SIMULATION RESULTS

Gain = 3.7 dBi

SWR = 3.1

Impedance = 155 - j 8.18 ohms

HIGH IMPEDANCE/SWR - WILL NOT GIVE GOOD RESULTS WITHOUT IMPEDANCE MATCHING

IMPEDANCE MATCHING BY "TRANSMISSION LINE+CAPACITOR" TECHNIQUE

Using Smith Chart:

Capacitor to be inserted = 3.8 pF (4 pF will do)

Coax length (from antenna) where Capacitor should be inserted = n x λ/2 + 80.8mm Coax of VF=0.85,

where n is any integer.

ACTUAL IMPLEMENTATION

This is a two step SWR improvement process.

STEP (1): Trim RG6 feed coax at the pigtail till value of R becomes close to 50 ohms.

STEP (2): Add a capacitor in series with core wire of coax to nullify +X component of impedance. Location of capacitor: between pigtail and filter.

By doing the STEP (1) ONLY, impedance changes from 155-j8.2 (TP1 on Smith Chart) to 50+j38.3 (TP2 on Smith Chart). This results in changing SWR from 3.1 to 2.1, which gives a big improvement in performance.

Doing STEP (2) after doing STEP (1) results in impedance becoming 50+j0, and SWR=1, a perfect match.

Note: Unfortunately I have miss-calibrated my antenna analyzer using a 75 ohm resistor. Now it is not resetting to factory calibration of 50 ohms. I have ordered a 50 ohm dummy load resistor. Waiting for delivery to re-calibrate the Analyzer with 50 ohms load. I therefore could not actually do the impedance matching. Following only show the steps I will do when my Analyzer is re-calibrated.

Gain = 3.7 dBi

SWR = 3.1

Impedance = 155 - j 8.18 ohms

HIGH IMPEDANCE/SWR - WILL NOT GIVE GOOD RESULTS WITHOUT IMPEDANCE MATCHING

IMPEDANCE MATCHING BY "TRANSMISSION LINE+CAPACITOR" TECHNIQUE

Using Smith Chart:

Capacitor to be inserted = 3.8 pF (4 pF will do)

Coax length (from antenna) where Capacitor should be inserted = n x λ/2 + 80.8mm Coax of VF=0.85,

where n is any integer.

ACTUAL IMPLEMENTATION

This is a two step SWR improvement process.

STEP (1): Trim RG6 feed coax at the pigtail till value of R becomes close to 50 ohms.

STEP (2): Add a capacitor in series with core wire of coax to nullify +X component of impedance. Location of capacitor: between pigtail and filter.

By doing the STEP (1) ONLY, impedance changes from 155-j8.2 (TP1 on Smith Chart) to 50+j38.3 (TP2 on Smith Chart). This results in changing SWR from 3.1 to 2.1, which gives a big improvement in performance.

Doing STEP (2) after doing STEP (1) results in impedance becoming 50+j0, and SWR=1, a perfect match.

Note: Unfortunately I have miss-calibrated my antenna analyzer using a 75 ohm resistor. Now it is not resetting to factory calibration of 50 ohms. I have ordered a 50 ohm dummy load resistor. Waiting for delivery to re-calibrate the Analyzer with 50 ohms load. I therefore could not actually do the impedance matching. Following only show the steps I will do when my Analyzer is re-calibrated.

Last edited: Mar 21, 2017