CN212517462U

CN212517462U - Tuning duplexer, radio frequency circuit and communication equipment

Info

Publication number: CN212517462U
Application number: CN202022190598.9U
Authority: CN
Inventors: 陈志军; 杜雅
Original assignee: Shenzhen Gongjin Electronics Co Ltd
Current assignee: Shenzhen Gongjin Electronics Co Ltd
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2021-02-09
Anticipated expiration: 2030-09-29

Abstract

The embodiment of the application provides a tuning duplexer, a radio frequency circuit and a communication device, wherein the tuning duplexer comprises: the first input port and the second input port are used for feeding in signals of different frequency bands, the public output port is used for feeding out signals, and the low-pass filter, the high-pass filter, the first resonance unit, the second resonance unit and the combining unit are arranged on the same side of the input port; the first input port, the low-pass filter and the first resonance unit are sequentially connected, the second input port, the high-pass filter and the second resonance unit are sequentially connected, and the first resonance unit and the second resonance unit are combined by adopting a T-shaped structure and then are connected to the common output port. The tuning duplexer can restrain a parasitic passband on a low-pass filter, and has the characteristics of low insertion loss in the passband, high isolation, good out-of-band pole selectivity, wide stopband, low cost and the like.

Description

Tuning duplexer, radio frequency circuit and communication equipment

Technical Field

The application relates to the technical field of duplexers, in particular to a tuning duplexer, a radio frequency circuit and communication equipment.

Background

With the development of the WIFI technology and the wireless communication technology, the frequency spectrum is less and less, the frequency resource division is more and more fine, and the interference phenomenon between the frequency bands is more and more serious, so the performance of the radio frequency transceiving front-end filter often determines the quality of a communication system, especially a communication system working in multi-mode and frequency division. Therefore, in a communication system operating in multiple modes or frequency division, in order to solve the mutual interference between the frequencies, a high performance duplexer needs to be provided.

SUMMERY OF THE UTILITY MODEL

In view of the above, the present application is directed to overcoming the deficiencies in the prior art and providing a tuned duplexer, a radio frequency circuit and a communication device.

An embodiment of the present application provides a tuned duplexer, including: the device comprises a first input port and a second input port for feeding signals of different frequency bands, a common output port for feeding out signals, a low-pass filter, a high-pass filter, a first resonance unit and a second resonance unit;

the first input port, the low-pass filter and the first resonance unit are sequentially connected, the second input port, the high-pass filter and the second resonance unit are sequentially connected, and the first resonance unit and the second resonance unit are combined by adopting a T-shaped structure and then are connected to the common output port.

In one embodiment, the length of the microstrip line corresponding to the first resonance unit is a quarter wavelength length of the center frequency of the high-pass filter; the length of the microstrip line corresponding to the second resonance unit is a quarter wavelength of the center frequency of the low-pass filter.

In the above embodiment, the characteristic impedance of each microstrip line is 50 ohms.

In one embodiment, each of the ports is a port having a characteristic impedance of 50 ohms.

In one embodiment, the microstrip line in the first resonance unit and/or the second resonance unit is a bent structure.

In one embodiment, the low pass filter is an elliptical low pass filter.

In one embodiment, the elliptical low pass filter is a 3 rd order elliptical low pass filter; the 3 rd order elliptic low-pass filter comprises a first capacitor, a second capacitor and an LC resonance unit, wherein one end of the first capacitor is connected with the first input port and one end of the LC resonance unit respectively, the other end of the LC resonance unit is connected with one end of the second capacitor and the first resonance unit respectively, and the other ends of the first capacitor and the second capacitor are grounded respectively.

In one embodiment, the high pass filter is a butterworth high pass filter.

