CN102751962A - Broadband active matching method and matching circuit for electronically small receiving antenna based on negative impedance conversion - Google Patents

Abstract

The invention provides an electrically small receiving antenna broadband active matching method based on negative impedance transformation. Introduce negative impedance transformation into the amplifier directly connected with capacitive electric small antenna, make it become negative impedance transformation amplifier, described negative impedance transformation obtains negative capacitance at the input terminal of amplifier, when the absolute value of negative capacitance is greater than the input of amplifier Capacitance, the equivalent negative capacitance is obtained at the input end of the amplifier, and the equivalent positive capacitance of the electrically small antenna input reactance cancels the negative capacitance, so that the input end of the active network is an equivalent negative capacitance. The active receiving antenna realized by the invention not only has broadband characteristics, but also has similar gain and signal-to-noise ratio performance as the enhanced Non-Foster (negative impedance) matching method, but the circuit is simpler, the comprehensive performance is good, and the amplification and negative impedance The transformation is realized in one circuit, and compared with the classical active receiving antenna, only a positive feedback capacitor is added.

Description

Broadband Active Matching Method and Matching Circuit for Electrically Small Receiving Antenna Based on Negative Impedance Transformation

technical field

The invention relates to a broadband matching method for an electrically small antenna, and also relates to a broadband matching circuit for an electrically small antenna.

Background technique

With the miniaturization of radio technology equipment, the requirements for antenna size in small spaces, and the wide frequency band of communication equipment, there is an increasing demand for broadband miniaturized antennas, which makes broadband and miniaturized antennas become a research hotspot at home and abroad. one of the subjects. In order to realize the miniaturization of the antenna, the electrically small antenna is widely used, but the electrically small antenna has the disadvantages of large input reactance and small radiation resistance, so that the passively matched electrically small antenna is limited by the gain bandwidth theory, and cannot achieve broadband and high efficiency. The classic active receiving antenna uses a high input impedance amplifier circuit to connect with the capacitive passive electric small antenna to form a whole, which realizes the wide frequency band of the electric small antenna, but this kind of active receiving antenna is affected by the amplifier circuit. The influence of the input capacitance is unavoidable, and high gain cannot be achieved. The gain of the active antenna can only be increased by increasing the amplification factor of the amplifier, which will deteriorate the nonlinear performance of the active antenna, and the output of this type of active antenna The signal-to-noise ratio is low.

The electrically small antenna with negative impedance matching can overcome the influence of the unavoidable input capacitance of the offset amplifier circuit. The literature "Li Wenxing. A New Method for Designing Active Antennas [J]. Acta Electronics, 1993, 21(7): 110-113." proposed a negative capacitance obtained by using a negative impedance converter to offset active antennas. The input capacitance of the antenna amplifier; the literature "Sussman-Fort, S.E, Rudish R.M., Non-Foster Impedance Matching of Electrically-Small[J].IEEE Transacationson Antennas and Propagation, 2009,57(8):2230-2241." introduced A kind of using the negative impedance obtained by the floating negative impedance converter to offset the input reactance of the electrically small antenna can only increase the gain and improve the signal-to-noise ratio to a limited extent. The document "Sussman-Fort, S.E. "Non-Foster vs. active matching of an electrically-small receive antenna" Antennas and Propagation Society International Symposium (APSURSI), pp1–4, 2010", proposed an enhanced Non-Foster ( Negative impedance) matching method can improve the gain and signal-to-noise ratio very well. Compared with the classic active receiving antenna, the output signal-to-noise ratio has about 5dB improvement. It is realized by inserting a floating negative impedance converter between the antenna and the amplifier circuit, but the inserted floating negative impedance converter makes the circuit structure complex and the nonlinear performance deteriorates.

Contents of the invention

The purpose of the present invention is to provide a broadband active matching of electrically small receiving antenna based on negative impedance transformation, which can not only realize the miniaturization and wide frequency band of the antenna, but also increase the gain of the electrically small antenna and improve the signal-to-noise ratio of the electrically small antenna. method. The object of the present invention is also to provide an electrically small receiving antenna broadband active matching circuit based on negative impedance transformation.

The purpose of the present invention is achieved like this:

The wideband active matching method of an electrically small receiving antenna based on negative impedance transformation of the present invention is: introducing a negative impedance transformation into an amplifier directly connected to a capacitive electric small antenna to make it a negative impedance transformation amplifier, the negative impedance transformation The negative capacitance is obtained at the input terminal of the amplifier, and when the absolute value of the negative capacitance is greater than the input capacitance of the amplifier, an equivalent negative capacitance is obtained at the input terminal of the amplifier, and the negative capacitance is offset by the equivalent positive capacitance of the electrically small antenna input reactance, Make the active network input an equivalent negative capacitance.

