Formula To Calculate Polarisation Of An Antenna

Calculate the polarisation characteristics of your antenna system with precision. Understand how E-plane and H-plane components affect your signal propagation.

Module A: Introduction & Importance of Antenna Polarisation

Antenna polarisation refers to the orientation of the electric field vector of the radio wave with respect to the Earth’s surface. This fundamental property determines how effectively an antenna can transmit or receive signals in a given orientation, making it crucial for wireless communication systems, radar applications, and satellite communications.

The polarisation of an antenna can be linear (vertical or horizontal), circular (right-hand or left-hand), or elliptical. Understanding and calculating antenna polarisation is essential because:

• Signal Strength Optimization: Proper polarisation matching between transmitting and receiving antennas maximizes signal strength and minimizes losses.
• Interference Reduction: Different polarisations can be used to separate signals in the same frequency band, reducing interference in crowded RF environments.
• Regulatory Compliance: Many wireless standards specify polarisation requirements that must be met for certification.
• System Performance: Polarisation affects key performance metrics like gain, directivity, and radiation pattern.

In modern wireless systems, polarisation diversity techniques are often employed to improve reliability and data throughput. For example, MIMO (Multiple-Input Multiple-Output) systems frequently use dual-polarised antennas to create multiple independent communication channels within the same frequency band.

Figure 1: Visual representation of different antenna polarisation types and their electric field orientations

Module B: How to Use This Polarisation Calculator

Our antenna polarisation calculator provides precise calculations for various polarisation parameters. Follow these steps to get accurate results:

1. Enter Operating Frequency:
   • Input your antenna’s operating frequency in MHz (e.g., 2400 for 2.4GHz Wi-Fi)
   • Frequency affects wavelength, which influences polarisation characteristics
2. Specify E-Plane and H-Plane Amplitudes:
   • E-Plane (Electric field) amplitude in dB relative to the main lobe
   • H-Plane (Magnetic field) amplitude in dB relative to the main lobe
   • These values typically come from antenna pattern measurements
3. Set Phase Difference:
   • Enter the phase difference between E and H components in degrees (0-360°)
   • 0° or 180° typically indicates linear polarisation
   • 90° or 270° with equal amplitudes indicates circular polarisation
4. Select Polarisation Type:
   • Choose between Linear, Circular, or Elliptical polarisation
   • The calculator will verify if your inputs match the selected type
5. Review Results:
   • Polarisation Ratio: Difference between co-polar and cross-polar components
   • Axial Ratio: Measure of circular polarisation purity (1 = perfect circular)
   • Polarisation Efficiency: Percentage of power in the desired polarisation
   • Polarisation Mismatch Loss: Signal loss due to polarisation mismatch
6. Analyze the Polarisation Chart:
   • Visual representation of your polarisation characteristics
   • Shows the relationship between E and H plane components
   • Helps identify potential issues in your antenna design

Figure 2: Example of calculator interface with sample inputs and resulting polarisation visualization

Module C: Formula & Methodology Behind the Calculator

The calculator implements several key equations from antenna theory to determine polarisation characteristics. Here’s the mathematical foundation:

1. Polarisation Ratio (PR)

The polarisation ratio compares the power in the co-polarised component to the cross-polarised component:

PR(dB) = 10 × log₁₀(P_co / P_cross)

Where P_co is the power in the desired polarisation and P_cross is the power in the orthogonal polarisation.

2. Axial Ratio (AR)

For elliptical and circular polarisation, the axial ratio describes the relationship between the major and minor axes of the polarisation ellipse:

AR(dB) = 20 × log₁₀((E_major + E_minor) / (E_major – E_minor))

Where E_major and E_minor are the amplitudes of the major and minor axes respectively. For perfect circular polarisation, AR = 1 (0 dB).

3. Polarisation Efficiency (η)

This metric indicates what percentage of the total radiated power is in the desired polarisation:

η = (P_co / (P_co + P_cross)) × 100%

4. Polarisation Mismatch Loss (PML)

The loss that occurs when the polarisation of the receiving antenna doesn’t perfectly match the incoming wave:

PML(dB) = -10 × log₁₀(cos²(ψ/2))

Where ψ is the angle between the polarisation vectors of the transmitting and receiving antennas.

