# Uniplanar log-periodic antenna with a perpendicular plane reflector dedicated to a radio wave camera system

Faicel Ouasli, Jean-Philippe Coupez, Patrice Pajusco, Christian Person

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Faicel Ouasli, Jean-Philippe Coupez, Patrice Pajusco, Christian Person. Uniplanar log-periodic antenna with a perpendicular plane reflector dedicated to a radio wave camera system. 2015 European Radar Conference (EuRAD), Sep 2015, Paris, France. pp.580-583, 10.1109/EuRAD.2015.7346367. hal-02524430

HAL Id: hal-02524430

https://hal.science/hal-02524430v1

Submitted on 27 Feb 2026

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# Uniplanar log-periodic antenna with a perpendicular plane reflector dedicated to a radio wave camera system

Faicel Ouasli, Jean-Philippe Coupez, Patrice Pajusco, Christian Person

Lab-STICC/MOM - Telecom Bretagne -

Technopôle Brest-Iroise CS 83818 - 29238 Brest Cedex 3 - France

f.ouasli@gmail.com

***Abstract***— In this paper, an uniplanar log-periodic antenna with a perpendicular plane reflector dedicated to a radio wave camera system is presented. The performance of this antenna are investigated over a wide frequency range, comparing between measured and simulated results. The measured return loss of the antenna exhibits a wideband performance between 1.5 and 4GHz (@VSWR=2). The proposed antenna has a good symmetrical radiation pattern in the E- and H-planes. This antenna configuration is suitable particularly for broadband phased antenna arrays where active circuits are integrated on the feed substrate. The developed antenna will be exploited in a future context of an ultra wideband antenna array, with performances in radiation independent from frequency, for a radio wave camera system.

***Index Terms***— printed log-periodic antenna, ultra wide band, phase center, radio wave camera.

## I. INTRODUCTION

Since the latest decade, there has been an explosive growth of mobile communications, with millions of subscribers around the world. This generalization of radio communications systems generates a constantly growing societal preoccupation concerning the electromagnetic waves effects on exposed persons. Thus, it's necessary to investigate on radio wave camera system to characterize the level of human exposure and enabling a given user to evaluate and visualize electromagnetic radiation sources detectable at a given location, over a given frequency range of interest. This system requires the use of a dual polarized ultra-wide band antenna array. The choice of the antenna differs depending on the selected antenna array solution and the required agility constraints in the covered area. In this work, we have chosen a log-periodic-like printed structure as a basic antenna. This configuration offers broad band characteristics and radiation performance independent of the frequency [1][2].

The basic idea of log-periodic antenna consists in using elements of varying lengths, which resonate at different frequencies. Electrical connections from feed conductors to opposed radiating elements are alternated to provide 180° phase shift between successive elements. A 180° phase shifting between adjacent elements is obtained by crisscrossing or

transposing elements between the feed elements [1][3]. In this case, a little energy is radiated by the adjacent closely spaced short elements because the phase between these elements is almost in opposite, thus their interference effects are very small. The mechanical phase reversal between these elements produces a phase progression so that antenna radiates in the direction of the shorter elements direction [1][3].

Alternative to the crisscross connection, the antenna can be fed from a coaxial line [1]. In this case, the 180° phase reversal between adjacent elements is obtained.

Planar log-periodic dipole antennas are printed in a double side of the substrate in order to allow a switch between the connections of the adjacent elements and obtain a 180° shift between them. A coaxial cable is used to feed the antenna from the smallest dipole element [4][5]. The antenna is designed on a double-layer substrate, and its dipole elements, fed by the stripline in the middle metallic layer, are cross-symmetrically distributed on the top and the bottom metallic layer, respectively. But double-layer substrate configuration increases the cost of the antenna. The use of coaxial transmission line can prohibits a direct integration with microwave and monolithic integrated circuits.

In this paper we investigate a new configuration of CPS (coplanar strip)-fed printed log-periodic dipole antenna with a perpendicular plane reflector. The antenna is printed on the same side of the substrate and therefore is easily constructed and can be used to develop a printed dual polarized log-periodic dipole antenna. Furthermore, the feeder is located on the bottom, i.e. directly on the longest dipole element which facilitates the use of perpendicular feed.

This antenna will be used to design and develop a broadband antenna array with a dynamically adjustable radiation pattern for a radio wave camera system.

In the next part, we present the design and a configuration of a developed uniplanar log-periodic dipole antenna. Some simulations and experimental results will be also given.

## II. ANTENNA DESIGN AND EXPERIMENTAL RESULTS

A picture of the developed antenna prototype on an FR4 epoxy substrate (relative permittivity εr=4.3 and loss tangent tgδ=0.02) is given on Figure 1. The substrate size of the
antenna is 174×74mm×1.6mm³, and that of the plane reflector is 100×100×1.6mm³. The total number of radiating elements is 15.

