FI110556B - Combined duplex filter and antenna solution - Google Patents

Description

110556

The invention relates generally to filter and antenna structures for radio equipment and in particular to the connection of a duplex filter to the antenna of a radio equipment.

Duplex filters are commonly used to separate the transmit and receive signal in radio equipment that transmit and receive via 10 same antennas at different frequencies. A duplex filter is a three-port circuit member comprising a transmitter, receiver, and antenna port. The radio signal introduced to the transmitter port at the transmission frequency sees the signal path leading to the receiver port as high impedance, whereby the transmit radio frequency power is not significantly directed to the receiver port but is directed through the antenna port to the antenna from radiated radio signal. Similarly, the receiving frequency radio signal received through the antenna and antenna port sees the direction of the transmitter port as high impedance, whereby it is directed to the receiver port and thereby to the receiver parts of the radio device. The difference between the transmit and receive frequencies is called the duplex interval. In contrast to the antenna switch, the operation of the duplex filter is generally not based on a switch function where the signal flow of the sig-20 signal is controlled, for example, by semiconductor switches, but by the different frequency response characteristics of the filter components.

* *!. In the following description, mobile radio is exemplified as a radio device. A duplex filter is generally implemented on a modern mobile phone transmission; '25 conductor resonators, which may be for example helix, coaxial, microstrip: or ceramic resonators. By combining those built for different resonant frequencies. i: resonators and by arranging the connections between them appropriately provide the desired function. When the antenna is connected to the antenna port, it is followed by an impedance matching which adapts the impedance of the antenna port to the impedance of the antenna itself.

: 30. ·: ·. The duplex filter's transmission branch, i.e. the signal path from the transmitter port to the antenna port, must • be constructed to withstand the transmitting power of a radio device, typically 0.6 to 1.2 W (DAMPS, Digital: · Advanced Mobile Phone System) or 0.8 - 2 W (GSM system, Groupe Speciale; 35 Mobile). In the receiving branch, i.e. the signal path from the antenna port to the receiver port, no. · · \ Would require almost the same power duration for the received radio power, but for some exceptional situations, the conventional branch has had to be dimensioned for nearly the same power transmission power as the transmission branch.

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In particular, exceptional situations are those in which, for one reason or another, there is no antenna or similar radiating element connected to the antenna port, which means that the transmitted radio signal sees the antenna port as an open terminal, reflecting back to the receiving end. If, on the receiving side, the reflected signal reaches parts that are proportional to the normal milliwatts of radio power normally received, it can destroy these parts.

An exceptional situation may arise, for example, in a mobile phone having a retractable an-10 transducer comprising a separate helix portion and a whip portion, one connected to the antenna port when the antenna is inserted into the phone casing and the other connected to the antenna port when the antenna is withdrawn. In an intermediate situation, it may be that neither is connected to the antenna port. In a mobile phone with a detachable antenna, it may also occur that the phone transmits even if the 15 antennas are disconnected. The abnormal situation may also be caused by an antenna breakage or damage to the antenna connector as a result of phone drop or improper use. The impedance that the signal to be transmitted will exceptionally see depends on the length of the transmission line between the filter and the antenna, the location and connection of any impedance matching members, and in the event of damage the nature and location of the damage.

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For filter technology, it would be advantageous for a duplex filter receiving wand. : No need to scale for high power. For example, small surface! 'The use of SAW filters (Surface Acoustic Wave) in mobile telephones;'; lime would be an advantage, but these filters are currently only durable. Y 25 0.04-0.1 W power.

:.:: Solutions are known in the art in which a duplex filter comprises an antenna port between a antenna port and a low power reception filter designed to attenuate a radio power reflecting so high in the receiving branch that: that it does not damage the receive filter 'f': 'SAW filter used as the input filter. However, these solutions have it. the disadvantage is that the power suppression or attenuation circuit always attenuates the received signal to some extent, thereby reducing the reception signal / noise ratio.

