Novel compact CPW-fed antennas with harmonic suppression are presented and investigated in detail. By inserting symmetrical slots connected to the end of CPW transmission line in the ground plane, and exploiting parasitic technique, harmonic suppression, compact size, as well as wide bandwidth are obtained. General performances of the proposed antennas are studied by equivalent transmission line circuits. Moreover, the steps of constructing such harmonic suppression antennas are derived. Eventually, the experiment results verified the validation of the proposed harmonic suppression antennas.
The harmonic suppression antenna (HSA) has become very attractive due to its great advantages such as low cost, small size, and easy integration in wireless communication and microwave power transmission (MPT) systems [
In this paper, several novel compact CPW-fed antennas with harmonic suppression are presented. In order to suppress the harmonic frequencies, symmetrical slots connected to the end of CPW-fed transmission line are etched on the ground plane. Moreover, by employing parasitic technique, bandwidth enhancement is also achieved. General performances of the proposed antennas are investigated by equivalent transmission line circuits. Furthermore, the steps of constructing such HSAs are derived. Eventually, the experiment results verified the validation of the proposed HSAs.
A normal open-ended CPW-fed transmission line, as shown in Figure
(a) A normal open-ended CPW-fed transmission line. (b) The geometry of antenna 1 and (c) The equivalent transmission line circuits for antenna 1.
To achieve the desired resonant frequency, we can take (
Antenna 1 was printed on a dielectric substrate with thickness of 1.6 mm, and relative permittivity of 4.5. Simulation and optimization were performed with the commercial software CST. And the final results, with the optimized parameters listed in Table
Antenna dimensions.
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(a) The simulated return losses of antenna 1 and (b) The simulated input impedance of antenna 1.
To obtain the harmonic suppression, additional antenna structures which act as a wide-band stop filter are usually required for microwave-fed antennas [
The fundamental resonant frequency is supposed to be
(a) The impedance of purely reactive loaded transmission line. (b) The geometry of antenna 2 and (c) The equivalent transmission line circuits for antenna 2.
Antenna 2 is printed on a dielectric substrate with thickness of 1.6 mm, and relative permittivity of 4.5. Two symmetrical short-ended transmission lines were connected with the end of the symmetrical slots, respectively, as shown in Figure
We can also take (
(a) The simulated return losses of antenna 2 and (b) The simulated input impedance of antenna 2.
The bandwidth limitation of antenna is probably the most serious problem in the practical applications of engineering. In order to improve the bandwidth of the proposed HSA, parasitic technique is applied, as shown in Figure
(a) The geometry of antenna 3 and (b) The equivalent transmission line circuits for antenna 3.
The equivalent transmission line model of the two pairs of symmetrical slots.
(a) The simulated return losses of antenna 3 and (b) The simulated input impedance of antenna 3.
General approach of constructing capacitive CPW-fed slot type HSA can be summarized from what have mentioned above. Briefly, the design procedures are as follows: etching symmetrical slots connected with the end of the CPW-fed transmission line in the ground plane, calculate the slot length according to the equivalent transmission line circuits, and try to make the pure resistive input impedance obtained only at the desired fundamental resonant frequency, carefully adjust the parameters until optimized results are achieved, if wideband is required, extra slots can be connected with the end of the CPW transmission line, repeat step 1 to make sure the pure resistive input impedance only achieved at the desired resonant frequency, and it is close enough to the earlier one, carefully adjust the parameters until best results are obtained.
In order to verify the validation of the proposed antennas, experiments were carried out, and the measured results are plotted in Figures
The simulated and measured return losses for (a) antenna 2 and (b) antenna 3.
The radiation patterns at different frequencies (at 2.45 GHz, 4.9 GHz and 7.35 GHz) for antenna 1, antenna 2 and antenna 3 are also demonstrated in Figures
The radiation patterns at different frequencies for: (a) antenna 1, (b) antenna 2, and (c) antenna 3.
In this paper, CPW-fed antennas with harmonic suppression including the second and third harmonic frequencies are demonstrated and investigated. By etching symmetrical slots connected to the end of the CPW-fed transmission line in the ground plane, and exploiting parasitic technology, both compact size and wide bandwidth are achieved. The proposed antenna has been verified through the equivalent circuit analysis and experimental results. General construction approach of such kind of HSA has also been derived. Given the merits such as compact size, good harmonic suppression, as well as wide bandwidth, the proposed HSA is very attractive for wireless communication and microwave power transmission applications.
This work was supported by the National Natural Science Foundation of China (nos. 61172115 and 60872029), the High-Tech Research and Development Program of China (no. 2008AA01Z206), the Aeronautics Foundation of China (no. 20100180003), and the Fundamental Research Funds for the Central Universities (no. ZYGX 2009J037).