Design of Active Integrated Antenna for Dual Frequency Image Rejection

Abstract: This paper is discusses a new configuration of integrated antenna for dual frequency operations and image frequency rejection. Microstrip patch antenna is design in such away to operate in dual frequencies band. The RF 90° hybrid, LNA’s, mixers, LO and IF coupler are integrated to a dual frequency microstrip patch antenna to produce a single module of integrated antenna system that can perform for in dual-band frequencies. The design technique and simulation result for active integrated antenna (AIA) with image rejection is presented.


INTRODUCTION
Nowadays, microwave antennas have been widely used especially in achieving the objective of maximal integration for personal communication system. These antennas can be mounted on the surface of high performance aircrafts, satellites, missiles, mobile phones and others.
Integrated antennas are a combination of solid-state devices and circuits with printed antenna structures and comprise of integrated radio system elements that are fabricated using inexpensive printed circuit techniques [1] . The area of integrated antennas has become an important area of research because it can give excellent results in term of efficiency, compactness, lightweight and low cost compared to the conventional systems. The main disadvantage of microstrip antenna is an intrinsic limitation in bandwidth, which is due to the resonant nature of the patch structure [2 ]. This problem gives a new motivation for research on solutions to overcome the bandwidth limitations of the microstrip antenna. Therefore, for applications that need to increase the bandwidth for operating at two separate sub-bands is represented by dual-frequency microstrip antenna [3,4] . This antenna can be more useful for system that can receive and transmit at the same time.
Image reject is the process whereby the image to the RF signals is channelized into two different ports using phase cancellation technique [5] . It is useful in reducing the cost and complexity due to expensive preselection for the front-end receiver. Therefore, this paper introduces an image reject system that can operate for dual frequency. Proposed DFIA image reject mixer (IRM) system: The first active integrated antenna (AIA) with image rejection has been introduced by Maci and Gentili [6] . The proposed configuration is similar to that but with the phase shift rearranged and useful for dual frequency operation. The image reject mixer (IRM) comprises of two-balanced mixer of any topology driven in quadrature by the amplified radio frequency (RF) signal. The LO leads an in-phase power divider that drives each mixer and the IF output power is combined in quadrature. Figure 1 shows the block diagram of the proposed IRM system.
In principle, dual frequency patch antenna should operate with similar features in both term of radiation and impedance matching at two separate frequencies.
There are many techniques to obtain dual frequency patch antenna, such as orthogonal-mode, multi layer patch and reactively loaded. Maci and Gentili [2] introduces many of these techniques where one of the techniques is used in the system. A single layer slotted square patch antenna is used to provide the dual frequency operation. Using two pairs of orthogonal slots as shown in Fig. 1 produces the dual frequency antenna.
Design methods: A square patch antenna of length and width of 35 mm is designed using FR4 with dielectric constant of 4.5, height of 1.6 mm. The slots length is 29 mm and the width is 1 mm. The slots are 1mm away from the patch edges. The square patch antenna is simulated using Advanced Design System (ADS) momentum analysis software from Hewlett Packard Company. The simulation result shows that the square patch antenna designed can perform dual band frequencies at 2.031 GHz with return loss around-     Fig. 2. MGA-83563 Low Noise Amplifier from Agilent Technology is used to boost the received signal because of the high gain provided which is around 22 dB (from 0.5 GHz to 6 GHz). A balanced resistive FET mixer is designed using Agilent ATF-34143. The mixer operates at 0 DC bias at the drain and only need the gate to be biased while the source is grounded. A 90° hybrid coupler is used to combine the two IF output at 70 MHz. The square patch antenna is connected to the LNA and IRM through via hole to complete circuit of the DFIA with image rejection as shown in Fig. 3. The system is simulated using ADS Harmonic Balance circuit simulator.

DISCUSSION
The simulation result show that the square patch antenna designed can perform dual band frequencies.
The patch antenna needs to be combined with RF 90° hybrid to perform 90° phase difference between two RF signals that will be used in the proposed IRM system. Using phase calculation techniques, image rejection can be achieved as shown from the simulation results. Phase cancellations are performed with image rejection of around 10 dB. Therefore, this architecture introduces a new technique in up/down-conversion and modulation, thus it is suitable as a transmitter and receiver at the same time that can support more than one wireless standard through the use of the dual frequency operations.