GPS Patch Antenna Considerations - MRC Components

GPS Patch Antenna Considerations 

Advanced Material On TECHnology

n Antenna Element 

Contents 

n Impedance and Resonant Frequency 

n Axial Ratio 

n Voltage Standing Wave Ratio (VSWR) 

n Bandwidth 

n Result of Measurement 

AMOTECH 2

Antenna Element 

n The antenna’s size and shape 

n compact size using ceramic material 

n RHCP(Right Hand Circular Polarization) patch 

Offset fed 

rectangular patch 

Slotted square 

patch 

Truncated corner 

square patch 

AMOTECH 3

Antenna Element 

n AMOTECH - GPS Patch Antenna 

25 

25 4 

2.6 

0.5 3 

¥Õ0.8 

n compact size : 25mm × 25mm × 4mm 

n excellent temperature stability 

n (silver plated) truncated corner square patch 

¥Õ3.0 

AMOTECH 4

Impedance and Resonant Frequency 

n An antenna’s impedance depends on many factors : 

n how it is constructed, 

n how it is fed, 

n and to some degree, the surrounding environment 

n Amicrostrip patch antenna placed in a plastic enclosure 

(radome), for example, can have its resonant frequency 

shifted downward by several MHz, depending on 

n the thickness of the radome 

n its dielectric constant 

n and the distance between the antenna face and inner radome. 

AMOTECH 5

Impedance and Resonant Frequency 

n Radome effect on resonant frequency 

n Final Assembly 

AMOTECH 

GPS Patch Antenna 

PCB 

Infinite Ground 

Sheild Can 


70by70 Ground 

SMA Type 

Connector 

Radome 

Double Sided 

Adhesive Tape 

n Assembly without radome 

Return Loss [dB] 

0 

-5 

-10 

-15 

-20 

-25 

-30 

Frequency shift caused by 

radome 

different environment 

n Patch on 70 by 70 ground 1540 1550 1560 1570 1580 1590 1600 1610 1620 1630 

Frequency [MHz] 

The final assembly obtains optimized 

operation over 1575.42MHz ± 3MHz 

Final Assembly 

Assembly without Radome 

Patch on 70 by 70 GND 

AMOTECH 6

n General description 

Axial Ratio 

n To be maximally sensitive to GPS signals, the ideal GPS 

antenna should be perfectly RHCP 

n The more elliptically polarized it is, the lower its RHCP 

sensitivity 

n The degree of ellipticity is given by the antenna’s axial ratio 

n Good GPS antennas have an axial ratio in the zenith direction 

of 3dB or better. 

n A measurement of the VSWR alone does not guarantee the 

antenna’s axial ratio performance. 

AMOTECH 7

n Measure the Axial Ratio 

n The GPS Patch antenna 

transmits at the desired 

frequency. 

n Rotates the linear 

polarization probe 

n AR = A - B , in dB 

B 

A 

Polarization 

ellipse 

¥è 

Axial Ratio 

n Measuring system in AMOTECH 

3 m 

Spectrum 

Analyzer 

rotate test 

probe 

7.26 m 

 

Signal 

Generator 

AMOTECH 8 

PC

Voltage Standing Wave Ratio 

n An important consideration is the antenna-receiver connection. 

This is achieved with a transmission line, usually a coaxial cable. 

n To maximize signal transfer from the antenna to the receiver, we 

must minimize power loss. 

n Power may be lost if the coupling between the antenna and the 

cable is imperfect and also within the cable itself. 

n To prevent power loss at the interface between the cable and the 

antenna, the impedance of the cable and the antenna must be the 

same. 

n The formula for relating mismatch loss to VSWR is: 