In one embodiment, the butterworth high pass filter is a butterworth high pass filter of order 5; the 5-order Butterworth high-pass filter comprises a third capacitor, a fourth capacitor, a first microstrip line subunit, a second microstrip line subunit and a third microstrip line subunit, wherein the second input port, the third capacitor, the fourth capacitor and the second resonance unit are sequentially connected, one end of the first microstrip line subunit is connected with a node between the second input port and the third capacitor, one end of the second microstrip line subunit is connected with a node between the third capacitor and the fourth capacitor, one end of the third microstrip line subunit is connected with a node between the fourth capacitor and the second resonance unit, and the other ends of the first microstrip line subunit, the second microstrip line subunit and the third microstrip line subunit are grounded.

In the above embodiment, one or more of the first microstrip line sub-unit, the second microstrip line sub-unit and the third microstrip line sub-unit adopt a bent structure.

In one embodiment, the impedance of each microstrip line subunit is taken as an equivalent inductance impedance.

Another embodiment of the present application provides a radio frequency circuit including the tuned duplexer described above.

Yet another embodiment of the present application provides a communication device including the radio frequency circuit described above.

The embodiment of the application has the following advantages:

the tuning duplexer of this application connects low pass filter and high pass filter respectively through adopting first resonance unit and second resonance unit to first resonance unit and second resonance unit adopt and are connected to public output port after the T type structure combines, and the tuning duplexer through above-mentioned structural design not only can restrain the parasitic passband on the low pass filter, and it is low still to have the insertion loss in the passband, and the isolation is high, and the outband pole selectivity is good, wide stop band, characteristics such as with low costs.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.

Fig. 1 shows an overall architecture schematic diagram of a tuned duplexer of an embodiment of the present application;

fig. 2 is a schematic structural diagram illustrating each resonance unit and a T-shaped branch combiner of the tuning duplexer according to the embodiment of the present application;

fig. 3 shows a schematic diagram of an architecture of a 3 rd order elliptic low pass filter and a 5 th order butterworth high pass filter of a tuned duplexer in an embodiment of the present application;

figure 4 shows an application diagram of the tuned duplexer of an embodiment of the present application;

figure 5 shows a test schematic of a tuned duplexer of an embodiment of the present application;

fig. 6 shows a simulation diagram of S-parameter test of the tuned duplexer in the embodiment of the present application.

Description of the main element symbols:

1-tuning a duplexer; 10-a low-pass filter; 20-a high-pass filter; 30-a first resonance unit; 40-a second resonant cell; p1 — first input port; p2 — second input port; p3-common output port; 201-a first microstrip line subunit; 202-a second microstrip line subunit; 203-third microstrip line subunit.

Detailed Description

Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary only for the purpose of explaining the present application and are not to be construed as limiting the present application.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.

In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can include, for example, fixed connections, removable connections, or integral parts; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the templates is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Example 1

Referring to fig. 1, the present embodiment provides a tuning duplexer 1, which can be applied to various radio frequency communication devices or communication systems. The tuned duplexer 1 will be described in detail below.

Exemplarily, the tuned duplexer 1 has a three-port structure, and respectively includes a first input port P1, a second input port P2, and a common output port P3, where the two input ports are respectively used for feeding electromagnetic wave signals in different frequency bands, and the common output port P3 is used for feeding out the electromagnetic wave signals. The tuned duplexer 1 further comprises a low-pass filter 10, a high-pass filter 20, a first resonance unit 30 and a second resonance unit 40, which are located between the three ports, wherein the first input port P1, the low-pass filter 10 and the first resonance unit 30 are connected in sequence; the second input port P2, the high-pass filter 20 and the second resonance unit 40 are connected in sequence; the first resonance unit 30 and the second resonance unit 40 are combined in a T-shaped configuration and then connected to the common output port P3.

Exemplarily, the first resonance unit 30 and the second resonance unit 40 are each configured by using a microstrip line having a preset characteristic impedance, for example, a 50-ohm microstrip line or the like. As shown in fig. 2, the two microstrip lines are branched and connected in parallel at their ends to form a T-shaped structure, and the parallel combined output is connected to a common output port P3. Alternatively, when the T-shaped structure is formed, the lengths of the end sections of the two microstrip lines may be equal or nearly equal to form a T-shaped section close to symmetry, so that the isolation of the tuned duplexer 1 and the matching performance of each input port can be further improved.

