A CAVITY RESONATOR COUPLING TYPE POWER DISTRIBUTOR/POWER COMBINER

Abstract: A cavity resonator coupling type power distributor/­ power combiner which can be used either as a distributing amplifier or as a combining unit, and comprising a first cavity resonator having a single coupling terminal (7), a second cavity resonator (6) having a plurality of coupling terminals (8a...Bn), and a coupling window (9) or a coupling rod for electromagnetically coupling the second cavity resonator with the first coupling resonator, whereby a wide bandwidth of microwave electric power can be distributed or combined.

Description: The present invention relates to a cavity resonator coupling type power distributor/power combiner. More particularly, it relates to a distributor/combiner for distributing or combining microwave electric power between a single coupling terminal and a plurality of coupling terminals. In recent years, attempts have been made to use semiconductor amplifier elements such as gallium-arsenide (GaAs) field effect transistors (FET's) instead of conventional traveling-wave tubes, in order to amplify signals in the microwave band. The semiconductor amplifier element, however, has an output power of several watts at the most, and when it is necessary to amplify the high frequency signal of a large electric power, such elements must be operated in parallel. Because of this, it is accepted in practice to distribute input signals in the microwave band into a plurality of channels with a microwave distributor, to amplify the signals of each channel using a semiconductor amplifier element, and to combine the amplified output signals of each of the channels into a signal of one channel using a microwave combiner, thereby obtaining a high frequency large electric power. The electric power, however, is lost when the phases and the amplitudes of the microwave electric power distributed by the microwave distributor are not in agreement, or when the microwave electric power is not combined in phase and in equal amplitude by the microwave combiner. It is, therefore, desired that the phases and the amplitudes of microwave signals be uniformly distributed in the microwave distributor and in the microwave combiner. It is also necessary that the distributor and the combiner itself lose as little electric power as possible. A cavity resonator may be effectively used as a distributor or a combiner because it can provide a high coincidence of both phase and electric power between the input and the output thereof. Conventionally, only a single cavity resonator is used. A single cavity resonator, however, has, by its character, a too narrow wave bandwidth to be used as a distributing amplifier or a combiner. Therefore, a single cavity resonator cannot be practically used as a distributor or a combiner. US-A-4 143 334 discloses a microwave oscillator having features corresponding to those of the preamble of accompanying claim 1. According to the present invention, there is provided a cavity resonator apparatus, comprising: a first cavity resonator means having a single coupling terminal for coupling with an input/output signal; a plurality of coupling terminals; and coupling means for electromagnetically coupling with said first cavity resonator means; characterised in that: said apparatus is a cavity resonator coupling type power distributor/power combiner selectable to function as one of a distributor and a combining unit in conjunction with multiple amplifiers, said power distributor/power combiner further comprising: a second cavity resonator means, having a cylindrical shape, having said plurality of coupling terminals for coupling with a plurality of output/input signals and connected to said multiple amplifiers and resonating in a TM 0,m,0 mode, where m is a positive integer; said coupling means being provided for electromagnetically coupling said second cavity resonator means with said first cavity resonator means. An embodiment of the present invention can provide a cavity resonator coupling type power distributor/power combiner which can distribute or combine microwave electric power in a wide bandwidth. An embodiment of the present invention can provide a cavity resonator coupling type power distributor/power combiner in which two cavity resonators are electromagnetically coupled by a coupling means, and whereby the coupling coefficient between the two cavity resonators and the resonant frequency of one of the two resonators can be easily adjusted. Reference is made, by way of example, to the accompanying drawings, wherein : Figure 1 is a schematic cross-sectional view of a conventional power distributor/power combiner employing a single cavity resonator; Fig. 2 is an equivalent circuit diagram of the power distributor/power combiner shown in Fig. 1; Fig. 3 is a schematic cross-sectional view of a cavity resonator coupling type power distributor/power combiner, according