, make up directional coupler 35 .

Signals from transmission part 41 are inputted to filter 31 through capacitor C 11 . Filter 31 is a notch low pass filter which removes unnecessary harmonic signals contained in the signals from transmission part 41 . Filter 31 has fundamental frequencies of 4.9 to 5.85 GHz. The second harmonic frequencies are from 9.8 to 11.7 GHz, and the third harmonic frequencies are from 14.7 to 17.55 GHz. Signals outputted from filter 31 are inputted to antenna switch circuit 33 through adjustment line 13 D made of stripline. The signals inputted through adjustment line 13 D are emitted from antenna 44 or 45 selected by antenna switch circuit 33 , after passing through capacitor C 13 or C 14 .

On the other hand, signals received by antenna 44 or 45 selected by antenna switch circuit 33 through capacitor C 13 or C 14 are inputted to filter 43 through capacitor C 12 . Filter 43 removes unnecessary signals from the received signals, and outputs them to reception part 42 . Reception part 42 demodulates the signals from filter 43 .

FIGS. 2 to 7 show the respective layers of a multilayer substrate in the case where the antenna switch module of the present embodiment is compliant with IEEE802.11a. FIG. 2 shows first layer P 1 , which is the uppermost layer. First layer P 1 is provided thereon with switching element B 1 , inductors L 1 to L 4 , capacitors C 1 , C 2 and resistors R 1 , R 2 so as to form antenna switch circuit 33 . Switching element B 1 is made up of PIN diodes D 1 to D 4 . First layer P 1 is further provided thereon with capacitor C 12 , filter 43 , and capacitor C 5 and resistor R 5 which are components of directional coupler 35 .

FIG. 3 shows second layer P 2 having ground parts 5 A and 5 B thereon. FIG. 4 shows third layer P 3 having coupling line 15 thereon, which is a component of the directional coupler. FIG. 5 shows fourth layer P 4 having filter 31 and adjustment line 13 D thereon. FIG. 6 shows fifth layer P 5 having ground part 4 thereon. FIG. 7 shows sixth layer P 6 provided thereon with electrodes 6 A to 6 E. With layer P 1 as the uppermost layer, layers P 2 to P 6 are arranged from above in this order. The antenna switch module of the present embodiment is connected with another device via P 6 .

The substrate of the antenna switch module of the present embodiment is made from low-temperature co-fired ceramics having a dielectric constant of 7.4, and is 5.4 mm by 4.0 mm and 0.7 mm in thickness. Ground parts 4 , 5 A and 5 B; striplines 11 A to 11 D and 13 A to 13 C; adjustment line 13 D; and coupling line 15 are formed by printing conductive paste mainly composed of silver powder.

In the present embodiment, striplines 11 A to 11 D, 13 A to 13 C and adjustment line 13 D formed on the fourth layer have a characteristic impedance of 50 ohms, and a line width of 0.1 mm in the case of the low-temperature co-fired ceramics of the present embodiment. Filter 31 is made up of striplines 11 A to 11 D and 13 A to 13 C. Stripline 11 A is connected with striplines 13 A and 13 B at junction point E 1 . Stripline 11 B and 11 C are connected with striplines 13 B and 13 C at junction point E 2 .

Stripline 11 D is connected with stripline 13 C and adjustment line 13 D at junction point E 3 . In order to reduce the size of filter 31 , striplines 11 B, 11 C, 13 B and 13 C are connected in the shape of a cross at junction point E 2 . Striplines 11 A to 11 D are open at one side, and have line lengths of ¼ wavelengths of 17.55 GHz, 14.7 GHz, 11.7 GHz and 9.8 GHz, respectively. Consequently, striplines 11 A, 11 B, 11 C and 11 D have a voltage swing of 0 at junction points E 1 to E 3 at 17.55 GHz, 14.7 GHz, 11.7 GHz and 9.8 GHz, respectively. In other words, striplines 11 A to 11 D are open stubs.

These striplines are bent to reduce the filter size, while keeping an interval long enough not to cause line coupling. In this embodiment, the line interval is made to be not less than 0.15 mm. Filter 31 may be made up of, instead of the ¼ wavelength open stubs, ½ wavelength short stubs whose each one side is grounded. In this case, it is necessary to insert a DC cut capacitor between filter 31 and antenna switch circuit 33 .

The line lengths of striplines 13 B and 13 C are determined in such a manner that in the condition where striplines 11 A to 11 D are connected with each other, the impedance when junction point E 1 is seen from the stripline 13 A side and the impedance when junction point E 3 is seen from adjustment line 13 D can be 50 ohms at the fundamental frequencies. For example, in the case of the low-temperature co-fired ceramics of the present embodiment, striplines 13 B and 13 C have line lengths of 2.3 mm and 2.45 mm, respectively.

Stripline 13 A is connected to round conductor 3 . The fourth and fifth layers are connected with each other through via hole V 1 . The fifth layer is connected with electrode 6 A on the sixth layer through via hole V 2 . Round conductor 8 connects between via holes V 1 and V 2 . Electrode 6 A on the sixth layer is connected with transmission part 41 through C 11 .

