JP2008135883A - High-frequency power monitor circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently monitor high-frequency electric power without extra loss of the high-frequency electric power flowing through a main signal line. <P>SOLUTION: An antenna (for example, a patch antenna) 20 is disposed at a position where no coupling (direct electromagnetic coupling) is caused for the main signal line (for example, a microstrip) 10 on a dielectric substrate 11, and a leak radio wave inevitably radiated from the main signal line 10 is received by the antenna 20 to efficiently monitor the high-frequency electric power flowing through the main signal line 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-frequency power monitor circuit, and more particularly to a high-frequency power monitor circuit that monitors the power (signal level) of a high-frequency signal flowing in a main signal line on a dielectric substrate in a contactless manner.

  In wireless communication devices typified by base stations and mobile stations (cell phones), RF signals are amplified by a high-frequency amplifier and transmitted from an antenna, and transmission power is monitored and fed back to the amplifier for constant output control (Auto Power Control). In particular, when monitoring millimeter wave or microwave power, it is necessary to perform monitoring in a non-contact manner so as not to adversely affect reflection and circuit impedance by bringing the monitor circuit into contact with the main signal circuit. Further, the ratio between the main signal power and the monitor power needs to be constant (linear) regardless of the magnitude of the main signal power. In order to satisfy such conditions, conventionally, as shown in Patent Documents 1 and 2, for example, high frequency signal wave power is obtained by coupling (electromagnetic coupling) a directional coupler to a part of the main signal circuit. I was monitoring.

  FIG. 5 is a diagram for explaining the prior art. FIG. 5A shows a typical configuration in which a directional coupler is used for monitoring high-frequency power. In the figure, reference numeral 10 denotes a microstrip (transmission path) that transmits a main signal, and includes a strip conductor (main line) 12 provided on the surface of the dielectric substrate 11 and a ground conductor 13 on the back surface. A directional coupler 50 includes a strip conductor (sub-line) 51 coupled over λ / 4 of the main line 12, and one of the sub-lines 51 is connected to the monitor port MP and the other is a resistor. The terminal circuit 53 is terminated by a termination circuit 53 composed of 54 and a ground line 55.

In such a configuration, out of the high-frequency signal power flowing through the transmission line 10, the monitor output Pf proportional to the power going from the terminal (1) to (2) is taken out regardless of the power going from the terminal (2) to (1). be able to. That is, when the power input to the terminal (1) of the transmission line 10 is Pi, a fraction of the power Pf appears at the terminal (3) of the sub line, and the terminal (4) further reduces to 1/10. The following power Pr appears. The coupling C in this case is
C = 10 log (Pi / Pf)
And the directivity D is
D = 10 log (Pf / Pr)
It is represented by Furthermore, if the power passing through the transmission line 10 to the terminal (2) is Po, the insertion loss L is
L = 10 log (Pi / Po)
It is represented by

FIG. 5B shows a specific example of the relationship between the gap s and the degree of coupling C of the directional coupler. Graph (1) → (4) shows the degree of coupling between terminals (1) and (4), and graph (1) → (3) shows the degree of coupling between terminals (1) and (3), both of which are in X band. The characteristic in (8-12GHz) is shown. The horizontal axis represents the ratio s / h between the gap s and the thickness h of the substrate 11. When paying attention to the graph (1) → (3), the monitor power of the directional coupler becomes about −5 dB by bringing the gap s close to 0, but the gap s is 3 of the substrate thickness h (for example, 0.5 mm). When it is about double, the degree of coupling C is -30 dB or less, and there is almost no coupling.
JP2002-223135 JP 2000-49273 A

  However, as in the case where the directional coupler is used, if the method is to extract and monitor a part of the main signal power, the main signal transmission path always has an insertion loss, so the transmission efficiency is remarkably high. It was getting worse.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a high-frequency power monitoring circuit capable of efficiently monitoring the high-frequency power without giving a special loss to the high-frequency power flowing through the main signal line. Is to provide.

