JPS6117421B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vehicle antenna, and aims to improve antenna efficiency.

The equivalent circuit for medium waves in this type of commonly used antenna is shown in FIG. Here, 15PF and 80Ω are the radiation impedance of the antenna in the AM band, and are constant unless the length is changed. Also, 65PF is the capacity of the cable.

In such an equivalent circuit, in order to extract the maximum available power from the power supply 5, the load side impedance Z ₂
If Z ₂ =R ₂ +jX ₂ , it is necessary to set R ₂ =R ₁ and X ₂ =−X ₁ due to conjugation. Here, the actual values of R ₁ , X ₁ are
At 1MHz, R ₁ = 2.8Ω, X ₁ = 2.1KΩ, and the ratio of the real component to the imaginary component is 2100/2.8=750.

The input section of the receiver is as shown in FIG. 2, but when expressed as an equivalent circuit, it is as shown in FIG. 3. Here, r is the resistance that the coil has, r=ωL/Q, and R is the input impedance of the amplifier.
Therefore, to make this circuit resonate, X ₂ =
Since it has to be -2100Ω, even if the maximum L and Q that can be realized now are 70, r = 2100/70 = 30
I become Ω. That is, at the time of resonance, the situation is as shown in FIG. 4.

e=e ₀ R/2.8+30+R p=e ² /R=R/(2.8+30+R) ² e ₀ ^2Power that can be extracted here (power that can be supplied to R)
is for R=30Ω+2.8Ω=32.8Ω, and P=
It becomes 0.0076e ₀ ² .

Now, if we compare this power with the maximum available power when r is ignored, (R=2.8Ω) P _AV =e ² /R=R/(2.8+R) ² e ₀ ² =0.0893e ₀ ² p/P _AV =0.085, and only 1/12 of the maximum available power is delivered to the amplifier.

The present invention eliminates these drawbacks and will be described below. First, in Figure 4,
Either reduce the resistance of the inductance (30Ω), or increase the resistance (2.8Ω) seen from the input terminal of the receiver. Now, when looking at the resistance of inductance, r=ωL/Q, where ω is determined as the reception frequency. The Q cannot be made large either from the standpoint of making the coil or adjusting the bandwidth as necessary. Therefore, it is possible to reduce L.
That is, it is necessary that the reactance seen from the input end be small (capacitance large).

Therefore, when using an element that tends to have resistance, such as an inductance, it is easier to ignore Q if it is placed before the antenna cable rather than after the receiver input terminal.

The antenna capacitance is C _A and the series inductance is L
_A , the antenna resistance is R _A , and the angular frequency is ω, then
What was R _A −j1/ωC _A becomes R _A −j1/ωC _A +jωL _A =R _A −j(1/ωC _A −ωL _A ), and if we set it so that the imaginary component is always positive, we get This means that the antenna capacity has increased.

FIG. 5 shows this equivalent circuit, FIG. 6 shows the resistance component calculated by converting it into impedance seen from the receiver input terminal, and FIG. 7 shows the reactance component seen from the same location.

Therefore, by inserting an inductance between the antenna feeding point and the cable and setting it appropriately, it is possible to increase the resistor component (reduce the reactance component) of the impedance seen from the receiver input terminal. In other words, in FIG. 3, since L can be made small, r can be made small with the same Q. Moreover, since the resistance seen from the input end to the antenna side becomes larger, R can be made large, and the influence of r can be made small.

If we insert 0.5mH as L in Figure 5 and look at the case of 1MHz, it will become as shown in Figure 8, and the power consumed by R
P′ becomes P′=e ₁ ²・R/(28.6+5+R) ² =e ₀ ²・5/2.8・0.00744=0.0133e ₀ ² . Comparing this with the previous power P, it is an improvement of P'/P=0.0133/0.0076=1.79=2.4 db, and the antenna efficiency is improved.

Note that it can also be used for the VHF band if sufficient capacity is provided in parallel to the newly provided inductance L to pass the VHF band signal.

As is clear from the above description, according to the present invention, antenna efficiency can be increased by providing a specific inductance.

[Brief explanation of the drawing]

Figure 1 is an equivalent circuit diagram of a conventional automotive antenna.
Figure 2 is a circuit diagram of the reception input section of a car radio, Figure 3
Figure 4 is an equivalent circuit diagram, Figure 4 is an equivalent circuit diagram when the antenna resonates with the radio, Figure 5 is an equivalent circuit diagram of an in-vehicle antenna according to an embodiment of the present invention, Figure 6,
FIG. 7 is a characteristic diagram thereof, and FIG. 8 is an equivalent circuit diagram including an antenna and a radio section. 6...Inductance.

Claims (1)

[Claims] 1. An inductance is provided between the antenna body and the feeder line, and resonance is caused by the sum of the radiation capacitance of the antenna and the electrostatic capacitance between the antenna and the vehicle body at a frequency above the upper limit of the reception band. Features of automotive antennas. 2. The vehicle-mounted antenna according to claim 1, wherein the inductance is provided with a capacity sufficient to pass a VHF band signal in parallel.