5. Stokes Parameters

For complete polarisation description, we use Stokes parameters:

S₀ = E₀²
S₁ = (E_a² – E_b²)
S₂ = 2E_aE_b cos(δ)
S₃ = 2E_aE_b sin(δ)

Where E_a and E_b are orthogonal field components and δ is their phase difference.

The calculator combines these equations with your input parameters to provide comprehensive polarisation analysis. For circular and elliptical polarisation, we additionally calculate the tilt angle of the polarisation ellipse using:

τ = (1/2) × arctan(S₂ / S₁)

For more detailed information on antenna polarisation theory, consult the ITU-R Recommendation RS.1008 which provides comprehensive guidelines on antenna measurements including polarisation characteristics.

Module D: Real-World Examples & Case Studies

Understanding how polarisation calculations apply to real-world scenarios helps appreciate their practical significance. Here are three detailed case studies:

Case Study 1: Wi-Fi Router Antenna Optimisation

Scenario: A network engineer is designing a dual-band Wi-Fi router (2.4GHz and 5GHz) for optimal coverage in an office environment with many reflective surfaces.

Parameters:

• Frequency: 2412 MHz (2.4GHz band)
• E-plane amplitude: 0 dB (reference)
• H-plane amplitude: -0.5 dB
• Phase difference: 85°
• Polarisation type: Elliptical

Calculator Results:

• Polarisation Ratio: 3.2 dB
• Axial Ratio: 2.1 dB
• Polarisation Efficiency: 87.4%
• Polarisation Mismatch Loss: 0.6 dB

Analysis: The slightly elliptical polarisation helps mitigate multipath fading in the reflective office environment. The 0.6 dB mismatch loss is acceptable and provides better performance than pure linear polarisation in this scenario.

Implementation: The engineer chooses to maintain this polarisation configuration, as the slight efficiency loss is outweighed by the improved resistance to multipath interference.

Case Study 2: Satellite Communication Link

Scenario: A satellite ground station needs to communicate with a geostationary satellite using circular polarisation to maintain consistent signal strength regardless of satellite orientation.

Parameters:

• Frequency: 11200 MHz (Ku band)
• E-plane amplitude: 0 dB
• H-plane amplitude: 0 dB
• Phase difference: 90°
• Polarisation type: Circular

Calculator Results:

• Polarisation Ratio: ∞ dB (theoretical)
• Axial Ratio: 0 dB (perfect circular)
• Polarisation Efficiency: 100%
• Polarisation Mismatch Loss: 0 dB (with matching antenna)

Analysis: The perfect circular polarisation (axial ratio = 0 dB) ensures maximum power transfer regardless of the relative orientation between the ground station and satellite antennas. This is crucial for satellite communications where the polarisation of the received signal may vary.

Implementation: The ground station uses a helical antenna designed for circular polarisation, achieving the calculated perfect match and eliminating polarisation fading.

Case Study 3: 5G MIMO Base Station

Scenario: A telecom operator is deploying a 5G base station using dual-polarised antennas for MIMO operation in an urban environment.

Parameters (for each polarisation):

• Frequency: 3500 MHz (mid-band 5G)
• Polarisation 1: Linear Vertical (E-plane: 0 dB, H-plane: -20 dB, Phase: 0°)
• Polarisation 2: Linear Horizontal (E-plane: -20 dB, H-plane: 0 dB, Phase: 0°)
• Cross-polarisation isolation: 25 dB

Calculator Results (for each polarisation):

• Polarisation Ratio: 20 dB
• Axial Ratio: N/A (linear polarisation)
• Polarisation Efficiency: 99.0%
• Polarisation Mismatch Loss: 0.04 dB (with matching antenna)

Analysis: The high polarisation ratio (20 dB) ensures excellent isolation between the two polarisations, which is critical for MIMO operation. The minimal mismatch loss (0.04 dB) indicates nearly perfect polarisation matching.