:: ': 35 It is an object of the present invention to provide an antenna and a duplex filter structure in which: ·'; the components of the receiving branch may be dimensioned for substantially lower power transmission power without risking damage in exceptional circumstances such as those described above. It is also an object of the invention to provide an antenna and a 3 110556 duplex filter structure, the receiving branch of which may employ surface acoustic filters without a separate power suppression or attenuator circuit. It is a further object of the invention to provide an antenna and a duplex filter structure suitable for serial production of modern cellular phones 5 in terms of size, characteristics and manufacturing costs. It is a further object of the invention to provide an antenna and duplex filter structure in which transmission line losses and space requirements are minimized.

The objects of the invention are achieved by an integrated solution in which the antenna is connected directly to the antenna port of the duplex filter structure.

10

The antenna and duplex filter construction according to the invention is characterized in that said antenna is connected directly from its feed point to the antenna port of said duplex filter.

15 In order to avoid a situation where the transmission power is reflected from the open antenna port back to the duplex filter, one has to make sure that the antenna port is never open. In the arrangement according to the invention, this is done so that the radiating antenna element is connected directly from its feed point directly to the antenna port of the duplex filter without transmission lines or coaxial conductors.

Further, the structure of the invention includes tracking the impedance matching of the antenna in the duplex filter itself.

The combined antenna and duplex filter structure of the invention comprises a duplex; ', An internal filter having a transceiver and antenna port, and an antenna; 25 antenna directly connected to its nip port. It is not the case with the invention; it is essentially the technique by which the filter is implemented or the antenna structure used. In a preferred embodiment, the filter may comprise helix or ceramic resonators. Since the receiving branch does not have to be dimensioned for high power resistance, it can advantageously comprise a surface acoustic filter. Antenna • 30 Voltage-Helicopter-Antennae composite structure and can be pulled out. The antenna may also be a planar antenna (PIFA, Planar Inverted F-Antenna), *. RCDLA (Radiation Coupled Double L-Antenna) or Micro Strip (Micro Strip / Patch Antenna). The structure of the invention is disposed in a cellular telephone or '' corresponding radio device according to a preferred embodiment such that the outer shell of the device:: *: 35 protects the antenna or at least the antenna feed point and the duplex filter. · · '. mechanical connection between the antenna port.

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Since the transmission power is never reflected in the direction of the receiver port, the receiving filter can be dimensioned for significantly lower power than hitherto, thus utilizing, for example, the properties of SAW filters. The invention also provides the advantage, compared to the prior art, that the impedance matching required by the antenna can be made directly in the duplex filter, utilizing in part its pre-formed parts. The duplex filter components can also be designed such that its antenna port impedance directly matches the antenna feed impedance, whereby no separate impedance matching is required. The structure of the invention also minimizes transmission line losses that are typical of a prior art cellular phone in which the antenna is connected to a duplex filter by a coaxial cable or transmission line.

The invention will now be described in more detail with reference to exemplary preferred embodiments and the accompanying drawings, in which Fig. 1a schematically shows a prior art antenna and duplex filter structure, Fig. Ib schematically illustrates an antenna and duplex filter structure according to the invention; Figure 2a illustrates a preferred embodiment of the structure according to the invention; Figure 2b shows another preferred embodiment of the structure according to the invention, Figure 3a shows a third preferred embodiment of the structure according to the invention, Figure 3b shows a fourth preferred embodiment of the structure according to the invention; ·. Figure 4 illustrates a fifth preferred embodiment of the structure according to the invention: 35. Fig. 5 illustrates in more detail another mechanical connection method which can be used to carry out the structure according to the invention, Figs. 6a-6c show schematically preferred embodiments of the structure according to the invention in a mobile phone, Fig. 7a further illustrates another mechanical connection method Fig. 7b shows the structure of Fig. 7a with the movable part of the antenna inserted, Figs. 8a and 8b schematically show a preferred positioning of the structure shown in Figs. 7a and 7b in a mobile phone, Fig. 9 shows a sixth preferred embodiment of the structure 9 in a mobile phone.

In the pictures, the same reference numerals are used for like parts.

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Fig. 1a schematically shows a prior art antenna and duplex filter structure in which the antenna 1 is connected to the antenna port 3 of the duplex filter 2a. via coaxial conductor 4. The structure further comprises an impedance matching circuit 5 near the junction of the coaxial conductor 4 and the antenna 1. Figure Ib is a schematic diagram of a structure according to the invention in which the antenna 1 is directly connected from its feed point to the antenna port 3 of the duplex filter 2b. The structure according to the invention does not require a wire between the filter and the antenna.