The electrically small receiving antenna broadband active matching circuit based on negative impedance transformation includes an operational amplifier U1, a DC blocking capacitor _C1 is connected to the passive antenna and the non-inverting input terminal 3 of the operational amplifier U1, and _C2 is a DC blocking capacitor at the output end of the active network , the first resistor R _O is connected to the output terminal 6 of the operational amplifier U1 and the input terminal of the low-pass filter U2, the second resistor R _F is connected to the output terminal 6 of the operational amplifier U1 and the inverting terminal 2, and the third resistor R _G is connected to the inverting terminal 2 of the operational amplifier U1 Between the phase terminal 2 and the ground, the low-pass filter U2 is connected to the first resistor R _O and the DC blocking capacitor C ₂ at the output terminal of the source network.

The invention provides a broadband active matching method and circuit for an electrically small receiving antenna based on negative impedance transformation technology. The realized active receiving antenna not only has broadband characteristics, but also matches the enhanced Non-Foster (negative impedance) matching method. It has similar gain and signal-to-noise ratio performance, but the circuit is simpler and the overall performance is good. The amplification and negative impedance transformation are realized in one circuit. Compared with the classic active receiving antenna, only one positive feedback capacitor is added.

The present invention introduces negative impedance transformation into the amplifier directly connected with the capacitive electric small antenna to make it a negative impedance transformation amplifier. The effect of negative impedance transformation is to obtain negative capacitance at the input end of the amplifier. When the absolute value of the negative capacitance is greater than When the input capacitance of the amplifier, the equivalent negative capacitance can be obtained at the input of the amplifier. Since the input reactance of the electrically small antenna is capacitive reactance, it can be equivalent to a positive capacitance, which can be offset with the equivalent negative capacitance of the input terminal of the active network, so that the input terminal of the active network is an equivalent negative capacitance, realizing broadband matching, and making the active network The signal at the input terminal is larger than the source signal received by the antenna, and the active network has an equivalent input gain, which can effectively increase the antenna gain and improve the signal-to-noise ratio.

The negative impedance converter in the present invention is characterized in that it can realize positive capacitance characteristic conversion in a wide frequency band. The negative impedance converter is realized by introducing a positive feedback element into the amplifier circuit, and the required negative impedance is obtained by adjusting the amplifier amplification factor and the positive feedback relationship. . The amplifier circuit involved in the present invention can be realized by adopting such as an operational amplifier circuit whose input stage is a field effect transistor, an amplifier circuit composed of discrete transistors, etc., and can obtain an effective negative capacitance at the input end of the active network through negative impedance transformation. Source network circuit implementation.

Compared with the prior art, the present invention has significant advantages:

1. Due to the introduction of negative impedance transformation, the equivalent negative capacitance is obtained at the input end of the active network, which matches the capacitive electric small antenna. The bandwidth of the active antenna has nothing to do with the electric small antenna, but only depends on the active network. Bandwidth, enabling wide frequency bands for electrically small antennas.

2. The input terminal of the active network is equivalent to a negative capacitance, which can provide energy and match with the small capacitive antenna, so that the signal at the input terminal of the active network is larger than the source signal received by the antenna, that is, there is an input of the active network Gain, combined with the mid-amplifier gain of the active network, enables higher active antenna gains.

3. The input end of the active network is equivalent to a negative capacitance, which is matched with the capacitive electric small antenna. There is an input gain of the active network, which can significantly improve the output signal-to-noise ratio of the active receiving antenna of the present invention and obtain higher sensitivity.

4. Negative impedance conversion is realized in the same active network as the amplifier circuit, which has the characteristics of simple circuit and good comprehensive performance.

Description of drawings

Fig. 1 is a schematic diagram of the present invention;

Fig. 2 is the circuit diagram that the present invention adopts operational amplifier implementation example;

FIG. 3 is a measurement of equivalent input gain for an implementation example of an operational amplifier of the present invention.

Detailed ways

Below in conjunction with the accompanying drawings, the present invention will be described in more detail by taking the negative impedance matching single whip electric small antenna as an example:

The electric small antenna with negative impedance matching is related to the input impedance of the electric small antenna when designing the negative impedance active circuit. The input impedance of the single whip electric small antenna is as follows:

The input resistance of a single whip antenna is:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 40</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="h"\; filenames="HDA00001882805900013.png"\; state="\{\{state\}\}">h</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

The input reactance of a single whip antenna is:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 60</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}\frac{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cot</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;h</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Where h is the height of the antenna, λ is the free-space wavelength, and a is the radius of the single-whip antenna. The input resistance of the electric small antenna is much smaller than the input reactance. For the convenience of analysis, the resistance of the single whip electric small antenna can be ignored, and the capacitance is equivalent to a constant in the wide frequency band.