In this embodiment, the lengths of the microstrip lines of the first resonant unit 30 and the second resonant unit 40 are respectively a quarter wavelength of the center frequency of the filter connected to each other. In order to better describe the microstrip lines of the respective first and

second resonance units

30 and 40, the microstrip line constituting the first resonance unit 30 is referred to as a first microstrip line, and the microstrip line constituting the second resonance unit 40 is referred to as a second microstrip line.

Exemplarily, the first resonance unit 30 is connected to the low pass filter 10, and the length of the first microstrip line is a quarter wavelength length of the center frequency of the high pass filter 20. The second resonant unit 40 is connected to the high pass filter 20, and the length of the second microstrip line is a quarter wavelength of the center frequency of the low pass filter 10. For example, if the design frequency of the tuned duplexer 1 is 2412 to 2482MHz and 5180 to 5850MHz, the length of the first microstrip line is a quarter wavelength of the center frequency of the high frequency band 5180 to 5850 MHz; and the length of the second microstrip line is a quarter wavelength of the center frequency of the low-frequency band 2412-2482 MHz. It is understood that the operating frequency of the tuned duplexer can be set according to actual requirements, and the two operating frequency bands are only one example.

In this embodiment, it is preferable that the first resonance unit 30 and the second resonance unit 40 each employ a microstrip line having a characteristic impedance of 50 ohms. Of course, the value of the characteristic impedance may be within an acceptable error range, such as 46-52 ohms, considering that some errors may exist in the actual design. Further, for three ports, each port is a 50 ohm impedance matched port.

It can be understood that the first resonant unit 30 and the second resonant unit 40 both use quarter-wavelength 50 ohm microstrip lines, and the two microstrip lines are connected in parallel at the end part to form a T-shaped node, that is, after two branches are combined, the two microstrip lines are connected to the common output port P3, so that the signal of the transmission frequency of the filter of the other side is short-circuited when the working filter passes through, and then becomes an open circuit after passing through the impedance of the quarter-wavelength transmission line, and thus the two filters will not affect each other, the isolation between the ports can be improved, and the mutual influence of the two input ports can be reduced.

In order to reduce the occupied area of each microstrip line, in the present embodiment, the microstrip lines in the first resonant unit 30 and the second resonant unit 40 may both adopt an S-shaped (also called snake-shaped) bent structure, as shown in fig. 2. It can be understood that when the lengths of the first microstrip line and the second microstrip line are longer, if the linear structure design is adopted, the size of the whole resonator is increased, and the S-shaped structure design can well reduce the size of the resonator, so that the tuning duplexer 1 can obtain a smaller size on the premise of optimizing the performance, thereby reducing the occupied area of the tuning duplexer in an actual product, greatly reducing the cost and the like.

In this embodiment, the low-pass filter 10 can let the low-band frequency in the pass band pass through without attenuation, and plays roles of attenuation and suppression on the signal higher than the low-band frequency; the high-pass filter 20 can be used to pass high-band frequencies within the passband, suppress spurious passbands occurring in the low-pass filter 10, and expand stopband width. For example, if the design frequency of the duplexer is 2412-2482 MHz and 5180-5850 MHz, the low pass filter 10 can let 2412-2482 MHz pass through without attenuation, and effectively suppress other signals higher than the frequency; the high-pass filter 20 can let 5180-5850 MHz pass through without attenuation, and plays roles of attenuation and inhibition for signals with frequency higher than the frequency.