: ': 30 Figure 2a shows a structure according to the invention in which a duplex filter is: ·. the TX branch filter comprises helix resonators 6 and the receiving branch filter - the data RX is a surface acoustic filter 7. The filter support structure is a circuit board 8 made of low-loss material with comb-like branches supporting 1 '*: supports helix; : 35 resonators, called a combed helix filter, and it is in itself •. the type of filter known to a person skilled in the art. Strip conductors are provided on the surface of the circuit board 8 in a manner known per se, for conductor connections and a wiring harness for attaching the required separate components, such as switching diodes.

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For the sake of clarity, the strip conductors, coupling patches, and discrete components that are not essential to the invention are not shown in the figures. The pin-acoustic filter 7 of the receiving branch RX is fixed to the surface of the circuit board 8 and is provided with the necessary wiring connections by strip conductors. In order to achieve proper operation of the resonators and to prevent electromagnetic interference, the filter is protected by a cover made of electrically conductive material which is not shown in Fig. 2a for clarity.

2a, the antenna port 3, transmitter port 9 and receiving port 10 of the duplex filter are the connection points formed on the circuit board 8. According to the invention, the antenna 1 is directly connected to the antenna port 3. The impedance of the duplex filter antenna port 3, which is fitted directly to the antenna input impedance in the preferred embodiment of the invention, is determined by the

The antenna and duplex filter structure shown in Fig. 2b corresponds to the structure of Fig. 2a, but the TX filter portion of the transmission branch is implemented by ceramic resonators. The body of the resonators is a block 11 made of dielectric ceramic material and the resonators 12 are holes formed thereon and coated with electrically conductive material. The ceramic body block 11 is attached with a low loss. a substrate made of a material, i.e. a circuit board 8, the surface of which is used in the same way to form strip conductors and switching pads (not shown) as described in connection with Figure 2a. The antenna port 3, the transmitter port 9 and the receiver * 25 receiver port 10 are also the connection points formed on the circuit board 8. Antenna 1: according to the invention is directly connected to antenna port 3. Also such structure ί is generally protected by a cover made of electrically conductive material.

t · a

In the embodiments of Figures 2a and 2b, some of the helical or ceramic resonators; ': 30 may be used in the receiving branch, whereby the transmission branch filter is composed of co-: resonators and the receiving branch filter comprises both resonators. that the surface acoustic filter 7.

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Fig. 3a shows a filter structure in which both the TX TX and the receiving hook::: The 35 RX filter portion only comprises helix resonators 6. This type of * '' filters do not have the same power duration problem as the surface. acoustic filters, but connecting the antenna 1 directly to the filter antenna port 3 achieves other advantages of the invention, i.e. the transmission line losses and space requirements are small and the impedance of the filter 110 1106 datt antenna port can be designed directly to correspond to the antenna input impedance. The structure of Fig. 3b corresponds to Fig. 3a, but with ceramic resonators 12 as filter resonators.

5 As technology advances, it is likely that in the future it will be possible to produce surface acoustic filters with a high power rating that can also be used in the transmission branch of a duplex filter. Fig. 4 shows a combined antenna and duplex filter structure according to the invention, in which a surface acoustic filter 7, 13 is used as a filter for both the TX and the receiving branch RX. In this case, the structure size is likely to be significantly smaller than with current filter technology. Although the power resistance requirement does not limit the construction of the structure, it is advisable to connect the antenna 1 directly to the antenna port 3 of the filter according to the invention in order to minimize transmission line losses and provide impedance matching in the most advantageous manner.

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Figure 5 shows one arrangement for attaching an antenna to a filtered one. Figure 5 corresponds to the structure of Figure 2b, in that the TX branch filter of the transmission branch is implemented by ceramic resonators 12 and the R branch filter RX filter is a surface acoustic filter 7. The antenna connector 15 is fixedly connected to the filter structure, in this case to the circuit board 8. In the vicinity of the connector, the circuit board may have matching elements (not shown in the figure) to match the impedance of the filter antenna port to the antenna 1 '. 'Input impedance. Figure 5 is a dashed line showing the outline of the electrically conductive protective casing 16 on the filter.

