JPH06112720A - Radio receiver - Google Patents

Abstract

PURPOSE:To provide a radio receiver that has high antenna efficiency by providing a negative resistance circuit in order to eliminate a partial loss resistance of a loop antenna. CONSTITUTION:A negative resistance circuit 2 is connected to a terminal 1a of a loop antenna 1. The circuit 2 uses a Colpitts oscillator circuit (c) with its negative resistance value set at-R. In such a constitution, the resistance Rt of an antenna system is set as Rt=Ra-kR, that is, smaller than the equivalent series resistance Ra. In this where, (k) means a resistance conversion coefficient when a parallel circuit of the circuit 2 of the value-R and a capacitance C1 is converted into a series circuit. Under such conditions, the antenna efficiency Aeff is set as Aeff=Rr/Rt=Rr/(Ra-kR), that is, the denominator is reduced by kR compared with the conventional Aeff=Rr/Ra. Therefore the coefficient Aeff is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver having a loop antenna.

[0002]

2. Description of the Related Art Conventionally, in a radio receiver provided with a small loop antenna, as shown in FIG.
The capacitances C1 and C2 are connected to the terminals 1a and 1b of the antenna 1, respectively, and the base of the high frequency amplification transistor Q1 is connected to the terminal 1b through a matching capacitance C3. (B) of the same figure
Is an equivalent circuit when the loop antenna 1 is replaced with an equivalent series resistance Ra and an equivalent series inductance La. That is, the magnetic field component of the incoming radio wave is converted into an antenna current by the loop antenna 1, and this antenna current is supplied to the high frequency amplification transistor Q1 via the impedance matching circuit composed of the capacitances C1 and C3.

[0003]

By the way, the equivalent series resistance Ra of the loop antenna 1 is 2 as shown in the following equation.
It is divided into two components. Ra = Rr + Ro where Rr is a radiation resistance, that is, an equivalent load resistance when the loop antenna 1 is used for transmission, and Ro is an ohmic resistance, that is, a loss resistance. And the antenna efficiency A
eff is expressed by the following equation since the equivalent series resistance Ra can be regarded as the total resistance of the antenna system. Aeff = Rr / Ra Here, the equivalent series resistance Ra, that is, (Rr + Ro) is 28
It becomes about 1 ohm in the 0 MHz band, and most of it is occupied by the loss resistance Ro, and the radiation resistance Rr becomes about 1/10 of the loss resistance Ro. Therefore, the antenna efficiency Aeff is extremely low at 10 percent or less.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a radio receiver having high antenna efficiency.

[0005]

In order to achieve the above object, the present invention provides a negative resistance circuit for canceling a part of the loss resistance of the loop antenna.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the embodiments shown in the drawings. FIG. 1A is a circuit diagram showing the configuration of the antenna system of the present embodiment, and FIG. 1B is a circuit diagram showing the loop antenna 1 with an equivalent series resistance Ra and an equivalent series inductance L.
2 is an equivalent circuit diagram replaced with a (in FIG. 1, the same circuit components as those in FIG. 2 are designated by the same reference numerals). As can be seen from FIG. 1 described above, in the present embodiment, the negative resistance circuit 2 is connected to the terminal 1a of the loop antenna 1 in the conventional example. Then, as the negative resistance circuit 2, a Kolwitz oscillation circuit type circuit as shown in FIG. 7C is used, and the negative resistance value is (-R) as shown in FIG. (In addition, the resistance Rj is a resistance used for adjustment of a negative resistance value in the same figure (c)).

In this embodiment constructed as described above, the resistance Rt of the antenna system is smaller than that in the conventional example, that is, the equivalent series resistance Ra, as shown by the following equation. Rt = Ra-kR Here, k is a resistance conversion coefficient when a parallel circuit of the negative resistance circuit 2 having a resistance value (-R) and the capacitance C1 is converted into a series circuit. Then, the antenna efficiency Aeff in this case is as follows. Aeff = Rr / Rt = Rr / (Ra-kR) That is, the antenna efficiency Aeff in the conventional example is represented by Rr / Ra as described above, and in the present example,
As in the above formula, in Rr / (Ra-kR), the denominator is k
It is smaller by R, and the antenna coefficient Aef is correspondingly smaller.
f will be large. In this case, in order to prevent the circuit from becoming unstable and oscillating due to the excessive decrease of the circuit resistance of the antenna system, the above (Ra-kR) is equivalent to 70 to 90% of the equivalent series resistance Ra (as described above, at 280 MHz, equivalent). Since the series resistance Ra is about 1 ohm, it is preferable to limit it to 0, 7-0, 9 ohms) when used at this frequency.

Further, in the case of the present embodiment, the Q of the antenna system is improved by the function of the negative resistance circuit 2, so that the receiving filter characteristic is improved and the interference wave removing capability is also improved.

As described above in detail, the present invention is
Since the present invention relates to a radio receiver provided with a negative resistance circuit that cancels a part of the loss resistance of the antenna, it is possible to provide a radio receiver with high antenna efficiency.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional example.

[Explanation of symbols]

 1 loop antenna 1a terminal 1b terminal 2 negative resistance circuit C1 capacitance C2 capacitance C3 capacitance Q1 high frequency amplification transistor La equivalent series inductance Ra equivalent series resistance Ro loss resistance Rr radiation resistance

Claims (1)

[Claims] 1. A radio receiver having a loop antenna, comprising a negative resistance circuit for canceling a part of loss resistance of the loop antenna.