  The high-frequency power monitor circuit according to the first aspect of the present invention has an antenna disposed at a position where no coupling occurs with respect to the main signal line on the dielectric substrate, and leaks radio waves radiated from the main signal line. And the high frequency power flowing through the main signal line is monitored.

  In the present invention, the configuration in which the leaked radio wave inevitably radiated from the main signal line is received by an antenna provided at a position where coupling (electromagnetic coupling) does not occur, without causing a separate insertion loss to the main signal line, The main signal power can be monitored efficiently.

  Note that an example of the “position at which coupling does not occur with respect to the main signal line” refers to an example of the graph (1) → (3) in FIG. 5B when the main signal line is a microstrip. As can be seen from the above, it is said to be a position away from the main signal line by 2 to 3 times or more of the dielectric substrate thickness h (for example, 0.5 mm).

   In the second aspect of the present invention, the antenna comprises a planar antenna having a planar conductor provided on the surface of the dielectric substrate and a ground conductor on the back surface. Therefore, a high-frequency power monitor circuit using an antenna can be mounted in a small and inexpensive manner. Preferably, the exemplary planar antenna is a half-wave patch antenna.

   In the third aspect of the present invention, the center frequency of the signal to be monitored is shifted from the center frequency of the main signal. As will be described later, a relatively high reception sensitivity (antenna gain) is obtained in a frequency region in which the center frequency of the signal to be monitored is shifted from the center frequency of the main signal (for example, about 10 to 20%) by electromagnetic analysis of the planar antenna. Obtained.

  The high-frequency power monitor circuit according to the fourth aspect of the present invention is configured as an array antenna by arranging a plurality of element antennas at predetermined intervals at positions where no coupling occurs with respect to the main signal line on the dielectric substrate. The leakage radio wave radiated from the main signal line is received by the array antenna and the high frequency power flowing through the main signal line is monitored. In the present invention, a high reception gain can be obtained in the array antenna by combining the reception outputs of the respective element antennas in phase.

   In the fifth aspect of the present invention, a circuit composed of a main signal line and an antenna is shielded by a metal case. Therefore, it is possible to properly monitor only the high-frequency power of the main signal line without interference from unnecessary radio waves (noise) from the outside.

As described above, according to the present invention, the high frequency power of the main signal line can be monitored efficiently, which greatly contributes to the improvement of transmission efficiency. In particular, improvement of power efficiency in mobile devices contributes to longer battery life.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings. FIG. 1 is a diagram showing a configuration of a high-frequency power monitor circuit according to the first embodiment, FIG. 1 (A) is a perspective view of the monitor circuit, and FIG. 1 (B) is a side view of the monitor circuit viewed in the y-axis direction. Is shown. In the figure, 11 is a dielectric substrate made of glass epoxy or the like for mounting a high-frequency circuit, 12 is a strip conductor on the surface of the substrate, 13 is a ground conductor on the back of the substrate, and 21 is for mounting an antenna provided at a position opposite to the substrate 11. A dielectric substrate, 22 is an antenna conductor on the surface (lower surface in the figure) of the substrate 21, 23 is a ground conductor on the back surface (upper surface in the figure), 14 is a metal housing for protecting and shielding the high-frequency circuit, and 15 is metal. It is a lid member which consists of. The ground conductors 13 and 23 on the back surface can be substituted by grounding the metal casing 14 and the lid member 15 and can be omitted. This also applies to other embodiments described later.

  The strip conductor 12 forms a microstrip (main signal line) 10 together with the dielectric substrate 11 and the ground conductor 13 on the back surface, and transmits a high-frequency signal input from the input port IP to the output port OP. In general, transmission loss in a microstrip is roughly divided into three types: dielectric loss of the substrate 11, conductor loss of the conductor 12, and radiation loss of radio waves radiated into the air. Of these, the effective power monitoring is made possible by effectively utilizing the radiation loss. For example, when the relative dielectric constant εr = 4 and the thickness h = 0.5 mm of the substrate 11, the ratio of the substrate thickness h to the wavelength λ at a monitor signal frequency of 10 GHz (wavelength λ≈16 mm) is 0.5 / 16 = 0. 0.032, and there is a considerable radiation loss even with this substrate thickness h.