On ground part 4 , part of the conductor pattern is cut in the form of a circle with a diameter not to cause electromagnetic coupling due to via hole V 2 . In the present embodiment, round conductor 8 has a diameter of 1.25 mm, and a via hole diameter of 0.5 mm. Round conductor 3 has a diameter of 0.75 mm in consideration of positional deviation or positional variation between round conductor 3 and the via hole due to manufacturing errors.

On the sixth layer, electrodes 6 A to 6 E are formed by printing conductive paste mainly composed of silver powder. Electrode 6 A receives signals from transmission part 41 through capacitor C 11 . Electrodes 6 C and 6 D supply power to operate antenna switch circuit 33 . A plurality of electrodes 6 E assure a ground potential. The round electrode on the sixth layer has a diameter of 1 mm. In order to fix the potential of ground part 4 on the fifth layer, electrodes 6 B, which are rectangles of 0.8 mm by 1.4 mm, are formed at the positions of ±0.7 mm from the center of the sixth layer in such a manner as to be symmetric with respect to the center. Electrodes 6 B each include via holes, which are arranged in two columns and five rows at an interval of 0.3 mm by 0.5 mm, and are connected with ground part 4 .

Adjustment line 13 D is connected with round conductor 7 , and is further connected with terminal T 1 of antenna switch circuit 33 shown in FIG. 2 through via hole V 3 connecting between the fourth and second layers, and via hole V 4 connecting between the second layer and antenna switch circuit 33 .

FIG. 8 shows the structure of antenna switch circuit 33 of the antenna switch module of the present embodiment. In FIG. 8 , antenna switch circuit 33 includes terminals T 1 to T 4 . Terminal T 1 receives signals from transmission part 41 . Terminal T 2 outputs signals from antenna 44 or 45 to reception part 42 . Terminal T 3 is connected with antenna 44 through capacitor C 13 . Terminal T 4 is connected with antenna 45 through capacitor C 14 . Antenna switch circuit 33 is provided with switch units S 1 and S 2 . Switch unit S 1 electrically connects/disconnects terminal T 1 and terminals T 3 , T 4 . Switch unit S 2 electrically connects/disconnects terminal T 2 and terminals T 3 , T 4 .

Switch unit S 1 includes PIN diode D 1 connecting between terminal T 1 and the cathode and between terminal T 3 and the anode, and PIN diode D 2 connecting between terminal T 1 and the anode and between terminal T 4 and the cathode. Switch unit S 2 includes PIN diode D 3 connecting between terminal T 2 and the anode and between terminal T 3 and the cathode, and PIN diode D 4 connecting between terminal T 2 and the cathode and between terminal T 4 and the anode. PIN diodes D 1 to D 4 make up switching element B 1 .

Inductor L 1 and capacitor C 1 are connected in series with each other between ground 5 B and the junction point of terminal T 1 and PIN diode D 1 . Inductor L 2 and capacitor C 2 are connected in series with each other between ground 5 B and the junction point of PIN diode D 1 and terminal T 3 . Inductor L 3 and capacitor C 1 are connected in series with each other between ground 5 B and the junction point of terminal T 2 and PIN diode D 4 .

Inductor L 4 and capacitor C 2 are connected in series with each other between ground 5 B and the junction point of PIN diode D 4 and terminal T 4 . The junction point of inductors L 1 , L 3 and capacitor C 1 is connected with electrode 6 C through resistor R 1 . The junction point of inductors L 2 , L 4 and capacitor C 2 is connected with electrode 6 D through resistor R 2 .

Resistors R 1 and R 2 control the direct currents flowing to PIN diodes D 1 to D 4 . Capacitors C 1 and C 2 bypass high frequency components to ground 5 B. Inductors L 1 to L 4 block the high frequency components and supply direct current voltages to PIN diodes D 1 to D 4 . Supplying a positive direct-current voltage to electrode 6 C makes PIN diodes D 2 and D 3 “ON”. Supplying a positive direct-current voltage to electrode 6 D makes PIN diodes D 1 and D 4 “ON”.

FIG. 9 is an equivalent circuit diagram when a PIN diode as a component of the antenna switch circuit of the present embodiment is “ON”, and the PIN diode is made up of inductors L 31 to 33 , capacitor C 31 and resistor 31 . FIG. 10 is an equivalent circuit diagram when the PIN diode of the present embodiment is “OFF”, and the PIN diode is made up of inductors L 34 and L 35 , capacitors C 32 and C 33 , and resistor 32 . In FIG. 4 , coupling line 15 , together with capacitor C 5 and resistor R 5 , makes up directional coupler 35 by being in parallel with adjustment line 13 D via the ceramics layer.

The operation of the antenna switch module of the present embodiment thus structured will be described as follows.