Illustratively, the low-pass filter 10 may be a low-pass filter with better flatness in-band and narrower transition band and better out-of-band selectivity. For example, in one embodiment, an elliptical low pass filter will be employed. The filter with the elliptic structure has the characteristics of ripples in a pass band, a stop band and the like, can obtain narrower transition bandwidth and smaller stop band fluctuation, and has higher pole suppression and selectivity in the stop band, so that the filter has better suppression effect on high-band frequency and the like. Generally, the higher the order, the narrower the transition bandwidth of the elliptic low-pass filter will be, and the more significant the suppression effect on the high frequency band will be. The selection of the order can be selected according to actual requirements, so as to achieve the balance between performance and cost.

Illustratively, the high-pass filter 20 may be a high-pass filter with better flatness in-band and flatter stop-band. For example, in one embodiment, a butterworth high pass filter will be employed. Similarly, the order may be selected according to actual requirements, and is not limited herein.

The tuning duplexer provided by the embodiment adopts a microstrip stop band tuning technology, and the low-pass filter and the high-pass filter are respectively connected with a quarter-wavelength microstrip line in series, combined by adopting a T-shaped structure at the tail section and then connected to a common output port, so that the parasitic passband on the low-pass filter can be inhibited, the problem of periodicity of the microstrip line is solved, and the isolation degree of two input ports is improved through impedance transformation of a quarter-wavelength transmission line; the band stop is adjustable by adjusting the parameters of each filter, the size of the resonance unit can be greatly reduced by bending the microstrip line, and the size of the whole tuned duplexer is reduced on the premise of ensuring the performance optimization.

Example 2

Referring to fig. 3, based on the foregoing embodiment 1, for the tuned duplexer of this embodiment, on the basis of using the elliptic low-pass filter and the butterworth high-pass filter, the elliptic low-pass filter further uses an elliptic low-pass filter of 3 th order or more than 3 rd order; the butterworth high pass filter will employ a butterworth high pass filter of order 5 or higher. In practical applications, the order can be selected according to practical requirements to balance the cost and performance.

The following description will be given of the structure of each filter and a simulation test of the performance of the duplexer, taking a tuned duplexer including a 3 rd order elliptic low-pass filter and a 5 th order butterworth high-pass filter as an example.

Exemplarily, as shown in fig. 3, the 3 rd order elliptic low pass filter mainly includes a first capacitor C1, a second capacitor C2, and an LC resonance unit. Specifically, one end of the first capacitor C1 is connected to the first input port P1 and one end of the LC resonant unit, the other end of the LC resonant unit is connected to one end of the second capacitor C2 and the first resonant unit 30, and the other ends of the first capacitor C1 and the second capacitor C2 are both grounded. The LC resonant unit is formed by connecting an inductor L0 and a capacitor C0 in parallel.

The resonant frequency of the LC resonance is tuned and selected according to the high and low frequency dependence of the duplexer. In one embodiment, the resonant frequency is 2 times the fundamental frequency, which serves as a rejection point to reduce the blocking effect of the frequency doubling on the high band. Wherein, the values of the inductor L0 and the capacitor C0 which are connected in parallel are respectively L and C, and the resonant frequency f is₀The calculation formula of (a) is as follows:

for example, if the design frequency of the duplexer is 2412-2482 MHz and 5180-5850 MHz, then, taking the center frequency point of the frequency band 2412-2482 MHz as the fundamental frequency, the resonant frequency of the LC resonance will take a value 2 times of the fundamental frequency, and further, the values of the parallel inductance and capacitance can be determined.

Exemplarily, the 5 th order butterworth high pass filter mainly includes a third capacitor C3, a fourth capacitor C4, a first microstrip line subunit 201, a second microstrip line subunit 202, and a third microstrip line subunit 203. Specifically, the second input port P2, the third capacitor C3, the fourth capacitor C4 and the second resonant unit 40 are sequentially connected, wherein one end of the first microstrip line sub-unit 201 is connected to a node between the second input port P2 and the third capacitor C3; one end of the second microstrip line subunit 202 is connected to a node between the third capacitor C3 and the fourth capacitor C4; one end of the third microstrip line subunit 203 is connected to a node between the fourth capacitor C4 and the second resonance unit 40, and the other ends of the first microstrip line subunit 201, the second microstrip line subunit 202, and the third microstrip line subunit 203 are all grounded. It is understood that the first microstrip line sub-unit 201, the second microstrip line sub-unit 202 and the third microstrip line sub-unit 203 are grounded microstrip lines.