Implementation: The base station uses cross-polarised antennas with ±45° orientation to achieve both polarisation diversity and spatial diversity, significantly improving data throughput in the urban environment.

These case studies demonstrate how polarisation calculations directly impact real-world wireless system performance. The calculator helps engineers make informed decisions about antenna selection and configuration.

Module E: Comparative Data & Statistics

Understanding how different polarisation configurations perform across various applications helps in making optimal design choices. The following tables present comparative data:

Table 1: Polarisation Characteristics by Application

Application	Typical Frequency	Common Polarisation	Typical Axial Ratio (dB)	Polarisation Efficiency	Mismatch Loss (dB)
Wi-Fi (2.4GHz)	2400-2483 MHz	Linear or Elliptical	1.5-3.0	85-95%	0.2-0.7
Wi-Fi (5GHz)	5150-5850 MHz	Linear or Dual	1.0-2.5	90-97%	0.1-0.4
4G LTE	700-2600 MHz	±45° Linear	N/A	95-99%	0.02-0.2
5G mmWave	24-40 GHz	Dual Linear or Circular	0.5-2.0	92-99%	0.05-0.3
Satellite TV (DBS)	12.2-12.7 GHz	Circular	0.1-0.5	98-99.9%	0.004-0.04
GPS	1575.42 MHz	Right-hand Circular	0.1-0.3	99.5-99.9%	0.002-0.02
Radar Systems	1-40 GHz	Linear or Circular	0.5-3.0	80-98%	0.1-0.8
Amateur Radio	144-148 MHz	Linear or Circular	1.0-4.0	75-95%	0.2-1.0

Table 2: Polarisation Mismatch Loss Impact on System Performance

Mismatch Loss (dB)	Power Loss (%)	Impact on Wi-Fi (2.4GHz)	Impact on 4G LTE	Impact on Satellite	Impact on Radar
0.1	2.3%	Minimal (≈1% throughput reduction)	Negligible	Negligible	Minimal range reduction
0.5	10.9%	Noticeable (≈5-8% throughput reduction)	Minor capacity reduction	Small increase in BER	Moderate range reduction
1.0	20.8%	Significant (≈15-20% throughput reduction)	Noticeable capacity reduction	Clear BER degradation	Substantial range reduction
2.0	36.9%	Severe (≈30-40% throughput reduction)	Major capacity reduction	Significant BER increase	Large range reduction
3.0	50.1%	Critical (≈50%+ throughput reduction)	Severe capacity loss	Unusable link in many cases	Extreme range reduction
5.0	68.4%	Connection likely lost	Complete capacity loss	Link failure	System may not function

The data clearly shows that even small polarisation mismatch losses can significantly impact system performance, particularly in high-frequency applications like 5G and satellite communications. Maintaining proper polarisation alignment is crucial for optimal wireless system operation.

For more comprehensive statistical data on antenna polarisation performance, refer to the NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management which includes extensive measurements and standards for various wireless applications.

Module F: Expert Tips for Optimal Antenna Polarisation

Based on decades of RF engineering experience, here are professional tips to optimize your antenna polarisation:

General Polarisation Optimization Tips

1. Match Polarisation Types:
   • Always ensure transmitting and receiving antennas use the same polarisation type
   • For linear polarisation, align the elements precisely (vertical to vertical, horizontal to horizontal)
   • For circular polarisation, use the same rotation direction (both right-hand or both left-hand)
2. Consider Environmental Factors:
   • Reflections can change polarisation – use circular or elliptical polarisation in multipath environments
   • Vertical polarisation generally performs better for ground wave propagation
   • Horizontal polarisation may be better for sky wave (ionospheric) propagation
3. Optimize for Your Frequency:
   • Below 1 GHz: Linear polarisation often suffices
   • 1-6 GHz: Consider dual-polarisation for MIMO systems
   • Above 6 GHz: Circular or elliptical polarisation helps with rain fade and multipath
4. Measure and Verify:
   • Use a network analyzer or antenna range to measure actual polarisation characteristics
   • Verify axial ratio for circular/elliptical antennas (should be < 3 dB for good performance)
   • Check cross-polarisation discrimination (> 20 dB is excellent for linear polarisation)
5. Account for Mechanical Tolerances:
   • Even small mechanical misalignments can degrade polarisation performance
   • Use precise mounting hardware and alignment procedures
   • Consider wind loading effects on outdoor installations