2 

⎛ ⎛ VSWR-1 ⎞ ⎞ 

Mismatch_Loss(dB)=10log⎜1- ⎜ ⎜ ⎟ ⎟ 

⎝VSWR+1⎠ ⎟ 

⎝ ⎠ 

AMOTECH 9

Bandwidth 

n Operating bandwidth is defined as frequency range 

satisfied following: 

n VSWR (< 2.0) or Return loss (< 10 dB) 

n Axial ratio (< 3.0 dB) 

n GPS patch antenna designed by AMOTECH satisfies 

all criteria over the operating frequency range of 

1575.42 MHz ± 3 MHz. 

AMOTECH 10

Result of Measurement 

n GPS Antenna installed on Infinite Ground 

Geometry of final assembly Axial Ratio 

AMOTECH 

GPS Patch Antenna 

PCB 


Sheild Can 

SMA Type 

Connector 

Radome 

Double Sided 

Adhesive Tape 

0 

1565 1570 1575 1580 1585 

AMOTECH 11 

Axialratio [dB] 

12 

10 

8 

6 

4 

2 

Frequency [MHz]


n GPS Antenna installed on Infinite Ground 

CH1 S22 LOG 5 dB/ REF 0 dB 

PRm 

Cor 

Avg 

10 

Hld 

MARKER 1 

1.57542 GHz 

Return Loss Smith chart 

3 4 

17 May 2000 13:18:10 

CENTER 1. 575 000 000 GHz SPAN . 200 000 000 GHz 

1 

2 

1:-29 . 366 dB 1. 575 420 000 GHz 

CH1 Markers 

BW : . 019597108 GHz 

cent : 1. 576044505 GHz 

Q: 80 . 422 

1_ loss : -29 . 366 dB 

CH1 S22 1 U FS 


AMOTECH 12 

PRm 

Cor 

Avg 

10 

Hld 

MARKER 1 

1.57542 GHz 

1 

2 

17 May 2000 13:18:39 

1: 53 .414 -824 . 22 m 122 .57 pF 1. 575 420 000 GHz 

4 

3 

CH1 Markers 

2: 54 .098 

-304 .69 m 

1. 57604 GHz 

3: 95 .941 

-4 . 6016 

1. 56624 GHz 

4: 40 .080 

-28 . 146 

1. 58584 GHz


n GPS Antenna installed on 70mm×70mm Ground 


PRm 

Cor 

Avg 

11 

Hld 

MARKER 1 

1.57604 GHz 


3 4 

2 

17 May 2000 13:20:18 


1 

1:-32 . 796 dB 1. 576 040 000 GHz 

CH1 Markers 

BW : . 025996459 GHz 

cent : 1. 575217893 GHz 

Q: 60 . 594 

1_ loss : -32 . 796 dB 



AMOTECH 13 

PRm 

Cor 

Avg 

11 

Hld 

MARKER 1 

1.57604 GHz 

1 

2 

17 May 2000 13:20:33 

1: 52 .219 -748 . 05 m 135 .00 pF 1. 576 040 000 GHz 

4 

3 

CH1 Markers 

2: 52 .740 

0. 3691 

1. 57521 GHz 

3: 77 .301 

31 . 188 

1. 56221 GHz 

4: 28 .793 

-13 . 788 

1. 58821 GHz


n GPS Antenna installed on 50mm×50mm Ground 


PRm 

Cor 

Avg 

16 

Hld 

MARKER 1 

1.57116 GHz 


3 4 

2 

1 

17 May 2000 13:24:44 

1:-23 . 136 dB 1. 571 160 000 GHz 

CH1 Markers 

BW : . 021365209 GHz 

cent : 1. 570216250 GHz 


Q: 73 . 494 

1_ loss : -23 . 136 dB 



AMOTECH 14 

PRm 

Cor 

Avg 

16 

Hld 

MARKER 1 

1.57116 GHz 

1 

2 

17 May 2000 13:25:01 

1: 50 .771 -6 . 9941 14 .483 pF 1. 571 160 000 GHz 

4 

3 

CH1 Markers 

2: 51 .322 

-6 . 7988 

1. 57021 GHz 

3: 96 .062 

3. 5078 

1. 55953 GHz 

4: 33 .186 

-21 . 324 

1. 58089 GHz


n GPS Antenna without Ground 


PRm 

Cor 

MARKER 1 

1.57004 GHz 


1 

3 4 

2 

17 May 2000 13:27:44 