The structure according to the invention is preferably located in a mobile phone or other radio device so that the outer casing of the device protects both the filter and at least in part the antenna, and in particular the antenna port of the antenna and the duplex filter, from bending and shock. Figures 6a-6c show different investment alternatives. Reference numeral 17 denotes a cellular telephone circuit; and the number 18 denotes the outer casing of the phone, which can be shaped in four different ways. In Fig. 6a, the helix antenna 1a is used as an antenna, whereby the assembly according to the invention formed by it and the duplex filter 2b is quite small and compact. It can be located on the top of the mobile phone so that the duplex filter 2b 35 is attached to the circuit board 17 of the phone and the helix antenna 1a is pointed. in this embodiment, the outer casing 18 of the mobile phone is shaped such that it encloses all the parts, thereby providing a very sturdy construction and a simple exterior styling.

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In the embodiment of Fig. 6b, a whip antenna Ib is used which is substantially longer in the longitudinal axis than the helix antenna of its electrical length. In this case, it is generally not advisable to enclose the entire antenna Ib within the outer casing 18 of the telephone, but part of the antenna remains visible. The exterior 18 of the telephone serves to provide a barrier to the base of the antenna Ib and the junction of the Senja duplex filter 2b. The visible part of the antenna is made flexible so that it can withstand bending and other mechanical stress. A variation of the same structure is shown in Fig. 6c, in which, due to the structure of the duplex filter 2b, its antenna port is located at one end relative to its elongated appearance. Hereby, the filter 2b can be mounted on the circuit board 17 10 vertically relative to the directions of the picture. Other installation directions are also possible.

The structure according to the invention can also be used when the antenna of the radio device has to be pulled out or otherwise moved. This is often the case with mobile phones, which need to be transported to the lowest possible position in the transport position, but require a longer antenna for the best connection quality. Many retractable antennas having both helix and whip sections are known in the art. Reference is made in particular to the antenna structure disclosed in Finnish Patent Application FI-952742 (LK-Products Oy: Dual acting antenna), comprising a fixed helix portion and a movable whip portion which, when retracted, forms a serial connection with said helix portion. Fig. 7a shows an exemplary way of connecting such an antenna according to the invention as part of a combined antenna and duplex filter structure. The filter uses a ceramic filter 12 on the transmission branch and a surface acoustic filter 7 on the receiving branch.

; Antenna connector 15 is fixedly connected to a low loss filter circuit board 8 and; The necessary wiring connections between it and the other parts of the filter are made by strip conductors 14. An antenna coupler 15 is fixedly connected to the antenna helix portion 19 and: has a hole in the middle of the connector where the whip portion 20 can be reciprocated.

In the embodiment of Fig. 7a, the conductive cover 16 of the duplex filter covers only the filters 12 and 7, but it can also be shaped such that the antenna connector ': 30 15 is inside it. In the situation of Figure 7a, the whip portion 20 is withdrawn, whereby .1. it forms a serial connection with the helix portion 19. In Fig. 7b, the whip portion 20 is inserted with the helix portion 19 acting as the radiating antenna of the telephone. The illustrated structure, in which the helix portion 19 is fixedly connected to the antenna connector: 15, has the advantage that no radiating: would be connected to the filter antenna port.

Figures 8a and 8b correspond to Figures 7a and 7b illustrating an exemplary positioning of the structure shown therein in a cellular phone when the antenna whip portion 20 is retracted 9 110556 (Fig. 8a) and retracted (Fig. 8b). The outer casing 18 of the telephone is preferably shaped to cover the helix portion 19. The casing has a hole in which the whip portion 20 can be reciprocated. Other types of placement and formatting options are also possible.

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Figure 9 schematically shows an alternative for using a planar antenna as part of the combined antenna and duplex filter structure of the invention. The figure shows a duplex filter 2b enclosed in an electrically conductive envelope with a PIFA antenna 2110 (Planar Inverted F-Antenna) known per se to a person skilled in the art connected to one end of the envelope. The filter housing acts as a short-circuiting element essential for antenna operation and is supplied from the antenna port 3 in the center of the filter. Instead of the PIFA structure shown in the figure, other antennae known per se, such as microstrip and RCDLA (Radiation Coupled Double L-Antenna) antennas, can be used.