to an embodiment of the present invention; Fig. 4 is an equivalent circuit diagram of the cavity-resonator coupling type power distributor/power combiner; Fig. 5 is a graph showing frequency-voltage characteristics of the conventional power distributor/power combiner in Fig. 1 and of the cavity resonator coupling type power distributor/power combiner. Fig. 6 is a schematic cross-sectional view of the power distributor/power combiner shown in Fig. 3, showing an example of the configuration of the electric field therein; Fig. 7 is a cross-sectional view of a cavity-resonator coupling type power distributor/power combiner, according to another embodiment of the present invention; Fig. 8 is a cross-sectional view of a cavity resonator coupling type power distributor/power combiner, according to still another embodiment of the present invention; Fig. 9 is a part of the detailed cross-sectional view of Fig. 8; and Fig. 10 is a partial cross-sectional view of a cavity-resonator coupling type power distributor/power combiner, according to a still further embodiment of the present invention. Before describing the preferred embodiments of the present invention, a conventional cavity resonator will first be described with reference to Figs. 1 and 2. Figure 1 shows a schematic cross-sectional view of a conventional power distributor/power combiner. In Fig. 1, a cavity resonator 1, for example, a cylindrical type, has a single coupling terminal 2 and a plurality of coupling terminals 3a to 3n. The single coupling terminal 2 has a disk-type antenna 21 for establishing an electric field coupling between the coupling terminal 2 and the cavity resonator 1. The coupling terminals 3a to 3n respectively have magnetic field coupling loops 31a to 31n for establishing a magnetic field coupling between the cavity resonator 1 and the coupling terminals 3a to 3n. When microwave electric power is supplied to the coupling terminal 2, the microwave electric power is distributed and output from the coupling terminals 3a to 3n. In this case, the cavity resonator 1 functions as a power distributor. When microwave electric power is supplied to the coupling terminals 3a to 3n, the electric power is combined and output from the single coupling terminal 2. In this case, the cavity resonator 1 functions as a power combiner. Figure 2 is an equivalent circuit diagram of the power distributor/power combiner shown in Fig. 1. In Fig. 2, between the single coupling terminal 2 and the plurality of coupling terminals 3a to 3n, a resonance circuit 1a having a resonance frequency f₀ is connected. The frequency characteristic of the cavity resonator 1 is determined by the frequency characteristic of the resonance circuit 1a. The resonance circuit 1a has, by its character, a too narrow bandwidth, as illustrated in Fig. 5 by a broken curve C₀. Therefore, the single cavity resonator 1 shown in Fig. 1 can deal with only a very narrow bandwidth of microwave electric power. Such a narrow bandwidth is not practical for use in a power distributor or a power combiner. Embodiments of the present invention will now be described. Figure 3 shows a schematic cross-sectional view of a cavity resonator coupling type power distributor/power combiner according to a first embodiment of the present invention. In Fig. 3, two cavity resonators 5 and 6 are electromagnetically coupled through a coupling window 9. The first cavity resonator 5 has a single coupling terminal 7 at the upper side thereof. The single coupling terminal 7 has, at one end, an antenna 71 for establishing an electric field coupling between the single coupling terminal 7 and the first cavity resonator 5. The second cavity resonator 6 has a plurality of coupling terminals 8a to 8n at the bottom side thereof. The coupling terminals 8a to 8n respectively have magnetic field coupling loops 81a to 81n for establishing a magnetic field coupling between the second cavity resonator 6 and the coupling terminals 3a to 3n. The top plan view of the first cavity resonator 5 may have any desired shape, such as a rectangle, hexagon, or a circle. Preferably, the first cavity resonator 5 has a cylindrical shape, and the second cavity resonator 6 also has a cylindrical shape. Generally, the resonant mode in the first and second cavity resonators 5 and 6 when they are of a cylindrical type can be expressed as TE ϑ,r,z or TM ϑ,r,z , where ϑ, r, and z are components in the cylindrical polar coordinate system, and for which the transverse field pattern is similar to that of the TE ϑ,r mode or TM ϑ,r mode in a corresponding cylindrical waveguide, and for which z is the number of half-period field variations along the axis. The TM 0,m,0 mode, where m is a positive integer, is suitable for use in the cavity resonator coupling type power distributor/power combiner because it is easy to separate the associated mode from other undesired resonant modes. In a TM 0,m,0 mode, the