Advanced Techniques for Professional Applications

• Polarisation Diversity:
  • Use two antennas with orthogonal polarisations to combat fading
  • Common in Wi-Fi access points and cellular base stations
  • Can provide 2-5 dB diversity gain in multipath environments
• Adaptive Polarisation:
  • Advanced systems can dynamically adjust polarisation for optimal performance
  • Requires sophisticated signal processing and antenna designs
  • Used in some military and satellite communication systems
• Polarisation Reconfigurable Antennas:
  • Emerging technology allows electronic switching between polarisation states
  • Can adapt to changing propagation conditions in real-time
  • Useful for cognitive radio and software-defined radio applications
• Cross-Polarisation Interference Cancellation:
  • Advanced receivers can suppress cross-polarised interference
  • Improves capacity in polarisation-diverse systems
  • Used in modern cellular networks and satellite communications
• Polarisation Shaping:
  • Design antennas with specific polarisation patterns for particular applications
  • Example: Elliptical polarisation with specific axial ratio for rain fade mitigation
  • Requires sophisticated electromagnetic simulation tools

Common Mistakes to Avoid

1. Assuming Perfect Polarisation:
   • Real antennas always have some imperfections
   • Always account for manufacturing tolerances and environmental effects
2. Ignoring Cross-Polarisation:
   • Even “linear” antennas have some cross-polarised components
   • Cross-polarisation can cause interference in diversity systems
3. Overlooking Feed Line Effects:
   • Cables and connectors can affect polarisation, especially at higher frequencies
   • Use proper cable routing and high-quality connectors
4. Neglecting Frequency Dependence:
   • Polarisation characteristics can vary across the antenna’s frequency range
   • Always check performance at both ends of your operating band
5. Improper Measurement Techniques:
   • Polarisation measurements require careful setup and calibration
   • Use proper anechoic chambers or far-field ranges for accurate results

For additional professional guidance, consult the IEEE Antennas and Propagation Society resources, which provide extensive research and standards on antenna polarisation techniques.

Module G: Interactive FAQ About Antenna Polarisation

What’s the fundamental difference between linear and circular polarisation?

Linear polarisation occurs when the electric field vector remains in a fixed plane as the wave propagates. Circular polarisation happens when the electric field vector rotates in a circular motion as the wave travels, completing one full rotation per wavelength.

Key differences:

• Propagation: Linear polarisation is more susceptible to orientation issues and multipath fading. Circular polarisation maintains consistent reception regardless of antenna orientation (within limits) and handles multipath better.
• Implementation: Linear polarisation is simpler to implement with basic dipole or patch antennas. Circular polarisation typically requires more complex antenna designs like helices or patches with specific feed arrangements.
• Applications: Linear is common in point-to-point links where antenna orientation can be controlled. Circular is preferred in mobile applications, satellite communications, and environments with many reflections.
• Polarisation Mismatch: Linear polarisation experiences complete signal loss (theoretically infinite attenuation) when crossed at 90°. Circular polarisation maintains some reception even with orientation mismatches.

In practice, most “circular” polarisation is actually elliptical, with axial ratios typically between 0.5-2 dB for good performance.

How does polarisation affect Wi-Fi performance in home networks?