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Fig. 10 shows an exemplary way of positioning the structure of Fig. 9 in a mobile phone. Because the planar antenna is preferably located entirely within the housing of the cellular telephone, its placement must take into account the probable operating position of the cellular telephone in order to optimize the antenna and minimize radiation to the user.

The preferred location is at the top and back of the mobile phone, whereby:: the antenna is positioned as far away from the user's body as possible in normal operating position and the radiator characteristics of the antenna are minimized by the release hand. The radiation pattern of the planar antenna is directional and its maximum gain direction should point away from the user's body.

: The application of the structure according to the invention to mobile phones has been discussed above. However, the examples provided are not intended to be limiting, but it will be apparent to one skilled in the art that the invention may be applied to a wide variety of filter and antenna structures in all types of radio equipment, preferably UHF and, '. VHF frequencies but also in other frequency bands.

The invention solves the power endurance problem of the receiving branch of a duplex filter, whereby very small filters, for example surface acoustics, can be used; 35 filters. The invention does not require any special specialized work steps and is not particularly expensive. components or materials, making it well suited for serial production of cellular radio equipment.

Claims (12)

An antenna and duplex filter structure for a radio apparatus comprising an antenna (1; 1a; 1b; 19, 20) and a duplex filter (2b), the antenna comprising a feed point and the duplex filter comprising - a transmitter port (9) for feeding a signal to be transmitted and a receiver port (10) for output of a received signal, characterized in that the duplex filter further comprises an antenna supply point (3) for conducting a signal to be transmitted to the antenna and for transmitting a signal. signal to be received from the antenna, and said antenna (1; 1a; 1b; 19, 20) is connected from its supply point directly to the duplex filter to provide a combined antenna and duplex filter construction at said antenna supply point (3). Construction according to claim 1, characterized in that said duplex filter (2b) comprises a transmission branch (TX) between said transmission port (9) and said antenna supply point (3) and a reception branch (RX) between said antenna supply point (3) and said reception port (10). ), and said receiving branch (RX) comprises a surface acoustic filter (7) (SAW, Surface Acoustic Wave). Combined construction according to claim 2, characterized in that said transmission branch (TX) comprises ceramic resonators (12). : 25 Combined construction according to claim 2, characterized in that said: transmit branch (TX) comprises helix resonators (6). Combined construction according to claim 2 or 3, characterized in that said receiving branch (RX) further comprises ceramic resonators. . : 30; .. Combined construction according to claim 2 or 4, characterized in that said receiving branch (RX) further comprises helix resonators. Combined construction according to claim 1, characterized in that:. 35 duplex filter (2b) is fully constructed with ceramic resonator technology (12). 8. Combined construction according to claim 1, characterized in that said duplex filter (2b) is fully constructed with helix resonator technology (6). 13 110556 Combined construction according to claim 1 or 2, characterized in that said duplex filter (2b) is fully constructed with surface acoustic filter technique (7, 13). Combined construction according to any preceding claim, characterized in that said antenna (1) is one of the following: a helix antenna (1a), a rod antenna (1b), a combined helix and rod antenna (19, 20), an extendable antenna (20), microstrip antenna, a reverse planar F antenna (21) (PIFA, Planar Inverted F antenna), a radiation coupled dual L antenna (RCDLA, Radiation Coupled Double L antenna). 10 A radio mobile apparatus comprising a housing (18), an antenna (1) and a duplex filter (2b), said antenna comprising a supply point and said duplex filter comprising - a transmitter port (9) for feeding a signal to be transmitted and a receiver port (10) for output of received signal, characterized in that the duplex filter further comprises an antenna supply point (3) for conducting a signal to be transmitted to the antenna and for conducting a signal to be received from the antenna, and said antenna (1; 1a; 1b; 19, 20) is connected from its feed point directly to the duplex filter for. Providing a combined antenna and duplex filter construction at said antenna feed point (3), wherein the combined structure is substantially located within said housing (18), said housing. * is designed to protect at least said location to which the antenna is connected in the · duplex filter. 25 :; 12. A radio mobile device according to claim 11, characterized in that it is a mobile phone in a cellular measurement.