The equivalent circuit of a negative impedance matching capacitive electrically small antenna is shown in Figure 1, where E is the field strength at the point where the antenna is located, h _eff is the effective height, A _V is the gain of the amplifier, and the input capacitance of the active network is C _i , the positive feedback capacitor C _N is introduced into the amplifier to perform negative impedance transformation, V _s is the voltage received by the antenna, V _i is the voltage at the input terminal of the active network, and the equivalent input voltage gain of the active network can be obtained as:

$\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; V</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Define C _N ′=(1-A _V )C _N as the negative capacitance equivalent to the input terminal of the active network after C _N is transformed by negative impedance, C=C _i +(1-A _V )C _N is the active network, etc. Effective input capacitance, obviously, adjusting A _V and C _N can make active network equivalent input capacitance C<0. When C<0, V _i >V _s can be obtained from formula (3), indicating that the signal at the input end of the active network is larger than the source signal received by the antenna, and there is an input gain of the active network, which can effectively increase the gain of the antenna , and from the Sussman-Fort enhanced Non-Foster (negative impedance) matching method, it can be seen that the existence of the input gain of the active network can improve the signal-to-noise ratio of the antenna.

The essence of a negative impedance converter is a positive feedback circuit. For an electrically small antenna with negative impedance matching, there are potential unstable factors, and stable working conditions must be satisfied in practical applications.

According to formula (3), the condition for the stable operation of the negative impedance converter is C _a +C _i +(1- _AV )C _N ≠0, combined with the condition of negative impedance transformation A _V >1, the choice of A _V must satisfy A _V >1 and C _a +C _i +(1-A _V )C _N >0, namely

1<A _V <1+(C _a +C _i )/C _N (4)

However, in order to make the antenna work in the state of V _i >V _s , it is required that -C _a <C<0, we can get

1+C _i /C _N ＜A _V ＜1+(C _a +C _i )/C _N (5)

That is to say, within the required operating frequency range of the active antenna, the selection of A _V must satisfy formula (4) or (5), and the out-of-band satisfies

A _V <1+(C _a +C _i )/C _N (6)

to prevent self-excitation.

Formulas (5) and (6) are the conditions that A _V must meet when designing this kind of active receiving antenna with negative impedance matching.

Fig. 2 is according to the principle of the present invention, uses operational amplifier U1 to realize the single-whip electric small antenna demonstration implementation example of negative impedance matching, _C1 is connected to the non-inverting input end 3 of passive antenna and operational amplifier U1 as DC blocking capacitor, C ₂ is the DC blocking capacitor at the output end of the active network, R _O is connected between the output end 6 of U1 and the input end of U2, R _F is connected between the output end 6 of U1 and the inverting end 2, and R _G is connected between the inverting end 2 of U1 and the ground. U2 is connected to matching resistors R _O and C ₂ , the voltage amplification factor of the active network is A _V ＝1+R _F /R _G , and the load voltage gain of the active receiving antenna is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

The antenna voltage gain V _a depends on the feedback capacitance C _N , adjusting C _N can change the equivalent input capacitance C of the active network, and at the same time change the gain and signal-to-noise ratio of the antenna. It is worth noting that the adjustment of _CN must meet the stable working conditions. The test result of the equivalent input voltage gain V _i /V _s of the active network is shown in Figure 3. In Figure 2, when the equivalent capacitance of the small single-whip electric antenna is selected as C _a =15pF, it can be seen from Figure 3 that the With the increase of the equivalent input capacitance |C| of the active network, the closer to C _a =15pF, the equivalent input voltage gain V _i /V _S of the active network also increases obviously, and the better the signal-to-noise ratio of the antenna is improved , such as C=-13.3pF, the equivalent input gain is nearly 9 times, but compared with C=-10.4pF, the voltage gain curve changes much more drastically, indicating that the stability of the antenna becomes worse, that is, |C| is also indispensable limited approach to C _a .

Claims (2)

1. A kind of electrically small receiving antenna broadband active matching method based on negative impedance transformation, it is characterized in that: introduce negative impedance transformation in the amplifier directly connected with capacitive electric small antenna, make it become negative impedance transformation amplifier, so The above negative impedance transformation obtains a negative capacitance at the input terminal of the amplifier. When the absolute value of the negative capacitance is greater than the input capacitance of the amplifier, an equivalent negative capacitance is obtained at the input terminal of the amplifier. The negative capacitance cancels out, making the input of the active network an equivalent negative capacitance. 2. An electrically small receiving antenna broadband active matching circuit based on negative impedance transformation, which is characterized in that it includes an operational amplifier (U1), and a DC blocking capacitor (C ₁ ) is connected to the same phase of the passive antenna and the operational amplifier (U1). Input terminal (3), the first resistor (R _O ) is connected to the output terminal (6) of the operational amplifier (U1) and the input terminal of the low-pass filter (U2), and the second resistor (R _F ) is connected to the output terminal of the operational amplifier (U1) (6) and the inverting terminal (2), the third resistor (R _G ) is connected between the operational amplifier (U1) inverting terminal (2) and ground, and the low-pass filter (U2) is connected to the first resistor (R _O ) DC blocking capacitor (C ₂ ) from the output of the source network.

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