# US 10,309,998 B2 · Method and apparatus for remotely determining antenna input impedance

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- Number: US 10,309,998 B2
- Document ID: US10309998B2
- Status: Granted
- Kind: B2
- Application number: 15/219,368
- Filed: 2016-07-26
- Published: 2018-02-01
- Granted: 2019-06-04
- Earliest claimed: 2016-07-26
- Applicants: Martin F. Jue
- Inventors: Martin F. Jue
- Web page: https://patentgrep.com/patent/US10309998B2

## CPC

- G01R 29/10: Radiation diagrams of antennas
- H04B 1/40: Circuits
- H04B 17/104: {of other parameters, e.g. DC offset, delay or propagation times}
- H04B 17/12: of transmit antennas, e.g. of the amplitude or phase
- H04B 17/13: of power amplifiers, e.g. gain or non-linearity
- H04B 17/23: Indication means, e.g. displays, alarms, audible means
- H01Q 1/50: Structural association of antennas with earthing switches, lead-in devices or lightning protectors
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H04B: TRANSMISSION
- H01Q: ANTENNAS, i.e. RADIO AERIALS (radiators or antennas for microwave heating H05B6/72)

## Abstract

A system for remotely measuring antenna input impedance utilizing an automatic antenna tuner in which, for any tuner, the tuner input impedance may be established by the values of the components in the circuit at the time that the SWR is at a minimum, with these values being automatically available in terms of the components that are switched in to achieve low SWR. Once having established the input impedance to the tuner, the complex conjugate of the tuner input impedance yields the antenna input impedance, with antenna input impedance sensed at full power at a position remote from the antenna input.

## Claims

### Claim 1

An apparatus for remotely measuring a feed point impedance of an antenna, the apparatus comprising:
an automatic antenna tuner including capacitive and inductive components that are switched into a tuner circuit of the automatic antenna tuner to achieve a minimum standing wave ratio (SWR), wherein the automatic antenna tuner is configured to automatically sense a frequency of a transmitter communicatively coupled therewith;
a processor for calculating the antenna feed point impedance based on the sensed frequency of the transmitter, values of the switched-in components that are utilized to achieve the minimum SWR, and a measured length of a feedline between the automatic antenna tuner and a feed point of the antenna; and
a display coupled to the processor for displaying the calculated antenna feed point impedance.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the values of the components at the minimum SWR are derived from switch states of switches utilized to switch the components into the tuner circuit when the minimum SWR has been achieved.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the remotely sensed antenna feed point impedance is given by a complex conjugate of a tuner input impedance at a time of tune.

### Claim 4 (depends on 3)

The apparatus of claim 3, wherein for an L-network, the complex conjugate of tuner input impedance is Zant=Rin−jXin, where:
for R less than 50 ohms, Zin=Rin+jXin, where:
Rin=RXc2/(R2+Xc2); and
Xin=XL−[R2XC/(R2+XC2)], where:
R is a transmitter output impedance; and
Zin is the tuner input impedance; and
for R greater than 50 ohms, Zin=Rin+jXin, where:
Rin=RXc2/[R2+(XL−Xc)2], representing a resistance of the antenna;
Xin=−Xc[XL(XL−Xc)+R2]/[R2+(XL−Xc)2], representing a reactance of the antenna; and
Zant=Rin−jXin.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein:
capacitance Xc is a combined capacitance of all capacitive elements of the number of components that are switched in to achieve the minimum SWR; and
inductance XL is a combined inductance of all inductive elements of the number of components that are switched in to achieve the minimum SWR.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the automatic antenna tuner is further configured to receive input pertaining to both the length and a velocity factor of the feedline between the antenna and the automatic antenna tuner.

### Claim 7 (depends on 6)

The apparatus of claim 6, wherein the processor is further configured for calculating the antenna feed point impedance based on the length and the velocity factor of the feedline.

### Claim 8

A method for remotely sensing an antenna input impedance of an antenna coupled to a transmitter utilizing a feedline, the method comprising:
utilizing an automatic antenna tuner to tune the antenna to the transmitter; and
detecting the antenna input impedance utilizing characteristics of the automatic antenna tuner when the automatic antenna tuner has tuned to a minimum standing wave ratio (SWR), wherein:
the automatic antenna tuner includes capacitive and inductive elements that are switched in to achieve the minimum SWR; and
the detecting includes:
utilizing values of the switched-in elements to compute the antenna input impedance; and
measuring a length of the feedline between the automatic antenna tuner and an antenna feed point.

### Claim 9 (depends on 8)

The method of claim 8, wherein the detecting includes:
ascertaining a velocity factor of a transmission line.

### Claim 10 (depends on 9)

The method of claim 9, wherein the detecting includes:
ascertaining a frequency at which the antenna is driven.

### Claim 11 (depends on 8)

The method of claim 8, wherein:
the capacitive and inductive elements are switched into a circuit of the automatic antenna tuner utilizing switches; and
the detecting includes:
ascertaining switch states of the switches when the minimum SWR is achieved.

### Claim 12 (depends on 8)

The method of claim 8, further including:
displaying a calculated antenna input impedance.

### Claim 13 (depends on 12)

The method of claim 12, wherein the calculated antenna input impedance is displayed at the automatic antenna tuner, such that the antenna input impedance is detected and displayed remote from an antenna feed point.

### Claim 14 (depends on 8)

The method of claim 8, wherein the detecting of the antenna input impedance is performed at full transmitter power.

### Claim 15 (depends on 8)

The method of claim 8, wherein the detecting of the antenna input impedance is performed without using a low-power antenna analyzer.

### Claim 16

A method for remotely determining an antenna input impedance of an antenna by utilizing an automatic antenna tuner and deriving the antenna input impedance from characteristics of the automatic antenna tuner without utilizing an antenna analyzer, wherein the deriving utilizes:
values of capacitive and inductive elements switched in to the automatic antenna tuner to achieve a minimum standing wave ratio (SWR); and
a measured length of a feedline between the automatic antenna tuner and an antenna feed point for the antenna.

### Claim 17 (depends on 16)

The method of claim 16, wherein determining the antenna input impedance is performed at full transmitter power so as to minimize effects of any local high-power radio frequency (RF) energy that could swamp a measurement made in the determining and to detect effects of transmitter power on the antenna.