1:-13 . 217 dB 1. 570 040 000 GHz 

CH1 Markers 

BW : . 009909594 GHz 

cent : 1. 569743510 GHz 


Q: 158 . 41 

1_ loss : -13 . 217 dB 



AMOTECH 15 

PRm 

Cor 

MARKER 1 

1.57004 GHz 

2 

1 

3 

17 May 2000 13:27:57 

1: 37 .344 14 .777 1. 4980 nH 1. 570 040 000 GHz 

4 

CH1 Markers 

2: 35 .217 

11 . 643 

1. 56961 GHz 

3: 38 .666 

-26 . 533 

1. 56465 GHz 

4: 96 .687 

1. 4766 

1. 57457 GHz


n GPS Antenna without Radome on Infinite Ground 

Geometry of assembly without radome 


Axial Ratio 

0 

1570 1575 1580 1585 1590 1595 

AMOTECH 16 


12 

10 

8 

6 

4 

2 

Frequency [MHz]


n GPS Antenna without Radome on Infinite Ground 


PRm 

Cor 

Avg 

10 

Hld 

MARKER 1 

1.5815 GHz 


3 4 

17 May 2000 14:18:22 


1 

2 

1:-24 . 581 dB 1. 581 500 000 GHz 

CH1 Markers 

BW : . 021975607 GHz 

cent : 1. 583006891 GHz 

Q: 72 . 035 

1_ loss : -24 . 581 dB 



AMOTECH 17 

PRm 

Cor 

Avg 

10 

Hld 

MARKER 1 

1.5815 GHz 

1 

2 

17 May 2000 14:18:50 

1: 52 .887 5. 3477 538 . 16 pH 1. 581 500 000 GHz 

4 

3 

CH1 Markers 

2: 55 .631 

6. 2891 

1. 58300 GHz 

3: 95 .930 

4. 7422 

1. 57201 GHz 

4: 35 .635 

-24 . 199 

1. 59399 GHz


n GPS Antenna without double sided adhesive tape 


PRm 

Cor 

Avg 

11 

Hld 

MARKER 1 

1.57726 GHz 

Return Loss 

3 4 


1 

2 

17 May 2000 14:22:33 

1:-24 . 604 dB 1. 577 260 000 GHz 

CH1 Markers 

BW : . 020971366 GHz 

cent : 1. 578946411 GHz 

Q: 75 . 291 

1_ loss : -24 . 604 dB 


Smith Chart 


AMOTECH 18 

PRm 

Cor 

Avg 

11 

Hld 

MARKER 1 

1.57726 GHz 

4 

1 

2 3 

17 May 2000 14:22:55 

1: 54 .336 4. 3496 438 . 90 pH 1. 577 260 000 GHz 

CH1 Markers 

2: 56 .379 

5. 1270 

1. 57894 GHz 

3: 95 .063 

9. 0820 

1. 56846 GHz 

4: 34 .949 

-23 . 455 

1. 58943 GHz


n GPS Patch Antenna on 70 by 70 AMOTECH Test Jig 

Geometry of patch antenna 

70by70 Ground 

Axial Ratio 

0 

1585 1590 1595 1600 1605 1610 1615 

AMOTECH 19 


12 

10 

8 

6 

4 

2 

Frequency [MHz]


n GPS Patch Antenna on 70 by 70 AMOTECH Test Jig 


PRm 

Cor 

Avg 

16 

Hld 

MARKER 1 

1.60186 GHz 

Return Loss 

17 May 2000 13:31:03 

1:-24 . 491 dB 1. 601 860 000 GHz 

3 4 


1 

2 

CH1 Markers 

BW : . 023749519 GHz 

cent : 1. 602020404 GHz 

Q: 67 . 455 

1_ loss : -24 . 491 dB 


Smith Chart 


AMOTECH 20 

PRm 

Cor 

Avg 

16 

Hld 

MARKER 1 

1.60186 GHz 

1 

2 

17 May 2000 13:31:28 

1: 55 .262 -3 . 4277 28 .986 pF 1. 601 860 000 GHz 

4 

3 

CH1 Markers 

2: 55 .158 

-3 . 5430 

1. 60202 GHz 

3: 86 .254 

24 . 543 

1. 59014 GHz 

4: 32 .359 

-20 . 197 

1. 61389 GHz

GPS Patch Antenna Considerations - MRC Components

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