
Guides


 Evaluating EMF Compliance  Part 1: A Guide to FarField RF Exposure Assessments
 Design Guidelines for Skeleton Slot Antennas: A SimulationDriven Approach
 Simplified Modeling for Microstrip Antennas on Ungrounded Dielectric Substrates: Accuracy Meets Simplicity
 Fast Modeling of a Monopole Supported by a Broadcast Tower
 Linking LogPeriodic Antenna Elements Using Transmission Lines
 Wave Matching Coefficient: Defining the Practical NearFar Field Boundary
 ANSOF Mastery: Adding Elevated Radials Quickly
 How to Merge Projects
 On the Modeling of Radio Masts
 The Equivalent Circuit of a Balun
 ANSOF Antenna Simulation Best Practices: Checking and Correcting Model Errors


 ANSOF Antenna Simulation Software  Version 8.90 Release Notes
 ANSOF 8.70: Enhancing Your Antenna Design Journey
 Introducing ANSOF 8.50: Enhanced Antenna Design & Simulation Software
 Get Ready for the Next Level of Antenna Design: ANSOF 8.50 is Coming Soon!
 Explore the CuttingEdge World of ANSOF Antenna Simulation Software!
 Upgrade to ANSOF 8.20  Unleash Your Potential
 ANSOF 8: Elevating Antenna Simulation to the Next Level
 New Release: ANSOF 7.90
 ANSOF 7.80 is ready!
 New ANSOF User Guide
 New Release: ANSOF 7.50
 ANSOF 7.20 is ready!
 New Release :: ANSOF 7.10 ::
 ANSOF 7.0 is Here!
 New Release :: ANSOF 6.40 ::
 New Release :: ANSOF 6.20 ::
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Models

 Modeling a JFed 5Element Collinear Antenna for the 2 m Band
 Simulating the Ingenious Multiband Omnidirectional Dipole Antenna Design
 The Loop on Ground (LoG): A Compact Receiving Antenna with Directional Capabilities
 Precision Simulations with ANSOF for Magnetic Loop Antennas
 ISM 433MHz Helical Antenna
 Radio Mast Above Wire Screen
 Square Loop Antenna
 Receiving Loop Antenna
 Monopole Above Earth Ground
 TopLoaded Short Monopole
 HalfWave Dipole
 Folded Dipole
 Dipole Antenna
 The 5in1 JPole Antenna Solution for Multiband Communications
 An 80 meters DX Antenna: A Spiral Loop

 Transmission Line Feeding for Antennas: The FourSquare Array
 LogPeriodic Christmas Tree
 Enhancing VHF Performance: The Dual Reflector Moxon Antenna for 145 MHz
 Biquad UHF Antenna Array
 145 MHz 5Element Array of Square Loops
 Broadside Dipole Array
 LogPeriodic Dipole Array
 Broadband Directional Antenna
 A Closer Look at the HF Skeleton Slot Antenna
 The 17m Band 2Element Delta Loop Beam: A Compact, HighGain Antenna for DX Enthusiasts
 Enhancing Satellite Links: The MoxonYagi Dual Band VHF/UHF Antenna
 Array of Snowflake Quads

Validation


 Simple Dual Band Vertical Dipole for the 2m and 70cm Bands
 Linear Antenna Theory: Historical Approximations and Numerical Validation
 Validating Panel RBS Antenna with Dipole Radiators against IEC 62232
 Directivity of V Antennas
 Enhanced Methodology for Monopoles Above Radial Wire Ground Screens
 Dipole Gain and Radiation Resistance
 Convergence of the Dipole Input Impedance
 Impedance of Cylindrical Antennas

Input Impedance and Directivity of Large Circular Loops
Assuming a uniform current distribution along a small circular loop > has allowed us to obtain closedform expressions for the radiation resistance and directivity. When the loop circumference is comparable to the wavelength, the current distribution cannot longer be assumed uniform but a Fourier series is applied to approximate it. Also, a delta gap voltage source is used as the excitation in the theory of large loops, so the drawbacks regarding lack of convergence of the input impedance will appear here as in the case of the cylindrical antenna with deltagap source. Nevertheless, the theoretical results are still useful as a reference frame.
In the theory of loops, the circumference C is measured in wavelengths, C/λ, and the wire thickness is taken into account via the Ω parameter,
where r is the loop radius, so C = 2πr, and a is the wire radius. Fig. 1 shows the computed radiation pattern in decibels for a loop with C/λ = 1 and Ω = 10. This pattern is quite similar to that shown in Fig. 5.12 of “Antenna Theory Analysis and Design” by Constantine A. Balanis, 4th Edition, Wiley 2016, for the same loop dimensions.
To establish a numerical comparison between ANSOF and theory, and to demonstrate that the radiation pattern in Fig. 1 is actually that predicted by theory, the following table shows the directivity in dBi of the circular loop antenna for various electrical sizes (C/λ) and thicknesses (Ω):
Ω  C/λ  D [dBi] Theory  D [dBi] ANSOF  Error % 
8  1  3.344  3.36  0.478 
10  1  3.412  3.411  0.0293 
12  1  3.442  3.439  0.0872 
20  1  3.476  3.473  0.0863 
Ω  C/λ  D [dBi] Theory  D [dBi] ANSOF  Error % 
8  1.48  4.626  4.684  1.25 
10  1.45  4.592  4.615  0.501 
12  1.43  4.523  4.54  0.376 
20  1.39  4.354  4.368  0.322 
We can see that the percentage error between the ANSOF and theoretical results is negligible from a practical point of view. The largest discrepancies, around 1%, appear when the loop is made of a thicker wire (Ω = 8) as we could have expected since ANSOF uses the exact kernel and the theoretical loop a thinwire approximation.
Regarding the loop input impedance, Fig. 2 shows the comparison between theory and ANSOF of the input resistance and reactance as a function of the loop circumference normalized to the wavelength and for a wire thickness of Ω = 10. A constant segmentation of 35 segments has been used in the ANSOF model, so each segment is about 7% of a wavelength long for the largest loop, C/λ = 2.5 (2.5/35 ~ 0.07).
It is remarkable that the agreement between theory and the computed results is quite satisfactory over such a large range of variation.