SPE-16-08-044/A/WY

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7. PCB Footprint & Application Recommendations

Traditional single-pin GPS patch antennas generate circular polarization by creating two

orthogonal field modes within the patch, one lagging in phase by 90° compared to the other.

These orthogonal modes are created by a number of means, including chamfering the patch and

offsetting the feed (pin) location. This function provides an excellent axial ratio (a measure of

circular polarization purity), but the axial ratio bandwidth tends to be lower than the impedance

or efficiency bandwidth of the antenna.

Dual-feed patch antennas, on the other hand, create circular polarization through what is perhaps

a more straightforward approach. Rather than using the aforementioned techniques to create the

required orthogonal modes, two separate feeds are instead used. Each feed creates a mode, and

the feeds are placed such that the modes are orthogonal. A 90° phase shift is applied externally

to one feed to fully realize circular polarization.

The advantage of this dual-feed structure is that the axial ratio bandwidth tends to be much

wider than for a comparable single-feed patch. This can yield improvements in interference and

multipath rejection for GLONASS and Beidou, and be more resilient to detuning the axial ratio.

The GPDF.47.A dual-band L1+L2 dual-feed patch antennas are created to realize these benefits.

However, there are a few key items to control when it comes to verifying the implementation of

this antenna:

1. Ground plane: the antenna needs to be placed on at least a 50*50mm ground plane.

2. Placement: center the antenna on the ground plane to minimizing detuning.

3. Feeding: the antenna uses four feed pins, two for each band (L1 and L2). Each band pair

should be fed with a hybrid coupler (Anaren XC1400P-03S) as shown below.

4. Transmission Lines: all feed lines need to be 50-ohm transmission lines. Microstrip or

Grounded Coplanar Waveguide (CPW-Ground) should be used.