  The antenna conductor 22 constitutes a half-wavelength patch antenna 20 together with the dielectric substrate 21 and the ground conductor 23 on the back surface, and receives a part of the radiated radio wave leaking from the microstrip 10 and outputs it to the monitor port MP. The size of an example of the patch antenna 20 for monitoring a high-frequency signal in the 10 GHz band is a = 7 to 8 mm (≈b), the thickness w of the substrate 21 is 1.6 mm, and the relative dielectric constant εr is 4.2. As shown in FIG. 1B, the microstrip 10 and the patch antenna 20 are separated to such an extent that they are not directly coupled (electromagnetically coupled), so that no coupling loss occurs in the microstrip 10. The standard of the distance at which no coupling occurs is, for example, three times or more the thickness h (0.5 mm) of the substrate 11. Further, the receiving sensitivity of the patch antenna 20 is increased by increasing the thickness w of the patch antenna 20 to, for example, 1.6 mm.

  Since the radiation loss component is radiated at a constant rate depending on the material and shape of the microstrip 10, in the present embodiment for monitoring a part of the radiation loss, the high-frequency power is supplied at a constant rate without depending on the main signal level. Can be monitored. Further, since a radiation component that inevitably causes a loss in the main signal line is used, it is not necessary to extract a part of the main signal power as in the conventional case, and transmission loss can be reduced. Further, by covering the entire monitor circuit with the metal casings 14 and 15, unnecessary radio waves from the outside can be blocked, and only the high frequency power of the main signal line 10 can be accurately monitored.

  FIG. 2 is a diagram showing the transfer characteristics of the high-frequency power monitor circuit according to the first embodiment, and shows the result of analyzing the monitor circuit of FIGS. 1 and 5 with an electromagnetic field simulator. In the figure, the dotted line corresponds to the case where the directional coupler 50 of FIG. 5 is used, the solid line corresponds to the case where the antenna 20 of FIG. 1 is used, and the characteristics L1 and L2 are the transfer characteristics from the input port IP to the output port OP. The characteristics M1 and M2 represent the transfer characteristics from the input port IP to the monitor port MP.

When viewed in the vicinity of 10 GHz, the transmission loss of the monitor circuit using the antenna 20 is improved by about 0.1 dB compared to that using the directional coupler 50, and the difference that cannot be ignored in the output stage where the power is high. It has become. Further, it can be seen from the characteristic curve of FIG. 2 that the center frequency of both circuits 20 and 50 is approximately 9.9 GHz, but the frequency characteristics of the monitor power are 9.7 to 9.8 GHz and 10 to 10 which are shifted from the center frequency. In the 2 GHz band, the monitor level M2 when the antenna 20 is used is clearly larger than the monitor level M1 when the directional coupler 50 is used, and the center frequency when the antenna 20 is used. It can be seen that it is advantageous to monitor in a band slightly shifted (about 10 to 20%) from (9.9 GHz in this example).

  Therefore, although not shown, it is preferable to provide a filter circuit that allows signals of 9.7 to 9.8 GHz or 10 to 10.2 GHz to pass through the monitor signal extraction line, so that high-frequency power is centered on signals in this band. It is possible to monitor.