magnetic field in the azimuthal direction and in the axis direction is constant. For example, the first cavity resonator 5 could be cylindrical and resonate with a TM 0,1,0 mode. Also, the cylindrical type second cavity resonator 6 could resonate with, for example, a TM 0,2,0 mode. Since the first cavity resonator 5 and the second cavity resonator 6 are electromagnetically coupled with each other through the coupling window 9, the device shown in Fig. 3 functions as a power distributor when microwave electric power is supplied to the single coupling terminal 7, so that distributed electric power is output from the coupling terminals 8a to 8n. Also, when microwave electric power is supplied to the coupling terminals 8a to 8n, the device in Fig. 3 functions as a power combiner, so that combined electric power is output from the single coupling terminal 7. Figure 4 is an equivalent circuit diagram of the device shown in Fig. 3. In Fig. 4, the first cavity resonator 5 has a resonance circuit 5a having a resonance frequency f₀₁. The second cavity resonator 6 has a resonance circuit 6a having a resonance frequency f₀₂. The difference between the resonance frequencies may be zero or may be a predetermined value, depending on the sizes of the cavity resonators 5 and 6. A coupling coefficient n₁ between the single coupling terminal 7 and the cavity resonator 5 is determined by the size and the position of the antenna 71. A coupling coefficient n₂ between the first cavity resonator 5 and the second cavity resonator 6 is determined by the size of the coupling window 9. A coupling coefficient n₃ between the second cavity resonator 6 and the coupling terminals 8a to 8n is determined depending on the size of magnetic field coupling loops 81a to 81n and the diameter of the conductors constituting the coupling terminals 8a and 8n. The size of each magnetic field coupling loop 81a, ..., or 81n corresponds to the hatched area surrounded by each conductor 8a, ..., or 8n and the side end of the second cavity resonator 6. Figure 5 shows the frequency-voltage characteristics of the conventional device shown in Fig. 1 and of the device shown in Fig. 3. In Fig. 5, the broken curve C₀ shows the conventional frequency-voltage characteristic realized by the single cavity resonator shown in Fig. 1; a solid curve C₁ shows a frequency-voltage characteristic realized by the device shown in Fig. 3 when the resonance frequency f₀₁ is equal to the resonance frequency f₀₂ under the condition that the coupling coefficient n₂ between the first and the second cavity resonators is made to be relatively small; and a dash-dot curve C₂ shows a frequency-voltage characteristic realized by the device shown in Fig. 3 when the resonance frequency f₀₁ is different from the resonance frequency f₀₂ or when the resonance frequencies f₀₁ and f₀₂ are equal under the condition that the coupling coefficient n₂ is made to be relatively great. As shown in Fig. 5, the solid curve C₁ has a wider flat bandwidth BW₁ than the bandwidth of the broken curve C₀ when the bandwidth within 0.2 dB of the uppermost output voltage of the curve C₁ is compared with that of the curve C₀. The flat bandwidth, i.e., 0.2 dB-bandwidth, for the cavity resonator coupling type power distributor/power combiner shown in Fig. 3 can be expected to be about twice as wide as that of the conventional single cavity resonator shown in Fig. 1, while the 3-dB bandwidth decreases by a factor 1/√2. When the resonance frequency f₀₁ is different from the resonance frequency f₀₂ , or when the resonance frequencies f₀₁ and f₀₂ are equal from each other but the coupling coefficient n₂ is made greater than that in the case of the curve C₁ , the dash-dot curve C₂ which is a double-humped resonance curve can be obtained, so that the bandwidth is expanded. As can be seen from the above, since the conventional curve C₀ is a single-humped resonance curve, its bandwidth cannot be made wider. Figure 6 shows an example of the configuration of the electric field in the device shown in Fig. 3. In Fig. 6, it is assumed that the first cavity resonator 5 is of a cylindrical type and resonates with a TM 0,2,0 mode so as to have an electric field E₁. The intensity of the electric field E₁ at the side wall of the resonator 5 is zero. At the center of the resonator 5, the intensity of the electric field E₁ is maximum. At a position distant from the center of the resonator 5 by 0.604r or 0.694r, where r is the radius of the first cavity resonator 5, the intensity of the electric field E₁ is local maximum. The coupling window 9 is so determined to have a radius equal to 0.694r or 0.604r. More generally, the diameter of the coupling window 9 is determined to be equal to the distance between two positions where the intensity of the electric field in the first cavity resonator has peak values, the two positions being symmetric with respect to the center of the first