FIG. 11 shows frequency characteristics of the antenna switch module of the present embodiment. Passing signal 51 is passed from stripline 13 A to terminal T 3 or T 4 . Reflected signal 52 is a reflected signal corresponding to passing signal 51 . In antenna switch circuit 33 , the impedance when terminal T 3 connected with capacitor C 13 is seen from terminal T 1 connected with adjustment line 13 D is referred to with Z 13 . The impedance when terminal T 2 connected with capacitor C 12 is seen from terminal T 4 connected with capacitor C 14 is referred to with Z 42 . The impedance when terminal T 4 is seen from terminal T 1 is referred to with Z 14 . The impedance when terminal T 2 is seen from terminal T 3 is referred to with Z 32 .

As shown in FIG. 11 , filter 31 formed on the fourth layer produces large attenuation poles with striplines 11 A to 11 D at the frequencies which are the second and third harmonics of the fundamental frequencies ranging from 4.9 GHz to 5.85 GHz. Furthermore, the length of adjustment line 13 D made up of the striplines is controlled so as to prevent the impedance Z 13 when stripline 13 A is seen from round conductor 7 at the second and third harmonic frequencies and the impedance Z 14 when antenna switch circuit 33 is seen from round conductor 7 from becoming complex conjugates of each other. In other words, impedances Z 13 and Z 14 are prevented from having an equal resistance component, and reactance components equal in size and opposite in sign.

The following is a more detailed description. Antenna switch circuit 33 , which operates properly as a switch at the fundamental frequencies ranging from 4.9 GHz to 5.85 GHz, does not operate properly as a switch at frequencies of the second and higher harmonics of the fundamental frequencies. This is due to the influence of the reactance component shown in FIGS. 9 and 10 . This situation is dealt with as follows. Measured data of antenna switch circuit 33 are inputted to an EM (electromagnetic) simulator. Next, the specifications of filter 31 made from low-temperature co-fired ceramics, that is, the actual layer structure and detailed requirements of the conductors such as conductor loss are inputted to the EM simulator. In the same manner, the specifications of adjustment line 13 D, that is, the actual layer structure and detailed requirements of the conductors such as conductor loss are inputted to the EM simulator. The length of adjustment line 13 D is changed to avoid a complex conjugate relation at the second and third harmonics, thereby obtaining favorable amount of attenuation and band width.

By using a notch low pass filter as the filter and controlling the length of adjustment line 13 D, an antenna switch module can be provided which reduces filtering loss so as to ensure high attenuation in a wide band at harmonic frequencies.

The directional coupler can be alternatively made up of adjustment line 13 D, coupling line 15 , capacitor C 5 and resistor R 5 . This allows more reflected waves to be detected from antenna 44 or 45 , thereby controlling the transmission condition of transmission part 41 .

As described hereinbefore, the antenna switch module of the present invention can easily reduce rebound components between two or more attenuation poles of the filter without degrading the amount of attenuation at the attenuation poles, thereby fully attenuating the harmonic components without increasing the number of stages of the filter.

In the present embodiment, it is alternatively possible to divide the ground part into ground part 5 A and ground part 5 B. Ground part 5 A is for antenna switch circuit 33 . Ground part 5 B is for striplines 13 B to 13 C and 11 A to 11 D composing the filter on the fourth layer, and stripline 13 A and round conductor 3 which are connected to transmission part 41 .

This division of the ground allows the image current to flow through ground part 5 A, and then into ground part 4 through via hole V 5 connecting between ground part 5 A and ground part 4 .

Then, the image current flowing through ground part 4 is flown into ground part 5 B through via hole V 6 connecting between ground part 4 and ground part 5 B. The path of the image current has a considerable line length at the second and higher harmonic frequencies of the fundamental frequencies ranging from 4.9 GHz to 5.85 GHz. In other words, the image current path functions as a choke coil for the current at the second and higher harmonic frequencies. As a result, in these frequencies, the antenna switch module of the present embodiment can obtain favorable amount of attenuation of 30 dB or higher.

The present embodiment takes up the case where the switching element of the antenna switch circuit is a PIN diode with excellent switch properties at high frequencies; however, the present invention is not limited to this case. Equivalent effects could be obtained by using as the switching element other electronic devices such as Ga (gallium) As (arsenic) switches having favorable switch properties at high frequencies, transistors, and electric field-effect transistors (FETs).

The filter or the adjustment line, which is formed of striplines in the present embodiment, could be formed of microstriplines to obtain the equivalent effects. Although four attenuation poles are used in the present embodiment, the number can be other than four. The filter, which is a notch low pass filter in the present embodiment, could be a polarized low pass filter to obtain the equivalent effects.

The filter, which is a low pass filter in the present embodiment, could be a band pass filter or a band rejection filter to obtain the equivalent effects. Although the multilayer substrate consists of six layers in the present embodiment, the number can be other than six.

As described hereinbefore, the antenna switch module of the present invention includes a filer which reduces transmission loss so as to achieve high attenuation in a wide band at harmonic frequencies and an adjustment line. Therefore, this is useful as an antenna switch module or the like including an antenna switch to switch antennas and a filter to remove spurious signals from the communication device.