<figure><img src="image_2.png" /><figcaption>Fig. 1. Configuration and prototype of the proposed log-periodic antenna.</figcaption></figure>

A broadband microstrip to CPS transition has been developed [6] to ensure both matching and perpendicular.

The lower perpendicularly positioned plane reflector is located a quarter wavelengths from the position of the apparent phase center at the lowest frequency. Its influence is mainly observed at this particular frequency, i.e. it operates as a perfect reflector.

For highest frequencies, the upper dipoles elements are excited gradually as shown in Figure 2. The log-periodic shape produces a particular behavior of each dipole element versus adjacent ones. Indeed, at a given frequency, one dipole of the array is resonating while the upper, respectively the lower one – acts as a director, respectively a reflector.

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /><figcaption>Fig. 2. Variation of a maximum E-field distribution as a function of frequency</figcaption></figure>

The variation of the reflexion coefficient S11 (dB) versus frequency is given on Figure 3. The measured return loss of antenna exhibits a wideband behaviour, from 1.5 to 4GHz (@VSWR=2). We note an excellent agreement between simulations and measurements.

<figure><img src="image_5.png" /><figcaption>Fig. 3. Measured and simulated reflection coefficient of the proposed antenna.</figcaption></figure>

Antenna radiation performance are reported on Figure 4 (normalized Gain versus frequency) in E and H planes. We note a good agreement between simulations and measurements. All the radiation patterns present a unidirectional behavior and a good symmetry.

<figure><img src="image_6.png" /></figure>
<figure><img src="image_7.png" /><figcaption>Fig. 4. Measured and simulated radiation patterns</figcaption></figure>

The measured 3dB-beamwidth of the main lobe varies between 54° to 88° in E-plane and between 58° to 104° in the H-plane.

The simulated realized gain of the antenna is shown in the Figure 5. It shows that the realized gain oscillates from 4.4 to 6.1dBi between 1.5 and 4GHz.

<figure><img src="image_8.png" /><figcaption>Fig. 5. The simulated variation of the Realized Gain(dBi) as a function of frequency</figcaption></figure>

The phase center is the particular point which allows the least phase variation within a defined solid angle. The phase center is not uniquely defined and depends on the plane of observation [3].

The simulated variation of the antenna apparent phase center position as a function of frequency is given in Figure 6.

<figure><img src="image_9.png" /><figcaption>Fig. 6. The simulated variation of the apparent phase center position as a function of frequency</figcaption></figure>

The calculation of the phase center is based on an iterative method which consists in the standard deviation minimization of the two dimensional copolar component phase patterns. The calculation is performed within the -3dB beamwidth. In order to determine the position of the phase center, we use a moving reference point method [7]. In Figure 6, we present the average of phase center positions of many pattern cuts. If we take the input of the transmission line (point O, figure 1) as the origin of the reference, we observe that the phase center position is moving a linear way as function of the frequency. This antenna has good performances in terms of radiation, compactness as well as spatial phase center variation.

### III. CONCLUSION

We have modelled, studied and developed a new printed uniplanar log-periodic antenna with a perpendicular plane reflector. The proposed antenna configuration is suited, especially in the context of broad band phased antenna arrays, which require integration of active circuitry on the feed substrate. Due to its structure and obtained good results, we plan to exploit this antenna on a bandwidth of more than one octave (from 1.5 to 4GHz) in a future context of an ultra wideband antenna array, with performances in radiation independent from frequency, for a radio wave camera system.

### REFERENCES

[1] D. Isbell, « Log periodic dipole arrays », *Antennas and Propagation, IRE Transactions on*, vol. 8, n°. 3, p. 260-267, 1960.

[2] R. DuHamel et D. Isbell, « Broadband logarithmically periodic antenna structures », in *IRE International Convention Record*, 1957, vol. 5, p. 119-128.

[3] C. A. Balanis, *Antenna Theory: Analysis and Design*, 3rd Edition. Hoboken, New Jersey: John Wiley & Sons, Inc., 2005.

[4] A. Paul et I. Gupta, « An Analysis of Log Periodic Antenna with Printed Dipoles », *Microwave Theory and Techniques, IEEE Transactions on* DOI: 10.1109/TMTT.1981.1130305, vol. 29, n°. 2, p. 114-117, 1981.

[5] A. A. Gheethan et D. E. Anagnostou, « Reduced size planar Log-Periodic Dipole Arrays (LPDAs) using rectangular meander line elements », *Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE*, p. 1-4, juill. 2008.
[6] F. Ouasli, J.-P. Coupez, P. Pajusco, et C. Person, « Broadband microstrip to coplanar strip line/slot line transitions on perpendicular substrates », in *European Microwave Week, EuMW2012*, Amsterdam, 2012.

[7] C. Menudier, R. Chantalat, M. Thevenot, T. Monediere, P. Dumon, et B. Jecko, « Phase Center Study of the Electromagnetic Band Gap Antenna: Application to Reflector Antennas », *Antennas and Wireless Propagation Letters*, IEEE, vol. 6, p. 227–231, 2007.