cavity resonator. By forming the coupling window 9 as mentioned above, the second cavity resonator 6 resonates with the same configuration of electric field E₂ as the electric field E₁. The size of the second cavity resonator 6 is so determined that the intensity of the electric field E₂ at the side wall of the second cavity resonator 6 is zero. Since the second cavity resonator 6 has the plurality of coupling terminals 8a to 8n, the radius of the second cavity resonator 6 is made larger than the radius of the first cavity resonator 5. By this construction, the coupling coefficient between the first cavity resonator 5 and the second cavity resonator 6 can be made large and without the generation of undesired modes in the first and the second cavity resonators 5 and 6. Therefore, in this coupling, disturbance of the electric field and the generation of higher order modes can be prevented, so that the distribution or combination of microwave electric power can be carried out stably. This type of coupling is referred to as mode coupling. The mode coupling can be realized not only with the above described TM 0,2,0 mode, but also by any mode type among the TM ϑ,r,z modes and the TE ϑ,r,z modes. Figure 7 shows a general cross-sectional view of a cavity-resonator coupling type power distributor/power combiner, according to a second embodiment of the present invention. In Fig. 7, a housing 10 made of metal houses a power distributor/power combiner. The power distributor/power combiner is constructed of a first cavity resonator 11 and a second cavity resonator 12. The first cavity resonator 11 has, at its top surface, a single coupling terminal 13. The single coupling terminal 13 is connected to a disk shaped antenna 14 for establishing an electric field coupling between the single coupling terminal 13 and the first cavity resonator 11. The second cavity resonator 12 has, at its bottom plate 10b, a plurality of coupling terminals 15a to 15n. In the second cavity resonator 12, a plurality of antennas 16a to 16n are respectively connected to the coupling terminals 15a to 15n. The antennas 16a to 16n function to establish a magnetic field coupling between the second cavity resonator 12 and the coupling terminals 15a to 15n. In this embodiment, the electromagnetic coupling between the first cavity resonator 11 and the second cavity resonator 12 is established by a coupling rod 17, instead of the coupling window 9 in the first embodiment. The second cavity resonator 12 also has, at the center of the bottom plate 10b, an adjusting screw 19 for controlling the resonance frequency of the second cavity resonator 12. The coupling rod 17 is fixed to the bottom metal plate 10a of the first cavity resonator 11 through a dielectric supporting member 18. The bottom metal plate 10a also functions as the top surface of the second cavity resonator 12. The bottom metal plate or the top surface 10a is part of the metal housing 10. The dielectric supporting member 18 has, at its center, a hole for the coupling rod 17. The coupling rod 17 has, at both ends, a disk type antenna 17a and a disk type antenna 17b, projecting into the first and the second cavity resonators 11 and 12, for establishing an electric field coupling between the first cavity resonator 11 and the coupling rod 17, and between the coupling rod 17 and the second cavity resonator 12, respectively. An adjusting screw 19 for adjusting the resonance frequency of the second cavity resonator 12 is provided at the center of the bottom surface 10b of the housing 10, i.e., at the center of the second cavity resonator 12. The height H₁ of the first cavity resonator 11 is 8 mm and the diameter D₁ is 36 mm. The first cavity resonator 11 operates in the TM 0,1,0 mode. The height H₂ and the diameter D₂ of the second cavity resonator 12 are 8 mm and 83 mm, respectively. The second cavity resonator 12 operates in the TM 0,2,0 mode. The power distributor/power combiner having a construction such as mentioned above can provide a 0.2 dB bandwidth of 600 MHz at 6 GHz, while the conventional single cavity resonator 1 shown in Fig. 1 can provide only a 0.2 dB bandwidth of 300 MHz. Thus, according to this embodiment, the 0.2 dB bandwidth is about twice that of the conventional device. In the second embodiment in Fig. 7, since the first cavity resonator 11 is coupled with the second cavity resonator 12 with respect to the electric field by means of the coupling rod 17 having the antennas 17a and 17b, the hole for penetrating the rod 17 can be made very small in comparison with the window 9 in the first embodiment in Fig. 3. Therefore, the electric field is not disturbed due to the window 9, and the coupling between the first and the second cavity resonators 11 and 12 can be made much stronger than in the first embodiment. The coupling coefficient between the first and the second cavity resonators 11 and 12 is determined by the size and the