Polarisation plays a significant but often overlooked role in Wi-Fi performance:

Single-Antenna Devices:

• Most Wi-Fi routers use vertical polarisation by default
• Laptops and phones typically have vertical or omnidirectional antennas
• Mismatch can occur if a device is laid flat (changing its effective polarisation)

Dual-Band Routers:

• 2.4GHz often uses vertical polarisation
• 5GHz may use different polarisations for different streams in MU-MIMO
• Some high-end routers use dual-polarised antennas (±45°) for diversity

Performance Impacts:

• Signal Strength: Proper polarisation matching can improve received signal strength by 3-10 dB
• Data Rates: Good polarisation alignment enables higher MCS (Modulation and Coding Scheme) indices
• Coverage: Optimal polarisation can extend range by 10-30% in typical home environments
• Interference: Cross-polarised antennas can reduce interference from neighboring networks

Practical Tips:

• For best performance, keep router antennas vertical (perpendicular to the floor)
• If using multiple routers (mesh networks), ensure consistent polarisation
• For devices with internal antennas (like smartphones), orientation matters – try different positions if signal is weak
• In multi-story homes, consider that polarisation may change as signals reflect off floors

Modern Wi-Fi 6 and 6E systems often use polarisation diversity techniques to automatically optimize performance, but proper initial setup still matters for best results.

Why do some antennas use dual polarisation (both horizontal and vertical)?

Dual-polarised antennas offer several significant advantages in modern wireless systems:

Primary Benefits:

1. Capacity Doubling (MIMO):
   • Allows two independent data streams in the same frequency channel
   • Essential for 4G LTE Advanced and 5G NR systems
   • Can theoretically double spectral efficiency
2. Polarisation Diversity:
   • Provides two reception paths with different fading characteristics
   • Improves reliability in multipath environments
   • Can provide 2-5 dB diversity gain without additional spectrum
3. Interference Mitigation:
   • Allows separation of co-channel signals by polarisation
   • Useful in dense urban deployments
   • Can improve SINR (Signal to Interference plus Noise Ratio)
4. Flexible Deployment:
   • Can serve both vertical and horizontal polarised clients
   • Useful in environments with mixed device orientations
   • Simplifies network planning

Technical Implementation:

• Common configurations use ±45° slant polarisation
• Requires careful design to maintain >20 dB isolation between polarisations
• Often implemented with cross-dipole or patch antenna arrays

Challenges:

• More complex feed networks required
• Potential for increased cross-polarisation interference if not properly designed
• Higher cost than single-polarised antennas
• Requires more sophisticated calibration procedures

Common Applications:

• Cellular base stations (4G LTE, 5G NR)
• Wi-Fi access points (802.11n/ac/ax)
• Point-to-point microwave links
• Radar systems
• Satellite communication ground stations

Dual-polarised antennas have become standard in most modern wireless systems due to their ability to significantly improve spectral efficiency and system reliability.

How does rain affect circularly polarised signals compared to linearly polarised?

Rain fade affects circular and linear polarisation differently due to the shape and orientation of raindrops:

Physical Mechanisms:

• Raindrops are approximately spherical at smaller sizes (<1mm) but become oblate (flattened) as they grow
• Oblate raindrops have different scattering properties for different polarisations
• The effect becomes significant at frequencies above ~10 GHz

Linear Polarisation Rain Fade:

• Vertical polarisation experiences less attenuation than horizontal
• At 20 GHz, horizontal polarisation may have 2-3 dB more loss than vertical
• At 40 GHz, the difference can reach 4-6 dB
• This is due to the preferred orientation of falling raindrops

Circular Polarisation Rain Fade:

• Circular polarisation experiences intermediate attenuation between vertical and horizontal linear
• At 20 GHz, typically 1-1.5 dB more loss than vertical linear
• At 40 GHz, typically 2-3 dB more loss than vertical linear
• The effect is less polarisation-dependent than linear

Quantitative Comparison (at 30 GHz, heavy rain 50 mm/h):

Polarisation Type	Attenuation (dB/km)	Relative Performance	Typical Applications
Vertical Linear	12.5	Best	Point-to-point microwave, some satellite
Circular (RH or LH)	13.8	Intermediate	Satellite communications, mobile
Horizontal Linear	15.2	Worst	Rarely used at high frequencies

Additional Considerations:

• Circular polarisation can help mitigate depolarisation effects from rain
• Dual-polarised systems (both circular senses) can provide diversity against rain fade
• At frequencies below 10 GHz, rain fade differences between polarisations are negligible
• Ice crystals in clouds can also cause differential attenuation by polarisation

Practical Implications:

• For terrestrial microwave links above 10 GHz, vertical polarisation is often preferred
• Satellite systems often use circular polarisation despite slightly higher rain fade, due to other advantages
• System designers must account for polarisation-specific rain fade in link budgets
• Adaptive polarisation systems can switch between types based on weather conditions

For detailed rain attenuation models, refer to the ITU-R Recommendation P.838 which provides specific attenuation coefficients for different polarisations and frequencies.

What’s the relationship between antenna polarisation and gain?

Antenna polarisation and gain are related but independent properties that together determine overall performance:

Fundamental Definitions:

• Gain: Measures how effectively an antenna directs radio frequency energy in a particular direction (compared to an isotropic radiator)
• Polarisation: Describes the orientation of the electric field vector as the radio wave propagates

Key Relationships:

1. Polarisation Mismatch Loss:
   • Even high-gain antennas will perform poorly if polarisation is mismatched
   • The effective gain is reduced by the polarisation mismatch loss
   • Formula: G_effective = G_actual – PML (where PML is polarisation mismatch loss in dB)
2. Pattern Distortion:
   • Polarisation imperfections can distort the radiation pattern
   • This may reduce the actual realised gain in certain directions
   • Particularly noticeable in high-gain directional antennas
3. Cross-Polarisation Components:
   • All real antennas have some cross-polarised components
   • These reduce the “pure” co-polarised gain
   • Cross-polarisation discrimination (XPD) quantifies this effect
4. Frequency Dependence:
   • Both gain and polarisation characteristics vary with frequency
   • Wideband antennas may have different polarisation properties at different frequencies
   • This can lead to gain variations across the operating band

Practical Example:

Consider a 20 dBi parabolic antenna with the following polarisation characteristics:

• Co-polarised gain: 20 dBi
• Cross-polarised level: -20 dB relative to co-polarised
• Polarisation mismatch with receiver: 3 dB

In this case:

• Effective co-polarised gain: 20 dBi – 3 dB = 17 dBi
• Cross-polarised interference: 20 dBi – 20 dB = 0 dBi (isotropic level)
• Actual realised gain in the desired polarisation is reduced by the mismatch

Design Considerations:

• High-gain antennas require more precise polarisation alignment
• A 1 dB polarisation mismatch on a 30 dBi antenna represents more absolute power loss than on a 10 dBi antenna
• Polarisation purity becomes more critical as gain increases

Measurement Challenges:

• Accurate gain measurement requires proper polarisation alignment
• Polarisation mismatch in test setups can lead to incorrect gain readings
• Specialized test ranges can measure gain by polarisation component

When selecting antennas, consider both gain and polarisation characteristics together. A slightly lower gain antenna with better polarisation match may outperform a higher gain antenna with poor polarisation alignment.

Can I improve my existing antenna’s polarisation performance?

Yes, there are several practical ways to improve an existing antenna’s polarisation performance:

Mechanical Adjustments:

1. Precise Orientation:
   • Ensure antenna is perfectly aligned with desired polarisation
   • Use a bubble level and protractor for accurate positioning
   • For linear polarisation, verify alignment with a known reference
2. Mounting Stability:
   • Use rigid mounts to prevent wind-induced movement
   • Check for sagging in long cable runs that might twist the antenna
   • Consider guy wires for large outdoor antennas
3. Balun/Feed System:
   • Ensure proper balun is used for balanced antennas
   • Check feed line connections for corrosion or damage
   • Verify impedance match throughout the system

Electrical Improvements:

4. Polarisation Filtering:
   • Add a polarisation filter to suppress unwanted components
   • Useful for reducing cross-polarised interference
   • Can improve axial ratio in circular polarised systems
5. Phasing Networks:
   • For dual-polarised antennas, adjust phasing to optimize polarisation
   • Can convert linear to circular polarisation with proper phase shift
   • Requires precise component values and layout
6. Ground Plane Optimization:
   • Improve ground plane for better polarisation purity
   • Ensure proper counterpoise for vertical antennas
   • Consider artificial ground planes for portable installations