  FIG. 3 is a diagram showing the configuration of the high-frequency power monitor circuit according to the second embodiment, and shows a case where the patch antenna 20 is mounted on the back surface of the metal lid member 15. 3A is a perspective view of the monitor circuit, and FIG. 3B is a side view of the monitor circuit viewed in the y-axis direction. The patch antenna 20 has a back surface (upper surface in the figure) of a dielectric substrate 21 attached in advance to the back surface of a metal lid member 15 and a planar rectangular (a≈b) antenna conductor 24 provided on the surface of the substrate 21. Configured. Further, the coaxial connector 40 is passed through substantially the center of the antenna 20, the external conductor 41 is connected to the ground conductor 23 (lid member 15), and the center conductor 42 is connected to the antenna conductor 24. When this lid member 15 is attached to the metal casing 14, a monitor circuit is completed and the entire circuit is shielded. In the present embodiment, the monitor port MP (corresponding to a power receiving point and a power feeding point) can be connected to the inner side of the end (edge) of the patch antenna 20, so that impedance matching can be easily obtained and reception characteristics are improved.

  FIG. 4 is a diagram showing the configuration of the high-frequency power monitor circuit according to the third embodiment, and shows a case where the monitor circuit is configured by an array antenna. 4A is a perspective view of the monitor circuit, and FIG. 4B is a side view of the monitor circuit viewed in the y-axis direction. A plurality of element antennas 31a to 31c are arranged at predetermined intervals at positions where no coupling occurs with respect to the main signal line 10 on the dielectric substrate 11. The size of each of the element antennas 31a to 31c may be the same as that in FIG. 1, and the array antenna 30 is formed by arranging them at element intervals along the transmission line 10 so that the reception outputs of the elements 31a to 31c are combined in phase. Constitute. When phase adjustment is required for in-phase synthesis, a phase shift circuit that changes the line length may be provided between the element antennas. Thus, by receiving the leaked radio wave radiated from the main signal line 10 by the array antenna 30, the high frequency power flowing through the main signal line 10 is monitored with a high antenna gain. Further, since the entire monitor circuit is sealed with the metal casing 14 and the lid member 15, the state of radio wave propagation in the internal space is stabilized, so that good reception characteristics can be obtained.

  In the above embodiment, an example of a rectangular patch antenna is described as a planar antenna, but the present invention is not limited to this. The plan view shape of the antenene conductor may be circular or elliptical. In addition to the planar antenna, various three-dimensional high-frequency antennas such as a half-wave dipole antenna and a monopole antenna can be used.

  Moreover, although several embodiment suitable for the said invention was described, it cannot be overemphasized that the structure of each part, control, a process, and these combination can be variously changed within the range which does not deviate from this invention. .

It is a figure which shows the structure of the high frequency electric power monitor circuit by 1st Embodiment. It is a figure which shows the transfer characteristic of the high frequency electric power monitor circuit by 1st Embodiment. It is a figure which shows the structure of the high frequency electric power monitor circuit by 2nd Embodiment. It is a figure which shows the structure of the high frequency electric power monitor circuit by 3rd Embodiment. It is a figure explaining a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Microstrip 11, 21 Dielectric board | substrate 12 Strip conductor 13, 23 Ground conductor 14 Metal housing 15 Cover member 20 Antenna 22, 24 Antenna conductor 30 Array antenna 31 Element antenna

Claims (5)

An antenna is disposed at a position where coupling does not occur with respect to the main signal line on the dielectric substrate, and leakage radio waves radiated from the main signal line are received by the antenna and high frequency power flowing through the main signal line is monitored. A high frequency power monitor circuit. 2. The high frequency power monitor circuit according to claim 1, wherein the antenna comprises a planar antenna having a planar conductor provided on the surface of the dielectric substrate and a ground conductor on the back surface. 3. The high frequency power monitor circuit according to claim 2, wherein a center frequency of the signal to be monitored is shifted from a center frequency of the main signal. The array antenna is configured by arranging a plurality of element antennas at a predetermined interval at a position where no coupling occurs with respect to the main signal line on the dielectric substrate, and leaked radio waves radiated from the main signal line are transmitted to the array antenna. A high frequency power monitor circuit that monitors the high frequency power that is received at the main signal line and flows through the main signal line. 5. The high frequency power monitor circuit according to claim 1, wherein a circuit comprising a main signal line and an antenna is shielded by a metal case.

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