In this embodiment, the first microstrip line subunit 201, the second microstrip line subunit 202 and the third microstrip line subunit 203 can adopt microstrip lines whose impedance is equivalent inductance. Furthermore, in one embodiment, one or more of the first microstrip line subunit 201, the second microstrip line subunit 202 and the third microstrip line subunit 203 may adopt a bent structure. It will be appreciated that the size and cost, etc. can be reduced by the bent structure.

Figure 4 shows a schematic diagram of a tuned duplexer with an elliptical low pass filter of order 3 and a butterworth high pass filter of order 5. The tuning duplexer is used for dual-mode communication, and the design frequency of the tuning duplexer is 2412-2482 MHz and 5180-5850 MHz. As can be seen from fig. 4, the three microstrip line sub-units in the high pass filter all adopt a bending structure to reduce the size.

Exemplarily, the tuned duplexer adopts a double-sided copper-clad dielectric plate as a substrate, wherein one side surface of the double-sided copper-clad dielectric plate is used for arranging a microstrip line layer and an element pad, and the element pad is used for arranging input ports P1 and P2, a common output port P3 and filters; the other side is a grounding layer. Wherein the dielectric plate with copper coated on both sides adopts epoxy glass fiber cloth laminated board made of common FR-4 grade material, and the relative dielectric constant epsilon of the epoxy glass fiber cloth laminated board_rIt was 4.5, and the dielectric loss was 0.022. Of course, the choice of the substrate can be determined according to the actual application scenario. In addition, because the microstrip line of the resonance unit and the microstrip line subunit in the high-pass filter are both designed by adopting a bending structure, the overall physical size of the tuning duplexer is only 3mm multiplied by 4mm, namely the volume of the whole duplexer is small.

In order to test the performance of the tuned duplexer, the microstrip lines in the two resonant units and the microstrip line sub-units in the filter are equivalent to respective required impedances, and meanwhile, the two input ports and the common output port P3 are also respectively used for a load with an external impedance of 50 ohms, as shown in fig. 5. Figure 6 shows an S-parameter simulation of the tuned duplexer. In fig. 6, the horizontal axes each represent the signal frequency of the tuned duplexer, the vertical axes of the curves represent different amplitudes, and the m points on the curves are frequency test points, where S11 (corresponding to S (1,1) in fig. 6), S22 (corresponding to S (2,2) in fig. 6), and S33 (corresponding to S (3,3) in fig. 6) represent parameters of impedance matching performance of the ports P1, P2, and P3 of the tuned duplexer, respectively; s12 (corresponding to S (1,2) in fig. 6) represents a parameter for tuning the isolation performance between the first input port P1 and the second input port P2 of the duplexer; s23 (corresponding to S (2,3) in fig. 6) represents the relationship between the input signal frequency and the output signal frequency of the tuned duplexer, wherein the signal is input from the common output port P3 and output from the second input port P2, and the corresponding mathematical function is: output power/input power (dB) ═ 20 × log | S23 |. Similarly, S13 (corresponding to S (1,3) in fig. 6) represents the relationship between the input signal frequency and the output signal frequency of the tuned duplexer, wherein the signal is input from the common output port P3 and output from the first input port P1, and the corresponding mathematical function is: output power/input power (dB) ═ 20 × log | S13 |.

