Implementation and design of S band PIN diode duplexer using dual band microstrip antenna and RF front end receiver

The proposed project focuses on design of duplexer along with front end RF receiver providing high isolation between receiver and transmitter that will work for S band applications like police radio, radar, mobile etc. Here the substrate material will be FR4 with dielectric constant of 4.4 and height of 1.6 mm.

The S band is part of the microwave band of the electromagnetic spectrum. It is defined by an IEEE standard for radio waves with frequencies that range from 2 to 4 GHz, crossing the conventional boundary between UHF and SHF at 3.0 GHz. The S band is used by weather radar, surface ship radar, and some communications satellites, especially those used by NASA to communicate with the Space Shuttle and the International Space Station, wireless network equipment.

Duplexer: A duplexer is an electronic device that allows bi-directional (duplex) communication over a single path. In radar and radio communications systems, it isolates the receiver from the transmitter while permitting them to share a common antenna. Most radio repeater systems include a duplexer. A duplexer is the network that permits a transmitter and receiver to use the same antenna, at or very near the same frequency. This is used in radar, where the returned signal is going to be very close to the transmitted frequency, such is the case in a T/R module. Whenever a single antenna is used for both transmitting and receiving, as in a radar system, an electronic switch must be used! Switching systems of this type are called duplexers. Switching the antenna between the transmit and receive modes presents one problem; ensuring that maximum use is made of the available energy is another. The simplest solution is to use a switch to transfer the antenna connection from the receiver to the transmitter during the transmitted pulse and back to the receiver during the echo pulse. No practical mechanical switches are available that can open and close in a few microseconds. Therefore, electronic switches must be used.

Duplexers are constructed in many forms,

Ferrite Circulators (hybrid-ring duplexer) or with pin diodes

The simplest solution would be here to use a ferrite circulator. However, it is complicated to make circulators for top performances up to many 100 kW in the practice. In addition, circulators have a decoupling of hardly more as 30 to 40 dB and cannot protect the highly sensitive receiver from the high transmit powers sufficiently.

Efficient pin diodes don't have this disadvantage.

Antenna: An antenna can be viewed as a device that converts a guided electromagnetic wave on a transmission line to a plane wave propagating in free space. Antennas are inherently bidirectional ,it can be used for both transmit and receive functions.

Front end RF receiver: The front end RF receiver includes reception with the help of antenna and local oscillator frequency followed by down-conversion using single-ended diode mixer and intermediate frequency at the output that can be used in communication system. The conventional design technique for a single ended diode mixer will be combined with the low-pass response of DGS to overcome the leakage RF and LO as well as other unwanted harmonics.

Block diagram of proposed project

The proposed project comprise of design of 1) microstrip antenna 2) PIN Diode duplexer 3) RF front end receiver includes LPF, Power Combiner and single diode mixer

1. Design microstrip patch antenna for reception of RF signal providing desirable response.

Combining antenna and mixer resulting in the proposed RF receiver.

2. Choose a suitable diode for the application. Factors affecting this choice include

operating frequency, available LO drive, cost versus performance trade-offs and package

style.

3. Design of duplexer for high isolation between receiver and transmitter.

4. Design the IF filter. In addition to having low insertion loss it is important that it presents

a high input impedance at the LO and RF frequencies.

5. Design the Wilkinson power divider for mixing RF and LO inputs that gives isolation

between the two inputs.

6. Design single ended diode mixer with simple divider and divider using stubs separately.

7. Combining each element for the design of a front end RF receiver.

8. Finally combination of duplexer, antenna and receiver to make a system.

Following are the steps:

Design of planar microstrip antenna

Design of duplexer that includes PIN diode limiter and hybrid coupler

Design of RF front end receiver including single ended diode mixer

Combining different element for final design, modification and simulation