System-Level Solutions:

7. Diversity Reception:
   • Use two antennas with orthogonal polarisations
   • Combine signals for improved reliability
   • Effective against multipath fading
8. Adaptive Polarisation:
   • Advanced systems can electronically adjust polarisation
   • Requires specialized hardware and software
   • Used in some military and satellite systems
9. Polarisation Tracking:
   • Systems can automatically adjust to maintain optimal polarisation
   • Useful for mobile or satellite communications
   • Implements feedback loops to maximize received signal

Measurement and Verification:

• Use a spectrum analyzer with tracking generator to measure polarisation
• For circular polarisation, measure axial ratio across the operating band
• Check cross-polarisation discrimination (XPD) for linear systems
• Field strength meters with polarisation selectivity can help optimize installation

When to Consider Replacement:

• If mechanical adjustments don’t achieve required polarisation purity
• When the antenna has physical damage affecting performance
• For applications requiring precision polarisation (e.g., satellite communications)
• When upgrading to newer technologies that need different polarisation characteristics

For most consumer applications, proper installation and orientation provide the majority of potential polarisation improvements. Professional systems may benefit from more advanced techniques like adaptive polarisation or diversity reception.

How does polarisation affect GPS and GNSS receiver performance?

Polarisation plays a crucial role in GPS and GNSS (Global Navigation Satellite System) performance due to the unique propagation characteristics of satellite signals:

Satellite Signal Polarisation:

• GPS L1 signal: Right-hand circular polarisation (RHCP)
• GPS L2 signal: RHCP
• GLONASS: RHCP for all signals
• Galileo: RHCP for E1, E5 bands
• BeiDou: RHCP for B1, B2, B3 bands

Receiver Antenna Requirements:

• Must match the satellite signal polarisation (RHCP)
• Typical axial ratios for GNSS antennas: 0.5-2 dB
• Polarisation mismatch > 3 dB can significantly degrade performance

Performance Impacts:

Axial Ratio (dB)	Polarisation Efficiency	Signal Loss (dB)	Position Accuracy Impact	TTFF Impact
0 (perfect)	100%	0	None	None
1	98.8%	0.05	<1%	<1%
2	95.5%	0.2	1-2%	1-3%
3	89.1%	0.5	3-5%	3-8%
6	60.3%	2.2	10-20%	15-30%
10	25.1%	6.0	>50%	>100%

Multipath Mitigation:

• RHCP signals reflected from surfaces become LHCP
• RHCP antennas naturally reject these reflected LHCP signals
• This provides inherent multipath rejection (typically 10-20 dB)
• Critical for accurate positioning in urban canyons

Special Considerations:

• Ionospheric Effects:
  • Faraday rotation can change polarisation during ionospheric propagation
  • More significant at lower frequencies (L-band) and during geomagnetic storms
  • Can cause up to 108° rotation at L1 frequency during extreme events
• Antennas for High-Precision Applications:
  • Survey-grade antennas have axial ratios < 1 dB
  • Often use choke ring designs to reduce multipath
  • May include multiple elements for different frequency bands
• Portable Device Challenges:
  • Smartphone antennas often have poorer polarisation purity
  • Axial ratios of 3-6 dB are common in mobile devices
  • Device orientation affects effective polarisation

Practical Tips for GNSS Antenna Installation:

1. Ensure unobstructed view of the sky (especially low elevation angles)
2. Mount antenna on a stable, non-reflective surface
3. Avoid locations near metal structures that could cause multipath
4. Use high-quality low-loss cable to preserve signal integrity
5. For permanent installations, perform a site survey to check for multipath
6. Consider using a ground plane to improve polarisation purity

The circular polarisation used in GNSS systems provides excellent resistance to multipath interference and allows reliable reception regardless of receiver orientation, which is crucial for mobile navigation applications.