As can be seen from FIG. 6, when a signal is input from the common output port P3, only a signal with the center frequency of 2412-2482 MHz can be output from the first input port P1, and the insertion loss in the pass band is small; when a signal is input from the common output port P3, only a signal with the center frequency of 5180-5850 MHz can be output from the second input port P2, and the insertion loss in the pass band is small. In the stop band, the insertion loss of the working filter to the working frequency range of the non-working filter is reduced to below 25dB, which shows that the tuning duplexer has strong noise filtering capability and low interference degree on the transmitted signal, i.e. the tuning duplexer can enable the signals of the two frequency bands to pass through almost without attenuation, and can effectively attenuate and suppress the non-working frequency band and other frequency bands between the two frequency bands. Therefore, the tuning duplexer has the characteristics of low insertion loss in a pass band, high isolation, wider stop band, low cost, small size and the like.

The present application also proposes a radio frequency circuit, which may exemplarily include a tuned duplexer and an antenna, etc., wherein the tuned duplexer is to adopt the tuned duplexer in the

above embodiment

1 or 2. In wireless communication multi-system and integrated products, the space is often limited, the use of the tuning duplexer can reduce the occupied space and reduce the cost, and in addition, the isolation can be improved to ensure the receiving performance of each system product, and further ensure the communication quality of the system and the like.

The present application also proposes a communication device, such as a wireless phone, a mobile phone, a tablet, etc. having a communication function, wherein the communication device comprises the above-mentioned radio frequency circuit. By using the tuning duplexer structure in the above embodiment, the communication device can have better isolation in transmission and reception, thereby improving the quality of the communication system and the like.

In all examples shown and described herein, any particular value should be construed as merely exemplary, and not as a limitation, and thus other examples of example embodiments may have different values.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application.

Claims

1. A tuned duplexer, comprising: the device comprises a first input port and a second input port for feeding signals of different frequency bands, a common output port for feeding out signals, a low-pass filter, a high-pass filter, a first resonance unit and a second resonance unit;

2. The tuned duplexer of claim 1, wherein the first resonant unit and the second resonant unit respectively comprise microstrip lines, and a length of the microstrip line corresponding to the first resonant unit is a quarter wavelength length of a center frequency of the high-pass filter; the length of the microstrip line corresponding to the second resonance unit is a quarter wavelength of the center frequency of the low-pass filter.

3. The tuned duplexer of claim 2, wherein the characteristic impedance of each microstrip line is 50 ohms; each of the ports is a 50 ohm matched port.

4. The tuned duplexer of claim 2 or 3, wherein the microstrip lines in the first and second resonant units are meander structures.

5. The tuned duplexer of claim 1, wherein the low-pass filter is an elliptical low-pass filter; the high pass filter is a butterworth high pass filter.

6. The tuned duplexer of claim 5, wherein the elliptical low-pass filter is a 3 rd order elliptical low-pass filter; the 3 rd order elliptic low-pass filter comprises a first capacitor, a second capacitor and an LC resonance unit, wherein one end of the first capacitor is connected with the first input port and one end of the LC resonance unit respectively, the other end of the LC resonance unit is connected with one end of the second capacitor and the first resonance unit respectively, and the other ends of the first capacitor and the second capacitor are grounded respectively.

7. The tuned duplexer of claim 5, wherein the Butterworth high-pass filter is a 5 th order Butterworth high-pass filter; the 5-order Butterworth high-pass filter comprises a third capacitor, a fourth capacitor, a first microstrip line subunit, a second microstrip line subunit and a third microstrip line subunit, wherein the second input port, the third capacitor, the fourth capacitor and the second resonance unit are sequentially connected, one end of the first microstrip line subunit is connected with a node between the second input port and the third capacitor, one end of the second microstrip line subunit is connected with a node between the third capacitor and the fourth capacitor, one end of the third microstrip line subunit is connected with a node between the fourth capacitor and the second resonance unit, and the other ends of the first microstrip line subunit, the second microstrip line subunit and the third microstrip line subunit are grounded.

8. The tuned duplexer of claim 7, wherein one or more of the first, second and third microstrip sub-elements are of meander configuration.

9. A radio frequency circuit comprising a tuned duplexer according to any one of claims 1 to 8.

10. A communication device comprising the radio frequency circuit of claim 9.