position of the antennas 17a and 17b of the coupling rod 17. Therefore, in order to change the coupling coefficient, it is necessary to replace the coupling rod 17 with another coupling rod. To do this, it is necessary to disassemble the first and the second cavity resonators 11 and 12. Accordingly, the adjustment of the coupling coefficient is not easy, while the adjustment of the resonance frequency can be performed easily by means of the adjusting screw 19. Instead of the disk type antennas 17a and 17b, rod antennas may also be possible. In the third embodiment shown in Fig. 8, the difficulty of adjusting the coupling coefficient is substantially removed. In Fig. 8, the same portions as those in Fig. 7 are designated by the same reference characters or numerals. Reference numeral 20 designates a coupling window, 21 an adjusting screw for adjusting the resonance frequency of the second cavity resonator 12, and 22 an adjusting antenna for adjusting the coupling coefficient between the first cavity resonator 11 and the second cavity resonator 12, respectively. The bottom plate 10b of the housing 10 has, at its center, a tapped hole 23. The adjusting screw 21 is screwed and fixed through the tapped hole 23 to the bottom plate 10b. The resonance frequency can be controlled by the height h of the adjusting screw 21 projecting inside the second cavity resonator 12. The adjusting screw 21 has, at its center, a tapped hole 24 through which the antenna 22 is screwed and fixed. The coupling coefficient of the first cavity resonator 11 with the second cavity resonator 12 is determined by adjusting the position of the antenna 22 with respect to the coupling window 20 by screwing the antenna 22 in the tapped hole 24. As a result, adjustments of the coupling coefficient and of the resonance frequency can be carried out easily without disassembling the cavity resonators of the microwave power distributor/power combiner of this third embodiment. A more detailed structure of the adjusting screw 21 and the adjusting antenna 22 is shown in Fig. 9. In Fig. 9, reference numerals 27 and 28 represent locking nuts for tightly fixing the adjusting screw 21 to the bottom plate 10b, and the antenna 22 to the adjusting screw 21, respectively. The adjusting mechanism of the adjusting screw 21 and the antenna 22 is not restricted to the third embodiment shown in Figs. 8 and 9. Various constructions may be employed according to the present invention. For example, instead of forming the tapped hole 24 in the center of the adjusting screw 21, a supporting member 25 may be fixed under the bottom plate 10b, as shown in Fig. 10. In Fig. 10, a partial cross-sectional view of a power distributor/power combiner according to the fourth embodiment of the present invention is illustrated. The bottom plate 10b of the housing 10 also has, at its center, the tapped hole 23. An adjusting screw 21a is screwed and held in the tapped hole 23 to the bottom plate 10b. The adjusting screw 21a, however, does not have a tapped hole as in the embodiment in Fig. 8. Instead, the supporting member 25 has, at its center, a tapped hole 24a. An antenna 22a passes through a hole in the center of the adjusting screw 21a and is screwed into and fixed by the tapped hole 24a in the supporting member 25. In this fourth embodiment, the height of the adjusting screw 21a and the position of the antenna 22a can be adjusted independently. Reference symbols 27a and 28a represent locking nuts for tightly fixing the adjusting screw 21a and the antenna 22a to the bottom plate 10b and the supporting member 25, respectively. In the foregoing embodiments, the coupling between the first cavity resonator and the single coupling terminal, and the coupling between the second cavity resonator and the plurality of coupling terminals, are described as electric field coupling and magnetic field coupling, respectively. The present invention, however, is not restricted to the above-mentioned coupling. Any type of electromagnetic coupling may be possible without disturbing the electromagnetic field in the cavity resonators. From the foregoing description, it will be apparent that, according to the present invention, since two cavity resonators are coupled to distribute or combine power, the bandwidth of the power distributer/power combiner can be made wide in comparison with the conventional type. Also, a number of coupling terminals can be easily provided in the second cavity resonator. Further, by making the size of the coupling window equal to the distance between the peak values of the electric field in the cavity resonators, mode coupling can be realised without generating undesired modes, and therefore, power distribution or power combination can be carried out stably. Still further, by providing an adjusting screw and an antenna having a screw, adjustment of the resonance frequency and the coupling coefficient can be easily carried out.

