الفهرس 
The Duplexers, an Overview.Only 14 pages are availabe for public view
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Abstract
Due to the advent of the unlicensed wireless communication systems such as Bluetooth
and WLAN, in many communication devices, the demand upon microwave and millimeter
wave communication system applications increases. The primitive communication systems
which have the capability to transmit and receive at the same time, consists of two isolated
circuits. One circuit is used for transmitting and consists of a transmitter and a radiating
antenna. Another circuit is used for receiving and consists of a receiver and a receiving
antenna. Such system has some problems such as increasing the overall number of
components in the circuit and the transmitting and the receiving antennas must be placed
far enough apart that the transmitter signals don’t interfere with the receiver side. The
concept of the transceiver systems is becoming the solution to decrease the cost, size, and
weight. In transceiver systems the transmitting and the receiving circuits are integrated
together by using a common shared antenna for transmitting and receiving at the same
time. Although the transceiver system reduces the overall number of components in the
circuit, it faces the problem of poor isolation between the transmitting and the receiving
bands.
Conventionally, the transceiver system consists of a common shared antenna and a
duplexer or a circulator placed between the radio transmitting and the radio receiving
circuits, which is used to provide high isolation performance between them. The main
function of duplexer in the transceiver circuits is to protect the receiver from damage if a
high level RF signal, like those directly from a transmitter output is applied to the receiver
antenna. Although the duplexer provides high isolation between the transmitter and the
receiver, it increases the circuit size and cost. In addition, it needs a matching network.
This thesis presents high port isolation for dual-band of frequency, orthogonally polarized
proximity coupled rectangular microstrip patch antenna operating at 2.5 GHz band signal
at the transmitting port and 2.0 GHz band signal at the receiver port. The proposed system
consists of a proximity coupled rectangular microstrip patch antenna with two orthogonal
feeding lines. The two orthogonal feeding lines are used as filters. By this technique one
can achieve higb degree of port isolation between the transmitting and the receiving ports
of the microstrip patch antenna. The later system can be achieved by placing a lowpass filter (LPF) at the transmitting port of antenna for suppressing the higher order harmonic
frequency components generated by the integrated power amplifier and a bandstop filter
(BSF) at the receiving port of antenna for passing the desired receiving frequency band
signal operating at 2.0 GHz and filter out! suppression of unwanted transmitting frequency
band signal operating at 2.5 GHz band at R.x port. The two filters were designed utilizing
two different shapes of defected ground structure (DGS) units placed underneath the two
rnicrostrip feeding lines. A parametric study for both the DGS units is presented. Also, a
design formula for getting the 3dB cut off frequency for both DGS units is obtained. The
design and simulation of the aforementioned system (i.e. the antenna and the microstrip
filters integrated with DGS units) was achieved by using electromagnetic simulation IE3D
Zeland ver. 12. The fabrication of the proposed circuit was carried out on RTlDuroid 5880
dielectric substrate with dielectric constant er=2.2 and substrate thickness of 3Imil. The
measured and simulated results of the proposed dual frequency proximity coupled patch
antenna shows a higher port isolation than the conventional dual frequency proximity
coupled patch antenna by about 20dB.