DESIGN OF TOOTHED LOG PERIODIC ANTENNA UTKARSH SHUKLA(087) Under guidance of UTPAL TRIPATHI(088) Mr. Deepak Gangwar PRIYANKA VERMA (32073) (Ass. Prof.) SUMIT MISHRA(083) ECE

CONTENT Introduction Brief history Types Structure Working About software Design parameters and their values Design of LP Toothed antenna Results Advantages Applications References

INTRODUCTION Log periodic antenna is the extended versions of most familiar Yagi Uda antennas.  log-periodic antenna (LP, also known as a log-periodic array or log periodic beam antenna/aerial) is a broadband, multi-element, directional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. That is why it is known as log-periodic.

Brief History Log periodic antenna was invented by Dwight E. Isbell,Raymond DuHamel and was licensed by University of Illinois at Urbana-Champaign. The main aim of invention of this type of antenna was to increase the useful frequency band of UHF & VHF antennas.

Types of LP antenna The main types of log periodic array include: Zig zag log periodic array Trapezoidal /toothed log periodic Slot log periodic V log periodic Log periodic dipole array Here we are going to explain the design and result pattern of log periodic toohed antenna.

Structure of LP antenna The most common is the log periodic dipole array basically consists of a number of dipole elements. These diminish in size from the back towards the front. The element at the back of the array where the elements are the largest is a half wavelength at the lowest frequency of operation. 

The initial design based on the concept of the log-periodic structure was the log- periodic toothed planar antenna (LPTPA), as shown in Figure.

Working- The log periodic antenna is fed at the point where the elements connect together. The feeder polarity is reversed between successive elements. Then as the signal progresses down the antenna a point is reached where the feeder reversal and the distance between the elements gives a total phase shift of about 360 degrees. At this point the effect which is seen is that of two phased dipoles (active region)

The elements outside the active region receive little direct power. The active region is dependent upon the frequency of operation, angle between the elements and their dimensions.

About software The software we used in the designing of LP Toothed antenna is HFSS. HFSS software is used for designing and simulation of different type of antennas and wave guide structures (TEE junction, cavity etc.)

Design- Nonplanar trapezoidal tooth log-periodic (LP) antennas are investigated by combining the wisdom of theoretical design procedures with the power of accurate numerical simulation environments. Here we have investigated the following characteristics of an LP Toothed Antenna. 1- return loss 2-directivity 3-impedance

Design parameters used Rn= distance of nth tooth from feed Rn+1= distance of n+1 tooth from feed α = angle between tooth Wn = width of nth tooth Φ = angle between arms

Parameter values Frequency of operation- 4 – 10 GHz Outer radius- 17.91 mm Tau-.65 Sigma- .81 Delta angle- 45 Beta angle-45 Port gap width- 7.164 mm Substrate thickness- 62 mil Substrate dimension along x- 41.19 Substrate dimension along y- 41.19

DESIGN EQUATIONS The initial design based on the concept of the log-periodic toothed structure Follows the angle concept, if one tooth has a width W0 the next smaller one is W0 wide, the third is 2W0, and so on . Let the width of the widest tooth be W1, which is approximately one quarter wavelength corresponding to the lower frequency limit. Then, the width of nth tooth, Wn, is Wn = W1n Also, log Wn =log W1 +n log  Geometric ratio- σ=rn/R n σ=√ τ

Design Environment Frequency of operation (fo): The resonant frequency of the antenna must be selected appropriately(4-10GHz for our design) Dielectric constant of the substrate (εr, which is 2.1 for our design) Height of dielectric substrate (h, 62 mil as taken here)

Design of LP toothed antenna

RESULT OBSERVED FOR FREQUENCY 4- 10GHZ…..

Return loss pattern

2d gain

3d gain

Advantage log periodic antenna is able to provide directivity and gain while being able to operate over a wide b/w. It is nearly frequency independent. This type of RF antenna design is directional. It is normally capable of operating over a frequency range of about 2:1.

Applications It is used in wide band systems and ultra wide band systems. Also used in reflector feeds. Used for TV antenna. The applications where we are most concerned with bandwidth but not with gain, it can replace Yagi Uda antenna.

Reference Radio-Electronics.com Antenna theory by C. BALANIS Antenna design manual prescribed in HFSS Wikipedia.org Log-Periodic Antenna Design Using Electromagnetic Simulation by Özgür Ergül* and Levent Gürel,Department of Electrical and Electronics Engineering , Bilkent University Ankara, Turky

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