Loop antenna and design method for loop antenna

• US 10,720,706 B2
• Filed: 06/08/2018
• Issued: 07/21/2020
• Est. Priority Date: 06/20/2017
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Sasaki, Ai-ichiro, Kodate, Junichi
• Primary Examiner(s): Baltzell, Andrea Lindgren
• Application Number:
  US16/620,965
• Publication Number:
  US 20200203832A1
• Time in Patent Office: 774 Days
• Field of Search: 343700 R
• CPC Class Codes: H01Q 19/02 Details fastening of an element on a boom H01Q1/1228
• CPC Class Codes: H01Q 7/08 Ferrite rod or like elongated core
• CPC Class Codes: H04B 5/0081 with antenna coils loop aerials H01Q7/00
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/43 Antennas
• CPC Class Codes: H04B 5/48 Transceivers

Abstract

Even when at least one of a capacitor (C₁) connected to a main loop and a capacitor (C₂) connected to an amplification loop cannot be set to an optimal value, a current value of a current (I₂) flowing on the amplification loop can be made sufficiently large by setting the capacitors (C₁, C₂) based on any of an optimal C2 curved line, an optimal C1 curved line, and an optimal C1 straight line that pass through an optimal point (C₁^opt, C₂^opt) of the capacitors (C₁, C₂) and extend along a ridge of contour lines each joining the points where the magnitude of the current (I₂) is equal on a diagram showing a relation of values of the capacitors (C₁, C₂) with the magnitude of the current (I₂).

Claims

1. A loop antenna comprising:

a main loop being an open loop connected to any of a signal source and a reception circuit;

an amplification loop being a closed loop having the same shape as the main loop;

a first resistor connected in series to the main loop;

a first capacitor connected in series to the main loop;

a second resistor connected in series to the amplification loop; and

a second capacitor connected in series to the amplification loop, wherein

the main loop and the amplification loop have equal self-inductance,

a resistance value of the first resistor is a larger value than a resistance value of the second resistor,

at least one of the first capacitor and the second capacitor is a fixed capacitor,

a magnitude of a current flowing on the amplification loop is expressed by using the resistance value of the first resistor, the resistance value of the second resistor, a capacitance value of the first capacitor, a capacitance value of the second capacitor, and the self-inductance,

a combination of the capacitance value of the first capacitor and the capacitance value of the second capacitor to maximize the magnitude of the current is expressed by any of an optimal curved line and an optimal straight line each of which passes through an optimal point indicated with the capacitance value of the first capacitor and the capacitance value of the second capacitor when the magnitude of the current is maximized in orthogonal coordinates adopting the capacitance value of the first capacitor and the capacitance value of the second capacitor as respective axes, and

the combination of the capacitance value of the first capacitor and the capacitance value of the second capacitor is determined based on any of the optimal curved line and the optimal straight line.

2. The loop antenna according to claim 1, wherein

the first capacitor is the fixed capacitor, and

the optimal curved line is expressed by a formula defined as:

3. The loop antenna according to claim 1, wherein

the second capacitor is the fixed capacitor, and

the optimal curved line is expressed by a formula defined as:

4. The loop antenna according to claim 1, wherein

the second capacitor is the fixed capacitor, and

the optimal straight line is a straight line passing through the optimal point and having a slope equal to −

1.

5. The loop antenna according to claim 2, wherein

the second capacitor is a variable capacitor, and

the capacitance value of the variable capacitor is adjusted to a value obtained by using the capacitance value of the fixed capacitor and the optimal curved line.

6. The loop antenna according to claim 1, wherein

both of the first capacitor and the second capacitor are the fixed capacitors, and

the combination of the capacitance value of the first capacitor and the capacitance value of the second capacitor is a combination in which a distance from a point indicated with the capacitance value of the first capacitor and the capacitance value of the second capacitor to any of the optimal curved line and the optimal straight line is shortest.

7. The loop antenna according to claim 1, wherein the capacitance value of the first capacitor and the capacitance value of the second capacitor are values on any of the optimal curved line and the optimal straight lines.

9. The loop antenna according to claim 3, wherein

the first capacitor is a variable capacitor, and

the capacitance value of the variable capacitor is adjusted to a value obtained by using the capacitance value of the fixed capacitor and the optimal curved line.

10. The loop antenna according to claim 4, wherein

the first capacitor is a variable capacitor, and

the capacitance value of the variable capacitor is adjusted to a value obtained by using the capacitance value of the fixed capacitor and the optimal straight line.

8. A design method for a loop antenna provided with

a main loop being an open loop connected to any of a signal source and a reception circuit,

an amplification loop being a closed loop having the same shape as the main loop,

a first resistor connected in series to the main loop,

a first capacitor connected in series to the main loop,

a second resistor connected in series to the amplification loop, and

a second capacitor connected in series to the amplification loop, wherein

the main loop and the amplification loop have equal self-inductance,

a resistance value of the first resistor is a larger value than a resistance value of the second resistor,

at least one of the first capacitor and the second capacitor is a fixed capacitor,

a magnitude of a current flowing on the amplification loop is expressed by using the resistance value of the first resistor, the resistance value of the second resistor, a capacitance value of the first capacitor, a capacitance value of the second capacitor, and the self-inductance,

a combination of the capacitance value of the first capacitor and the capacitance value of the second capacitor to maximize the magnitude of the current is expressed by any of an optimal curved line and an optimal straight line each of which passes through an optimal point indicated with the capacitance value of the first capacitor and the capacitance value of the second capacitor when the magnitude of the current is maximized in orthogonal coordinates adopting the capacitance value of the first capacitor and the capacitance value of the second capacitor as respective axes, and

the method includes determining the combination of the capacitance value of the first capacitor and the capacitance value of the second capacitor based on any of the optimal curved line and the optimal straight line.