Claims: A cavity resonator apparatus, comprising: a first cavity resonator means (5,11) having a single coupling terminal (7,13) for coupling with an input/output signal; a plurality of coupling terminals (8,15); and coupling means (9,17,20) for electromagnetically coupling with said first cavity resonator means (5,11); characterised in that: said apparatus is a cavity resonator coupling type power distributor/power combiner selectable to function as one of a distributor and a combining unit in conjunction with multiple amplifiers, said power distributor/power combiner further comprising: a second cavity resonator means (6,12), having a cylindrical shape, having said plurality of coupling terminals (8,15) for coupling with a plurality of output/input signals and connected to said multiple amplifiers and resonating in a TM 0,m,0 mode, where m is a positive integer; said coupling means (9,17,20) being provided for electromagnetically coupling said second cavity resonator means (6,12) with said first cavity resonator means (5,11). A cavity resonator apparatus as set forth in claim 1 wherein said first cavity resonator means (5,11) has a cylindrical shape and resonates in a TM 0,n,0 mode, where n is a positive integer equal to or smaller than m. A cavity resonator apparatus as set forth in claim 1 or 2, wherein a metal housing (10) forms said first (11) and second (12) cavity resonator means; and wherein said coupling means comprises: a metal plate (10a) disposed between and separating said first cavity resonator means (11) and said second cavity resonator means (12), said metal plate being integral with said metal housing (10) of said cavity resonator coupling type power distributor/power combiner and having a centre; a dielectric support member (18) passing through the centre of said metal plate (10a) and having a centre; and a coupling rod (17) passing through the centre of said dielectric supporting member and having antennas (17a,17b) at each end of said coupling rod for establishing electric field coupling between said first cavity resonator means (11) and said coupling rod (17) and between said second cavity resonator means (12) and said coupling rod. A cavity resonator apparatus as set forth in claim 1 or 2, wherein said coupling means comprises a coupling window (9,20) coupling said first cavity resonator means (5,11) with said second cavity resonator means (6,12). A cavity resonator apparatus as set forth in any preceding claim, wherein the single coupling terminal (7,13) of said first cavity resonator means (5,11) includes an antenna (71,14) inside said first cavity resonator means for establishing electric field coupling. A cavity resonator coupling type power distributor/power combiner as set forth in any preceding claim, wherein each of the plurality of coupling terminals (8) of said second cavity resonator means includes a magnetic field coupling loop (81). A cavity resonator apparatus as set forth in claim 1 or 2, wherein said coupling means comprises a metal plate (10a) forming a bottom metal plate of said first cavity resonator means (11) and a top surface of said second cavity resonator means (12) and having a coupling window (20) coupling said first cavity resonator means with said second cavity resonator means. A cavity resonator apparatus as set forth in claim 4 or 7, wherein said positive integer n exceeds one and the diameter of said coupling window (9,20) is equal to the distance between two positions where the intensity of the electric field in the first cavity resonator means (5,11) has peak values, said two positions being symmetric with respect to the centre of said first cavity resonator, whereby, mode coupling without generation of undesired modes is established between said first cavity resonator means (5,11) and said second cavity resonator means (6,12). A cavity resonator apparatus as set forth in claim 4, 7 or 8, further comprising an adjusting screw (21,21a) for controlling the resonance frequency of said second cavity resonator means (12) and an adjusting antenna (22,22a) for controlling the coupling coefficient between said first cavity resonator means (11) and said second cavity resonator means (12) by controlling the position of said adjusting antenna with respect to the position of said coupling window (20), said second cavity resonator means (12) comprising a bottom plate (10b) opposite to said coupling window (20), said adjusting screw and said adjusting antenna being mounted on said bottom plate (10b). A cavity resonator apparatus as set forth in claim 9, wherein said bottom (10b) of said second cavity resonator means has a first tapped hole (23) for receiving said adjusting screw (21), and said adjusting screw has a second tapped hole (24) for receiving said adjusting antenna (22). A cavity resonator apparatus as set forth in claim 9, wherein said bottom plate (10b) of said second cavity resonator means has a first tapped hole for receiving and holding said adjusting screw (21a), said adjusting screw has a hole (23) for receiving said adjusting antenna, and a supporting member (25) being fixed to said bottom plate (10b), said supporting member (25) having a second tapped hole (24a) for receiving and holding said adjusting antenna.

Inventors: KANEKO, YOSHIAKI, OKUBO, NAOFUMI, SAITO, TOSHIYUKI
Applicants: FUJITSU LIMITED
Application year: 1984
Main classification: H01P5
IPC codes: H01P5